IJERD – International Journal of Environmental and Rural Development (2013) 4-1

Research article
erdManagement of Municipal Sewage Sludge by
Vermicomposting Technology: Converting a Waste into a
Bio fertilizer for Agriculture
CHULEEMAS BOONTHAI IWAI*
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
Email: chuleemas1@gmail.com; chulee_b@kku.ac.th

MONGKON TA-OUN
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

THAMMARED CHUASAVATEE
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

PRAWEENA BOONYOTHA
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
Received 5 January 2013

Accepted 27 March 2013(*Corresponding Author)

Abstract This paper reports on the feasibility of utilization of vermicomposting
technology using the earthworm Eudrilus eugeniae for managing municipal sewage sludge
by conversion into beneficial bio-fertilizer. Sewage sludge was used at various
concentrations 1, 5, 10, 15, 20, and 25% to test for avoidance behavior of the earthworm.
The mix of sewage sludge with cassava wastes and cow dung was subjected to compost
treatment with and without earthworm treatment for 30 days. During the study period data
was collected on the surviving earthworms, biomass together with chemical analysis ofwastes before and after treatment. The results indicate that 5% concentration of sludge
mixed with cassava waste was ideal for Eudrilus eugeniae to treat. There was a decrease inpH, organic carbon concentration, C:N ratio, and an increase in electrical conductivity(EC), nitrogen, potassium and phosphorus concentrations in all the vermireactors. Total
Kjeldhal nitrogen (TKN), available phosphorus and potassium concentrations wereincreased compared to compost without earthworm treatment at 50, 24, and 10%
respectively. The heavy metal concentrations (Cr, Cu, Cd, Pb and Hg) in final
vermicomposts were lower than in initial feed mixtures. The earthworm biomass wasincreased 40-90% and could survive 60% from the beginning. Therefore, the present study
showed that vermicomposting of municipal sewage sludge into bio-fertilizer is feasible
and provides a safe, simple, economic and practical alternative method to resolve theproblem of management of sewage sludge.
Keywords waste management, safe fertilizer, agriculture

INTRODUCTION
In Thailand, municipal sewage sludge from domestic wastewater treatment is generated in large
quantities, is hazardous and creates problem for safe disposal due to the presence of certain soil
contaminants, such as organic compounds, heavy metals, and human pathogens. Sewage sludge
generated in huge quantities has led to indiscriminate and inappropriately timed application of
untreated sludge to agricultural fields as fertilizer because of its nutrient content, especiallynitrogen and phosphorus. The problem of sludge disposal and management exists in otherdeveloping countries and probably prevails also in other parts of the world. Indiscriminate disposalof sewage sludge on agricultural fields induces soil and plant toxicity and creates depressive effects
on the metabolism of soil microorganisms by drastically modifying physico-chemical andⒸ ISERD

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biological environments of soil. Therefore it is absolutely essential for sewage sludge to undergo
additional stabilization treatment prior to agricultural use (Hait and Tare, 2011).
The organic matter and high nutrient contents of municipal sewage sludge have promoted its
application to agricultural land as an organic fertilizer. However, heavy metals in domestic andindustrial wastewater are concentrated in sewage sludge at high levels with the total content
ranging from 0.5 to 2% on a dry weight basis and at 6% in extreme conditions (Gupta and Garg,2008). Therefore, concerns for the safe application of sewage sludge are mainly focus on the heavy
metal contamination that can arise. Copper and cadmium often have high concentrations in sewage
sludge and may affect the health of people and animals through the food chain if sludge is applied
improperly. Methods for decreasing the contents and bioavailability of these elements in sewage
sludge are worthy of research. Unlike organic compounds, metals cannot be degraded (Lasat, 2000).
To decrease the contents and bioavailability of heavy metals usually requires their removal. Suchan approach can be prohibitively expensive. Also, the metal removing process often employs
stringent physicochemical agents, which can dramatically inhibit soil fertility with subsequent
negative impacts on the ecosystem. Another method is to use chemical immobilization
amendments to reduce metal bioavailability. The addition of chemical immobilization amendments
may only immobilize lethal levels for restricted periods of time and introduce other harmful
chemicals. Phytoremediation is recognized as the most commercially and environmental friendly
technology available (Lasat, 2000), but up to now, only a limited number of plants have been foundto have the phytoaccumulation ability and much less can be used for field phytoremediation
because of low biomass production. There is a need for ecologically as well as economicallysustainable technologies which enable recovery of recyclable constituents from sewage sludge as it
is rich in nutrients and has high organic matter content. Vermicompost technology is ecologicallyand economically sustainable and has been widely used for processing of sewage sludge over theyears (Sinha et al., 2010). Therefore, this study aimed to assess the feasibility of utilization ofvermicomposting technology by using the earthworm (Eudrilus eugeniae) for ameliorating themunicipal sewage sludge by conversion into beneficial bio fertilizer.
METHODOLOGY
Earthworms and substrate: Earthworms, Eudrilus eugeniae, were randomly obtained from stock
cultures maintained in the earthworm culture laboratory at Khon Kaen University. Stockearthworms were cultured in the laboratory on partially decomposed cow dung mixed with cassava
waste. Sewage sludge with approximate water content of 75-85% was taken directly from the SiPhaya Wastewater Treatment Plant in Bangkok, Thailand. The sludge was shade dried in thelaboratory to remove excess water. The chemical characteristics of the sewage sludge and bulking
materials are shown in Table 1.
A study of the toxicity of sewage sludge on the survival of earthworms: The study of the
toxicity of sewage sludge on the avoidance behavior of earthworm was performed with different
concentrations of sewage sludge at 1, 5, 10, 15, 20 and 25% using 10 earthworms in a plastic
containers containing 100 g of (dry weight basis) substrate material; avoidance behaviour ofearthworms was observed every day.
A study of the survival and the growth of earthworms affected by sewage sludge mixed withcassava industrial wastes: This study included 4 sub-experiments; 1. Vermicompost mixed withcassava pulp 2. Vermicompost+ 5% sewage sludge mixed with cassava pulp 3. Vermicompost withcassava peel 4. Vermicompost + 5 % sewage sludge mixed with cassava peel. This experimentused   a   “Completely   Randomized   Design”   (CRD)   with   three   replications.   Ten   earthworms   were  released into plastic pot containers containing 100 g (dry weight basis). The weight of earthworms
was recorded before and after 30 days. After 7 days, the survival rate of earthworm was measured.
Cassava waste was chosen in this study because cassava industry is main industry in this area andproduces a considerable amount of waste per day.

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Vermicomposting process
Experiment design: The vermicompost (VCP) (with earthworm) and compost (without
earthworm) experiment was conducted in plastic buckets (35 cm diameter and 40 cm depth) andused cassava pulp, cassava peel and 5% sewage sludge in the process. The experimental design was
CRD with 3 replications with the mixture at a rate of 75%: 25% (cassava industrial wastes: soil
mixture). The 25% in soil mixture was composed of Nampong soil and cow manure. The moisture
content in the mixture was adjusted to 70-80% of WHC (Water Holding Capacity) by water and 10
earthworms/1 kg were added to the mixed material which was covered with a dark net to prevent
earthworm escape and direct exposure to light (Wang et al., 2012). The time of study were 0 and 30
days at room temperature between 28±2 OC
Chemical analysis: The weight of the system and chemical parameters of substrate were measured
in all treatments before introducing earthworms and after vermicomposting for 30 days. The
earthworms were separated by hand at the end of the period. The growth rate of composting
earthworms in this system was then analyzed according to the method described by Suthar (2009).
(1) Analysis of sewage sludge and earthworms; A total of 40 g compost and vermicompost wascollected from each container using multi-point sampling at random. The samples were
homogenized, dried at 40°C in a ventilated oven, and then passed through 100-mesh sieves after
grinding into small pieces. The pH of compost (CP) and vermicomposting (VCP) was measured
using a digital pH meter in 1/2.5 (w/v) deionized water. Total organic carbon was determined by
the partial-oxidation method (Walkley and Black, 1934). Total N (total nitrogen) was measured by
the micro Kjeldahl method (Jackson, 1973; Bremner and Mlvaney, 1982). Total P (TP) was
determined by digestion with acid (HNO3: H2SO4:HClO4 (5:2:1). The sample used 1:10 mixed acid(w/v). Water-soluble P (WSP) was measured in Deionized water extraction ratio VCP and CP 1:25
(W/V) and shaken for 2 hours. Exchangeable phosphorous (Exch. P) was determined using the
Bray II extraction method (Schroth et al., 2003). The totals from P solutions were determined using
the ascorbic acid molybdenum blue method by UV spectrophotometer (Murphy and Riley, 1962).
(2) Heavy Metal Analysis; Total heavy metals (Cr, Cu, Cd, Pb and Hg) concentrations were
determined by the HF-HNO3-HClO4 digestion method and HNO3-H2SO4 digestion method,respectively. The heavy metals were extracted using the diethylene-triaminepentaacetic acid
(DTPA) extraction method. The heavy metal concentrations of all extracts were determined byatomic absorption spectrophotometry (AAS). About 20 g of initial earthworms in stock culturesand final earthworms at each treatment with equal weight were separated from containers and thenkept in culture dishes in the dark for two days to empty their gut content, after which they were
washed in distilled water to remove excess material from their bodies. Next, the earthworms weresacrificed by freezing and dried at 105 °C for 24 hours in a ventilated oven. Prior to analysis, theearthworms were cooled to room temperature, then ground and passed through a 20-mesh sieve.
The metals concentrations (Cr, Cu, Cd, Pb and Hg) in earthworm tissue from different treatmentgroups were analyzed using the same method as described for sludge metal contents.
Statistical Analysis: One-way ANOVA was used to analyze the significant differences among
different vermicomposters   for   studied   parameters.   Tukey’s   test   was   performed   to   identify   the  homogeneous type of vermicomposters for the various parameters. The probability levels used forstatistical significance of tests were p < 0.05.
RESULTS AND DISCUSSION
Sewage sludge had negative impact on earthworm. Avoidance behavior of the earthworm  Eudrillus
eugeniae (% avoidance) when exposed to different concentrations of sewage sludge was showed inTable 2. However, when mixed sewage sludge with cassava waste, earthworms   could   survive   in  vermicompost  at  5%  sewage  sludge  and  also  increased  weight.  After  30  days,  vermicompost  with  cassava   pulp   could   increase   nutrients   and   reduce   Cr, Cu, Pb and   Hg concentrations in   sewage  sludge  by  2.31, 14.03, 1.80 and  33.75% , respectively and vermicompost  with  cassava  peel  could  reduce   Cu and   Hg by 34.270 and   14.504%, respectively. The results are shown in Tables 1-6.
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Cassava peel could help to reduce heavy metal by addition to vermicomposting and was better thancassava pulp. Vermicomposting resulted increase in total N (TN), total P (TP) and total K (TK) as
compared to the initial compost material depending on different bulk material. The study showedthat the vermicomposting significantly improved the availability of nutrients in sewage sludge.
Moreover, vermicomposting considerably reduced the availability of heavy metal presumably byforming organic-bound complexes. The environmental conditions and characteristics of eachmaterial in general showed significant effect on the transformation and availability of nutrients andheavy metals (Hait and Tare, 2012). Cassava pulp is acidic with low electrical conductivity (EC)and is distinct from Cassava peel which has higher pH and EC (Table 1) and cow dung had both
high pH and EC together with high available-P (Table 1).
Table 1 Physico-chemical characteristics of primary sewage sludge and bulking
material for vermicompost
Material
Cassava  pulp
Cassava  peel
Soil
Cow  Dung
Sludge  100%
Sludge  5%pH
4.21 ± 0.11
6.72 ± 0.08
7.76 ± 0.03
8.09 ± 0.12
6.13 ± 0.03
6.81 ± 0.06

Material
Cassava  pulp
Cassava  peel
Soil
Cow  dung
Sludge  100%
Sludge  5%

TP (%)
0.083 ± 0.001
0.208 ± 0.006
0.034 ± 0.002
0.080 ± 0.001
0.191 ± 0.001
0.044 ± 0.003

EC (µS/cm)
328.33 ± 22.30
666± 26.66
543.33 ± 7.57
5263.33 ± 234.59
1446± 44.51553± 95.82
TN (%)
0.205 ± 0.008
0.133 ± 0.016
0.044 ± 0.002
0.927 ± 0.012
2.710 ± 0.020
0.119 ± 0.007

Avail-P (%)
0.002 ± 0.00
0.010 ± 0.00
0.002 ± 0.00
0.033 ± 0.00
0.020 ± 0.00
0.011 ± 0.00

OM (%)
70.072 ± 3.50
8.552 ± 0.45
0.585 ± 0.07
32.092 ± 3.90
26.908 ± 0.95
1.713 ± 1.31

K (%)
0.174 ± 0.006
0.213 ± 0.006
0.038 ± 0.000
1.719 ± 0.081
0.088 ± 0.000
0.048 ± 0.003

Table  2  Avoidance  behavior  of  earthworm,  Eudrillus eugeniae (% avoidance) exposed
to different concentrations of sewage sludge
Concentration  of  sewage  sludge (%)
1
5
10
15
20
25

%  Avoidance  of  Eudrillus eugeniae
20
100
100
100
100
100

Table 3 Earthworm weight in different vermicomposting treatments
Treatment
Vermicompost  +  cassava  pulp
Vermicompost  +  cassava  pulp  +5%  sludge
Vermicompost  +  cassava  peelVermicompost  +  cassava  peel  +5%  sludge

Earthworm  weight  (g/earthworm)
0 day(g)
0.413
0.499
0.433
0.482

30 day(g)
0.000
0.765
0.475
9.005

Increased  weight (%)
0.00
34.76
8.83
94.65

Table 4 Earthworm survival in different vermicompost treatments
Treatment
Vermicompost  +  cassava  pulp
Vermicompost  +  cassava  pulp  +5%  sludge
Vermicompost  +  cassava  peelVermicompost  +  cassava  peel  +5%  sludgeⒸ ISERD

172%  survival
100
98
96
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Table 5 Physico-chemical characteristics of initial waste mixtures, compost andvermicompost obtained from different vermicomposters (g/kg) by earthworm  after 30 days
Initial
0 day

pH
CP*
30 dayVCP**
30 dayVermicompost  +  cassava  pulp

8.06 B

8.91 B

9.26 A

Vermicompost  +  cassava  pulp  +5%  sludge

8.31 A

9.06 A

8.96 B

Vermicompost  +  cassava  peel

8.07 B

8.38 C

7.62 D

Vermicompost  +  cassava  peel  +5%  sludge

8.00 B

8.12 D

7.79 C

Initial0 day
0.160 C

TN (%)
CP*
30 day0.310 B

VCP**
30 day0.210 D

0.351 A

0.524 A0.136 D
0.207 B

Treatment

Treatment
Vermicompost  +  cassava  pulp
Vermicompost  +  cassava  pulp  +5%  sludge
Vermicompost  +  cassava  peelVermicompost  +  cassava  peel  +5%  sludge

Treatment
Vermicompost  +  cassava  pulp
Vermicompost  +  cassava  pulp  +5%  sludge
Vermicompost  +  cassava  peelVermicompost  +  cassava  peel  +5%  sludge

EC (µS/cm)
CP*
30 dayVCP**
30 day2660.00 A

2019.00 D

2666.67 A

2630.00 B

2306.67 B

2830.00 A

2280.00 B

2176.67 C

Initial
0 day
12.872 A

OM (%)
CP*
30 day21.148 A

VCP**
30 day6.219 C

0.343 B

14.016 A

17.364 AB

12.835 B

0.206 C

0.261 C9.590 BC5.740 D

6.193 C

0.300 B

0.594 A

7.974 C5.934 D11.814 B

Initial0 day
0.012 D

Avail-P (%)
CP*
30 day0.023 A

VCP**
30 day0.018 C

Initial
0 day
0.015 BTP (%)
CP*
30 day0.575 D

VCP**
30 day0.496 C

0.017 A

0.023 A

0.024 B

0.036 A

0.978 A

0.819 A

0.016 B

0.002 C

0.015 D

0.009 C0.590 C0.497 C

0.015 C0.019 B

0.025 A

0.034 A

0.699 B

0.785 B

Initial0 day
1712.67A
1446.00
C
1434.33
C
1598.33
BK (%)
Initial
CP*
VCP**
0 day
30 day30 dayVermicompost  +  cassava  pulp
0.375 B
0.426 B
0.396 C
Vermicompost  +  cassava  pulp  +5%  sludge
0.411 A
0.541 A
0.524 A
Vermicompost  +  cassava  peel0.304 C0.280 C
0.332 D
Vermicompost  +  cassava  peel  +5%  sludge
0.280 D
0.401 B
0.449 B*CP = Compost without earthworm **VCP = Vermicompost with earthworm
Mean values followed by different letters in the same column are statistically different(ANOVA;;  Tukey’s  test,  p  <  0.05)
Treatment

Table 6 Heavy metal concentration (mg/kg) in initial sewage sludge and compost,
vermicompost and earthworm after 30 days2/
2/
2/
Heavy  metal  in  S1
S2
  Earthworm
initial  sewage  sludge
CP*
VCP**
CP*
VCP**
S1
S2
(mg/kg)Cr
73.533
9.736
9.516
9.680
5.237
2.051
2.351
Cu
667.628
40.24235.29036.79827.406
7.746
4.815
Cd
1.189
0.088
0.108
0.079
0.086
0.172
0.172
Pb
113.904
11.24911.050
7.724
7.884
2.351
1.786
Hg
4.450
0.321
0.240
0.150
0.131
0.038
0.048
*CP = Compost without earthworm **VCP = Vermicompost with earthworm
S1=  Vermicompost  with  cassava  pulp  +5% sludge. S2=  Vermicompost  with  cassava  peel  +5% sludge  1/
Test  method: In house method based on EPA 3052 2/  Manual on Fertilizer Analysis, APSRDO.DOA; 4/2551

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CONCLUSION
This study indicates that sewage sludge at 5% could be managed by earthworm treatment throughvermicompost technology, which could be a potential technology to convert toxic organic waste
into nutrient rich biofertilizer. The feasibility of using earthworms to mitigate the metal toxicity
and to enhance the nutrient profile in sludge might be useful to improve the sustainability of land
restoration practices on a low-input basis.
ACKNOWLEDGEMENTS
This research project was funded by The National Research Council of Thailand (NRCT) andNational Science and Technology Development Agency (NSTDA) in 2012 and Research Center
for Environmental and Hazardous Substance Management (EHSM), Khon Kaen University.
Thanks are extended to the Division of Land Resource and Environment, Faculty of Agriculture,
Khon Kaen University for use of the research facility, Integrated Water Resource Management
Research and Development Center in Northeast Thailand and GWRC. The authors would like tothank Prof. Barry Noller, University of Queensland, for English editing and suggestions for the
manuscript.
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