沙漠研究 22-1, 227 -230 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－Anaerobic Degradation of Halophyte Biomass for Biogas Production
Natalya AKINSHINA*1)2), Daisuke NAKA2), Kristina TODERICH3), Azamat AZIZOV1) and Hidenari YASUI2)
Abstract: Anaerobic degradation of wild halophytes (Kalidium caspicum, Salicornia europaea and Climacoptera lanata) fromsolonchaks of Kyzylkum desert in comparison with conventional glycophyte Panicum coloratum was studied. Lab-scale reactors
were fed with dried and milled plant biomass. Tests were operated under batch and continuous mode at mesophilic (M) andthermophilic (T) temperatures. High concentrations of chlorides, sulphates, sodium and potassium and low contents of nutrientswere revealed in the biomass. Batch-tests showed that total methane-yields at M and T conditions were similar. Maximum
biogas was produced in result of anaerobic digestion of Kalidium caspicum (about 1000 mL CH4 from 1L of sludge at T andM-conditions); 950/900 mL/L was obtained in result of digestion of Salicornia europaea at T and M respectively; digestion ofPanicum coloratum produced about 900/800 mL/L and Climacoptera lanata - 880/700 mL/L. It was revealed that 72-90% oforganic fractions of K.caspicum and 54-90% of S.europaea can be decomposed to CH4 at 35ºC within 30-days whereas
approximately 50-70% of organic matter was decomposed due to anaerobic degradation of C.lanata and P.coloratum. AtT-conditions about 60-70% organic matter of the biomass was conversed into methane. Incubation at 55ºC accelerated the CH4conversion rate up to 2 times. Time differences of the anaerobic decomposition of various halophytes are related to variation oflignin content, different concentrations of nutrients and other chemical compounds in the biomass. Preliminary studies ofanaerobic digestion of plant biomass under continuous mode demonstrated that it is possible to get about 300-500 mL CH4 from 1Lof anaerobic digestion sludge per day.
Key Words: Anaerobic digestion, Biogas, Halophyte biomass

1. Introduction
Recently, a number of reasons to find alternative energy
sources have become obvious:• Carbon-contained energy sources of the Earth areexhaustible;• Many developing countries are on the way to multiply theirenergy demand;• Energy resources become the main causes of many
political and military conflicts around the world.
Biogas is one of types of renewable energy; actually it isgenerated from organic materials as they decay.
Biogasification (methane fermentation) is a technology forrecovering methane from an organic matter in anaerobicreactor. It is also referred to as “anaerobic digestion”. The
main component of biogas is CH4 (55-70%) and CO2(30-45%).
On a worldwide basis, the biogas production process has
significance as a robust and easily to establish low-cost
technology for the treatment of organic matter like food waste,agricultural residuals, sewage sludge, animal slurry, manureand so on. In developing countries of Asia and Africa
thousands of simple small-scale reactors are under operation

now (Wang and Li, 2005; Yadvika et al.; 2004, Omer andFadalla, 2003). Their benefits are related to sustainable waste
management combined with decentralized energy production.
Currently, reduction of salinization in arid areas is one of
the most important challenges for human life, at least 20% ofworld arable lands and more than 40% of irrigated lands areunder salinization. Every year the area of salt affected land
increases with 10 million hectares. Uzbekistan loses about
20000 hectares in a year by reason of high salinization orwaterlogging (Baknell et al., 2003). It is clear, thatconventional crops can not grow in those conditions and soabandoned lands are being increased rapidly. That is thereason why it is necessary to develop agricultural production
under saline conditions.
Cultivation and sustainableutilization of wild or domesticated halophytic and salt-tolerant
plants could play important role for salinity control,
remediation of saline lands and improving of livelihood ofrural communities in Central Asian region. Halophytes
provide desalination of soils. Until recently, no serious
research efforts had been made in Central Asia on theutilization of biomass of halophytes. It is known, that many
halophytes have importance as grain, fodder, technical or
medicinal plants. Moreover, some kinds of inedible plantbiomass from high saline environments could become an* Corresponding Author: n.akinshina@yahoo.com
University str., NUUz, Tashkent, 100174, Uzbekistan
1) Department of Applied Ecology, The National University of Uzbekistan named after Mirzo.Ulugbek, Uzbekistan
2) Faculty of Environmental Engineering, The University of Kitakyushu, Japan3) International Center for Biosaline Agriculture sub-offce for Central Asia and Caucasus

important source of renewable sustainable energy in arid lands.
The main goals of presented research are:
 To study possibility of anaerobic digestion (AD) of
some halophyte biomass for methane-gas production;
 To compare AD of halophytes in mesophilic andthermophilic conditions in lab-scale experiments.

2. Materials and Methods
Anaerobic degradation of plant biomass for biogas
production was studied. This is a complex microbial process
in which organic compounds are degraded into methane,carbon dioxide and hydrogen by variety of anaerobes. The
treatment systems can be classified by their dominantmicroorganisms: mesophilic (used at 30 to 40ºC) andthermophilic (used at 50 to 60ºC). Obtained biogas is usually
utilized as fuel or for electricity production. Fermented
residues of the process can be used as liquid fertilizer and row
material of compost.
It is a 4-stage process: hydrolysis, acidification,acetogenesis and methanogenesis.
In the first phaseanaerobic bacteria use enzymes to decompose high molecularorganic substances such as proteins, carbohydrates, cellulose
and fats into low molecular compounds. During the second
phase acid forming bacteria continue the decomposition
process into organic acids, carbon dioxide, hydrogen sulphideand ammonia. Acid bacteria form acetate, carbon dioxideand hydrogen during the acetogenesis phase.
Themethanogenesis phase involves methane forming bacteria
producing methane, carbon dioxide and water.
Three wild halophytes (Kalidium caspicum, Salicornia
europaea and Climacoptera lanata) were taken from wet anddried solonchaks of Kyzylkum desert (Uzbekistan).
Conventional glycophyte Panicum coloratum was taken forcomparison. Plant biomass was dried at 105ºC during 24
hours and well-milled before the investigation.
Lab-scale experiments on anaerobic degradation of thebiomass were conducted in batch and continuous modes.
Water bathes were used as heaters for batch type reactors withstirring or shaking. Continuous mode reactors (4L glass
cylinders with automatic stirring and heating control) were fed
by dried biomass every day (retention time - 20 days, organic
loading rate - 3.3 gCOD/L).
Concentrations of Cl-, F-, NO3-, SO42-, PO43- in water
extracts of the biomass (0.1g DM1 in 100 mL distill water
stirred 1 hour and filtered through 0.45 µm) were measured
according to standard methods using Ion Chromatography
System DIONEX ICS-1000, IonPac AS11-HC Column.
1DM – dry matterSoluble organic carbon (Sol.org.C) was measured in thesame water extracts using Total Organic Carbon Analyzer
TOC-L CSH/CSN Standalone Model (“Shimadzu”).
Ash for the analysis was prepared by burning of plant dry
matter in melt pots at 600ºC during 1 hour. Element analysisof plant materials was conducted using Varian Atomic
Absorption Spectrophotometer AA240FS by standard method.
“OriginPro7.5” was used for statistical analysis ofexperimental data.

3. Results and Discussion
Taking into consideration that examination of biomass
properties is necessary before planning gasification,measurements of water content, total mineral content andsoluble organic carbon concentration were conducted.
Results are presented in Table 1.
It was revealed that the halophytes contain very highconcentrations of mineral compounds (about 40-50% of DM)
as contrasted with conventional grass (5% of DM). It
confirms that they are strong euhalophytes and can remove
significant amounts of various salts from saline environment
and accumulate them in plant tissues. Two fold solubleorganic carbon concentrations in comparison with other plants(about 166 g/kg DM) were determined in DM of Kalidium
caspicum.
Ion chromatographic analysis of water extracts of thebiomass detected high content of chlorides and sulphates in thehalophytes; about 100-200 and 20-70 g/kg DM respectively(Table 2). Salicornia europaea contained the highest
Cl--concentration (228.4 g/kg DM) and Climacoptera lanata
had the highest SO42--content (68.93 g/kg DM). Low
concentrations of phosphorus and traces of ammonium(essential nutrients for bacterial community) were revealed in
the plant biomass. Kalidium caspicum contained significant
amount of NO3--ions as compared to the other plants.
High contents of Na (130-170 g/kg DM) and K (20-45g/kg DM) were determined in the halophyte biomass (Table 3).
This fact can be considered as disadvantage for using ofhalophyte biomass for biogas production in anaerobic
conditions as it is known that toxicity by salts for anaerobic
bacteria is usually associated with the cations and not with theanions of the salts (Carlos Augusto de Lemos Chernicharo,2007).
To avoid toxic effects of high concentrations of sodium andpotassium in anaerobic digesters continuously fed byhalophyte biomass it is necessary to adjust hydraulic retention
time and organic loading rate correctly. The other way is aco-digestion and mixed feed (for instance, halophytes +conventional energy plants, halophytes + manure, etc.).

Results obtained from batch-tests have showed that total
methane-yields at mesophilic and thermophilic conditions
were similar (for instance, see Fig. 1). Maximum biogas wasproduced in result of anaerobic digestion (AD) of Kalidium
caspicum (about 1000 and 1100 mL CH4 from 1L of sludge atT and M-conditions); 950/900 mL/L can be produced by
Salicornia europaea at T and M-conditions respectively; AD ofPanicum coloratum can generate approximately 900/800 mL/L
and Climacoptera lanata – 880/700 mL/L.
In result of numerous batch-mode experiments it wasrevealed that about 60-70% organic matter of the plant biomass
can be decomposed at 55°C. At 35ºC 72-90% of organic
fraction of Kalidium sp. and 54-90% of Salicornia sp. can beconversed to CH4 during 30-days incubation period andTable 1. Dry matter content, total mineral content and soluble organic carbon concentration of plant biomass.
Plant species

Dry matter

Total mineral content,

Total mineral content,

Soluble organic carbon,

content, %% from fresh weight% from dry weightg/kg DM

Kalidium caspicum

23.01 + 0.39

9.47 + 0.6

42.84 + 2.48

165.67 + 26.8

Climacoptera lanata

21.76 + 0.5

10.09 + 0.44

51.62 + 6.6

81.67 + 1.54

Salicornia europaea

18.35 + 1.27

6.75 + 0.76

38.64 + 1.64

77.33 + 8.8

Panicum coloratum

not measured

not measured

5.01 + 0.15

81.18 + 0.27

Table 2. Anion content of plant biomass.
g/kg DM
Kalidium sp.

Climacoptera sp.

Salicornia sp.

Panicum sp.

-Cl105.29 + 17.52

165.53 + 18.01

228.41 + 55.27

14.35 + 2.41

SO42NO3PO4-23.36 + 2.36

68.93 + 6.74

30.91 + 7.63

1.92 + 0.1

24.15 + 4.91

1.17 + 0.34

1.29 + 0.75

4.78 + 0.67

4.36 + 1.07

1.03 + 0.31

2.18 + 0.96

1.51 + 0.11

0.94 + 0.06

0.99 + 0.06

0.509 + 0.031

0.64 + 0.04

FTable 3. Concentrations of some metals in plant biomass.
g/kg DM
Kalidium sp.

Climacoptera sp.

Salicornia sp.

Panicum sp.

Na

153.59 + 10.59

169.69 + 10.36

133.07 + 7.7

2.14 + 0.09

K

18.72 + 0.73

21.57 + 0.94

45.01 + 2.422.53 + 0.005

Mg

3.49 + 0.47

4.45 + 0.19

8.09 + 0.06

1.11 + 0.01

Ca

3.04 + 0.07

4.54 + 0.07

3.57 + 0.17

Not measured

Fe1.02 + 0.08

0.37 + 0.06

1.04 + 0.04

0.14 + 0.005

1.Mesophilic conditions

2.Thermophilic conditions(35ºC, F/M=0.2, CODADL=21.47 g/L)

(55ºC, F/M=0.2, CODADL=20.5 g/L)

Kalidium caspicum
1100
300

Kalidium caspicum

1000
300

900

1000

250
250

150

500
400

100

300

MPR, mL/L/d600

200
600
150
400
100

200

50

100
00051015Time, days

202520050005

1015Time, days

Fig.1. Methane production rates and cumulative methane yields at anaerobic digestion of plant biomass.

20025MP, mL/L

800

700200MP, mL/LMPR, mL/L/d800

Table 4. Share of different organic fractions (in respect of biodegradability) of plant biomass.
*Slowly convertible to CH4*Very slowly convertible to CH4Inert
Organic fractions (%):
Meso
ThermoMeso
ThermoMeso
ThermoKalidium caspicum4039>3032<3029

Climacoptera lanata2135>2927.5<5037.5

Salicornia europaea1924>3943<4233

41.5>2120<443635
Panicum coloratum*On the basis of AD-kinetics analysis (according to CH4-production rate) we determined at least two main types of organic fractions with different
rates of digestion by anaerobic bacteria: slowly and very slowly convertible to CH4.

approximately 50-70% of organic matter of Climacoptera sp.
and Panicum sp. can be digested at the same conditions.
Incubation at 55ºC accelerated CH4 conversion rate up to 2times due to specific thermophilic microorganism’s reaction
rates.
Under laboratory experiments about 80% of
cumulative methane yield at T-conditions was obtained within
5-7 days, at M-conditions it took 25-30 days. Higher rates offermentation under thermophilic conditions have not led to ahigher cumulative methane production. There were no big
differences in the total methane yield at 35ºC and 55ºC.
Probably, it is related with similar biodegradability of plantbiomass for thermophilic and mesophilic bacterialcommunities. It is necessary to continue studies of anaerobic
digestion of the plant biomass to determine exactly amounts ofinert organic matters and other organic compounds in respectof velocity of their biodegradation.
Shares of different organic fractions of the biomass werecalculated on the base of data on COD-conversion percentage
during AD at mesophilic and thermophilic conditions, results
are shown in Table 4. It was revealed that 30-50% of theorganic fractions were inert and not capable to be biodegraded.
Biomass of Kalidium capsicum was degraded better than otherplants.
The diversity of the conversion efficiencies could beattributed to different chemical composition of halophytes
biomass. It was displayed that any plant biomass contains atleast three fractions with various biodegradable kinetics.
Differences in the anaerobic decomposition of the halophytes
are associated with the variation of lignin content, which isconsidered as hardly biodegradable organics, different nutrientsconcentrations and some chemical compounds, which areconsidered as inhibitors for an anaerobic digestion.
Preliminary study of anaerobic digestion of plant biomass
under continuous mode demonstrated possibility to get about300-500 mL CH4 from 1L of anaerobic digestion sludge per day.

4. Conclusion
Biomass of halophytes should be considered as a valuable
source of renewable energy production.
Anaerobic digestion is the most widely used method oforganic waste and agricultural residuals disposal, it reduces thetotal mass of wastes significantly, produces energy andgenerates liquid or solid fertilizers, and it makes the process
profitable from economical and environmental point of view.
It is clear that using of halophytic biomass for biogas
production in saline arid lands gives numerous advantages.
There are usually no other conventional crops or wild
glycophytes in conditions of saline land or water resources,
where halophytes can survive. There are no any competitions
for land or water use in those areas. In addition, often there
are no any other sources of energy for households of small
local communities in remote desert areas under salinization.
Moreover, soil desalination and melioration could be achievedin result of cultivation of halophytes. Thus, it is necessary toemphasize low resource cost, environmental benefits andimproving of living standards of local communities owing toutilization of saline plant biomass for biogas production.

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