Doctor of Environmental Science in Graduate Schoolof Environmental Science The University of Shiga
Prefecture

From Waste to Resource: Optimizing Biochar with
Eggshell for Effective Phosphate Adsorption andSustainable Fertilization

by Protima Sarker

Supervisor: Professor Masahiro Maruo
Graduate School of Environmental Science
The University of Shiga Prefecture

“To myself I am only a child playing on the beach, while vast oceans of truth lie
undiscovered before me.”— Isaac Newton

ACKNOWLEDGEMENT
I would like to express my deep appreciation and gratitude to my supervisor, prof. Dr. Masahiro
Maruo, for the patient guidance and mentorship he provided to me, all the way from when I
was first considering applying to the Ph.D. program in the Division of Environmental
Dynamics, Graduate School of Environmental Science through to completion of this degree.
Prof. Dr. Masahiro Maruo is a very kind person with a genuinely good nature and down-toearth humility, and I am truly fortunate to have had the opportunity to work with him. I am
thankful to prof. Dr Nakoi Hata, Department of Bioresources Management, School ofEnvironmental Science for his cooperation in the cultivation of Japanese mustard spinach. I am
grateful to professor Md. Khabir Uddin from Jahangirnagar University, Bangladesh for his
guidance and inspiration throughout the research program. I express special gratitude to the
Monbukagakusho Scholarship Program at The University of Shiga Prefecture under the Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT). Gratitude isextended to prof. Hiroki Takeshita and prof. Hiroshi Miyamura for permitting me to use FTIR
and EDX at the department of Materials Science, School of Technology, The University of
Shiga Prefecture. We would like to thank M. Nakatsu and S. Koyanagi, the members of thelaboratory of Graduate School of Environmental Science, The University of Shiga Prefecture,
for their cooperation during sample preparation and experiments. I am extremely thankful to
Dr. Xin Liu for his support in data analysis and giving valuable advice throughout this study. I
am grateful to Arvin Bitanga Marcaida to assist me in SEM analysis. I specially would like togive my thanks to my friend Janelle Laura Junio Gacad, and other lab mates for theircooperation and encouragement. My deepest gratitude to my father and mother, who always
supported me from my childhood for my education and encouraged me to pursue my goal. I
am thankful to my husband Prosenjit Kumar Das and my dearest daughter Hridita Das for his
support and encouragement during my research and study. I would like to extend my thanks to
my sister who always encourage me during my mental struggling time and his husband whotake care my parents during pandemic time. I am thankful to my in-laws for their support andinspiration. Without support of all my family members, teachers and friends and theirinspiration I could not pursue this degree.

I

FUNDING
This Research was supported by Monbukagakusho Scholarship Program at The University of
Shiga Prefecture under the Japan Ministry of Education, Culture, Sports, Science andTechnology (MEXT) to Protima Sarker (2019-2023).

II

CONTENTS
PAGES
ACKNOWLEDGEMENTI

FUNDINGIITABLE OF CONTENTIII

LIST OF FIGURESVIILIST OF TABLES

IX

ABSTRACTXI

CHAPTER 1: GENERAL INTRODUCTION

1

1.

IMPORTANCE OF PHOSPHORUS REMOVAL

2

2.

DIFFERENT TECHNOLOGIES FOR PHOSPHATE REMOVAL

3

3.

ADSORPTION PROCESS FOR PHOSPHATE REMOVAL

34.

BIOCHAR AS AN ADSORBENT

45.

EGGSHELL AS AN ADSORBENT

5

5.1 RAW AND THERMALLY MODIFIED EGGSHELL

5

5.2 CHEMICALLY MODIFIED EGGSHELL

6

5.3 BIOCHAR WITH EGGSHELL

6

6.

CHARACTERISATION OF THE ADSORBENT

7

7.

ADSORPTION ISOTHERM

88.

THERMODYNAMIC STUDY89.

ADSORPTION KINETICS

9

10. EFFECTS OF OTHER PARAMETER ON ADSORPTION PROCESS

9

11. COMPERATIVE STUDY

10

12. DESORPTION

11

13. OBJECTIVE OF THIS RESEARCH

11

14. THESIS CONTENT

12CHAPTER 2 Effects of the different mixing ratio of Bamboo char and eggshell
powder on phosphorus adsorption mechanism: Adsorption isotherm andthermodynamics analysis.
III

17

1.

INTRODUCTION

18

2.

MATERIALS AND METHODOLOGY

20

2.1 PREPERATION OF WORKING SOLUTION

20

2.2 PREPERATION OF ADSORBENT

20

2.3 ADSORPTION EXPERIMENT

20

2.4 PHOSPHATE MEASUREMENT PROCEDURE

21

2.5 PHOSPHORUS ADSORPTION CAPACITY

21

2.6 ADSORPTION ISOTHERM AND THERMODYNAMIC ANALYSIS

22

2.7 ADSORBENT DOSE

23

2.8 CHARACTERIZATION

23

RESULTLS AND DISCUSSION

24

3.1 ADSORPTION ISOTHERM

24

3.2 EFFECTS OF TEMPERATURE

24

3.3 EFFECTS OF ADSORBENT AMOUNT

26

3.4 CHARACTERIZATION

26

3.4.1 SEM IMAGE AND EDX SPECTRUM

26

3.4.2 FTIR ANALYSIS

27

SUMMARY

27

3.

4.

CHAPTER 3 Adsorption kinetic study and influence of the pH, anions, andorganic matter on phosphate removal using calcinated eggshell and bamboo

42char as adsorbent.
1.

INTRODUCTION

43

2.

MATERIALS AND METHODOLOGY

47

2.1 PREPERATION OF WORKING SOLUTION

47

2.2 PREPERATION OF ADSORBENT

47

2.3 ADSORPTION KINETICS

47

2.4 ADSORPTION KINETIC MODEL

48

2.5 EFFECTS OF PH, CO-EXISTIONG ANIONS AND ORGANIC ACIDS

48

2.6 IMPLICATION OF BE 1:1 ADSORBENT ON NATURAL AND
TREATED WASTEWATER

49

2.7 ORGANIC P (GLYPHOSATE) REMOVAL

50

2.8 STATISTICAL ANALYSIS

50
IV

3.

4.

RESULTLS AND DISCUSSION

51

3.1 ADSORPTION KINETICS

51

3.2 EFFECT OF pH

51

3.3 EFFECTS OF ANIONS

52

3.4 EFFECTS OF ORGANIC ACIDS

52

3.5 IMPLICATION ON NATURAL WATER AND COMPERATIVE STUDY

53

3.6 ORGANIC P (GLYPHOSATE) REMOVAL EFFICIENCY USING BE 1:1

53

3.7 COST ESTIMATION OF ADSORBENTPREPARATION

54

SUMMARY55

CHAPTER 4 Desorption study and effectiveness of the recovered
phosphate as fertilizer after adsorption using eggshell derived bamboo

68

char.
1.

INTRODUCTION

69

2.

METHODS AND METHODOLOGY71

2.1 DESORPTION STUDY

71

2.1.1 WATER EXTRACTION METHOD

71

2.1.2 NAC EXTRACTION METHOD

71

2.2 POT EXPERIMENT

71

2.2.1 FIRST EXPERIMENTAL CONDITION

72

2.2.2 SECOND EXPERIMENTAL CONDITION

72

2.2.3 THIRD EXPERIMENTAL CONDITION

73

2.3 HALF-STRENGH HOGLAND SOLUTION PREPERATION73

RESULTLS AND DISCUSSION

75

3.1 DESORPTION CAPACITY

75

3.

3.2 EFFECTIVENESS OF PHOSPHORUS CONTAINING BIOCHAR AS
FERTILIZER (POT EXPERIMENT)

4.

75

3.2.1 FIRST EXPERIMENT

75

3.2.2 SECOND EXPERIMENT

75

3.2.3 THIRD EXPERIMENT

75

3.3 DISCUSSION

76
77

SUMMARYVCHAPTER 5 CONCLUSION

86

1.

CONCUTSION

87

2.

RECOMMENDATION89

REFERENCE

90

VI

LIST OF FIGURESPAGES

CHAPTER 2
FIGURE 1a) Scanning Electron Microscope (SEM). b) FTIR spectrometer

29

Adsorption isotherms of phosphorus with different forms on (a)CE, (b) BE 2:1, (c) BE 1:1. The solid and dashed lines indicated
FIGURE 2

the fitted Langmuir and Freundlich model, respectively. Error bar

31

indicates standard deviation.
Linear regression of ∆Gº (KJ/mole) against Temperature (T),FIGURE 3

where slope ΔS° (J/mol·K) and ΔH° (KJ/mole) was obtained fromthe intercept and slop, a) BE 1:1 as adsorbent b) BE 2:1 as33

adsorbent.
Phosphorus (P) adsorption capacity at different adsorbent
materials (CE, BE 1:1, BE 2:1, BE 10:1) in different amounts
FIGURE 4(0.01, 0.05, 0.1 g) (pH: 7; Initial P concentration: 100 mg/L;

35

Temperature: 25 ºC; Time: 24 h). Error bar indicates standard
deviation.
FIGURE 5
FIGURE 6

SEM image of CE (a, b) and BE 1:1(c, d) before and after
adsorption
SEM image of calcinated BE 2:1 (a, b) and BE 10:1 (c,d) before
and after adsorption.

36
37

EDX spectrum of distribution of the a) Phosphate b) Calcium c)
FIGURE 7

Oxygen d) EDX spectrum mapping for elemental composition of
BE 1:1 after adsorption.

38

EDX spectrum of distribution of the a) Phosphate b) Calcium c)
FIGURE 8

Oxygen d) EDX

spectrum mapping for elemental composition

39

of BE 2:1 after adsorption.
FTIR analysis of (a) CE and (b) BE 2:1 at 600, 700, and 800 °C,
FIGURE 9

respectively, and (c) BE 1:1, BE 2:1, BE 10:1, and CE and BC at

40

800 °C.
FIGURE 10

FTIR spectra for BE 1:1 before and after adsorption, BE 2:1 andCE after adsorption.

VII

41

CHAPTER 3
FIGURE 1
FIGURE 2

Distribution of phosphate species as a function of pH.
P adsorption kinetics on (a) CE and (b) BE 1:1 adsorbents. qt:
amount of adsorbed P ions. Error bars indicate standard deviation.
Effect of pH on phosphate removal using Eggshell, BE 1:1; Initial

FIGURE 3

concentration 100mg/L, Dose 0.01g, Temperature 25ºC.

46
56
60

Effect of coexisting anions on P removal (pH: 7; initial P
FIGURE 4

concentration: PO4-P 100 mg/L; dose: 0.01 g of BE 1:1;
temperature: 25 °C; time: 24 h). Error bars indicate standard

61

deviation.
FIGURE 5

Effect of organic acids on phosphate removal efficiency, pH 7,
Initial concentration 100mg/L, Dose 0.01g, Temperature 25 ºC.

62

CHAPTER 4
FIGURE 1

Plants growth for first experiment.

80

FIGURE 2

Plants growth for second experiment.

82

FIGURE 3

Effects of BE(1:1)+P on plant growth (experiment).

84

FIGURE 4

Law of the Minimum.

85

VIII

LIST OF TABLES
PAGES

CHAPTER 1
TABLE 1

Adsorption isotherm

14

TABLE 2

Adsorption kinetics of calcined eggshell and biochar

15

TABLE 3Comparative adsorption capacity of the different types of
eggshell based adsorbent

16

CHAPTER 2
TABLE 1Fitting parameters of the adsorption isotherm equilibrium forphosphate onto CE and various BE (1:1, 2:1, 10:1) samples.

30

Thermodynamic parameters and Langmuir separation factor for
TABLE 2the adsorption of phosphate in different adsorbents (BE 1:1, BE

32

2:1).
TABLE 3

Adsorption nature (Langmuir separation factor)

34

CHAPTER 3
TABLE 1

Adsorption kinetics parameters of P on CE and BE 1:1.

57

TABLE 2

Results after using bamboo char as adsorbent.

58

TABLE 3Component analysis of bamboo powder.

59

TABLE 4

Anions and cations of Seri and USo River.

63

TABLE 5TABLE 6TABLE 7

Implication of the BE 1:1 adsorbent for phosphate removal fromriver and treated water.
Comparative study on the phosphate removal efficiency
Organic phosphorus (glyphosate) adsorption capacity using
BE1:1

64
65
66

Organic phosphorus (glyphosate) adsorption capacity using
TABLE 8bamboo char, calcinated eggshell powder and raw eggshell
powder.
CHAPTER 4

IX

67

TABLE 1

Results of P desorption using water extraction and NAC
extraction method.
First Experiment. Growth parameter of the Japanese mustard

78
79

spinach in the four experimental conditions (Exp I-IV). LR:
TABLE 2length of the root; HS: height of shoot; LL: length of the largest
leaf; WRW: wet root weight; DRW: dry root weight; WSW: wetshoot weight; DSW: dry shoot weight. SD: standard deviation.
Second experiment, Growth parameter of the Japanese mustard

81

spinach in the four experimental conditions (Exp I-IV). LR:
TABLE 3length of the root; HS: height of shoot; LL: length of the largest
leaf; WRW: wet root weight; DRW: dry root weight; WSW: wetshoot weight; DSW: dry shoot weight. (Without additional
nutrient).
Third experiment. Growth parameter of the Japanese mustard
spinach in the four experimental conditions (Exp I-IV). LR:

TABLE 4length of the root; HS: height of shoot; LL: length of the largest
leaf; WRW: wet root weight; DRW: dry root weight; WSW: wetshoot weight; DSW: dry shoot weight. (Using Half-strength
Hoagland solution for other plant nutrients)

X

83

ABSTRACT
Phosphorus is an important element for the plant growth, and it is used as a fertilizer. It is alimited and non-renewable resources in the earth. But when the excessive amount ofphosphorus goes into waterbody, it works as a nutrient for aquatic plants and algae and causes
eutrophication. So, the recovery of the phosphate from water is very important to avoid
eutrophication and recover phosphate to use as fertilizer.
Phosphate recovery using adsorption is a very attractive and effective method. Nowadays
different types of natural bio waste material are used for phosphate recovery. Using biochar
only is not suitable for phosphate adsorption because of the negative surface charge of thebiochar. But metal modified biochar has good phosphate adsorption capacity. Sometime theadsorbed material could not be used as fertilizer because of presence of heavy metal in modifiedadsorbent.
Eggshell decorated biochar exhibits excellent phosphate adsorption capacity than only biochar.
Moreover, calcium is not toxic. That’s why current study was intended to recover the phosphatefrom wastewater using a most convenient procedure and available materials. Bamboo andeggshell were used as an available natural ingredient which was not used for phosphaterecovery before. Since bamboo char is the source of carbon and eggshell as the resource for
CaCO3, would be used as a metal cation which has great affinity for phosphate. So, thecombination of pure biochar with calcite could be a good adsorbent material to recoverphosphate from wastewater. Another objective of this study was to examine the phosphatedesorption using DI water at different temperature and the effectiveness of the phosphateloaded materials as P fertilizer on Japanese mustard spinach cultivation for the sustainable
management of the P adsorbed material.
Bamboo and eggshell adsorbent were prepared for different mixing ratio and temperature (600,
700, and 800°C) to find out effective ratio and calcination temperature. To investigate thefeasibility of calcined bamboo and eggshell for phosphate removal, different calcination
temperature, initial concentration, temperature, time, dose rate, pH, and presence of different
ions was examined. Adsorption mechanism was understood by adsorption isotherm,
thermodynamics study, and adsorption kinetics. Morphological changes and characterizationof the adsorbent after calcination and adsorption were identified by the SEM image, EDX
spectra and FTIR analysis. The maximum P adsorption capacity of the BE 1:1 and BE 2:1 wasfound 95.14 mg/g and 98.40 mg/g respectively. For CE, BE 1:1 and BE 2:1 adsorbent, the data
XI

were well fitted by Langmuir model, and it indicates the monolayer adsorption on thehomogenous surface of the adsorbent. Thermodynamics results revealed that the Gibbs freeenergy ΔG of the BE 1:1 and BE 2:1 at 298 K, ΔG was positive indicates the process was not
spontaneous. But after increasing temperature the reaction was spontaneous. Langmuir
separation factor (RL) value indicates the favorable adsorption conditions for phosphate.
Characterization of adsorbent was identified by FTIR, and SEM image. From FTIR analysis
the formation of the band at 1021 cm-1 was observed, which clearly indicated the presence ofphosphate after adsorption on BE 1:1. From kinetic study it has been found that the experiment
data were better fitted the pseudo second order model which explain that adsorption procedure
was chemisorption process. Presence of different ions (anions and organic acids) and pH of thesolution also influence the phosphate adsorption mechanism. But calcined BE 1:1 is noteffective for the organo-phosphorus herbicide glyphosate removal which is beneficiary for thisresearch because it will not compete with phosphate for active sides and don’t makecontamination in application of phosphate adsorbed material as fertilizer.
In this study phosphate desorption in Milli-Q water and NAC extraction method was examined.
Then phosphate dropped biochar was applied on pot experiment for Japanese mustard spinach
cultivation. From the experiment it was found that phosphate desorption in Milli-Q water wasvery low. Because the bonding between calcium and phosphate is very strong. So, the reuse of
the adsorbent is not a good option. But the phosphate loaded eggshell modified bamboo char
was effective as slow-release fertilizer for the Japanese mustard spinach cultivation. So, thephosphate loaded eggshell modified bamboo char has potentiality to use in plant cultivation asa phosphorus fertilizer.

XII

General Introduction

Chapter 1

CHAPTER 1
General Introduction

1General Introduction

Chapter 1

1. Importance of phosphorus removal
Phosphorus is the structural component of biomolecules (e. g. DNA, RNA, ATP etc) which is
known as growth nutrient of the plants and other organisms (Hong et al., 2020; Santos et al.,2019). It is an important micronutrient for plant metabolism, root, and shoot growths, andreproductive development (Neelam et al., 2017). Mineral fertilizer extracted from thephosphoric rock and manure are the main source of phosphorus used for the food production(Vaccari et al., 2019). The pressure of food production due to overpopulation has been
increasing the inefficient use of the phosphorus fertilizer. The rising demands of thephosphorus fertilizer will deplete the phosphorus reserve within few decades (Xie et al., 2014).
Plants needs only small amount of phosphorus, but the extra residual phosphorus accumulates
in the soil after plant uptake (Syers et al., 2008). This excessive amount of phosphorus enters
the surface water and causes tremendous growth of algae and aquatic plants which is known asalgal bloom (Lee et al., 2019). When the algae and aquatic plants die, bacteria use dissolve
oxygen to decompose and deplete the dissolved oxygen. This sever water pollution is known
as eutrophication. Algae blooms causes several significant negative impacts on the aquatic
environment because the floating layers or surface scums may prevent photosynthesis,
enormous algal biomass decomposition causes oxygen depletion and some algae such as
Microcystis releases toxins (Bhateria et al., 2016). It is a very harmful process not only forsubmerged macrophytes and but also for aquatic animals due to turbidity, malodor, andhypoxic/anoxic conditions (Liu et al., 2018).
The source of phosphorus might be natural (weathering process of phosphate rock) andanthropologic. The human originated source of phosphorus are point sources (synthetic
detergent in domestic wastewater) and non-point sources (agricultural run-off) (Rockström etal., 2009; Steffen et al., 2015; George et al., 2017). The discharge standard of phosphorus in
Japan is 1 mg/L, China is 0.5 mg/L (GB18918-2002), and the US standard is 50 μg/L (1994)(Zhou et al., 2014). In natural water and wastewater, orthophosphate, polyphosphates, andorganic phosphorus are the major form of phosphorus. Polyphosphates and organic phosphorus
are converted to orthophosphate by hydrolysis/or microbial mobilization (Habiby et al., 2019).
At the same time, phosphorus is a non-renewable resource and its reservation in nature arelimited (Cooper et al., 2011). Sewage wastewater, sludge, manure, and other animal byproducts are the biological waste contain certain amount of phosphorus which can be recovered,and European Union has exposed their attention on phosphorus recovery from wastewaters(Santos et al., 2019). Recovery of phosphorus from the wastewater might be the alternative2

General Introduction

Chapter 1

source of the phosphorus resource. Meanwhile phosphorus removal is the eutrophication
control measure for the environmental management.
2. Different Technologies for phosphate removal
Different types of technologies are available to remediate phosphorus pollution. These
processes can be classified as chemical methods (precipitation, crystallization, anion exchange,
and adsorption), biological methods (assimilation, enhanced biological phosphorus removal,
constructed wetlands, wastewater stabilization pond), and physical methods (microfiltration,
reverse osmosis, electrodialysis, and magnetic separation) (Benyoucef and Amrani, 2011;
Bhojappa, 2009). But every method has some advantages and disadvantages. Physical methods
are not cost effective and efficient (Karachalios, 2012).
Biological treatments have certain limitations, because this process is controlled by
microorganism metabolic activity, which is influenced by environmental conditions, especiallytemperature. (Clark et al., 2005). Chemical precipitation generates huge amount of sludge
during and post phosphate removal processes, such as separation, squeezing. To combat thisside effect, sludge disposal is required (Loganathan et al., 2014). Among these, adsorption has
been considered as the best option for the removal of phosphate from wastewater. Because theoperation and maintenance process are simple and cost effective with high removal efficiency.
This process is also environmentally friendly due to less sludge generation and low energy
consumption. Moreover, it is the best technology to remove and recover phosphate fromwastewater (Park et al., 2015; Lin et al., 2017).
3.

Adsorption process for phosphate removal

Adsorption is defined as the accumulation of a substance at the interface between two phasessuch as solid and liquid or solid and gas. The substance that accumulates at the interface iscalled ‘adsorbate’ and the solid surface on which adsorption occurs is ‘adsorbent’. Adsorption
process occurs at the surface of the solids due to the unbalanced forces of attraction. If theadsorption happens due to weak Van der Waals forces, it is called physical adsorption. If theprocess is governed by chemical bonding between adsorbent and adsorbate molecule thenadsorption is referred as chemisorption (Bhatnagar et al., 2010). There are diverse range ofmaterials are used as adsorbents for the phosphate removal like, clay-based adsorbents(Othman et al., 2018), carbon alike materials (Gisi et al., 2016), metal-based materials (Zhang
et al., 2017; Lin et al., 2019;) and chitosan (Xu, 2020).
3

General Introduction

Chapter 1

Biomaterials used in adsorbent preparation are gaining interest because they are frequently
biodegradable, renewable, and less toxic. Using biomass wastes for this purpose also has theadvantage of ensuring agricultural waste management. (Bacelo et al., 2020). Still regenerationof phosphate from wastewater as fertilizer is an important matter for environmental
sustainability. Research on the phosphate recovery using low-cost material is going on. So, it
is necessary to find efficient, low cost and ecofriendly material to recover phosphorus as analternative of the chemical fertilizer.
4.

Biochar as an adsorbent

At the present time biochar has achieved the popularity as a potential adsorbent for pollutant
remediation because of high efficiency, low cost, environment friendly, excellent stability, highporosity, easy preparation, and operation (Tan et al., 2015; Jeong et al., 2016). Commercial
activated carbon also very effective as adsorbent but not cost effective.
Biochars are carbon-rich products produced from biomass using pyrolysis process at thetemperatures below 700oC under the oxygen-limited condition (Lehmann, 2007; Zhang et al.,2011; Zheng et al., 2013). Sometime activation process has been performed in the presence ofoxygen in the furnace chamber (Parez et al., 2020). This modification of the condition
decreases the carbon content and positive charge of the biochar as well as concurrently increasein negative charges, oxygen content, and contents of carboxylic and phenolic functional groups(Ramola et al., 2014). The properties and functions of those biochar are highly depending on
the feedstock materials and production condition (Zhang et al., 2015a).
A broad range of materials were used as a bio adsorbent such as sugarcane bagasse (Ramola
et al. 2014), Soybean milk residues (okara) (Nguyen et al. 2013), Sawdust (li et al. 2018),
Bamboo (Isa et al.,2016) and micro algae (Jung et al., 2016) etc. Biochar contains negative
surface charge can adsorb cationic pollutants like heavy metal (Kılıç et al.,2013) and dye (Liaoet al., 2012).
Pure carbon adsorbents are not efficient for phosphate adsorption due to its negative surface
charge (Li et al., 2017, 2018a). To improve the phosphate adsorption capacity of the biochar
researchers are searching for different methods such as, (i) cationization (e.g. metal loading,grafting with ammonium type chemicals), (ii) anionization (e.g. surface coating with sulphate),(iii) activation (e.g. thermal, chemical and steam activation) (Nguyen et al., 2014).
Impregnation of exogenous metal elements into biomass through the pyrolysis under oxygenlimited condition is known as cationization process (Li et al., 2018a, 2018b; Vikrant et al.,4General Introduction

Chapter 12018). Some metal elements (Al, Fe, etc) incorporated in biomass to produced metal-based
biochar show excellent adsorption of anionic pollutants (Loganathan et al., 2014).
Metal cations such as Ca2+, Al3+, Fe3+, and La3+ have strong affinity for phosphate, which cansignificantly improve the phosphate adsorption performance of biochar (Haghseresht et al.,2009; Huang et al., 2015; Yang et al., 2014; Yin et al., 2016). However, Al3+, Fe3+, and La3+
can be released in aqueous solution under redox or acidic conditions and have toxic effects onaquatic environment and organisms (Mitrogiannis et al., 2017; Haghseresht et al., 2009).
Different calcium containing clay minerals, such as attapulgite (Kim et al., 2018), sepiolite(Yin et al., 2011, 2013), goethite (Li and Stanforth, 2000), bauxite (Altundoǧan and Tümen,2003), and dolomite (Karaca et al., 2004) have phosphate removal efficiency and nontoxic
characteristic. But these are expensive.
5.

Eggshell as an adsorbent

Eggshell contains calcite which is about 11% of the total egg weight (Meski et al., 2011;
Oliveira et al., 2013). Every year globally eight million tons of eggshell waste has been
generated and disposed as solid waste which is a big environmental concern because of creating
unpleasant smell and microbial contamination (De Angelis et al., 2017). According toEuropean Union (EU) regulations, the eggshell is a hazardous waste due to its abundance which
imposes high disposal costs for the food industry (P´erez et al., 2020).
Due to the presence of CaCO3, the sorption capacity of eggshell has been attracted byresearchers for removal of organic (dye) (Elkady et al., 2011), inorganic (heavy metal)(Pettinato et al., 2015) pollutants and anions (nitrate, phosphate) (Ahmad et al., 2018; Photiou
et al., 2021) in wastewater. Eggshell is also used as a soil amendment material (Margarida etal., 2017). It has been found that during adsorption process calcined eggshell react withphosphate and the calcined waste could not be reused because of the irreversible nature of thechemical reaction. That’s why P containing eggshell possess high potentiality to use as
fertilizer on agricultural field (K€ose and Kıvanç, 2011).

5.1 Raw and thermally modified Eggshell
Thermally modified eggshell has been produced using calcination process (Tangboriboon etal., 2012; Köse and Kıvanc, 2011; Torit et al., 2019; Yirong and Vaurs, 2019; Santos et al.,2019; Lee et al., 2022). Köse and Kıvanc (2011) found that calcination of the eggshell start5

General Introduction

Chapter 1

from the 600 °C and fully calcined at 800 °C temperature. During calcination process CaCO3
convert into CaO due to the higher temperature and form calcium hydroxide Ca(OH)2 at longer
calcination time at 900°C for 3 h due to the reactive moisture adsorption (Tangboriboon et al.,2012; Panagiotou et al., 2018). Calcined eggshell contain CaO or Ca(OH)2 would adsorb more
phosphate than raw eggshell powder with high content of CaCO3 (Krogstad et al. 2005).
Because of the high solubility of Ca(OH)2 and CaO in solution could lead to the formation of
Ca5(PO4)3(OH) and CaHPO4 crystals generated by Ca-P precipitation (Yin et al., 2014).

5.2 Chemically modified eggshell
Eggshell modified with metal salt like Al, Mg, and Fe salts and hydroxides has been proven as
good adsorbent. Iron hydroxide-eggshell (Mezenner et al., 2009), Al-eggshell (Guo et al., 2017;
Zhang et al., 2017), Mg-eggshell (Ahmed et al., 2017), FeCl3 eggshell (Xu et al., 2018),
hydroxyl-Eggshell (Ribeiro et al., 2020; Almeida, et al. 2020) have been investigated andshown effectiveness for phosphate adsorption.
Before modification with metal salt and hydroxide, eggshells were cleaned and dried in ovenat 100°C /105°C (Zhang et al., 2017; Guo et al., 2017; Xu et al., 2018). After that eggshell
powder was immersed in 100 ml solution of AlCl3 (0.29 mol/l) for 24 h with stirring speed 150
rpm at 30°C to equilibrium. Then, the particles were centrifuged and dried, screened through asieve of 100 mesh, and subsequently used for sorption experiments (Zhang et al. 2017). Ironhydroxide-eggshell was prepared by mixing the eggshell and FeCl3, 2H2O (Mezenner et al.,2009; Xu et al., 2018).

5.3 Biochar with eggshell
Biochar modified with eggshell is gaining attraction because of the effective phosphateremoval efficiency. Moreover, P loaded biochar could be a potential source of fertilizer.
Agricultural waste-based biochar with eggshell is a low cost and ecofriendly adsorbent to treat
the eutrophication problem of the waterbody (Marschner et al., 2013). Pyrolyzed eggshell withrice husk (Liu et al., 2019), palm fiber (P´erez et al., 2020), rape straw (Cao et al., 2020),
tobacco stalks (He et al., 2020), sugarcane bagasse (Liao et al., 2022), Palm mesocarp fiber(Pérez et al., 2022), and potato peels (Quisperima et al 2022) were investigated as adsorbent
for phosphate removal. Calcium modified biochar was prepared at high temperature under N2
6

General Introduction

Chapter 1

atmosphere because eggshell starts decomposition at 650°C and is completely decomposed at
800°C (Shen et al., 2018). Liu et al. (2019) suggested that eggshell modified rice straw showed
good phosphate adsorption capacity and produce high amount of hydroxyapatite precipitate(HAP) on its surface or within the pores after the adsorption of phosphate. After phosphateadsorption eggshell modified rice straw rich in P, which is a necessary nutrient for plant growth.
Applying it as a fertilizer to the soil can play a dual role in improving soil physical properties
and increasing soil P content.
For present study, “bamboo” was used for biochar and eggshell was used as a calcium source.
Bamboo is a common and available source of biomass in Asian countries. The benefit of using
bamboo is after pyrolysis at high temperature it produces high density and porous structurecompared to wood biochar, which enhances adsorption capacity (Zhao et al., 2008). There areover 90 genera of bamboo with more than 1200 species which occupies more than 14 million
ha land of the world. Among them 80 % of all bamboo species and forests are found in Southand Southeast Asia, including China, India, and Myanmar (FAO, 2007). Therefore, it is anavailable and cheap material to produce biochar.

6.

Characterization of the adsorbent

After pyrolysis process the adsorbent material shows different physical properties and chemicalcompositions than the raw materials. The surface area, pore size and pore volume has been
increased after addition of eggshell (Liu et al., 2019). The ratio of eggshell and fiber,
temperature may affect the properties of the adsorbent materials (P´erez et al., 2020). Due tothe high temperature of the calcination and pyrolysis process CaCO3 of the eggshell has beenchanged into CaO-Ca(OH)2 (Santos et al., 2019). Phosphate adsorption can be identified by the
FTIR SEM, and EDX analysis. The crystal formation of phosphate on the surface of theadsorbent and disappearance of the pore space can be seen from the SEM image before andafter adsorption (Liu et al., 2019; P´erez et al., 2020; Cao et al., 2020). SEM analysis showedthat morphology of eggshell modified biochar has been changed after pyrolysis process.
Eggshell containing biochar has broaden pores which form when CaCO3 of eggshell isthermally decomposed into CO2 during calcination process. After phosphate adsorption, pores
replaced with large amounts of flocculent precipitates (Liu et al., 2019). He et al. 2020, foundthat Mg modified eggshell and biochar has rough surface. The surface roughness of eggshelland Mg doped biochar was also increased with granulation and macroporous structure. The
7

General Introduction

Chapter 1

presence of MgO in Mg doped biochar produces a sharp peak 459 cm−1 and Mg(OH)2 in
eggshell/Mg doped biochar produce absorption peak around 3700 cm−1 in FTIR analysis. And
the peak appeared at 1420 cm−1 and 878 cm−1 were attributed to the vibration of CO32−
molecules. From FTIR analysis it was found that only biochar is not effective for phosphateadsorption. But for eggshell and biochar 1:1 ratio, a strong and narrow -OH stretching vibration
band appears at 3641 cm−1 and a new stretching vibration band can also be observed at 871cm−1
which disappeared after phosphate adsorption. The peak appeared at 1024 cm−1 after theadsorption by eggshell and biochar 1:1 indicated the phosphate stretching vibration band (Liuet al., 2019; P´erez et al., 2020).
7.

Adsorption Isotherm

Adsorption process of phosphate depends on the different condition that control the adsorption
such as initial concentration of the adsorbate solution. The adsorption process is monolayer, or
multilayer can be identified by the Langmuir model and Freundlich model. Langmuir model
describes the monolayer adsorption due to precipitation and hydrogen bonding acting forces,
and Freundlich model represents multi-layer adsorption process caused by Van der Waals
adsorption, electrostatic attraction, etc. (Kong et al., 2018; Wang et al., 2018). From literature
it has been found that the eggshell modified biochar data were better fitted by Langmuir model
indicating monolayer adsorption (Table 1).
Calcined biochar shows lower adsorption capacity than the calcined eggshell and biochar
mixture because of absence in active metal in the biochar (Liu et al., 2019; Cao et al., 2020).
Cao et al. (2020) experimented calcined bio char, eggshell modified biochar and calcium
modified biochar. Where eggshell modified biochar showed higher equilibrium adsorption
amount than calcium modified biochar (109.7 mg g-1 and 101.0 mg g-1, respectively) because
eggshell contains nitrogen- rich organic matter (e.g., protein), which form hydrogen bonding
and positive charge adsorption sites (Zhang et al., 2015b; Yamazaki et al., 2016).

8.

Thermodynamic Study

Liu et al. (2019) found from the thermodynamic analysis that the adsorption is a endothermic
reaction where phosphate spontaneously react with CaO/Ca(OH)2. If the temperature of thereaction increases the phosphate adsorption capacity also increases. He et al. (2020) found that
phosphorous adsorption capacity decrease with increasing temperature indicates the8General Introduction

Chapter 1

exothermic reaction. The ambient temperature should not be too high or too low at 100–500
mg P L-1 and 25 ℃ is the optimal temperature for the adsorption by eggshell modified tobacco.
For high concentration, there is a large amount of P, and the increase of temperature intensifies

the thermal movement of molecules and increases the probability of collision between
phosphate and the active sites of EM-C24(Ca-Mg-Biochar), thus improving the adsorption
effect. However, temperature changes disrupt thermal and chemical balance, causing
dissolution/precipitation reactions to move (He et al., 2020). Excessive high temperature is notconducive to exothermic adsorption and will cause the precipitation dissolution equilibrium
reaction related to chemical adsorption to move towards the dissolution direction and thus
reducing the adsorption effect.
9.

Adsorption kinetics

Adsorption kinetics indicates the rate of the adsorption. Adsorption kinetics can be analyzed
using Pseudo first order model and Pseudo second order model. Pseudo first order model
indicates the adsorption reaction is controlled by the diffusion process and Pseudo second ordermodel indicates the adsorption reaction is controlled by the chemical adsorption process. In
Chemical adsorption process the adsorbent and the adsorbate exchange or share electrons toform new compounds (Lalley et al., 2016). Table 2 shows that the eggshell and biochar-based
adsorbent better fitted the Pseudo second order model which indicates the chemisorption. Liuet al. (2019) found that within 2 h fast adsorption rate was identified after that the reaction rate
became slow, then adsorption equilibrium was obtained within about 6 h for all E-C and BC
samples. The reason of the fast initial reaction is rapid diffusion of ions from the solution to
the external adsorbent surfaces, then the slower adsorption process was explained by internalporous diffusion (Zhao et al., 2011). Since the active adsorption site of the eggshell modified
biochar has increased so the diffusion process also changed into chemical sorption process.
Adsorption process of only biochar is a physical adsorption process governed by a weak Van
der Waals interaction (Cao et al., 2020).

10. Effects of other parameters on adsorption process
pH has a great influence on the adsorption reaction. Because the form of the phosphate varies
due to the changes of the pH, while the functional group of the surface of the adsorbent alsochanges. The ionization constant of phosphoric acid is affected by pH of the point of zero
9General Introduction

Chapter 1

charge (pHpzc) indicating the pH where surface charge is zero. When the reaction occurs below
the pHpzc then the phosphate adsorbed by adsorbent by electrostatic attraction. The solution
pH above the pHpzc creates negative charge on the surface of adsorbent from eggshell modified
biochar which chemically reacts with phosphate (Liu et al., 2019; P´erez et al., 2020). Eggshell
modified palm fiber showed 100 % of P removal when pH is above 10 (P´erez et al., 2020).
Mg-loaded tobacco stalk biochar showed good adsorption capacity under acidic condition. In
the range of pH 3-5 the phosphate adsorption capacity was 235.8–237.8 mg P g−1. The
adsorption capacity was decreased in alkaline condition. The first reason of this phenomenon
is dissociation constant. Phosphate has three pK value such as 2.14, 7.20 and 12.37 at 25°C
(Bacelo, et al., 2020). When the pH of the solution about 5.5 and 10, H2PO4- and HPO42- thepredominant species. When pH is greater than 12.7 then PO43- is the predominant species (Choiet al., 2019). When pH increases H2PO4− is change into HPO42− is more difficult to be adsorbed
because of higher adsorption energy. That’s why the adsorption capacity decreases (Li et al.,2017; Zhang et al., 2020). The second reason is that the increase of the pH value of the solutionchanges the degree of protonation and deprotonation which affect the electrostatic adsorption.
And finally, the OH− in the solution will compete with the phosphate ion for active adsorption
sites under high pH conditions (He et al., 2020).
Wastewater contains different anions which may compete with phosphate to occupy the active
site of the adsorbent. Phosphate adsorption capacity was experimented with co-existing ion
NO3−, HCO3−, SO42− and Cl−. The anions NO3− and Cl− had limited effect on the adsorption
process of phosphate, even in the case of high ion concentrations up to 1 mol L-1 for Cl−, theadsorption amount of phosphate remained at a high level. On the other hand, HCO3−, SO42−
had significant negative effect on the adsorption of phosphate on the E-C material, because
they can combine with Ca2+ to form insoluble or poorly soluble substances to reduce the active
sites on the surface of E-C 1:1(Liu et al., 2019). He et al. (2020) also found that the presenceof Cl− and CO32− had no effect on the removal efficiency of phosphate for Eggshell modified
biochar. In case of NO3− , removal of phosphate was increased. It has been found that SO42−
leads to the reduction of the phosphate removal efficiency of EM-C24 (Ca-Mg-Biochar).
11. Comparative study
Raw eggshell/ calcined eggshell, biochar modified eggshell and chemically modified eggshell
was used by several researcher. Maximum adsorption capacity and removal efficiency has been

10

General Introduction

Chapter 1

represented as a comparative study on adsorption capacity of different types of eggshell based
adsorbent in Table 3.
12. Desorption
Desorption is the inverse of the adsorption where adsorbate separates from the adsorbent
substrate (Havlík 2008). Desorption study of the phosphate has been carried out to find thereusability of the adsorbent after adsorption. It is also important to understand the solubility ofthe phosphate in water and plant availability (Haddad et al., 2018). There are some desorption
processes like thermal desorption and chemical desorption. Some chemicals are soluble inwater at low pH or high pH. Desorption process depends on the types of the chemicals andtheir molecular bond. Phosphorus fertilizer solubility is necessary to understand the Pavailability for the plant. The solubility of the P fertilizer has been investigated in water, weekacid and strong acid condition. Different types of organic fertilizer are used as P fertilizer like,compost, animal residue, meat and bone meal, sewage sludge and vegetable residue (Kratz etal., 2010). To understand the chemical equivalence of this fertilizer to the commercial mineral
fertilizer different types of extraction method are used by researchers such as neutral
ammonium citrate (NAC), Iron bag, NaHCO3 and H2O extractions method which are very
effective for P extraction (Duboc et al., 2022).

13. Objective of this research
The main objective of this research is to investigate the feasibility of using Bamboo charand eggshell ash to remove phosphorus from wastewater and the applicability ofphosphate containing materials as a fertilizer. The aims of this study are to prevent
eutrophication of surface water by removing phosphate nutrient using natural, cost effective,
ecofriendly material which is an alternative use of the agricultural waste materials. Moreover,recovery of the phosphate is beneficiary for agricultural application as fertilizer.
The objectives of the study are
1. Preparation of the adsorbent material from bamboo and eggshell powder using
calcination process at high temperature and different mixing ratio.
2. Investigate the phosphate adsorption capacity and mechanism of the adsorbent
materials prepared from bamboo and eggshell powder using adsorption isotherm,
11General Introduction

Chapter 1

kinetic, and thermodynamics study. Determine the characterization of the adsorbent
before and after phosphorus adsorption process by the SEM image, FTIR analysis and
XRD analysis.
3. Examine the effects of pH, adsorbent dose, adsorbent ratio, co-existing anions, andorganic acids on the phosphate removal process.
4. Evaluate the desorption of the phosphate from adsorbent material and the applicationof P loaded material as a fertilizer in lab scale.

14. Thesis content
This study is organized into 4 sectionsFirst chapter is general introduction which explain the importance of phosphate removalfrom wastewater, different types of phosphate removal methods, significance of using
adsorption process and using natural waste material as an adsorbent for phosphate removal.
Different types of modification process of eggshell to improve the adsorption efficiency.
Second chapter is Effects of the different mixing ratio of Bamboo char and eggshell
powderonphosphorus

adsorption

mechanism:

Adsorption

isotherm

andthermodynamics analysis.
In this chapter effects of initial concentration, temperature adsorbent dose, bamboo andeggshell ratio was described because these factors may affect the phosphate removal process.
Adsorption mechanism was identified using adsorption isotherm (Langmuir and Freundlich
isotherm model) and thermodynamic study. Adsorption nature was calculated using Langmuir
separation factor. Adsorbent characteristic before and after phosphorus adsorption process wasanalyzed using FTIR (Fourier Transform Infrared Spectroscopy) analysis, SEM (ScanningElectron Microscope) image and EDX (Energy Dispersive X-ray spectroscopy) analysis
Third chapter is Adsorption kinetic study and influence of the pH, anions and organic
matter on phosphate removal using calcined eggshell and bamboo char as adsorbent.
Where effects of time, pH, co-existing anions, and organic acids were explained. Adsorption
kinetic was analyzed using Pseudo first order kinetic model and Pseudo second order kinetic
model which is important to understand the adsorption mechanism. Implementation of BE 1:1
for the phosphate removal from the natural water and treated water was performed. Organic
12General Introduction

Chapter 1

phosphorus removal efficiency of BE 1:1 was tested. Then the cost of the adsorbent preparation
was estimated.
Forth chapter is Desorption study and effectiveness of the recovered phosphate after
adsorption using eggshell derived bamboo char as fertilizer.
In this chapter desorption study using water extraction and Neutral Ammonium Citrate (NAC)
was elucidated. After phosphorus recovery using bamboo+ eggshell 1:1 P adsorbed material
was used as fertilizer and the effectiveness was illustrated in this chapter.

13

General Introduction

Chapter 1

Table 1. Adsorption isotherm
Adsorbent

Conditions

Langmuir model
KL

qmax

Freundlich model
R2(L mg−1) (mg g-1)

KF

Reference
1/n

R2(mg(1−1/n)L1/ng−1)

EC 2:1

Calcined at 800 °C

3.88

204

0.992

109

0.149

0.764

EC 1:1

Dose: 0.01 g;

3.74

231

0.984

122

0.152

0.752

EC1:2

Temperature: 25 °C; Time: 24 h; 5.75

159

0.979

87.1

0.141

0.802

EC 1:4

pH: 7

8.06

96.4

0.999

59.6

0.112

0.748

0.0885

5.58

0.969

1.64

0.248

0.905

BC

Liu et al., 2019RS

0.05 g sorbent, (Initial con.,

0.01753.101

0.91990.21562.12900.8552

Cao et al., 2020

ERS

10−200mgP/L, 180 rpm

67.3

103.9

0.962492.49

28.62870.6447CRS

25 ± 0.5 °C for 24 h.

19.41

96.56

0.962980.3

17.99210.84843

ESF-1:10

20 mg adsorbent, Initial Conc. 5 -

-

0.999

-

-

0.919

P´erez et al., 2020
He et al., 2020

ppm, stirring at 200 rpm (2h).
M-C1

Calcined at 700°C for 2h

0.125

110.62

0.754

25.46

0.27

0.688

M-C2

Modified with MgCl2

0.078

206.68

0.923

34.84

0.35

0.890

M-C3

0.099

272.37

0.850

42.30

0.41

0.812

EM-C240.095

210.66

0.923

39.69

0.33

0.838

14

General Introduction

Chapter 1

Table 2: Adsorption kinetics of calcined eggshell and biochar
Adsorbent

Conditions

Pseudo first order model

Pseudo second order model

K (h−1)k2 (g mg−1 h−1)qe

R2

(mg g-1)

qe

ReferenceR2(mg g-1)

EC 2:1

Calcined at 800 for 2h

10.5

191

0.962

0.124

196

0.983

EC 1:1

Dosage: 0.01 g;

15.1

221

0.966

0.224

224

0.994

EC1:2

Temperature: 25 °C; Time: 24 h; 3.46

153

0.958

0.0352159

0.973

EC 1:4

pH= 7

6.586

74.7

0.952

0.0104

81.7

0.976

1.26

5.21

0.985

0.311

5.53

0.958

BC

Liu et al., 2019RS

0.05 g sorbent, (Initial Conc.,

0.14172.173

0.87280.038952.958

0.8646

Cao et al., 2020

ERS

10−200mgP/L, 180 rpm

2.266

104.7

0.99610.03646109.7

0.9906CRS

25 ± 0.5 °C for 24 h.

2.06

96.7

0.99610.03726101

0.9972

ESF-1:10

20 mg adsorbent, Initial Con. 5 --0.9484--0.9996P´erez et al., 2020
He et al., 2020

ppm, stirring at 200 rpm (2h).
M-C1

Calcined at 700 for 2h

0.46

100.350.926

0.0195

98.19

0.934

M-C2

Modified with MgCl2

0.36

196.270.963

0.0039209.32

0.976

M-C3

0.72

234.990.95

0.0065245.11

0.980

EM-C240.46

239.580.965

0.0019271.820.986

15

General Introduction

Chapter 1

Table 3: Comparative adsorption capacity of the different types of eggshell based adsorbent
P Adsorption

P Removal

Capacity (mg/g)

efficiency

Calcined waste eggshell

23.02

99%

Kose et al., 2011

Calcined eggshell-

99.06 %

Tangboriboon et al., 2012

Calcined eggshell

2-

Borhade et al., 2017

Calcined waste eggshells-

92%

Panagiotou et al., 2018

Eggshell ash

121

90%

Torit et al 2018

Salted Calcined eggshell

3.32 ± 0.06

96.2%

Yirong et al 2019

Calcined eggshell

108.2

-

Lee et al., 2022

Eggshell and Rice straw

231-

Liu et al., 2019

Eggshell and Rape Straw

109.7

-

Cao et al., 2020

72.0

83 %

P´erez et al., 2020

270

98.10%He et al., 2020

251.16-134-

Potato peels and eggshell

174.8

85.96%

Quisperima et al 2022

Iron Hydroxide-Eggshell

69.5

50%

Almeida et al., 2020

Magnesiothermal eggshell

43.33

100%

Mezenner et al., 2009

6.22

-

Ahmad et al., 2017

Al-Eggshell

11.52

99.06%

Gao et al., 2017

FeCl3-eggshell

3.95

99.13%

Xu et al., 2018

Iron oxyhydroxide-eggshell

328.9

-

Zhang et al., 2017

Adsorbent

Eggshell and Palm fiber
pyrolyzed
Tobacco stalks, mg, andeggshell
Sugarcane bagasse andeggshellPalm mesocarp fiber andeggshellAluminum-modified
eggshell

16

Reference

Liao et al., 2022
Pérez et al., 2022

Chapter 2

CHAPTER 2

Effects of the different mixing ratio of bamboo char andeggshell powder on phosphate adsorption mechanism:
Adsorption isotherm and thermodynamics analysis.
This section is partially based on manuscript:“Thermally modified bamboo-eggshell adsorbent for phosphate recovery and its
sustainable application as fertilizer” by Sarker, P., X. Liu, N. Hata, H. Takeshita,
H. Miyamura and M. Maruo published on Environmental Research (2023).
https://doi.org/10.1016/j.envres.2023.115992

17

Chapter 2

1. Introduction
Phosphorus is a nonrenewable resource which is an essential growth nutrient for plant andaquatic algae. The main source of phosphorus fertilizer is the phosphorus rock that is depletingso fast that after few decades later future generation will face the crisis of phosphorus (Honget al., 2020). On the other hand, eutrophication is major water pollution caused by excessive
release of phosphate as nutrient from sewage effluent and agricultural runoff (Xia, et al., 2020).
Phosphate released in water could be recovered and utilized as phosphate fertilizer to combat
severe water pollution and meet fertilizer demand (Kumari et al., 2020).
Although physical, chemical, and biological processes are effective for phosphate removal,each process has some drawbacks, such as expensive materials and maintenance costs. (Bacelo
et al., 2020). Adsorption has been used as an attractive alternative method to treat phosphoruscontaining wastewater, which is easy to operate, and effective (Bacelo et al., 2020; Veni et al.,2017). Traditional adsorbents such as activated carbon and artificial organic resin polymer, as
well as new type nano-adsorbents, have been found to be effective in phosphate adsorptive
recovery. (Kumar et al., 2017; You et al., 2018; Zong, 2013), but these materials are not costeffective and have the disposal problem after adsorption (Nguyen et al., 2014).
Removal of phosphate using different metals like Ca, La, Mg, Mn, Fe, and Al oxides hybrid
carbon composites had been introduced before. In some cases, the phosphorus adsorbed
material could not be used as fertilizer because of the presence of heavy metal in modifiedadsorbent (Haghseresht et al., 2009; Huang et al., 2015; Yang et al., 2014; Yin et al., 2016). As
a result, researchers are searching for a low-cost and environment friendly adsorbent material
for phosphate recovery (Veni et al., 2017). Different types of agricultural waste material havebeen used effectively as adsorbents for phosphate removal (Bacelo et al., 2020).
That’s the reason why the current study is planning to recover the phosphate from wastewaterusing a most convenient procedure and locally available biowaste materials. Bamboo andeggshells are available natural ingredients which was not used for phosphate recovery before.
Bamboo is a common, cheap, and readily available source of biomass in Asian countries. There
are over 90 genera of bamboo and more than 1200 species, which occupy more than 14 million
ha land worldwide. Eighty percent of bamboo species and forests are found in South andSoutheast Asia, including China, India, and Myanmar (Lobovikov et al., 2007). Compared withother types of biochar, such as wood, bamboo produces a high-density porous structure after
pyrolysis and increases adsorption capacity which is a benefit of using bamboo as biochar
18

Chapter 2(Zhao et al., 2008). Since bamboo char is the source of carbon and eggshells contain CaCO3
could be used as a metal cation which has great affinity for phosphate. Moreover, calcium is
not toxic (Quina et al., 2017). Since pure biochar is not effective for the phosphate removal,
the combination of pure biochar with calcium could be a good adsorbing material to recoverphosphate as fertilizer (Liu et al., 2019).
Adsorption isotherm study and thermodynamic analysis is very important to reveal theadsorption mechanism. Adsorption isotherm is very important to calculate whether the reaction
is monolayer or multilayer adsorption. Adsorption isotherm constant is necessary to calculate
Langmuir separation factor to understand whether the adsorption nature is favorable orunfavorable (Borhade et al., 2017). Thermodynamic analysis dictates the effects of temperature
on adsorption process, reaction spontaneity from Gibbs free energy (negative ΔG° indicate
spontaneous reaction), and enthalpy indicates the total energy available to do work, whether
the reaction is exothermic (positive enthalpy) and endothermic (negative enthalpy) nature.
Some adsorption process uptake heat energy from the environment and some reaction releaseheat energy (Kalaitzidou et al., 2022).

Entropy describes the degree of disorder andrandomness of the motion of the adsorbed molecules, and its level. Enthalpy-entropy evaluate
sorption reactions (physical and chemical phenomena) and the nature of the interactions
between the solute and solvent to cause the reactions, and that the relationship between theenthalpy and entropy for a specific reaction is linear (Trazzi et al., 2016).
In this study, calcined eggshell powder and different mixing ratios of bamboo and eggshell at
different calcination temperatures were investigated to prepare adsorbent. Then the differencesin the chemical structure of the adsorbent materials after calcination and after adsorption, wereidentified by the FTIR, SEM Image, and EDX analysis. Then the adsorption mechanism was
examined by the adsorption isotherm model and the thermodynamics analysis. Langmuir
separation factor (RL) was also calculated to understand the adsorption nature.

19

Chapter 2

2. Materials and Methodology
2.1 Preparation of working solution
Working solutions of potassium dihydrogen phosphate (KH2PO4) for experiments was
prepared by diluting the phosphate stock solution of 10 PO4-P g/L with distilled water.
Different initial concentrations of phosphate solution (5, 10, 25, 50, 100, and 150 PO4-P mg/L)
were prepared from the stock solution of 10 PO4-P g/L.

2.2 Preparation of adsorbent
Bamboo (Phyllostachys bambusoides) powder was collected from the Kentomu Co., Shiga,
Japan, and was oven dried at 105 °C for 24 h, then sieved through a meshes sieve (pore size:
0.3 mm) before use. Eggshell was collected from the cafeteria of The University of Shiga
Prefecture, Japan. Eggshell was washed several times with tap water and then was rinsed 3
times with MQW. It was oven dried as same as the bamboo to remove moisture content (Wanget al 2010). After the treatment, dried eggshell was grounded by mortar, and was passed throughthe same mesh sieve as that used for bamboo. 20 g mixture of bamboo and eggshell powder
was taken for calcination. To evaluate the effect of calcination temperature on eggshelldecomposition from CaCO3 to CaO, each sample was placed in a muffle furnace under threetemperatures (600, 700 and 800 °C) for 2 h, respectively. Previous study showed that theeggshell can be completely decomposed at 800 °C (Shen et al., 2018). Then, the calcinedmaterials were preserved in desiccator. Calcined bamboo mixed eggshell was denoted as BE;
calcined eggshell as CE, and only bamboo char (BC) was also prepared. To investigate theoptimal adsorption capacity of mixture of bamboo char and eggshell, different mass ratio wastested, i.e., BE 1:1, BE 2:1 and BE 10:1 at 800 °C, respectively.

2.3 Adsorption experiments
All the adsorption experiments were performed as batch experiments. Adsorbent material (0.01g) was placed in a 50 mL polyethylene tube containing a P solution (40 mL) at pH 7, and thepolyethylene tubes were agitated (220 rpm) at 25 °C. The suspension was filtered through 0.45
μm cellulose acetate filter paper (C045A047A, ADVANTEC, Japan) and the P concentration
was determined by spectrophotometer (U-2000A, Hitachi, Japan) at the wavelength of 880 nm
using molybdenum blue method with ascorbic acid as the reductant (Murphy and Riley, 1977).

20

Chapter 2

2.4 Phosphate measurement procedure
Phosphate was measured using molybdenum blue method with ascorbic acid by
spectrophotometer (U-2000A, Hitachi, Japan).
 Chemicals:
1. Conc. H2SO4 70 mL+500 mL MQ water
2. K(SbO)C4H4O6･1/2 H2O (1.3715 g) + 500 mL MQ water
3. (NH4) Mo7O24･4H2O (20 g) + 500 mL MQ water
4. Ascorbic acid: 1.76 g of Ascorbic acid dissolved into 100 mL of MQ water.
 Standard solution of P for the calibration curve:
0.1361 g of KH2PO4 was dissolved into water and adjusted the volume at 250 mL. This stock
solution contains 4000 µmol/L (4 mmol/L) of P was stored in a plastic bottle in a fridge. From
this stock solution, working standard solutions of 40, 20, 10, and 5 PO4-P µmol/L wereprepared in 100 mL volumetric flask.
 Working reagent preparation for phosphate measurement:
50 mL of 2.5 mol/L H2SO4, 5 mL of K(SbO)C4H4O6･1/2 H2O, 15 mL (NH4) Mo7O24･4H2O(20 g) and 30 mL ascorbic acid solutions were mixed to prepare working solution for phosphatemeasurement.
Phosphate determination process: 8 mL of sample was taken into 10 mL of test tube, 1.6 mL of working reagent wasadded, then 0.4 mL of water was added and mixed well.
 After 10 min, absorbance was measured using spectrophotometer at 880 nm with quartz
cell of 10 mm pathlength. Absorbance measurement should be completed within 30
min after addition of working reagent.
 Calibration carve (linier regression) was prepared in the same manner for thedetermination.
2.5 Phosphate adsorption capacity
The adsorption capacity (Qe, mg/g) of the sorbent material for P was calculated by massbalance as expressed in Eq. (1).
𝑄𝑄𝑒𝑒 =

𝑉𝑉(𝐶𝐶0 −𝐶𝐶𝑒𝑒 )𝑚𝑚…………………………(1)21Chapter 2

Where, C0 and Ce are the initial and equilibrium concentration of phosphate in solution (mg/L),
respectively; V is the volume of solution (L), and m is the adsorbent mass (g).

2.6 Adsorption Isotherm and thermodynamic analysis
Adsorption Isotherm
Adsorption isotherm was investigated by altering the initial P concentrations (0, 5, 10, 25, 50,
100, and 150 mg/L). The adsorptions were performed at 25 °C, pH 7, agitation speed at 220
rpm for 24 h using 0.01 g of BE 1:1 (800°C), BE 2:1 and CE (0.01 g) as an adsorbent.
Experimental data sets were fitted with the Langmuir and Freundlich isotherm models. R
Studio software was used for the isotherm models curve fitting (R Core Team 2021).

Langmuir models describe the monolayer adsorption on the homogenous surface of theadsorbent, where no interaction occurs between phosphate ion and the adsorbent surface(Habiby et al., 2019). Langmuir equation can be written as:
𝑄𝑄𝑒𝑒 = 𝑄𝑄𝑚𝑚𝑚𝑚𝑚𝑚 𝑏𝑏𝑏𝑏𝑏𝑏/(1 + 𝑏𝑏𝑏𝑏𝑏𝑏) ………………………….(2)where, Qmax represents the maximum adsorption capacity (mg/g). The Qe is the amount of P
adsorbed per gram of adsorbent at equilibrium state, b is the Langmuir constant which is related
to the amount of adsorption energy (L/g). b and Qmax are calculated by plotting Qe versus Ce,
where the b is the slope and the Qmax is the intercept of the linear Langmuir model.

The Freundlich isotherm model describes the multi-layer adsorption on heterogeneous surfaces
with non-uniform energy distribution overactive binding sites of the adsorbent (Abbasi, 2017).
1�

Qe = 𝐾𝐾𝑓𝑓 𝐶𝐶𝑒𝑒 ( 𝑛𝑛) ………………….(3)where, Kf represents the Freundlich affinity coefficient (mg(1-n)Ln/g), The Qe is the amount of
P adsorbed per gram of adsorbent at equilibrium state, Ce is the equilibrium solution
concentration (mg/ L) of the sorbate, and n is the Freundlich linearity constant which is related
to heterogeneity of the surface. n is the adsorption intensity. If n = 1, the partition between thetwo phases is independent of the concentration. If the value of 1/n is below 1, it indicates anormal adsorption. On the other hand, 1/n higher than 1 indicates cooperative adsorption(Borhade et al., 2017).
22

Chapter 2

Thermodynamic analysis
To examine the effect of temperature on phosphate adsorption, 0.01 g of adsorbent BE 1:1 andBE 2:1 was added in a polyethylene tube containing 40 mL of phosphate solution with different
initial concentrations (0, 5, 10, 25, 50, 100, and 150 PO4-P mg/L). Different initialconcentrations were prepared from 10 PO4-P g/L stock solution. The experiments were divided
into three groups, each of which oscillated for 24 h at three different temperatures of 25 °C,
35 °C, and 45 °C, respectively. After the oscillation, the mixed solution was filtered and thephosphate concentration in the filtrate was analyzed. All experiments were performed triplicate.
2.7 Adsorbent dose
Optimum adsorbent dose was investigated by adding three different amounts (0.01 g, 0.05 g,
and 0.1 g) of adsorbent of different BE ratio (CE, BE 1:1, BE 2:1, and BE 10:1) in 40 mL ofphosphate solution of 100 PO4-P mg/L. Then the solution was agitated at 200 rpm at pH 7,
25 °C temperature for 24 h. After filtration final phosphate concentration was measured. All
experiments were performed triplicate.
2.8 Characterization
The morphological changes of the adsorbent before and after adsorption was analyzed by using
Miniscope TM3030, (Hitachi, Japan) Scanning Electron Microscope (SEM) (Figure 1a).
Fourier transform infrared spectrometer (FTIR) spectra were observed by FT/IR-4100 (JASCO,Japan) (Figure 1b) to investigate the presence of the functional group after calcination andadsorption process. EDX or energy dispersive X-ray spectrometry was analyzed for theelemental composition of the P adsorbed material by X-ray microanalyzer EMAX-7000 with
Scanning Electron Microscope S-3200 N (Hitachi, Japan).

3. Result and discussion
23

Chapter 2

3.1 Adsorption isotherm
The Adsorption Isotherm model curve for the CE and BE adsorbent has been shown in Figure
2 which indicates that the phosphate adsorption capacity was enhanced with increasing initialconcentration of the solution. The experimental data were fitted by the Langmuir model, whereR² value is higher than the Freundlich model and similar result was obtained by Köse andKıvanc et al. (2011). Langmuir model describes the monolayer adsorption on the homogenous
surface of the adsorbent (Habiby et al., 2019). From adsorption isotherm study, maximum P
adsorption capacity (Qmax) values were found 95.14 and 98.40 PO4-P mg/g for the BE 1:1 andBE 2:1 ratio respectively, compared to that in CE (68.77 mg/g) (Table 1). That means after
addition of bamboo char the adsorption capacity of eggshell was increased. May be the additionof biochar increases the surface area of the adsorbent and the calcium from eggshell creates themetal modified biochar which is suitable for phosphate adsorption (Liu et al., 2019; P´erez etal., 2020; He et al.,2020). Whereas the lowest Qmax (24.26 PO4-P mg/g) was obtained for BE
10:1 adsorbent which indicates addition of excess amount of biochar (BE 10:1) was noteffective for phosphate adsorption. Similar result was found by Liu et al. (2019), who explained
this condition because of presence of less or no active site availability in adsorbent (Liu et al.,2019).
The high values of constant b and Kf indicates that the affinity between adsorbent and adsorbate
was good for the reaction. When the value of n (Freundlich linearity constant) is greater than2, it also indicates that temperature has effects on phosphate adsorption capacity and 1/n was<1, indicating natural adsorption (Guo et al 2017; Ahmed et al., 2017; Borhade et al., 2017).

3.2 Effects of Temperature
The temperature has a significant effect on the phosphate adsorption capacity. At different
temperatures the Langmuir model also showed that maximum phosphate adsorption capacity(Qmax) varies with temperature changes (Table 2). Thermodynamic analysis was calculated at
different temperatures. Effects of temperature were experimented with BE 1:1 and BE 2:1
adsorbent material. After increasing temperature to 308K the adsorption capacity wasdecreased from 298 K temperature, then it was increased to 318K temperature (Table 2).
Effects of temperature on phosphate adsorption process were observed for thermodynamic
analysis. Thermodynamic parameters describe the changes of the energy during adsorption
process. From the thermodynamic equation (4) and (5), ΔG° (KJ/mol) was calculated. ΔS°
24

Chapter 2(J/mol·K) and ΔH° (KJ/mol) was obtained from the intercept and slop of the linear plot of ΔG°
against temperature T (K) (Figure 3) (Liu et al., 2019). Thermodynamic equation has been
given bellow:
ΔG° = ΔH ° − 𝑇𝑇ΔS ° .........................(4)where, ΔG° was Gibbs free energy, ΔS° was Entropy, and ΔH° was enthalpy.
ΔG° = −𝑅𝑅𝑅𝑅 ln 𝑏𝑏………………….(5)where, R was the universal gas constant (8.314 J/mol·K), T was temperature (K), b is theLangmuir adsorption constant (L/mg) (Yu et al., 2020).
In case of BE 1:1 and BE 2:1 adsorbent, adsorption reaction was not spontaneous (ΔG > 0) at
298 K, (Table 2). The spontaneity of the reaction was increased with increasing reaction
temperature, but the maximum adsorption capacity was decreased to 308 K temperature thenincreased again to 318 K temperature. Negative enthalpy indicates the exothermic reaction(Zhu et al., 2018; Abdelhay et al., 2018) and in an exothermic adsorption reaction, the hightemperature decreases the phosphate adsorption capacity (Habiby et al., 2019). Positive entropyof the system means high randomness of the adsorbate and adsorbent in liquid solution (Liu etal., 2019).
Langmuir separation factor
Langmuir separation factor (RL) calculates the adsorption nature which can be identified by thefollowing equation (6) (Ajenifuja et al., 2017):
1

𝑅𝑅𝐿𝐿 = 1+𝑏𝑏𝐶𝐶 …………………………(6)0where b is the Langmuir adsorption constant, and C0 is the initial P concentration (mg/L).

According to the present experiment the RL value (Table 2) was found between 0 to 1 whichindicates favorable adsorption conditions for phosphate at different reaction temperatures andinitial concentrations. When the initial concentration was 0, RL value was 1 indicating linear
adsorption (Table 3).

25

Chapter 2

3.3 Effects of adsorbent amountTo find out the optimum dose of the adsorbent, different adsorbent amounts were used during
the experiment. Different mixing ratios of bamboo and eggshell were tried to find effective
adsorbent. Calcined eggshell powder and BE mixtures were found effective for phosphateremoval. From Figure 4 it has been seen that the phosphate adsorption capacity decreased after
adding more amount of adsorbent. high phosphate adsorption capacity was found 102.16 mg/g
for 0.01 g adsorbent of BE 1:1 ratio. After addition of more doses of adsorbent the removal
efficiency decreases because of less contact between phosphate ions and per unit mass of theadsorbents that means more unoccupied active sites did not take part in the adsorption process(Dragan et al., 2014). Additionally, repulsive force between active sites might slow down thereaction process (Torit et al., 2018) that’s why in the present study, 0.01 g has been chosen as
the optimum dose for highest phosphate removal capacity. Which may reduce unnecessary
adsorbent use and cost.

3.4 Characterization
3.4.1 SEM Image and EDX spectrum
The SEM images showed morphological differences before and after P adsorption. Figures 5
and 6 show an identical difference between calcined eggshell and the BE 1:1 because of theaddition of bamboo fiber. And after adsorption there were some accumulations of the
precipitant on the surface of the adsorbent (Liu et al., 2019).
Figure 6 shows the changes of the SEM image of calcined BE 2:1 and BE 10:1 before and after
adsorption, where the structure of the adsorbents was fiber like, because of the presence ofmore bamboo char (He et al., 2020). After adsorption in the SEM image of BE 10:1, noaccumulations have been noticed. EDX spectrum (Figure 7 and 8) of the BE 1:1 and BE 2:1
after adsorption illustrated the presence of phosphate after adsorption and the distribution of
the oxygen, calcium, and phosphate in the adsorbent material. From Figure 7 it has been seenthat the green color image of calcium (Figure 7b) is more intense than yellow color image ofphosphate (Figure 7a), which indicate there are some vacant active sites remaining in thematerial. Figure 8 also illustrates the similar results for BE 2:1. Therefore, the characterizationof the material before and after adsorption confirmed that the mixture of bamboo and eggshell
could adsorb phosphate from wastewater.
26

Chapter 2

3.4.2 FTIR analysis
The FTIR spectrum was analyzed on FTIR spectrometer (FT/IR-4100, JASCO, Japan) in therange of 4000–400 cm−1. Figure 9 (a) and (b) show FTIR spectrum within 4000–400 cm-1
wavenumber range for CE and BE 2:1 respectively, at different temperature 600°C, 700°C, and
800°C. The absorption peaks were observed at 1750.06 cm−1, 1411.89 cm−1, and 871cm−1
before calcination, and this fact confirmed the presence of CaCO3 (Borhade et al., 2017).
From Figure 9 (a) and (b) it can be observed that eggshell calcined at 600°C contain peak at
1750.06 cm−1, 1411.89 cm−1, and 871cm−1. That meant at 600°C CaCO3 was present in the CE
powder (Borhade et al., 2017), but at 700°C, 800°C the peak at about 710 cm−1 attributed tothe presence of CaO (Torit et al. 2018). For BE 2:1 sample calcination starts at 600°C. Similar
band was seen for BE 2:1 calcined at 600°C which indicate that after mixing bamboo powder
with eggshell calcination process need lower temperature than only eggshell powder. After
calcination the intensity of the band for CaCO3 decreases. Both bands at 710 cm−1 and 871cm−1
are absent in only BC (bamboo char) samples (Figure 9 c).
This modification process is suitable for phosphate adsorption (Torit et al., 2018). From Figure
10, it can be seen the changes of the FTIR spectra after the adsorption process. A clear new
band at 1024 cm-1 was observed after phosphate adsorption on BE 1:1 which was not visible
before adsorption. Only calcined eggshell also shows small stretch for phosphate adsorption
but BE1:1 shows deep band at 1024 cm-1 (Liu et al., 2019).

4. Summary
Modification of biochar with eggshell using calcination process is effective for P removal.
From adsorption isotherm study, maximum phosphate adsorption capacity for the CE, BE 1:1
and BE 2:1 was found 68.77 and 95.14 and 98.40 mg/g at 25 °C respectively. The experimental
data for the CE, BE 1:1 and BE 2:1 adsorbent was better fitted by the Langmuir model, whereR² value is higher than the Freundlich model. That means addition of bamboo powder enhances
the phosphate adsorption capacity where excess addition of biochar (BE 10:1) was not efficientfor phosphate adsorption.
Thermodynamic study was performed for different initial concentration at 25 °C, 35 °C, and
45 °C temperature. Then the thermodynamic study Langmuir separation factor (RL) was
calculated.
27

Chapter 2

For BE 1:1 and BE 2:1 ratio the reaction was not spontaneous at 298 K. The spontaneity of thereaction increased with increasing reaction temperature. Negative ΔH indicate the process is
exothermic, and Positive entropy of the system means the randomness of the adsorbate andadsorbent in liquid solution increases. and the calculated Langmuir separation factor (RL)
indicates the favorable conditions for phosphate adsorption. After using three different doses(0.01g, 0.05g and 0.1g) of the adsorbent of different mixing ratio, 0.01g doses of BE 1:1 andBE 2:1 was found better than other doses and mixing ratio. Maximum phosphate adsorption
capacity was found 102.16 PO4-P mg/g for 0.01g doses of BE 1:1.
Adsorbent materials were prepared mixing eggshell and bamboo powder in different mixing
ratio and different calcination temperatures were tried. After calcination the characterization of
the materials was performed by SEM image, EDX analysis and FTIR analysis. After
calcination at 600°C, 700°C, and 800°C temperature, FTIR band of CE and BE 2:1 showsdifference in the formation of CaO and CaCO3. The presence of stretching band at 871cm-1
indicates the formation of the -OH group after calcination process. Both bands at 710 cm-1 and871cm-1 are absent in only bamboo char sample and after adsorption process, they are almost
disappeared. A clear new band at 1021 cm-1 was observed after phosphate adsorption on BE
1:1 which was not visible before adsorption. Only calcined eggshell also shows small stretch
for phosphate adsorption. But BE 1:1 shows deep band at 1024 cm-1. SEM image also founddifference between before and after adsorption adsorbent image. There is some aggregation of
precipitate was noticed after adsorption. EDX analysis detects the presence of phosphate after
adsorption in adsorbed material. From the experiment it has been confirmed that the mixing
ratio of the bamboo and eggshell powder has influence on the adsorption process. So, it isnecessary to study more about adsorbent preparation and adsorption isotherm andthermodynamic for different adsorbent material to find most effective adsorbent for phosphateremoval.

28

Chapter 2a)b)Figure 1: a) Scanning Electron Microscope (SEM). b) FTIR spectrometer

29

Chapter 2

Table 1: Fitting parameters of the adsorption isotherm equilibrium for phosphate onto CE andvarious BE (1:1, 2:1, 10:1) samples.
Langmuir model
Adsorbents

Qmax(PO4-P mg/g)

Freundlich modelb (L/mg)

R2

Kf (mg(1-1/n)L1/n/g)

n

R2

CE

68.77

0.412

0.794

43.11

9.994

0.777

BE 1:1

95.13

0.438

0.857

60.27

9.994

0.838

BE 2:1

98.40

0.041

0.920

10.94

2.350

0.819

BE 10:1

24.26−0.180

0.464

26.07

9.994

0.094

30

Chapter 2

Figure 2: Adsorption isotherms of phosphate with different forms on (a) CE, (b) BE 1:1, (c) BE 2:1. The solid and dashed lines indicated the fitted
Langmuir and Freundlich model, respectively. Error bar indicates standard deviation.

31

Chapter 2

Table 2: Thermodynamic parameters and Langmuir separation factor for the adsorption of phosphate in different adsorbents (BE 1:1, BE 2:1).
Adsorbents
BE 1:1EE 2:1T (K)Qmax (mg/g)

RL

ΔG (KJ/mol)

298

95.13

0.31-0.01

1.98

308

87.17

0.16-0.006

-0.08

318

112.16

0.15-0.006

-0.34

298

98.40

0.83-0.14

7.91

308

65.14

0.07-0.002

-2.53

318

76.85

0.002-7.05E-05-12.0332

ΔS (J/mol.K)

ΔH (KJ/mol)

363.56-0.116305.73-0.997

Chapter 2

Figure 3: Linear regression of ∆G (KJ/mol) against Temperature (T), where slope ΔS (J/mol·K) and ΔH (KJ/mol) was obtained from the intercept
and slop, a) BE 1:1 as adsorbent b) BE 2:1 as adsorbent.

33

Chapter 2

Table 3: Adsorption nature (Langmuir separation factor)
RL

Adsorption nature(RL > 1)

Unfavorable(0 <RL < 1)

Favorable(RL=1)

Linear(RL < 0)Irreversible(Zhu et al., 2018, Ahmed et al., 2017)34

Chapter 2

Figure 4: Phosphate (P) adsorption capacity of different adsorbent materials (CE, BE 1:1, BE
2:1, BE 10:1) for different adsorbent amount (0.01, 0.05, 0.1 g) (pH: 7; Initial P concentration:
100 mg/L; Temperature: 25 ºC; Time: 24 h). Error bar indicates standard deviation.

35

Chapter 2

a)

b)

c)

d)

Figure 5: SEM images of CE (a, b) and BE 1:1(c, d) before and after adsorption

36Chapter 2

a)

b)

c)

d)

Figure 6: SEM images of calcined BE 2:1 (a, b) and BE 10:1 (c, d) before and after adsorption

37

Chapter 2

a)

b)

c)

d)

Figure 7: EDX spectrum of distribution of the a) Phosphate b) Calcium c) Oxygen d) EDX
spectrum mapping for elemental composition of BE 1:1 after adsorption.

38

Chapter 2

a)

b)

c)

d)

Figure 8: EDX spectrum of distribution of the a) Phosphate b) Calcium c) Oxygen d) EDX
spectrum mapping for elemental composition of BE 2:1 after adsorption.

39

Chapter 2

Figure 9: FTIR analysis of (a) CE and (b) BE 2:1 at 600, 700, and 800 °C, respectively, and (c) BE 1:1, BE 2:1, BE 10:1, and CE and BC at 800 °C.

40

Chapter 2

Figure 10. FTIR spectra for BE 1:1 before and after adsorption, BE 2:1 and CE after adsorptio

41

Chapter 3

CHAPTER 3

Adsorption kinetic study and influence of the pH, anions,and organic matter on phosphate removal using calcined
eggshell and bamboo char as adsorbent.

This section is partially based on manuscript:“Thermally modified bamboo-eggshell adsorbent for phosphate recovery and its
sustainable application as fertilizer” by Sarker, P., X. Liu, N. Hata, H. Takeshita,
H. Miyamura and M. Maruo published on Environmental Research (2023).
https://doi.org/10.1016/j.envres.2023.115992

42

Chapter 3

1. Introduction
Nowadays, eutrophication is a global environmental problem which is the most popular topic
for researchers (Charlton et al., 2018). Anthropogenically, huge amount of phosphorus
discharges into waterbody as agricultural runoff and synthetic detergent in domestic
wastewater. But when the excessive amount of phosphorus goes into waterbody, it works as anutrient for aquatic plants and algae and causes eutrophication (George et al., 2017). So, therecovery of phosphate from this source will be beneficiary for us. Among different phosphateremoval technologies, adsorption is a very convenient process because several natural materials
were used effectively as an adsorbent after different types of modification (Nguyen et al., 2014).
Different researchers used agricultural waste-based biochar with eggshell as a low cost andecofriendly adsorbent to treat the eutrophication problem of the waterbody (Zhou et al., 2021).
Pyrolyzed eggshell with rice husk (Liu et al., 2019), palm fiber (P´erez et al., 2020), rape straw(Cao et al., 2020) and tobacco stalks (He et al., 2020) was investigated as adsorbent forphosphate removal.
The present study emphasized on using natural ingredient for phosphorus removal. Bamboo
powder was used as carbon source and eggshell was used as calcium carbonate source. Purebiochar has a negative charge on the surface, which is suitable for removing heavy metals andorganic pollutants (Ramola et al., 2014; Yang et al., 2016), That’s why, some modification isnecessary to increase adsorption capacity for negatively charged pollutants like phosphate(Nguyen et al., 2014). Phosphate adsorption process might be controlled by physical adsorption
or chemical adsorption. This mechanism could be identified by the adsorption kinetics models.
Adsorption kinetic models are very useful to understand the phosphate adsorption process andreaction rate, and from the results of modeling, we can know whether the adsorption process iscontrolled by physical adsorption or chemical adsorption mechanism (Borhade et al., 2017).
Pseudo first order model indicates the adsorption reaction is controlled by the diffusion process
and Pseudo second order model indicates the adsorption reaction is controlled by the chemical
adsorption process. In chemical adsorption process, the adsorbent and the adsorbate exchangeor share electrons to form new compounds (Lalley et al., 2016).
From literature, it was found that the eggshell and biochar-based adsorbent better fitted thepseudo second order model which indicates the chemisorption (Liu et al., 2019; P´erez et al.,2020; He et al., 2020). Liu et al. (2019) found that adsorption rate was fast within 2 h after thatthe reaction rate became slow, then adsorption equilibrium was obtained within about 6 h for
43Chapter 3

all CE and BC samples. The reason for the fast initial reaction is rapid diffusion of ions fromthe solution to the external adsorbent surfaces, then the slower adsorption process was
explained by internal porous diffusion (Zhao et al., 2011). Since the active adsorption site of
the eggshell modified biochar has increased so the diffusion process also changed into chemical
sorption process. Adsorption process of only biochar is a physical adsorption process governedby a weak Van der Waals interaction (Cao et al., 2020).
Adsorption process has been influenced by the different factors such as, pH and presence of
co-existing anions (Kalaitzidou et al., 2022). pH is an important parameter which influences
the phosphate adsorption procedure in several ways. The dissolved form of phosphate in water
is dependent on the pH of solution. Phosphate has three different ionic stages at different pH.
When pH of the solution is in the range 2.15 - 7.20, the dominant form of phosphate is H2PO4(pKa1 as H3PO4: 2.15, and pKa2 as H2PO4-: 7.20), in the pH range 7.20 -12.33, HPO42- isdominant, and pH above pKa3: 12.33, PO43- becomes dominant (Mitrogiannis et al., 2017). pH
below 2 and pH above 7 are not suitable for phosphate adsorption (Pandi et al., 2021).
The surface charge of the adsorbent is also affected by the pH of the solution and point of zerocharge (pHpzc) of the adsorbent. Surface charge of the adsorbent affects phosphate adsorption
capacity. For eggshell modified biochar, pH above the pHpzc creates negative charge on thesurface of adsorbent which causes chemical interaction among phosphate and active site of theadsorbent (Liu et al., 2019; P´erez et al., 2020).
Natural water and wastewater may contain different types of anions and organic matter. Bothwaters contain chloride, bicarbonate, sulfate, and presence of these anions influences thephosphate removal efficiency because of competitive nature (Pandi et al., 2021). Domestic
wastewater also contains a high concentration of nitrate and sulfate ions. Quisperima et al.
(2022) used Ca-bio composites for P adsorption from real domestic water and found 91.6%
removal efficiency for P removal, 53.8% removal efficiency for NO3− removal but SO42−
adsorption capacity was very low.
Dissolved organic acid may affect phosphate removal efficiency after interacting with calciumof the adsorbent material (Alsherbi et al., 2022). To understand the influence of organic matteron phosphate adsorption, it is important to examine the phosphate removal efficiency in thepresence of other dissolved organic matter.
Some organic phosphorus from agricultural runoff (organo-phosphorus herbicide) andpharmaceutical wastewater also causes serious water pollution (Shushkova et al., 2016; Jiang
44

Chapter 3

et al., 2019). Glyphosate [N-(phosphonomethyl)-glycine] is a worldwide used organophosphateherbicide which contains three polar functional groups (-NH, -COOH and -PO3H2) (Rissouli
et al., 2017). It is commonly applied to control unwanted vegetation, weeds, and grasses (Heet al. 2019). But excessive amounts of pesticide and herbicide changes soil microbialcommunity composition and ecosystems and reduces crop tolerance (Sen et al., 2019), so it isharmful for the environment.
When glyphosate enter natural water system through the agricultural runoff, it causes waterpollution, and it may work as a source of phosphate for some microorganisms by utilizing C-P
lyase (Shushkova et al., 2016).
If glyphosate enters the bloodstream through the stomach and the skin cause acute and sublethal
and chronic toxic effect, which can be in the nerve paralysis and death of living beings (Veraet al, 2010). Moreover, it has teratogenesis, carcinogenesis, mutagenesis effects on humanhealth (Ramrakhiani et al., 2019). It is necessary to remove glyphosate from wastewater using
an effective, economic and environment friendly method.
The objectives of this study were (1) to understand the phosphate adsorption mechanism using
Pseudo first order kinetic model and pseudo second order kinetic model for calcined eggshell
powder and bamboo + eggshell adsorbent, (2) to examine the effects of pH and different anions
such as, Cl−, NO3−, CO32−, and SO42− on phosphorus removal capacity and the influence ofdifferent organic acids, such as citric acid, humic acid, and oxalic acid on phosphate removal
efficiency, and (3) to investigate the effectiveness of the glyphosate removal (organic
phosphorus) from wastewater.

45

Chapter 3

Figure 1: Distribution of phosphate species as a function of pH. (Currie et al., 2017)46

Chapter 3

2. Materials and methodology
2.1 Preparation of working solution
Working solutions of potassium dihydrogen phosphate (KH2PO4) for experiments wereprepared by diluting the phosphate stock solution of 10 PO4-P g/L with distilled water. 100
PO4-P mg/L working solutions were prepared by diluting the stock solution.

2.2 Preparation of adsorbent
Bamboo (Phyllostachys bambusoides) powder was collected from the Kentomu Co., Shiga,
Japan, and oven dried at 105°C for 24 h and finally sieved through a meshes sieve (0.30 mm)
before use. Eggshell was obtained from the cafeteria of The University of Shiga Prefecture,
Japan, which was washed several times with tap water and three times with distilled water, andwas oven dried at 105°C for 24 h to remove moisture content (Wang et.al 2010). Then it was
grounded by mortar to pass through a mesh sieve (0.30 mm).
20 g mixture of eggshell and bamboo shell powder 1:1 ratio was taken for calcination. Eachsample was placed in a muffle furnace and heated to 800 °C for 2 h. The thermal treatment
temperature of 800 °C was chosen since eggshell starts decomposition at 650 °C and iscompletely decomposed at 800 °C (Shen et al., 2018). After the furnace was cooled to room
temperature, the calcined material was denoted as BE (eggshell bamboo char). Calcined
eggshell (CE) was prepared using same procedure, and bamboo char (BC) was prepared also.

2.3 Adsorption kinetics
Adsorption capacity of phosphate was evaluated by mixing 0.01 g of CB, BE 1:1 and BE with
40 mL of 100 PO4-P mg/L solution in polyethylene tubes. The mixtures were oscillated at 220
rpm, pH 7 and 25 °C temperature. At defined time (5 min, 15 min, 30 min, 1 h, 2 h, 4 h, 6 h, 8
h, 12 h, 18 h, 24 h, 36 h, and 48 h), after adsorption the mixtures were collected, filtered, andfinal concentration of phosphate was analyzed by measuring the absorption at the wavelengthof 880 nm by molybdenum blue method using ascorbic acid (Murphy and Riley, 1977). U2000A (Hitachi, Japan) was used as spectrophotometer, and cell pathlength was 10 mm.

47

Chapter 3

2.4 Adsorption Kinetics model
Adsorption kinetics models are very useful to understand the phosphate adsorption process andrate. By fitting the empirical data, we can know whether the adsorption process is controlledby physical adsorption or chemical adsorption mechanism (Borhade et al., 2017). Pseudo firstorder and second order model were investigated using the data obtained from the phosphateadsorption capacity of different adsorbent time.

The adsorption capacity (Qe, mg/g) of the sorbent material for P was calculated by the massbalance as
𝑄𝑄𝑒𝑒 =

𝑉𝑉(𝐶𝐶0 −𝐶𝐶e )

(1)

𝑚𝑚

where, C0 and Ce (mg/L) are the initial and equilibrium P concentration in solution,
respectively, V (L) is the solution volume, and m (g) is the adsorbent weight.

In the following the linear form of the pseudo-first order relationship is shown:ln(𝑞𝑞𝑒𝑒 − 𝑞𝑞𝑡𝑡 ) = ln 𝑞𝑞𝑒𝑒 − 𝑘𝑘1 𝑡𝑡 ……………………(2)where, qt is the amount of ion per gram of adsorbent (mg/g) at time t and k1 is adsorption
constant (min−1), which is calculated by plotting the ln (qe – qt) versus t. (Foroutan et al., 2017).
The linear form of the pseudo-second order relationship is shown:
𝑡𝑡

𝑞𝑞𝑡𝑡

1

𝑡𝑡

= 𝑘𝑘 𝑞𝑞 2 + 𝑞𝑞 ……………….(3)
2 𝑒𝑒

𝑒𝑒

where k2 shows the second-order rate constant (g /mg.h). The qe and k2 values are determinedby plotting t/qt versus t (Habiby et al.,2019).
2.5 Effects of pH, co-existing anions, and organic acids●

To investigate the effect of pH on phosphate adsorption, 40 mL of 100 PO4-P mg/L
solution was added into a 50 mL polyethylene tube. The initial pH of the solution was
adjusted to different initial pH values (3, 5, 7, 9, and 11) by adding 0.1 mol/L NaOH or
0.1 mol/L HCl solutions. Then, 0.01 g of CE and BE 1:1 adsorbent was added andoscillated at 25 °C for 24 h, after that, the mixed solution was filtered through a 0.45
48Chapter 3

μm PES (Polyethersulfone) membrane filter, and the phosphate concentration and final
pH in the filtrate were measured, respectively.
● To test the effect of co-existing inorganic anions, 100 PO4-P mg/L solutions withvarious salts (KCl, KNO3, K2SO4, and KHCO3 at different concentrations (10, 20, 40,
60, 80, and 100 mg/L as final concentration) was mixed with 0.01 g of BE 1:1 adsorbent
in 50 mL polyethylene tube. After oscillating at 220 rpm, pH 7 and 25 °C temperaturefor 24 h, the supernatant was separated by filtration and analyzed. This experiment was
performed triplicate.
● Effects of organic ions- Citric acid, oxalic acid, and humic acid of each 100 mg/L and
200 mg/L solutions were mixed with 20 PO4-P mg/L solution. BE 1:1 adsorbent (0.01g)
was added in 40 mL of the solution of 100 and 200 PO4-P mg/L. Then the mixtures
were agitated at 200 rpm, pH 7 and 25 °C for 24 h. After filtration, final phosphateconcentration was measured. These experiments were performed triplicate.
2.6 Implication of BE 1:1 adsorbent on natural and treated wastewater
For this experiment 1 L of water samples were collected from three locations (Seri River:35°16'22.3"N 136°14'19.8"E, Uso river, 35°13'58.0"N 136°12'35.4"E, and outflow of treatedwastewater from Tohkubu Wastewater Treatment Plant at Hikone old harbor: 35°16'38.5"N
136°15'33.3"E). During sample collection water pH, EC and temperature was measured. pH
was measured using Pack test pH-PR (Kyoritsu chemical check lab corporation, Japan). EC
and temperature were measured by portable EC meter D-24 and 9382-10D sensor (HORIBA
corporation, Japan). After sample collection water was filtered with 0.45 μm PES(Polyethersulfone) membrane filter. Then 5 PO4-P mg/L phosphate was added to the sample
water, because the phosphate concentration of the water sample of this location is very low.
After that 0.01 g BE 1:1 adsorbent was added to the 40 ml of water sample and mixed at 200
rpm at 25 °C for 24 h, after that, the mixed solution was filtered through a 0.45 μm PES(Polyethersulfone) membrane filter. Then the final concentration of the inorganic phosphate
was measured by molybdenum blue method using ascorbic acid (Murphy and Riley, 1977). U2000A (Hitachi, Japan) was used as spectrophotometer, at 880 nm wavelength and cellpathlength was 10 mm. The anions and cations were measured using Ion Chromatography(DX-AQ, DIONEX, USA).

49

Chapter 3

2.7 Organic P(Glyphosate) removal using BE 1:1 adsorbent
A stock solution (50 mg/L) of the glyphosate (Fujifilm Wako Pure Chemical Cooperation,
Japan) was used to prepare different initial concentration (0, 5, 10, and 25 mg/L) of glyphosate
for organic phosphate adsorption study. For this experiment 0.01 g of the adsorbent material
was added to the 40 mL of the glyphosate solution in a 50 mL polyethylene tube and mixed at
200 rpm and 25° C for 24 h. The pH of the solution was maintained at 7 by adding 0.01 mol/L
NaOH. After adsorption the concentration of the phosphate was measured by ICP-MS (Neu
ION 1000, Perkin Elmer Co. Ltd.).
2.8 Statistical analysis
Pseudo first order kinetic model and pseudo second order kinetic model were analyzed using
R Studio software (R Core Team, 2021). Graphs describe the effect of pH, anions and organic
acids was produced using Microsoft-excel.

50

Chapter 3

3 Results and discussion
3.1 Adsorption kinetics
To understand the effects of time on phosphate adsorption process different contact time was
examined. From experimental data it was found the adsorption rates of P for CE and BE 1:1
increased after 1 h and equilibrium was reached after 4 h (Figure 2). The amounts of P adsorbed
at equilibrium time were 75.95 and 98.83 PO4-P mg/g for CE and BE 1:1, respectively (Table1). The experimental data was fitted by pseudo first order and pseudo second order kinetic
model. R2 value was calculated and highest R2 value was found for pseudo second order kinetic
model (Figure 2, Table 1). Pseudo second order model showed good correlation withexperimental data which indicates P adsorption process and adsorption rate was influenced bychemisorption (Agbovi et al., 2021), Which means calcium of the CE and BE 1:1 was reactedwith phosphate to form a strong new material by electron exchange process (Liu et al., 2019).
From the experiment (Table 2) it was found that only bamboo char is not suitable for phosphateadsorption. After using bamboo as an adsorbent, the concentration of phosphate was increased
at different time intervals, where initial concentration of phosphate solution was PO4-P 100
mg/L. It was assumed that phosphate was released from the adsorbent materials. To understandwhether phosphate was released from the bamboo char 0.01 g of BC (bamboo char) was added
to the 40 mL of MQ water at 220 rpm and 25° for 24 h. After filtration phosphate concentration
was measured, and 2.91 PO4-P mg/L phosphate was found from the bamboo mixed water.
Literature also showes that bamboo powder contain 0.03 % phosphate from the component
analysis (Table 3) (Fudano et al., 2016). Bamboo char without any modifican is not suitable
for the phosphate adsorption (Du et al., 2021).

3.2 Effects of pH
Different pH solutions were tested during experiments to understand the effects of pH on
phosphate adsorption process. Figure 3 shows that, For BE 1:1, at pH 5 and 7 (after adsorption
final pH 6 and 7), the highest P adsorption capacities of 103.28 and 111.22 mg/g were found,respectively. At pH 3 and 9 (After adsorption final pH 6 and 10) the lowest capacities of 8.7
and 35.99 mg/g were observed, respectively. From pH 5 to 7 the dominant form of phosphate
is HPO4 2- . After addition of the B+E 1:1 and CE, the final pH of each solution also increased.
51

Chapter 3

Calcined eggshell at 800 ºC contain Ca(OH)2, which increases the pH of the solution (Santos
et al., 2019). At pH below 5, physical interaction occurs between the adsorbent and phosphateion. But above pH 5 it forms a negative ion on the surface of adsorbent which increases thechemical interaction (Liu et al., 2019).
At high pH the adsorption capacity also decreases because the dominant form of phosphate inwater changes from H2PO4− to HPO42- which needs higher adsorption energy compared to
H2PO4− and difficult to be absorbed. The charge of the adsorbent also changes at high pH due
to the addition and removal of the proton of the adsorbent materials causing electrostaticadsorption. At high pH the presence of OH ion decreased the phosphate adsorption because itcompetes with phosphate ion for the active side of the adsorbent (He et al., 2022).
3.3 Effect of Anions
Generally, wastewater contain several types of anions like Cl−, NO3−, CO32−, and SO42−. So,
the presence of these anions may influence the adsorption capacity because they could competewith phosphate for the active site of the adsorbent (Loganathan et al., 2014). From Figure 4, it
has been seen that the presence of NO3− and Cl− has no significant effects on the phosphateadsorption capacity (Li et al., 2022). Whereas CO32− and SO42− decreased the P adsorption
from 94.58 to 3.2 PO4-P mg/g as the anion concentration increased from 10 to 80 mg/L (Figure4). This is because divalent anions may react more readily with Ca2+ from the eggshell than themonovalent anions (Das et al., 2006; Wang et al., 2017). It was revealed that the P adsorption
capacity decreased after increasing the concentration of the anions. Similar results were also
found by Liu et al., (2019) for eggshell + rice straw 1:1 ratio. This is the main limitation of thisprocess.
3.4 Effect of organic acids
Wastewater may contain different types of organic acid. To understand the effects of theorganic matter (citric acid, humic acid, and oxalic acid) on the phosphate removal efficiency
different concentration of organic acids (100 mg/l, and 200 mg/L) was experimented with 20
mg/L phosphate using BE 2:1 at pH 7. The results have been illustrated in Figure 5. It has beenfound that organic matter has influence on phosphate removal efficiency. The phosphateremoval efficiency was decreased more at high concentration (200 mg/L) of the organic acid.
Generally organic acids exist in water in anionic form which would compete for the active sites
on the adsorbent, thus reducing the phosphate removal efficiency (Afridi et al., 2019).
52

Chapter 3

3.5 Implication on natural water and comparative study
Table 5 shows the temperature, EC and pH which was measured during sample collection.
Phosphate concentration of the sample water collected from the Seri River, Uso river andtreated water was found 0.078, 0.116, and 0.86 mg/L respectively. Since the concentration wasvery low, for investigating phosphate removal efficiency 5 mg/L inorganic phosphate wasadded and the concentration was found 5.22, 5.16 and 5.19 mg/L respectively. After adsorption
the concentration was decreased and the removal efficiency was found 67.43, 71.12, and67.43 %, respectfully for the Seri River, Uso river and treated water (Table 5). In chapter 2,
phosphate adsorption capacity was examined for different initial concentrations. For initialconcentration of 5 mg/L, P adsorption capacity was found 22.97 mg/g. For both river waterand treated water, P adsorption capacity was found ~14 mg/g. This is because of theinterference of the coexisting ions and organic matter that is present in natural and wastewater(Pandi et al., 2021). Table 4 shows the presence of different anions and cations in Seri and Usoriver water (Table 4). Almeida et al., 2020 also found negative influence on the P adsorption
process, where removal efficiency was reduced from 99 % to 51.8 % for the effluent water.
Because phosphate adsorption was affected by the other anions and organic molecules.
There is very few research on the phosphate removal from real wastewater or natural waterusing adsorption. Table 6 shows the comparative study on the phosphate removal efficiency
performed by different researchers using different adsorbent materials. It has been seen thateggshell and eggshell based material is also effective to remove phosphate from real
wastewater.

3.6 Organic phosphorus (glyphosate) adsorption capacity using BE 1:1
From the experiment no adsorption of organic phosphorus (glyphosate) using BE 1:1, BC, CE
and Raw eggshell powder as an adsorbent was found (Table 7 and 8). The glyphosate moleculeis significantly larger than the phosphate molecule, it requires more space than phosphate. (Liuet al., 1999; Martin et al., 1999). From table 7 and 8 it has been seen that after adsorption using
BE 1:1 and bamboo char the final concentration of the phosphorus was increased. Because
bamboo powder contains phosphorus it has been found in literature (table 3) and experiments
also. Table 7 shows calcined eggshell and raw eggshell also not effective for the glyphosate
adsorption at pH 7 and 8.

53

Chapter 3This result is positive to fulfill the main objectives of this research work, Since the phosphorus
loaded material will be applied as fertilizer. If wastewater contain glyphosate and inorganic
phosphate, there would be no competition for the active site of the adsorbent material (DeGerónimo et al., 2022). Moreover, if glyphosate causes displacement of phosphate fromadsorbent and reacts with sorption site, it will need more amount of glyphosate application than
the regular application rate which is not cost effective (Barret. et al., 2007).
3.7 Cost estimation of adsorbent preparation
One of the main objectives of this work was to develop a low-cost adsorbent material fromlocally available waste material. Adsorbent preparation from waste material involves steps
such as material correction, washing, drying, and calcination, which should be included in thecost estimation (Li et al., 2018). The adsorbent material was prepared from the eggshell waste
and bamboo powder, which are available at no cost as waste materials. The adsorbent
preparation cost can be estimated from the drying and calcination cost (Mondal et al., 2016).
The energy used in the drying and calcination processes were calculated as 3.4 kW. However,
because the cost of energy and labor varies from country to country, the production cost also
varies (dos Reis et al., 2020).

4. Summary
In this study adsorption mechanism of the CE and BE 1:1 adsorbent material was analyzed
using pseudo first order kinetic model and pseudo second order kinetic model whether theadsorption process is physical adsorption or chemical adsorption. For CE and BE 1:1 the data
were better fitted by pseudo second order kinetic model which indicates that the adsorption
process has been governed by the chemisorption process. That means the calcium andphosphate ion have a strong bonding in this reaction (Loganathan et al., 2014). Adsorption
kinetics also determine the equilibrium time of the phosphate adsorption which is very
important to save time (Kumar et al., 2019). In this study the equilibrium time was observed
after 4 h. The amounts of P absorbed at equilibrium time were found 75.95 and 98.83 PO4-P
mg/g for CE and BE 1:1, respectively. To control the reaction environment pH of the reaction
environment is a very important factor because it determines the form of the orthophosphate in
the sample water. Maximum adsorption capacity was found for BE 1:1 after adsorption 103.28
mg/g at pH 5 where H2PO4¯ is the major form of the orthophosphate. At pH 7 the adsorption
capacity was also high, which condition is very similar to the natural environment. That’s what
pH 7 was used for different experiments. After that the effects of the co-existing inorganic
54

Chapter 3

anions and organic acids were examined. Anion has negative charge which competes withphosphate ion for the active site and reduced the phosphate adsorption capacity. Mainly sulfate
and carbonate ions decrease phosphate adsorption capacity. This is a major drawback of theadsorption process (Loganathan et al., 2014). Phosphate removal efficiency also decreases dueto the presence of organic acids which also compete with phosphate ion for the active site on
the adsorbent. This adsorption selectivity depends on the type of ions and their concentration.
In natural or wastewater contains several types of ions which creates a complex condition for
adsorption (Kumar et al., 2019). This is the primary flaw of this study which is difficult to
avoid. To optimize phosphate adsorption, it is necessary to regulate optimum dose of theadsorbent. To understand the effectiveness of the BE 1:1 adsorbent for the phosphate removalfrom the natural water and treated water, experiment was performed on collected rivers waterand treated water. Phosphate removal efficiency was found 67.43, 71.12, and 67.43 %,respectfully for the Seri River, Uso river and treated water which indicate BE1:1 adsorbent iseffective to remove phosphate from natural water and wastewater. Wastewater may containorganophosphorus from pharmaceutical waste and pesticides like glyphosate. In this study theadsorbent material was applied on the glyphosate mixed water and BE 1:1 was used as anadsorbent. But after the adsorption process, phosphorus concentration was not decreased whichindicates no adsorption happened. This result indicates that there is no interaction between BE
1:1 material and glyphosate. From literature it was found that the molecular structure of theglyphosate is larger than that of phosphate which inhibits the adsorption on the surface of theBE 1:1 adsorbent. So, it can be said there is no competition between phosphate and glyphosate
for the active sides which is positive for this research.

55

Chapter 3

Figure 2. P adsorption kinetics on (a) CE and (b) BE 1:1 adsorbents. qt: amount of adsorbed P
ions. Error bars indicate standard deviation.

56

Chapter 3

Table 1: Adsorption kinetics parameters of P on CE and BE 1:1.
Pseudo first-order
Adsorbent
CE
BE 1:1Qe (PO4-P
mg/g)
75.95
98.83

Pseudo second-orderK1 (1/h)

R2

0.286
0.363

0.684
0.965

57

Qe (PO4-P
mg/L)
88.62
112.6

K2 (1/h)

R2

0.003
0.003

0.707
0.979

Chapter 3

Table 2: Results after using bamboo char as adsorbent.
Time
(h)
5min
15min
30min
1h
2h
4h
6h
8h
12h
18h
24h
36h
48h

Initial concentration final concentration
P (mg/L)P (mg/L)
100
106.9
100
101.18
100
103.1
100
103.33100
104.49
100
95.68
100
112.14100
103.91
100
113.39100
104.55
100
112.4
100
102.6
100
101.5958

Chapter 3

Table 3: Component analysis of bamboo powder.
Component
Total N (%)

Average ± Std Error

Total P (%)

0.13 ± 0.03
0.47 ± 0.03

Total K (%)
Total CaO (%)
Total MgO (%)
Total C (%)
C/N(Fudano et al., 2016)

0.13 ± 0.03

0.04 ± 0.02
0.13 ± 0.03
41.68 ± 0.81
344.28 ± 51.76

59

Chapter 3

Figure 3: Effect of pH on phosphate removal using Eggshell, BE 1:1; Initial concentration 100
mg/L, Dose 0.01g, Temperature 25ºC.

60

Chapter 3

Figure 4: Effect of coexisting anions on P removal (pH: 7; initial P concentration: PO4-P 100
mg/L; dose: 0.01 g of BE 1:1; temperature: 25 °C; time: 24 h). Error bars indicate standard
deviation.

61

Chapter 3

Figure 5: Effect of organic acids on phosphate removal efficiency, pH 7, Initial concentration
100mg/L, Dose 0.01g, Temperature 25 ºC.

62Chapter 3

Table 4: Anions and cations concentration of Seri and USo River.
Location

Seri River
Uso River

pH

8.94
8.14

PO4
µM

Cl
PPM

NO3
PPM

SO4
PPM

Na
PPM

K
PPM

Mg
PPM

Ca
PPM

0.49
1.19

10.00
14.51

2.73
5.41

8.80
27.87

6.73
14.38

1.05
2.26

3.12
3.27

32.20
18.53

63

Chapter 3

Table 5: Implication of the BE 1:1 adsorbent for phosphate removal from river and treated water.

ample location

Temp ECºC
S/mpH

Phosphateconcentration
mg/L

Seri River
Uso River
Treated water

9.8
9.4
17.1

7.8
7.4
6.8

0.078
0.116
0.86

20.0
20.3
40.4

64

After
addinginorganic
phosphateof 5 mg/L
5.22
5.16
5.19

RemovalAfter
efficiency
adsorption%
final
concentration
1.69
1.49
1.69

67.62
71.12
67.43

Adsorption
capacity±Stdmg/g
14.1±0.37
14.67±0.53
13.98±0.31

Chapter 3

Table 6: Comparative study on the phosphate removal efficiency
Initial-final
concentration
mg/L

Removalefficiency%

Reference

5.9-1

80

Oliveira et al.,2015
Yu et al., 2010

Adsorbent

Sample water

Eggshellmunicipal
wastewater
inlet

fumed silica powder in
conjunction with pulverized
oyster shell

wastewater

5-

92

Chitosan modified iron-cobalt
nanoparticles

River water

-

58.7

eggshell and potato peel

domestic water

Eggshell functionalized withiron oxyhydroxide

Effluent water

10-5

domestic
wastewater

1.7−1

Eggshell ash

65

3.8 to 0.3

85.96

80

Issaian et al.,2020
Quisperima etal., 2022
Almeida et al.,2020
Torit et al.,2018

Chapter 3

Table 7: Organic phosphorus (glyphosate) adsorption capacity of BE1:1
Initial concentration

Final concentration(mg/L)

Mean± sd
(mg/L)

00.043±0.02

55.43±0.26

10

10.98±0.122527.24±0.29

66Chapter 3

Table 8: Organic phosphorus (glyphosate) adsorption capacity of bamboo char, calcined
eggshell powder and raw eggshell powder.
Initial concentration

Final concentration

mg/L

mg/L

7

0

11.57

Bamboo char

7

5

12.39

Calcined eggshell powder

7

0

0.12

Calcined eggshell powder

7

5

6.95

Raw eggshell powder

8

25

25.42

Calcined eggshell powder

8

25

25.72

Adsorbent

pH

Bamboo char

67

Chapter 4

CHAPTER 4

Desorption study and effectiveness of the recovered
phosphate as fertilizer after adsorption using eggshellderived bamboo char.

This section is partially based on manuscript:“Thermally modified bamboo-eggshell adsorbent for phosphate recovery and its
sustainable application as fertilizer” by Sarker, P., X. Liu, N. Hata, H. Takeshita,
H. Miyamura and M. Maruo published on Environmental Research (2023).
https://doi.org/10.1016/j.envres.2023.115992

68

Chapter 4

1. Introduction
Phosphorus recovery using adsorption is a very attractive and effective method (Bacelo et al.,2020). Nowadays different types of natural bio waste material are used for phosphorus recovery
such as sugarcane bagasse (Ramola et al. 2014), soybean milk residues (okara) (Nguyen et al.
2013), sawdust (li et al. 2018), bamboo (Isa et al.,2016), micro algae (Jung et al., 2016), and soon. Biochar alone is not suitable for phosphorus adsorption because of its negative surface
charge. But metal modified biochar has good adsorption capacity (Liu et al., 2019; P´erez etal., 2020) as it has positive charge. After adsorption the solubility of phosphorus from cation
modified biochar is very low because of the stronger attraction between cation and phosphorus
which decreases the availability of phosphorus for plants (Trazzi et al., 2016).
Calcium phosphate is not so much water soluble. At pH 6 and 7, P desorption using deionizedwater was only1.86% and 1.01%, respectively. But in acidic condition (pH 5), phosphorus
release increased to 18.16% (Li et al., 2018). Sometime simple salt also was used forphosphorus desorption. But using high concentration of the salt for phosphorus desorption is
not suitable for agriculture because it increases soil salinity. In alkaline solution, phosphorus
was not released from calcium phosphate (Loganathan et al., 2014).
Assessing plant availability of P fertilizer is important for the proper nutrient management to
reduce P fertilizer loss from agricultural fields (Elliot et al., 2005). Solubility and availabilityof the recovered P varies because of the chemical composition, but the assessment of the plant
availability is challenging (Duboc et al., 2022). The most effective method to assess plant
availability is direct application of the P recycled material on plant as fertilizer. But the growthexperiment is time consuming, and results show high deviations (Kratz et al., 2019). P fertilizer
solubility is measured using different extractors which indicate the P extraction capacity ofplant from the soil. It is also important to determine the doses of the fertilizer (Santos et al.,2018).
From the literature it has been found that the extraction methods of phosphorus rocks vary in
different country such as 2% citric acid is used in New Zealand, 2% formic acid in the EU, and
1 M ammonium citrate at pH 7 in the USA and Australia (Hedley and McLaughlin 2005).
Bioavailability of the phosphorus in biochar was predicted using chemical analysis such as, 2%
citric acid, 2% formic acid, and neutral ammonium citrate (NAC) extraction methods where
neutral ammonium citrate method showed accurate prediction of the P solubility from thesources (Santos et al., 2018). There are some P extraction methods such as water extraction,
NaHCO3 extraction, iron bag extraction, NAC extraction were used to predict the phosphorus
69Chapter 4availability from different types of phosphate fertilizer. For calcium phosphate, NAC extraction
method is effective (Kratz et al 2010; Duboc et al 2022). Low water solubility is a goodcharacteristic of slow-release P fertilizer so that it could be usable for long time. Otherwise,
phosphorus could be released fast and mixed with runoff to enter surface water (Duboc et al.,2022).
Plants can use P from the soil and fertilizer by different techniques such as releasing organic
acids. Microbial symbiosis and activity also enhance p solubility. Sometime plant modifies its
root structure to increase phosphorus uptake capacity. Solubility or release of phosphorus fromfertilizer may depends on soil pH and existence of organic acid. Increasing phosphorus
availability may increase fast crop production. So that recovered phosphorus could be used as
an alternative of the commercial fertilizer (Rech et al., 2019).
After P recovery from the wastewater the application of the phosphorus as fertilizer is very
important. Recently researchers have been emphasizing on this topic. There are very few
experiments were performed to understand the effectiveness of the recovered phosphorus
material as fertilizer. Li et al. (2018) used MgO-CaO Carbon composite, was produced by copyrolysis of sawdust and dolomite for phosphorus recovery and applied in plant cultivation. He
found the effectiveness of the material as slow-release fertilizer. The average growth height
and average fresh weight of Chinese brassica was measured for the phosphorus loaded
materials and control. Results was found much better for the phosphorus loaded materials thancontrol. Hong et al (2020) also used calcined sepiolite for phosphorus removal and applied as
fertilizer which was proved as an effective source of phosphorus fertilizer. Because bamboo
char improves soil quality (Ali et al., 2017) and eggshell powder is used as soil conditioner(Panagiotou et al., 2018), P-loaded materials could be used directly as a fertilizer to improvesoil quality. Examination of the effectiveness of these materials as fertilizers is necessary
before they are used in agricultural production.
In this study calcined eggshell modified bamboo char was used for phosphorus recovery fromwastewater. Then the phosphorus desorption study was performed using water extraction and
NAC extraction method. Then the effectiveness of the phosphorus loaded materials as P
fertilizer was examined measuring the growth index of the Japanese mustard spinach.

70Chapter 4

2. Materials and methods
2.1 Desorption study
2.1.1 Water extraction
For desorption study at first adsorption was performed according to chapter 2. Where the initialconcentration was 100 mg/l, 0.01 g adsorbent material was added to the 40 mL P solution andmixed at 200 rpm at 25°C temperature. After adsorption the solution was filtered by 0.45 μm
PES filter paper and phosphorus concentration was measured. Then 0.01 g material was added
to 40 mL MQ water and then shaken at different temperature 25, 35 and 45 °C for 1 day, 3days, and 5 days. Then phosphorus concentration was measured by spectrophotometer(HITACHI U-2000A) at the wavelength of 880 nm by Ascorbic acid method (Murphy et al.,1977).

2.1.2 Neutral ammonium citrate (NAC) extraction
For NAC extraction 0.1g of P loaded adsorbent material was added to NAC solution at pH 7
and shaken at 65 ºC for 1h. After extraction sample was diluted with 40 mL MQ water to makethe final volume 50 mL. Then the solution was filtered through 0.45 μm PES membrane filter
paper and the phosphorus concentration was measured on the ICP-OES (Duboc et al., 2022).
Amount of P released from the adsorbent was calculated by equations (Haddad et al., 2017):
𝐶𝐶

𝑄𝑄𝑑𝑑𝑑𝑑𝑑𝑑 = 𝑀𝑀𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡…………………………...(1)𝑉𝑉
𝑠𝑠

Qdes=Ctdes/Ms × V………………………(2)where, Qdes was released phosphorus amount (mg/g), Ctdes was final P concentration in thesolution (mg/L), V was the volume of the used solution (L), Ms was the amount of preloaded
adsorbent (g).

2.2 Pot experiment
To understand the effectiveness of the phosphorus loaded biochar several experiments were
performed. In this experiment P loaded BE 1:1 material was used, because the BE 1:1 adsorbent
showed the highest P adsorption capacity in chapter 2. Japanese mustard spinach was used as
71

Chapter 4plant material for the cultivation. 9 cm poly pot was filled with 200 g vermiculite and mixed
with 0.5 g phosphorus containing materials was placed in the incubator at 23℃ temperature,
photoperiod 16-h day/8-h night cycle, Light intensity > 150 μmolm-2s-1PPFD (maximum
intensity). In each experiment, four seeds were sown per pot at a depth of 5–10 mm, andthinning was started 1 week after sowing. After 2 weeks, only one plant per pot remained (Liet al., 2018). Pots should be set on trays and watered at least once every two or three days.

2.2.1 First experimental condition
1 g adsorbent (CE and BE 1:1) was added to 400 mL of 100 mg/L of P solution. After
adsorption, P adsorption capacity was found 40 mg/g, that means 1g material contains 40 mg
phosphorus. Then 1 g of CE and BE 1:1 with and without P was added to Soil +Vermiculite
3:1. Total 5 experiment set with triplicate was prepared for the first experiment are given
bellow:i.

Mixture of Soil and Vermiculite in 3:1 ratio with BE 1:1 loaded with phosphorus(SVer3:1 + BE 1:1 + P)ii.

Mixture of Soil and Vermiculite in 3:1 ratio with BE 1:1 material (SVer3:1+ BE 1:1)

iii.

Mixture of Soil and Vermiculite in 3:1 ratio with CE loaded with phosphorus (SVer3:1+ CE 1:1 + P)

iv.

Mixture of Soil and Vermiculite in 3:1 ratio with CE adsorbent material (SVer3:1 + CE
1:1)

v.

Mixture of Soil and Vermiculite in 3:1 ratio (SVer3:1) (Control)

2.2.2 Second experimental condition
0.5 g adsorbent (BE 1:1) was added to 400 mL of 500 mg/L of P solution. where 1 g material
contains 90 mg phosphate. In this experiment vermiculite was used as nutrient free material
which was used for control. Then 0.5 g P adsorbed materials were used mixed with vermiculite
to examine the effects of the phosphorus adsorbed material as fertilizer. In this experiment was
performed without adding others nutrient and total 3 experiment set with triplicate wereprepared as follows:i.

Vermiculite with BE 1:1 loaded with phosphorus (Ver+BE 1:1+P)

ii.

Vermiculite with BE 1:1 material (Ver+BE 1:1)

iii.

Vermiculite (ver) (Control)72

Chapter 4

2.2.3 Third experiment
0.5 g adsorbent (BE 1:1) was added to 400 mL of 500 mg/L of P solution. where 1g material
contains 90 mg phosphate. After adsorption process, P containing adsorbent material wasapplied as a fertilizer to evaluate its effectiveness as a fertilizer. Two experiments with triplicate
were conducted as follows:i.

vermiculite only (Ver) (Control)ii.

mixture of vermiculite and BE 1:1 with P addition (Ver + BE 1:1 + P)

Third experiment was performed using additional micro and macronutrients. The control
experiment was performed without phosphorus loaded material. In this experiment halfstrength Hoagland’s Solution was used as additional nutrient for continuous irrigation (Yan etal., 2013). After 21 days the plant growth index was measured. Root and shoot length were
measured by scale. Then wet and dry weights were weighed (IUW 200-D, As One, Japan).

2.3 Half-strength Hoagland solution preparation
In this experiment Half- strength Hoagland solution was used to supply additional nutrient to
the experimental plants. It was prepared from the 4-stock solution of the mixture of different
nutrients (Yan et al. 2013). A detail preparation process has been given bellowStock Solution 1: Mixture
Add gram amounts to distilled water to make 500 mL of stock solution:•

KNO3

3 mmol/L•

NH4Cl 0.5 mmol/L

•

MgSO4

1 mmol/L

Stock Solution 2: Calcium Nitrate•

Add gram amounts to distilled water to make 500 mL of stock solution:•

Ca(NO3)2 2.5 mmol/L

Stock Solution 3: A-Z (micronutrients)

73

Chapter 4

Add gram amounts to distilled water to make 100 mL, then put 45/4 mL (11.25 mL) solution
in 500mL bottle, fill to 500 mL liters using distilled water (discard excess):•

H3BO3 (boric acid) 2.9 grams•

MnCl2.4H2O (manganese chloride) 1.8 grams•

ZnSO4.7H2O (zinc sulfate) 0.2 grams•

CuSO4.5H2O (copper sulfate) 0.08 grams•

H2MoO4.H2O (molybdic acid) 0.09 grams

Stock Solution 4: Iron
Dissolve gram amounts in 100 mL of distilled water by heating to 60°C for one hour; let coolslightly and add distilled water to reach total volume of 500:•

FeSO4.7H2O (iron sulfate) 2.5/4 grams (0.625 g)•

Na EDTA (ethylene diamine tetra-acetic acid) 3.3/4 grams (0.825 g)

This nutrient solution used for continuous irrigation is a modified half-strength (0.5X)
Hoagland's solution. To make half-strength Hoagland’s for Fast Plants, mix the following
quantities of the four stock solutions and add distilled water to make a total volume of 1 L:•

2.0 mL Mixture (Stock Solution 1)•

2.5 mL Calcium Nitrate (Stock Solution 2)•

2.0 mL A-Z (Stock Solution 3)•

2.0 mL Iron (Stock Solution 4)74

Chapter 4

3. Result and discussion
3.1 Desorption capacity
The phosphorus desorption amounts from the BE 1:1 adsorbent were shown in Table 1. After
1 day desorption, the released phosphorus amount was found higher than after 3- and 5-daysdesorption into MQW. At 45 °C the desorption was comparatively higher than at 25°C and
35°C. Overall, the phosphorus desorption in MQW is very low, because the bonding between
calcium and phosphate is very strong which makes it water insoluble. For increasing thedesorption rate the pH of the solution must be below 5.5 (Loganathan et al., 2014). After
extraction using NAC extraction method the amount of desorbed phosphorus was found 48.68
mg/g was higher than water extraction process. In this process citric acid forms complex bondwith calcium and release phosphate which increase the solubility of calcium phosphate in NAC
solution (Barrow et al., 2017).

3.2 Effectiveness of the phosphorus containing biochar as fertilizer (Pot experiment)
3.2.1 First experiment
After 21 days of the experiment the plant growth index was measured. From Figure 1 and Table
2, it has been found that length of the root, shoot and largest leaf and the wet and dry weightof the root and shoot for 5 experiment set was very similar. This may be because of using
nutrient enriched soil material which was sufficient for plant growth.

3.2.2 Second experiment
After 21 days of the experiment the plant growth index was measured. From Figure 2 and Table
3, it has been found that length of the root, shoot and largest leaf and the wet and dry weightof the root and shoot for 3 experiment set was also very similar. This is because of using
nutrient free vermiculite which was not efficient for plant growth. Only phosphorus is notenough for plant growth. Other macro and micronutrients are necessary for plant growth(Ebelhar et al 2008).

3.2.3 Third experiment75

Chapter 4

Length of the root, shoot, largest leaf, wet and dry weight of the root and shoot was measured
after 21 days of seedling. There this a noticeable difference between two sets of experiment.
The length and weight of the plant cultivated with phosphorus dropped biochar was higher than
without phosphorus vermiculite (control). In the control experiment all other nutrients were
provided except phosphorus. Without phosphorus plant root and shoot development was notenough (Figure 3). From table 4, it has been seen that the length of the root and height of shootfor B+E 1:1 with P was 30.3cm and 11.5cm which is higher than the length of the root(19.3cm)
and height of shoot (7.3cm) of plant cultivated without phosphorus. The wet root weight andshoot weight for B+E 1:1 with P was 4.3g and 6.3g which was comparatively higher than the
without phosphorus plant’s wet root weight (0.68g) and shoot weight (0.16g). According toJustus von Liebig if one of the essential plant nutrients is deficient, plant growth will be poor
even when all other essential nutrients are abundant. In the 19th century, the German scientist
Justus von Liebig formulated the “Law of the Minimum” (Figure 4) (Ebelhar et al., 2008).

3.3 Discussion
Phosphorus is a vital plant nutrient which is a major component of ATP and DNA. ATP is theplant ‘energy’ which is necessary for photosynthesis, protein synthesis, nutrition distribution,
nutrient uptake, respiration, and genetic characteristics transportation. Phosphorus enhancesroot growth and influences early maturity, straw strength, crop quality and diseases resistance.
Phosphorus deficiency has significant negative impact on crop production (Upadhyaya et al.,2017). Using phosphorus fertilizer is a common practice for optimum crop production. There
are many commercial phosphorus fertilizers like rock phosphate, phosphoric acid, calcium
orthophosphates, ammonium phosphates, ammonium polyphosphate and nitric phosphates
which are generated from phosphorus rock mine. Traditionally animal bone was used as
phosphorus fertilizer. Total reserve of phosphorus in the world is very limited compared to thecurrent demand. For this reason, recovery of phosphorus from waste material is a goodalternative way to meet the huge demand of phosphorus (Samreen et al., 2019).
From the desorption study it has been found that phosphorus release with MQ water was very
low. because the bonding between calcium and phosphate is very strong. For this reason,
calcium phosphate is water insoluble (Loganathan et al., 2014). But NAC extraction method iseffective for phosphorus extraction from calcium phosphate because citrate ion replaces
phosphate ion and release phosphate from adsorbent (Duboc et al., 2022). Soil property has
great influence on phosphorus release. Soil organic matter and acidic condition enhance the76Chapter 4

phosphorus solubility. The slow-release property of this material is also suitable for agricultural
application. Because plant has different technique to uptake phosphorus from soil (Rech et al.,2018). The growth of plant of experiment 3 also proved that plant was capable to uptake
phosphorus from soil. That’s why there was huge difference in plant growth rate. Plant roots
release different types of low molecular weight compounds into the rhizosphere which isimportant for the chemical, physical, and biological interaction between roots of the plants andthe rhizosphere. These low molecular weight compounds help microorganisms to improve
nutrient uptake capacity, plant growth development and stress/ diseases resistance capacity(Yadav et al., 2015). Spinach plants release citric acid and malic acid in p deficient environment
which might be effective for phosphorus release from P loaded bio adsorbent material (Romaret al., 2001). Brassica species also release different types of organic acid where citric acid andmalic acid are the most abundant (Sousa et al., 2009). Brassica napus is a mustered family
plant release organic acid from the roots to use phosphorus from phosphate rock fertilizer(Haynes 1992). Hong et al. (2020) found that calcined sepiolite effectively removed phosphateand P-loaded sepiolite was applied to rice crop production. The P-loaded material increased
plant growth and biomass. Li et al. (2018b) synthesized a CaO-MgO carbon hybrid composite(sawdust and dolomite) and reclaimed phosphate fertilizer has been proven effective as a slowrelease fertilizer for agricultural production. The higher plant growth in the current study also
indicated that P-loaded material could be used as an alternative source of phosphate fertilizer.
4. Summary
This study revealed that phosphorus loaded eggshell modified bamboo char has potentiality touse in plant cultivation as a phosphorus fertilizer. Since the desorption capacity is very low in
MQ water. But in soil environment plants have mechanism to improve the P uptake capacity.
Which might influence the root and shoot development of the plants. So, the phosphorus
recovered from wastewater is applicable as a slow-release fertilizer. Further study should be
developed to enhance the solubility of the P loaded adsorbent material. So that it could be used
as commercial phosphorus fertilizer. A lab-scale fertilizer experiment was performed here, andthus the practical agricultural application of the material as a fertilizer should be examined
before commercial applications could be considered.

77

Chapter 4

Table 1: Results of P desorption using water extraction and NAC extraction method.
Extraction method

MQW

NAC

Time

Qdes (mg/g)
25 °C

35 °C

45 °C

1 day

1.54

0.79

1.97

3 days

0.52

0.67

1.77

5 days

0.54

0.29

0.48

1h

48.8

-

-

78

Chapter 4

Table 2. First Experiment. Growth parameter of the Japanese mustard spinach in the four experimental conditions (Exp I-IV). LR: lengthof the root; HS: height of shoot; LL: length of the largest leaf; WRW: wet root weight; DRW: dry root weight; WSW: wet shoot weight;
DSW: dry shoot weight. SD: standard deviation.

Experimental
condition

LR

HS

LL

Mean ± sd (cm)Exp. I: SVer 3:1 23.0±2.16

WRW

DRW

WSW

DSW

Mean ± sd (g)11.0±0.94

10.0±0.94

0.8±0.120.22±0.07

6.5±0.64

1.24±0.06

30.0±4.08

11.0±0.82

9.6±0.47

0.83±0.17

0.23±0.06

7.1±1.05

1.25±0.06

25.0±2.2

10.3±0.47

9.8±0.21

0.86±0.08

0.23±0.07

7.0±0.86

1.17±0.19

23±2.910.17±0.62

9.33±0.47

0.7±0.08

0.25±0.045

6.5±0.41

0.86±0.24

25.0±0.94

11.0±0.47

10.0±0.47

0.7±0.08

0.24±0.04

6.5±0.48

1.34±0.12+ BE 1:1 + P
Exp. II:
SVer3:1+ BE
1:1
Exp. III: SVer
3:1 + CE 1:1
Exp. IV: SVer
3:1 + CE 1:1 + P
Exp.V: SVer 3:1

79

Chapter 4

Figure 1: Plants growth for first experiment.

80

Chapter 4

Table 3. Second experiment, Growth parameter of the Japanese mustard spinach in the four experimental conditions (Exp I-IV). LR:
length of the root; HS: height of shoot; LL: length of the largest leaf; WRW: wet root weight; DRW: dry root weight; WSW: wet shootweight; DSW: dry shoot weight. (Without additional nutrient).

Experimental
condition
Exp. I: Ver

LR

HS

LL

Mean ± sd (cm)

WRW

DRW

WSW

DSW

Mean ± sd (g)5.66±0.47

2.17±0.23

1.36±0.26

0.01±0.001

0.006±4.7E-05

0.05±0.003

0.01±9.4E-05

4.6±0.94

2.0±0.00

1.4±0.14

0.012±0.003

0.0014±0.0002

0.067±0.002

0.01±0.006

72.0±0.82

2.0±0.00

1.16±0.24

0.063±0.061

0.002±0.0002

0.061±0.003

0.01±0.002

Exp. II: Ver +BE 1:1+P(unsaturated)
Exp. III: Ver+ BE 1:1 + P(saturated)

81

Chapter 4

Figure 2: Plants growth for second experiment.

82

Chapter 4

Table 4. Third experiment. Growth parameter of the Japanese mustard spinach in the four
experimental conditions (Exp I-IV). LR: length of the root; HS: height of shoot; LL: length of thelargest leaf; WRW: wet root weight; DRW: dry root weight; WSW: wet shoot weight; DSW: dryshoot weight. (Using Half-strength Hoagland solution for other plant nutrients)

Experimental
condition
Exp. I: Ver
Exp. II: Ver +BE 1:1 + P

LR

HS

LL

WRW

Mean ± sd (cm)

DRW

WSW

DSW

Mean ± sd (g)19.3±1.70

7.3±0

5.5±0

0.68±00.06±0.71

1.02±0.12

0.16±0.05

30.3±3.30

11.5±0.47

11.0±0.47

4.3±0.41

0.28±0.09

6.3±0.03

1.2±0.01

83

Chapter 4

BE1:1+P

Control

Figure 3: Effects of BE(1:1)+P on plant growth (experiment).

84

Chapter 4

Figure 4: Law of the Minimum (Ebelhar et al 2008)85

Chapter 5

CHAPTER 5

Conclusion

86

Chapter 5

1. Conclusion
This PhD research investigated the preparation of the adsorbent from locally available biowastematerial, where eggshell waste and bamboo waste was used to produce low-cost, andenvironment friendly adsorbent material. Effectiveness of the adsorbent material to recoverphosphorus and implementation of the P loaded adsorbent material as fertilizer after adsorption
was examined. Eggshell modified bamboo char after calcination has been proven as a good
adsorbent for phosphate removal from wastewater. From this experiment at the same time threeenvironmental problems were tried to be solved. First, using waste material for adsorbent
preparation is a good solution for solid waste and environmental management. Second,
removing phosphorus using adsorption process is beneficiary to reduce severe water pollution(eutrophication). Third, after adsorption the P loaded material could be used as fertilizer tomeet the huge demand of the phosphorus fertilizer.
In chapter 2, At first adsorbent material was prepared using different calcination temperature(600, 700, and 800°C) and mixing ratio of eggshell and bamboo powder (CE, BE 1:1, 2:1, 10:1
and BE). After calcination, SEM image and FTIR analysis was performed to understand themorphological and physicochemical changes. Then the materials were applied as adsorbent tounderstand its effectiveness under different initial concentration and temperature. Optimum
dose (0.01g) and effective mixing ratio (BE 1:1) was found from the experiment. Then theadsorption isotherm and thermodynamics was calculated and maximum phosphorus adsorption
capacity for the BE 1:1 and BE 2:1 was found 95.14 and 98.40 mg/g at 25 °C and nonspontaneous reaction was found for the BE 1:1 at 25°C. The reaction was spontaneous at 35
and 45 °C. Adsorption process was calculated by adsorption isotherm, where experimental data
were better fitted by the Langmuir adsorption isotherm model, indicating monolayer adsorption
on homogenous surface. Langmuir separation factor indicated favorable condition for thephosphorus adsorption in different initial concentration and temperature.
After phosphate adsorption experiments, presence of phosphorus in the adsorbent was
examined using FTIR, SEM image and EDX analysis. From FTIR analysis, a clear new bandat 1024 cm-1 was observed after phosphate adsorption on BE 1:1. SEM image showedmorphological changes and EDX analysis ensured the presence of phosphorus after adsorption
using adsorbent materials.

87Chapter 5

In chapter 3, influences of pH and co-existing anions in the phosphorus adsorption process
was investigated. Adsorption mechanism was calculated by adsorption kinetics, whereexperimental data were better fitted by the pseudo second order model. This result indicatesthat the adsorption process was controlled by the chemisorption process. Calcium ion has
strong affinity to the phosphate ion, and it created an intermolecular interaction on adsorption.
The amounts of P adsorbed were 75.95 and 98.83 mg/g for CE and BE 1:1, respectively.
Phosphate adsorption process was influenced by the pH of the reaction. Maximum adsorption
capacity was found from pH 5 to 7. Where pH 7 is neutral pH and like natural water. Presenceof different anions and organic acids in wastewater is usual. In presence of CO32−, and SO42−
phosphate adsorption capacity decreases. Presence of organic acids like humic acid, citric acidand oxalic acid also affects phosphorus adsorption capacity.
BE 1:1 adsorbent was applied on river water and treated wastewater. Where, 67.43, 71.12, and67.43 % phosphate removal efficiency was obtained for the Seri River water, Uso River water,
and treated wastewater of Tohokubu Wastewater Treatment Plant (Matsubara, Hikone, Shiga),
respectively. For river water and treated wastewater, the removal efficiency was also affectedby co-existing matters. But the phosphate removal efficiency from river and treated wastewaterusing BE 1:1 was good, and it was effective for real wastewater application. It is not easy to
avoid the influence of the co-existing ion. So, it is necessary to control the amount of theadsorbent to increase the phosphorus adsorption capacity.
Organic phosphorus removal efficiency was investigated using BE 1:1 adsorbent material on
glyphosate containing water and no adsorption of organic phosphorus from glyphosate wasfound from the experiment which is positive for the objective of this research. BE 1:1 isefficient for inorganic phosphorus removal and safe for fertilizer use because of no competitionand contamination of glyphosate from wastewater.
Cost estimation of adsorbent preparation is an important part of this study to apply incommercial scale. Since the labor cost and material cost varies country to country, energy used
for the adsorbent preparation was estimated. Total energy consumption was 3.4 KW.
In Chapter 4, Desorption study using water extraction method and neutral ammonium citrate(NAC) extraction method was performed. The desorption capacity in milli Q water was foundlower than the NAC extraction method (48.68 mg/g). This low solubility of the P loaded
materials is suitable to use as slow-release fertilizer. Then the P loaded BE 1:1 was applied on88Chapter 5

Japanese mustard spinach cultivation in different soil condition. Vermiculite (nutrient freematerial) was used for the cultivation where half strength Hoagland solution (without P) was
added to provide other macro and micronutrient. Plant growth was found higher for the P
loaded BE 1:1 than the control.
Though the phosphate of the adsorbed material release in water is very low because of strong
bond between calcium and phosphate. But the plant growth was good which indicates that thephosphate was taken up by plants. Plants have some mechanisms to uptake phosphate byreleasing organic acid which increase the plant availability of the phosphorus to uptake. In
nutrient enriched soil, there is no effects of P loaded biochar on plant growth. The slow-releaseproperty of P-loaded BE 1:1 material is suitable for long-term uses as sustainable fertilizer. Our
results demonstrate that adsorbent preparation from waste materials could convert waste into a
resource to control eutrophication and use the recovered P as a valuable fertilizer.
2. Recommendation
In future study, it is necessary to give emphasize on the improvement of the adsorption capacityand quality of the phosphorus loaded material to use as fertilizer.

1. Since the objective of this study was recovery of phosphorus from wastewater, researchshould focus on the interference of the other ions and organic matters likepharmaceutical contamination which could interfere with the maximum phosphorus
removal capacity.
2. The current experiment of the fertilizer application was performed in lab scale, but
practical application of the phosphorus loaded material as fertilizer in the agricultural
field is needed before commercial application. Farther experiment is necessary to
improve the plant availability of the fertilizer to make it commercially applicable.
3. Another future study could focus on the investigation of the preparation of theadsorbent using different waste material. So that at the same time we can control waterpollution and solid waste. Proper use of agricultural and industrial waste could convert
the waste material into resources. It will reduce the cost of the adsorbent preparationand improve the economic feasibility.

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