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Vermicomposting of source-separated human faeces for nutrient recycling
Waste Management 30 (2010) 50–56
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Vermicomposting of source-separated human faeces for nutrient recycling Kunwar D. Yadav a,*, Vinod Tare b, M. Mansoor Ahammed a a b
Department of Civil Engineering, SV National Institute of Technology, Surat 395 007, India Department of Civil Engineering, Indian Institute of Technology, Kanpur 208 016, India
a r t i c l e
i n f o
Article history: Accepted 22 September 2009 Available online 21 October 2009
a b s t r a c t The present study examined the suitability of vermicomposting technology for processing source-separated human faeces. Since the earthworm species Eisenia fetida could not survive in fresh faeces, modification in the physical characteristics of faeces was necessary before earthworms could be introduced to faeces. A preliminary study with six different combinations of faeces, soil and bulking material (vermicompost) in different layers was conducted to find out the best condition for biomass growth and reproduction of earthworms. The results indicated that SVFV combination (soil, vermicompost, faeces and vermicompost – bottom to top layers) was the best for earthworm biomass growth indicating the positive role of soil layer in earthworm biomass growth. Further studies with SVFV and VFV combinations, however, showed that soil layer did not enhance vermicompost production rate. Year-long study conducted with VFV combination to assess the quality and quantity of vermicompost produced showed an average vermicompost production rate of 0.30 kg-cast/kg-worm/day. The vermicompost produced was mature as indicated by low dissolved organic carbon (2.4 ± 0.43 mg/g) and low oxygen uptake rate (0.15 ± 0.09 mg O2/g VS/h). Complete inactivation of total coliforms was noted during the study, which is one of the important objectives of human faeces processing. Results of the study thus indicated the potential of vermicomposting for processing of source-separated human faeces. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Human excreta are a good source of organic matter and plant nutrients. The use of human excreta as fertilizer in agriculture has been a common practice in some parts of the world. Of late, considerable emphasis is being laid all over the world, especially in rural areas of developing countries, on adopting sanitation systems that use negligible quantities of water, promote cycling of nutrients, and envisage utilization of human excreta to produce fertilizers for supporting agricultural needs. Of the total nutrients in domestic waste, urine contains approximately 80% of the nitrogen (N), about 50% of the phosphorus (P) and nearly 60% of the potassium (K), while the faeces contain about 10% of the N, 25% of the P and 20% of the K (Vinnerås et al., 2006; Niwagaba et al., 2009). Since faeces contain lower concentration of heavy metals than farmyard manure and artificial phosphorus fertilizers, they can be considered as clean fertilizers (Schonning et al., 2002; Niwagaba et al., 2009). However, since faeces may contain pathogens, processing of faecal matter/faeces is necessary before this can be utilized as a fertilizer. Conversion of human excreta to good quality manure without any foul odour, flies and pathogen transmission is a challenging task.
* Corresponding author. Tel.: +91 9428398266. E-mail address: [email protected] (K.D. Yadav). 0956-053X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2009.09.034
Composting technology has been widely used for processing of source-separated human faeces (WHO, 2006; Niwagaba et al., 2009). To be effective, composting requires well-balanced conditions of moisture and aeration. In composting, pathogens are killed as a result of elevated temperatures and also competition with the favored thermophilic microbes (Faechem et al., 1983; Niwagaba et al., 2009). Several studies on composting of source-separated faeces have shown that a sufficiently high temperature for pathogen destruction is difficult to achieve, as temperatures normally increases by 10–15 °C above the ambient temperature (Bjorklund, 2002). Vermicomposting, on the other hand, is emerging as a most appropriate alternative to conventional aerobic composting. This process is not only rapid, easily controllable, cost effective, energy saving, and zero waste process, but also accomplishes most efficient recycling of organics and nutrients (Eastman et al., 2001). Vermicomposting is a viable low-cost technology system for the processing and treatment of organic solid wastes (Hand et al., 1988). It involves the joint action of earthworms and mesophilic microorganisms and does not involve a thermophilic stage. In contrast to traditional waste processing, vermicomposting results in the bioconversion of the waste into two useful products: the earthworm biomass and the vermicompost. Numerous studies have shown the ability of certain earthworm species such as Eisenia fetida (also known as brandling, red wiggler or manure worm), Eisenia andrei (red tiger), Lumbricus rubellus (red worms), to process a wide
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variety of organic matter such as animal excreta, sewage sludge, crop residual and agricultural wastes (Benitez et al., 1999; Bansal and Kapoor, 2000; Kaushik and Garg, 2004; Loh et al., 2005; Garg et al., 2006; Monroy et al., 2006; Suthar, 2008; Khwairakpam and Bhargava, 2009). Various physical/mechanical and biochemical processes are affected by earthworms. The physical processes include substrate aeration, mixing and actual grinding. The biochemical processes are affected by microbial decomposition of substrate in the intestines of the earthworms (Ndegwa et al., 2000). During this process, the important plant nutrients in the material are released and converted through microbial action into forms that are much more soluble and available to plants than those in the parent compounds (Ndegwa and Thompson, 2001). Eastman et al. (2001) have reported that vermicomposting technology is one of the best methods for reducing pathogen concentration in human faeces. While many studies have been reported in the literature on the use of vermicomposting for processing of different organic wastes, few studies reported its use in the processing of source-separated human faeces. Puri (2004) worked on the survivability and reproduction of E. fetida in human faeces and reported that their survival was possible only if the physical characteristics of faeces were changed along with the use of bulking material. Shalabi (2006) has attempted vermicomposting with partially degraded faecal matter by using two different earthworm species E. fetida and Dendrobena veneta at different temperatures. He concluded that faecal matter can be converted to mature compost by vermicomposting within 3 months if the temperature is kept between 20 and 30 °C. It was also found that CaCO3 addition to faecal matter resulted in a product with advanced maturity in terms of volatile solids, TOC and respiration activity. However, a lot more studies need to be conducted before the process can be applied for processing of human excreta. The objective of the present study was to assess the suitability of vermicomposting technology for processing of source-separated human faeces. For this, tests were conducted in three phases. In first two phases, conditions suitable for growth and reproduction of earthworm species E. fetida fed on human faeces were identified by providing soil and/or vermicompost as bulking/supporting medium. In the third phase a year-long study was conducted to assess the quality and quantity of vermicompost produced. 2. Materials and methods 2.1. Earthworms (E. fetida) Earthworm species E. fetida supplied by a Non-Governmental Organization (NGO) called ‘‘Baif” working in Gonda district, Uttar Pradesh, India was used in the present study. The NGO maintained the worm culture by feeding a mixture of partially degraded animal dung and plant residues such as leaves. The worm culture was subsequently developed outside the laboratory in specially made rectangular brick reactors of size 2000 1000 2000 mm. Proper drainage was provided by successive layers of blast slag, gravel and sand to avoid any water logging conditions. The reactors were covered with paddy sheds. Separate cultures that fed on partially degraded animal dung and human faeces were maintained by keeping optimum moisture levels. 2.2. Soil Earthworms normally prefer to perform most of their activities in the soil and hence are referred to as soil animals. It is with this background that soil is considered as an important supporting material for vermicomposting in this study. Soil collected from
Table 1 Characteristics of the soil used. Parameter
Value
pH Electrical conductivity, lmho/cm Water holding capacity, % Carbon, % Nitrogen, % % Sand (0.05–0.50 mm) % Silt (0.002–0.05 mm) % Clay (<0.002 mm) Bulk density, kg/m3
8.0 294 32 1.448 0.090 40 30 30 1120
an agricultural field from a village Barasirohi near Indian Institute of Technology, Kanpur was used in the study. Top 10 cm layer of soil was scrapped and objectionable materials in the soil were removed manually. It was then sifted and thoroughly mixed before used in different experiments. Some relevant characteristics of the soil used in the present study are presented in Table 1. 2.3. Bulking material Bulking material is needed for enrichment of the diversity of microbial population and enzymatic activities in addition to improving the physical environment for the sustenance in the experimental reactors. In the present study fresh and mature vermicompost was used as bulking/supporting material. It was collected from stock culture reactors. Partially degraded animal dung and human faeces were added to the reactors as feed to the earthworm species E. fetida to produce vermicompost. 2.4. Human faeces In the present study human faeces were collected from a nonflush, drop and store type of toilet from a village named Mandhana near IIT Kanpur. The toilet was designed to have separate seats for defecation and anal cleaning. Faeces were collected daily from 4 to 5 houses and thoroughly mixed before used for analysis, maintenance of earthworm stock, feeding in different experiments. The composition of human faeces is presented in Table 2. 2.5. Phase I: preliminary tests These tests were performed with an objective to assess the best conditions for earthworm biomass growth and reproduction by using different combinations of feed (faeces) and support materials (soil and/or vermicompost). The best combinations were used in further studies. The tests were conducted in the laboratory at room temperature (25 ± 2 °C) in transparent PVC reactors. The reactors (diameter 180 mm and depth 90 mm), with 0.025 m2 of exposed top surface area, were covered using perforated lids to provide proper air ventilation. One millimetre diameter perforations on the lid allowed exchange of gases but restricted the movement of worms out of the reactors. In these tests, six different combinations of up to four layers of feed and support materials were used. Details of the reactors with layer thickness used in each reactor are presented in Table 3. Three replicates were prepared for each combination. The soil was properly homogenized and moistened to the maximum water holding capacity prior to placing in the reactors. Experiments were conducted by applying a loading of 200 g of moist faeces (corresponding to a thickness of 15 mm) which was placed in the centre covering approximately 75% of the reactor surface area. Twenty mature earthworms having body weight of 0.25– 0.29 g were introduced in the reactors after 1 week of starting the reactors. A moisture content of 60–65% was maintained by regu-
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2.7. Phase III: bench scale experiment
Table 2 Characteristics of human faeces.
a
Parameter
Valuea
Moisture content, % Bulk density, kg/m3 pH Electrical conductivity, mmho/cm Volatile solids, mg/g dry weight Total carbon-C, mg/g dry weight Total organic carbon (TOC), mg/g dry weight Dissolved organic carbon (DOC), mg/g dry weight Total nitrogen (TN), mg/g dry weight C:N ratio Oxygen uptake rate, mg O2/g VS/h Phosphorous as P2O5, mg/g dry weight Potassium as K2O, mg/g dry weight Calcium, mg/g dry weight Magnesium, mg/g dry weight Sodium, mg/g dry weight Iron, mg/g dry weight Manganese, mg/g dry weight Zinc, mg/g dry weight Nickel, mg/g dry weight Total coliforms, MPN/g
80 ± 5 1200 ± 200 5.3 ± 0.2 60.0 ± 15.0 820 ± 50 425 ± 25 415 ± 15 25 ± 3 41.0 ± 4.0 10.5 ± 1.0 70.0 ± 5.0 11.0 ± 2.0 28.0 ± 1.7 32.0 ± 6.0 8.2 ± 1.5 8.5 ± 1.3 3.8 ± 0.9 0.27 ± 0.50 0.24 ± 0.04 0.009 ± 0.002 5.0 109
Values indicate mean ± standard deviation based on 48 samples.
larly sprinkling water over the entire period of the experiment. Reactors were manually examined after 15, 30, 45 and 60 days for survival and growth of earthworms by counting the number of cocoons and total biomass. 2.6. Phase II: scale-up tests The scale-up study was conducted with two promising combinations of SVFV and VFV. This study was conducted in open backyard of the Environmental Engineering Laboratory of IIT Kanpur during October 2004–January 2005 in brick reactors of dimension 300 300 600 mm at ambient temperature (5–30° C). The top surface of the reactors was covered with thick jute sheet. Details of the reactors with layer thickness are presented in Table 3. Thirty mature earthworms having approximately same body weight (0.25–0.29 g) were introduced in all the reactors after 1 week of starting the reactors. Experiments were conducted in duplicate and the loading of faeces was done monthly alternatively in two different half portion of the surface area for 4 months. All reactors were manually examined after 4 months for survival and growth of earthworms by counting the number of cocoons and mature earthworms. Vermicompost produced was also measured at the end of 4 months. Total weight of earthworms was estimated and average individual weight of the worms was calculated based on the number of earthworms present in reactor.
This experiment was conducted to study the quality and quantity of vermicompost produced from human faeces. Galvanized iron (GI) sheet reactor (300 mm length, 450 mm width and 300 mm depth) using VFV combination with 50 mm thick faeces layer sandwiched between 75 mm thick vermicompost layer was used in this study. The experiment was run continuously for 12 months at stocking density of 4.0 kg/m2 and feeding rate of 1.2–1.5 kg/m2/day. Feeding of fresh faeces was done at 7 days interval alternatively in two different half portion of the surface area. The experiment was run with four replicates. Some typical parameters, namely moisture content, pH, volatile solids, carbon content and nitrogen content were monitored after each feeding. The vermicompost produced was removed monthly and final vermicompost quality was assessed on termination of the reactor. 2.8. Chemical analysis For determination of pH and electrical conductivity of faeces, soil and compost, 1:10 suspension with de-ionized water was made. The water holding capacity was determined by submerging the material for 24 h in water and draining the excess water for 30 min. Moisture content was determined upon drying the samples to constant weight at 70 ± 2 °C for 24–72 h by using hot air oven. Organic matter content was obtained by burning the dried samples at 550 ± 5 °C. The analysis of pH, electrical conductivity, water holding capacity, moisture content and organic matter was done by methods as given in USDA and USCC (2002). The total carbon and nitrogen was determined by using Elemental Analyzer (Model: CE440, Leeman Labs Inc., USA) on dried samples. The metal analysis was done using atomic absorption spectrophotometer (Model: 220 FS, Varian, Australia) by digesting the samples (USEPA 3051 method modified for compost) in microwave digester (Model: V-800, Varshal Inc., USA). 2.9. Statistical analysis Various statistical analyses of the experimental data were performed using Microsoft Excel 2007. 3. Results and discussion 3.1. Preliminary tests The results of the preliminary tests are presented in Fig. 1. Earthworms became inactive within 15 min and died within an hour of introducing in faeces in the absence of any support media (Reactor F). Also, earthworms did not survive for more than 3 days
Table 3 Details of the reactors used in preliminary and scale-up tests.
a b
Reactor
Layer 1 (bottom-most layer)
Layer 2
Layer 3
Layer 4
Preliminary test SVFVa SVF VFV VF SF F Scale-up test
Soil(25)b Soil (25) Vermicompost (25) Vermicompost (25) Soil (25) Faeces (25)
Vermicompost (15) Vermicompost (15) Faeces (15) Faeces (15) Faeces (15) –
Faeces (15) Faeces (15) Vermicompost (15) – – –
Vermicompost (15) – – – – –
SVFV VFV
Soil (300) Vermicompost (300)
Vermicompost (75) Faeces (50)
Faeces (50) Vermicompost (75)
Vermicompost (75) –
S: soil; V: vermicompost; F: faeces. Numbers given in parentheses are thickness of each layer in mm.
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0 Days 15 Days 30 Days 45 Days 60 Days
175
Cocoons, Number
150 125 100 75 50 25 0
Total Biomass, g
25
0 Days 15 Days 30 Days 45 Days 60 Days
20
15
10
5
0 SVFV
SVF
VFV
VF
Reactors Fig. 1. Variation in total biomass growth and cocoons production in different reactors. (Earthworms did not survive in reactors S and SF and hence not shown in figure. Temperature: 25 ± 2 °C, relative humidity: 53 ± 2%.)
when the moisture was low in feed layer, soil supplied the moisture to the feed layer. Since soil is a good conducting material it also helped in controlling the temperature in the feed layer. Satvat and Tare (2004) also reported that soil layer positively influenced the survival of worms as it helped to maintain moisture in the vermicomposting and feed layer. Hundred percent earthworm’s mortality in reactors SF and F indicated that provision of support material such as compost/vermicompost either as separate layer beneath and/or above human faeces is necessary for survivability of earthworms. Fresh faeces have high amount of organic matter and high moisture content that promote formation of anaerobic conditions. In case of SF combination, due to movement of earthworms from inside to outside or vice-versa, the faeces spread to the entire surface of soil which resulted in anaerobic condition. Frederickson and Knight (1988) reported that in anaerobic conditions alcohol, ammonia, acetic acid and methane gas are produced which could be lethal to the earthworms. It was also observed that faeces were not accepted by earthworms until the conditions within feed became aerobic and/or the faeces were partially degraded. Neuhauser et al. (1988) reported that partial degradation, anaerobically or aerobically, of organic wastes is essential for survivability and growth of earthworms. Vermicompost as support material on above or beneath of fresh faeces helps (i) in preventing the faeces turning into anaerobic by absorbing the excess moisture, and (ii) in partial degradation by providing the active microbial biomass. Several researchers (Satchell, 1983; Mulongoy and Bedoret, 1989) reported that vermicompost helps in the degradation process by providing microbial biomass and enzymes. The individual weight of worms in different reactors varied between 0.30 and 0.58 g which is in the range of 0.30–1.26 g reported in the literature (Kaushik and Garg, 2004; Monroy et al., 2006). 3.2. Scale-up tests
in reactor SF where faeces were added above the soil layer. However, in all other reactors earthworms survived, grew and multiplied. It may be noted that the earthworms were introduced in all the reactors after 1 week of starting the reactors. It was realized that this period of precomposting helped (i) to eliminate anaerobic conditions, at least at the exterior of the feed, (ii) to reduce the concentration of mortality causing substances, and (iii) to make the feed acceptable to the earthworms. During this period, the feed pH increased from acidic to neutral, moisture content reduced by 20– 25%, and the levels of toxic volatile substances reduced significantly (data not shown). Gunadi et al. (2002), Garg et al. (2005, 2006) also reported that precomposting of waste was essential to avoid death of earthworm and to enhance the survivability of earthworms. Higher biomass growth of earthworms was found in reactors containing both soil and vermicompost. The total biomass growth was on an average 22–37% higher in reactors with soil bedding layer compared to those without soil layer. The total biomass (that is the weight of mature and unmature earthworms that are produced within the reactor) increased from 5.2 to 22.2 g within 60 days in SVFV combination. The biomass growth was higher in reactor SVFV compared to VFV. Similarly the biomass growth was higher in SVF compared to VF. This observation showed that provision of soil layer increases the biomass growth rate. This increase was possibly due to soil layer facilitating in maintaining a favorable environmental conditions inside the reactors by controlling the temperature and moisture. During the experiments, it was observed that soil layer works in two ways. When the moisture was higher, the soil helped in absorbing the excess moisture, and
Based on the preliminary tests, two combinations, SVFV and VFV, were selected for scale-up studies. Summary of results of these studies is reported in Table 4. In the scale-up studies, the individual weight of mature worms was similar (0.45 ± 0.01 g) in all reactors. The biomass growth and reproduction rate was higher in SVFV reactor compared to VFV reactor, similar to what was found in preliminary tests indicating the influence of soil layer on biomass growth. However, as can be seen from Table 4 soil did not affect the rate of vermicompost production as SVFV and VFV reactors showed similar levels. 3.3. Bench scale experiments As mentioned earlier bench scale experiments were conducted with VFV reactor for 1 year. Table 5 shows the characteristics of
Table 4 Summary of the results of the scale-up experiments after 4 months processing. Parameters
Total biomass (g) Earthworm, number Juvenile, number Cocoons, number Individual weight (g) Vermicompost quantity (g)
Reactor SVFV
VFV
120 ± 11.31 126 ± 11 280 ± 83 126 ± 17 0.45 ± 0.01 135 ± 21
94 ± 1.41 106 ± 23 212 ± 21 102 ± 25 0.45 ± 0.01 130 ± 14
Temperature: (5–30 °C); relative humidity: 50–70%; reactor surface area: 0.09 m2 number of earthworms introduced: 30; individual weight: 0.25–0.29 g, values are mean ± standard deviation.
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Table 5 Characteristics of vermicompost from human faeces. Parameter
Valuea
Faeces, kg dry weight loaded Vermicompost, kg dry weight produced Moisture content, % Bulk Density, kg/m3 Water holding capacity, % pH Electrical conductivity, mmho/cm Volatile solids, mg/g dry weight Total carbon-C, mg/g dry weight Total organic carbon (TOC), mg/g dry weight Dissolved organic carbon (DOC), mg/g dry weight Total nitrogen (TN), mg/g dry weight C:N ratio Oxygen uptake rate, mg O2/g VS/h Phosphorous as P2O5, mg/g dry weight Potassium as K2O, mg/g dry weight Calcium, mg/g dry weight Magnesium, mg/g dry weight Sodium, mg/g dry weight Iron, mg/g dry weight Manganese, mg/g dry weight Zinc, mg/g dry weight Nickel, mg/g dry weight Total coliforms, MPN/g
62 ± 5 25 ± 3 43 ± 5 720 ± 100 75 ± 5 8.0 ± 0.3 28.5 ± 3.0 340 ± 20 182 ± 12 175 ± 10 2.4 ± 0.43 28.0 ± 0.2 6.5 ± 0.5 0.15 ± 0.09 23.5 ± 2.5 65.0 ± 7.5 62.5 ± 11.5 19.5 ± 3.5 19.5 ± 7.0 8.0 ± 1.5 0.54 ± 0.16 0.48 ± 0.17 0.02 ± 0.006 <3.6
Temperature: (5–25 °C); relative humidity: 50–80%; reactor surface area: 0.135 m2; stocking density: 4.0 kg/m2; feed application rate: 1.2–1.5 kg/m2/day; replicates: 4. a Values indicate mean ± standard deviation based on 48 samples.
vermicompost produced from human faeces. Stocking density estimated on termination of the experiment was 3.2 ± 0.2 kg/m2 which was lower than the initial value of 4.0 kg/m2. This change in the stocking density showed that stocking density of 4.0 kg/m2 is not sustainable on a long-term basis. During the vermicomposting of the faeces, pH of the reactors started increasing and within a week it was above 9.0 (Fig. 2). After remaining constant for 2 weeks at that value, it started decreasing. The final pH of the vermicompost was 8.0 ± 0.31. The changes in pH are related to degradation of organics and formation of intermediate products such as ammonium ions and humic acids during the degradation process. Several authors have reported similar results (Short et al., 1999; Komilis and Ham, 2006). In the present study the volatile solids was reduced from 820 ± 50 mg/g to 340 ± 20 mg/g (58% reduction). Significant reduction in the volatile solids is one of the indicators used for compost maturity. Higher decrease in volatile solids means a more stable product indicating that earthworms play an important role in degradation of waste (Ramos et al., 2005; Shalabi, 2006).
10 9
pH
8 7 6 5 0
1
2
3
4
5
6
Week Temperature: 25±2OC; Relative Humidity: 53±2%; Replicates: 4 Fig. 2. Variation of pH during the vermicomposting of human faeces.
In the present study the total carbon was reduced from 425 ± 25 to 182 ± 12 mg/g while total organic carbon (TOC) content came down from 415 ± 15 to 175 ± 10 mg/g during vermicomposting. During processing of the faeces most of the organic carbon was oxidized and whatever carbon remained was not easily degradable. While the present study showed a TOC removal of 57%, different authors have reported TOC reduction values ranging between 26% and 66% during vermicomposting of wastes such as biosolids, sewage sludge and mixture of different organic waste with varying vermicomposting duration using different earthworm species (Elvira et al., 1998; Benitez et al., 1999; Nogales et al., 1999; Kaviraj and Sharma, 2003; Kaushik and Garg, 2004; Garg and Kaushik, 2005; Garg et al., 2005, 2006). The TOC reduction depends upon the degradable amount of organic carbon present in the waste. Dissolved organic carbon (DOC) was reduced from 25 ± 3 to 2.4 ± 0.43 mg/g during vermicomposting representing more than 90% reduction. DOC is the most easily degradable carbon fraction of the substrate because it gets easily dissolved in water. A higher reduction in the DOC is considered as an indicator of compost maturity. Ramos et al. (2005) reported soluble carbon less than 5 mg/g after 60 days of vermicomposting with different mixtures of biosolids with cow manure and oat straw. Several researchers (Elvira et al., 1998; Eggen and Vethe, 2001; Manna et al., 2003) reported DOC level of 3–15 mg/g after maturity of compost produced from different organic wastes. Nitrogen content in the vermicompost was 28 ± 0.2 mg/g compared to 41 ± 4 mg/g in the feed (faeces) corresponding to a loss of 32% on a dry weight basis. Though generally during biodegradation process nitrogen content increases due to mineralization of organic matter but in the present study the nitrogen was lost. As reported earlier, during the vermicomposting process pH increased to greater than 9 during the first 2 weeks and then remained constant at around 8. During the initial period nitrogen might have lost in the form of ammonia. Benitez et al. (1999) reported that 36% nitrogen content was lost during the vermicomposting of sewage sludge. Joseph, 1999 reported that composting microorganisms need 30 parts of carbon and 1 part of nitrogen in balanced diet. If the nitrogen content was very high then excess nitrogen will be lost in the form of smelly ammonia, and at low C/N ratio the nitrogen loss was high and it can be up to 60%. Martin and Dewes (1992) and Nogales et al. (1999) also reported similar results during vermicomposting. On the contrary, Garg et al. (2006) and Kaushik and Garg (2004) reported 1.8– 2.5 times higher nitrogen content during the vermicomposting of wastes. It is likely that the nitrogen content in the final compost depends upon the amount of nitrogen and C/N ratio of the feed. During vermicomposting, C/N ratio decreased from 10.5 to 6.5. Reduction in the C/N ratio was not in accordance with the reduction in carbon, presumably due to loss of nitrogen from the reactors during the degradation as mentioned earlier. A wide range of C/N ratio for mature compost has been reported in the literature (Benitez et al., 1999). This value depends upon the type of waste, and its degradation rate and the fate of carbon and nitrogen during the vermicomposting. This indicates that C/N ratio can not be used as maturity criterion for the vermicomposting if waste is rich in nitrogen. Oxygen uptake rate (OUR) or respiration rate is considered as one of the most reliable indicators for compost maturity. In the present study matured vermicompost had very low (0.15 mg/g) OUR compared to feed OUR of 70 mg/g. It is assumed that during the mineralization of waste, the microbial activity slows down and OUR gets reduced significantly. Several investigators (Paletksi and Young, 1995; Willson and Dalmat, 1996) have suggested that respiration activity is the most appropriate method to check the composting process stability.
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Total nutrient content in the vermicompost depends upon the characteristics of the raw material. On a dry weight basis, the nutrient content (excluding nitrogen) in the vermicompost was 2.1–2.4 times its value in the feed. Several researchers have reported higher content of N, P, K and micronutrients in vermicompost after processing. Tripathi and Bhardwaj (2004) reported that phosphorous and potassium contents were 1.36 and 2.14 times the initial concentration, respectively, after vermicomposting. In another study, total potassium concentration after the vermicomposting was reported to be 1.2–1.7 times the initial concentration (Garg et al., 2006). Though nutrients are required for assimilation of earthworms during the vermicomposting, the quantity required is very low compared to the total quantity present in the feed material. However, if expressed on a dry weight basis, the nutrients concentration showed an increase due to oxidation of organic matter during vermicomposting. Vermicompost production rate was found varying in the range 0.23–0.35 kg-cast/kg-worm/day with an average value of 0.30 kg-cast/kg-worm/day during the study. The vermicompost production rate generally depends on the characteristics of feed, environmental conditions and type of earthworm species. Gajalakshmi et al. (2001), Jain et al. (2003) reported that the vermicast production of 0.20–0.29 and 0.20–0.21 g-cast/g-worm/day for municipal solid waste and mixture of paper and cow dung, respectively. One of the important advantages of vermicomposting over composting is its ability to destroy pathogenic organisms. In the present study, no coliforms were detected in any of the mature vermicompost samples tested, while the faeces had an average coliform content of 5.0 109 MPN/g. In vermicomposting, killing of pathogens is prominently achieved through earthworm actions such as intestinal action, secretion of fluids and selective grazing (Bhawalkar, 1995; Dominguez and Edwards, 1997). 4. Conclusions The studies conducted have shown the potential of vermicomposting technology for processing source-separated human faeces. Precomposting of faeces in the presence of bulking material (vermicompost) is necessary to make the feed acceptable to earthworms. The presence of soil layer helped to increase earthworm biomass growth; it did not influence the vermicast production rate. Long-duration (1 year) study showed an acceptable earthworm stocking density of 3.2 kg/m2 and feeding rate of 1.2–1.5 kg/m2/day for processing of faeces. The vermicast production varied between 0.23 and 0.35 kg/kg-worm/day with an average value of 0.30 kg/kg-worm/day. The low levels of oxygen uptake rate and dissolved organic carbon indicated vermicompost maturity. Vermicomposting resulted in complete elimination of total coliforms. It was observed that C:N ratio can not be considered as a criterion for compost maturity for wastes with low C:N ratio. References Bansal, S., Kapoor, K.K., 2000. Vermicomposting of crop residue and cattle dung with Eisenia fetida. Bioresource Technology 73, 95–98. Benitez, E., Nogales, R., Elvira, C., Masciandaro, G., Ceccanti, B., 1999. Enzyme activities as indicators of the stabilization of sewage sludges composting with Eisenia fetida. Bioresource Technology 67, 297–303. Bhawalkar, U.S., 1995. Vermiculture Ecotechnology. Bhawalkar Earthworm Research Institute, Pune, India. p. 330. Bjorklund, A., 2002. The potential of using thermal composting for disinfection of separately collected faeces in Cuernacava, Mexico. Minor Field Studies No. 200. Swedish University of Agricultural Sciences, International Office. ISSN 14023237. Dominguez, J., Edwards, C.A., 1997. Effects of stocking rate and moisture content on the growth and maturation of Eisenia Andrei (Oligochaeta) in pig manure. Soil Biology and Biochemistry 29 (3–4), 743–746.
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Eastman, B.R., Kane, P.N., Edwards, C.A., Trytek, L., Gunadi, B., Stermer, A.L., Mobley, J.R., 2001. The effectiveness of vermiculture in human pathogen reduction for USEPA biosolids stabilization. Compost Science and Utilization 9 (1), 38– 49. Eggen, T., Vethe, Ø., 2001. Stability indices for different compost. Compost Science and Utilization 9 (1), 19–26. Elvira, C., Sampedro, L., Benítez, E., Nogales, R., 1998. Vermicomposting of sludge from paper mill and dairy industries with Eisenia andrei: a pilot-scale study. Bioresource Technology 63, 205–211. Faechem, R.G., Bradley, D.J., Garelic, H., Mara, D.D., 1983. Sanitation and Disease. Health Aspects of Excreta and Wastewater Management. World Bank Studies in Water Supply and Sanitation. John Wiley and Sons, New York. Frederickson, J., Knight, D., 1988. The use of anaerobically digested cattle solids for vermiculture. In: Edwards, C.A., Neuhauser, E.F. (Eds.), Earthworms in Waste and Environmental Management. SPB Academic Publishing, The Hague, pp. 33– 47. Gajalakshmi, S., Ramasamy, E.V., Abbasi, S.A., 2001. Towards maximising output from vermireactors fed with cow dung and spiked paper waste. Bioresource Technology 79, 67–72. Garg, V.K., Kaushik, P., Dilbaghi, N., 2006. Vermiconversion of wastewater sludge from textile mill mixed with anaerobically digested biogas plant slurry employing Eisenia fetida. Ecotoxicology and Environmental Safety 65 (3), 412– 419. Garg, V.K., Kaushik, P., 2005. Vermistablization of textile mill sludge spiked with poultry dropping by an epigeic earthworm (Eisenia fetida). Bioresource Technology 96, 1063–1071. Garg, V.K., Chand, S., Chhillar, A., Yadav, A., 2005. Growth and reproduction of Eisenia fetida in various animal wastes during vermicomposting. Applied Ecology and Environmental Research 3 (2), 51–59. Gunadi, B., Blount, C., Edwards, C.A., 2002. The growth and fecundity of Eisenia fetida (Savigny) in cattle solids pre-composted for different periods. Pedobiologia 46, 15–23. Hand, P., Hayes, W.A., Frankland, J.C., Satchell, J.E., 1988. The vermicomposting of cow slurry. Pedobiologia 31, 199–209. Jain, K., Singh, J., Gupta, S.K., 2003. Development of a modified vermireactor for efficient vermicomposting: a laboratory scale study. Bioresource Technology 90, 335–337. Joseph, J., 1999. The Humanure Handbook (A Guide to Composting Human Manure). Jenkins Publishing, Grove City, PA, USA, pp. 30–35. Kaushik, P., Garg, V.K., 2004. Dynamics of biological and chemical parameters during vermicomposting of solid textile mill sludge mixed with cow dung and agricultural residue. Bioresource Technology 94, 203–209. Kaviraj, S., Sharma, S., 2003. Municipal solid waste management through vermicomposting employing exotic and local spices of earthworm. Bioresource Technology 90, 169–173. Khwairakpam, M., Bhargava, R., 2009. Vermitechnology for sewage sludge recycling. Journal of Hazardous Materials 161, 948–954. Komilis, D.P., Ham, R.K., 2006. Carbon dioxide and ammonia emissions during composting of mixed paper, yard and food waste. Waste Management 26, 62– 70. Loh, T.C., Lee, Y.C., Liang, J.B., Tan, D., 2005. Vermicomposting of cattle and goat manures by Eisenia fetida and their growth and reproduction performance. Bioresource Technology 96, 111–114. Manna, M.C., Jha, S., Ghosh, P.K., Acharya, C.L., 2003. Comparative efficacy of three epigeic earthworm under different deciduous forest litters decomposition. Bioresource Technology 88, 197–206. Martin, O., Dewes, T., 1992. Loss of nitrogenous compounds during composting of animal waste. Bioresource Technology 42, 103–111. Monroy, F., Aira, M., Dominguez, J., Velando, A., 2006. Seasonal population dynamics of Eisenia fetida (Savigny, 1826) (Oligochaeta, Lumbricidae) in the field. Comptes Rendus Biologies 329 (11), 912–915. Mulongoy, K., Bedoret, A., 1989. Properties of worm cast and surface soil under various cover in the humid tropics. Soil Biology and Biochemistry 21, 197–203. Neuhauser, E.F., Loehar, R.C., Malecki, M.R., 1988. The potential of earthworm for managing sewage sludge. In: Edwards, C.A., Neuhauser, E.P. (Eds.), Earthworm in Waste and Environment Management. SPB Academic Publication, The Hague, Netherlands, pp. 9–20. Ndegwa, P.M., Thompson, S.A., 2001. Integrating composting and vermicomposting in the treatment and bioconversion of biosolids. Bioresource Technology 76, 107–112. Ndegwa, P.M., Thompson, S.A., Das, K.C., 2000. Effects of stocking density and feeding rate on vermicomposting of biosolids. Bioresource Technology 71, 5–12. Niwagaba, C., Nalubega, M., Vinnerås, B., Sundberg, C., Jonsson, H., 2009. Benchscale composting of source-separated human faeces for sanitation. Waste Management 29, 585–589. Nogales, R., Elvira, C., Benitez, E., Thompson, R., Gomez, M., 1999. Feasibility of vermicomposting dairy biosolids using a modified system to avoid earthworm mortality. 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Satvat, P.S., Tare, V., 2004. In-situ vermicomposting for reclaiming saline soils. In: Nineteenth International Conference on Solid Waste Management and Technology, Philadelphia, USA. Satchell, J.E., 1983. Earthworm ecology in forest soil. In: Satchell, J.E. (Ed.), Earthworm Ecology: From Darwin to Vermiculture. Chapman & Hall, London, UK, pp. 161–170. Schonning, C., Leeming, R., Stenstrom, T.A., 2002. Fecal contamination of sourceseparated urine based on the content of faecal sterols. Water Research 32, 1965–1972. Shalabi, M., 2006. Vermicomposting of fecal matter as a component of source control sanitation. Doktor-Ingenieur genehmigte Dissertation, Institute of Wastewater Management and Water Protection, Hamburg University of Technology, Germany. Short, J.C.P., Frederickson, J., Morris, R.M., 1999. Evaluation of traditional windrow composting and vermicomposting for the stabilization of waste paper sludge (WPS). Pedobiologia 43, 735–743.
Suthar, S., 2008. Bioconversion of post harvest crop residue and cattle shed manure into value-added products using earthworm Eudrilus eugeniae Kinberg. Ecological Engineering 32 (3), 206–214. Tripathi, G., Bhardwaj, P., 2004. Decomposition of kitchen waste amended with cow manure using an epigeic spices (Eisenia fetida) and an anecic spices (Lampito mauritti). Bioresource Technology 92, 215–218. USDA (United States Department of Agriculture), USCC (United States Composting Council), 2002. Test Methods for the Examination of Composting and Compost. Vinnerås, B., Palmquist, H., Balmer, P., Weglin, J., Jensen, A., Andersson, A., Jonsson, H., 2006. The characteristics of household wastewater and biodegradable waste – a proposal for new Swedish norms. Urban Water 3 (1), 3–11. WHO, 2006. Guidelines for the Safe Use of Wastewater, Excreta and Greywater. Excreta and Greywater Use in Agriculture, vol. 4. ISBN 92 4 154685 9. Willson, G.B., Dalmat, D., 1996. Measuring compost stability. Biocycle 27, 34–37.
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Vermicomposting of source-separated human faeces for nutrient recycling Kunwar D. Yadav a,*, Vinod Tare b, M. Mansoor Ahammed a a b
Department of Civil Engineering, SV National Institute of Technology, Surat 395 007, India Department of Civil Engineering, Indian Institute of Technology, Kanpur 208 016, India
a r t i c l e
i n f o
Article history: Accepted 22 September 2009 Available online 21 October 2009
a b s t r a c t The present study examined the suitability of vermicomposting technology for processing source-separated human faeces. Since the earthworm species Eisenia fetida could not survive in fresh faeces, modification in the physical characteristics of faeces was necessary before earthworms could be introduced to faeces. A preliminary study with six different combinations of faeces, soil and bulking material (vermicompost) in different layers was conducted to find out the best condition for biomass growth and reproduction of earthworms. The results indicated that SVFV combination (soil, vermicompost, faeces and vermicompost – bottom to top layers) was the best for earthworm biomass growth indicating the positive role of soil layer in earthworm biomass growth. Further studies with SVFV and VFV combinations, however, showed that soil layer did not enhance vermicompost production rate. Year-long study conducted with VFV combination to assess the quality and quantity of vermicompost produced showed an average vermicompost production rate of 0.30 kg-cast/kg-worm/day. The vermicompost produced was mature as indicated by low dissolved organic carbon (2.4 ± 0.43 mg/g) and low oxygen uptake rate (0.15 ± 0.09 mg O2/g VS/h). Complete inactivation of total coliforms was noted during the study, which is one of the important objectives of human faeces processing. Results of the study thus indicated the potential of vermicomposting for processing of source-separated human faeces. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Human excreta are a good source of organic matter and plant nutrients. The use of human excreta as fertilizer in agriculture has been a common practice in some parts of the world. Of late, considerable emphasis is being laid all over the world, especially in rural areas of developing countries, on adopting sanitation systems that use negligible quantities of water, promote cycling of nutrients, and envisage utilization of human excreta to produce fertilizers for supporting agricultural needs. Of the total nutrients in domestic waste, urine contains approximately 80% of the nitrogen (N), about 50% of the phosphorus (P) and nearly 60% of the potassium (K), while the faeces contain about 10% of the N, 25% of the P and 20% of the K (Vinnerås et al., 2006; Niwagaba et al., 2009). Since faeces contain lower concentration of heavy metals than farmyard manure and artificial phosphorus fertilizers, they can be considered as clean fertilizers (Schonning et al., 2002; Niwagaba et al., 2009). However, since faeces may contain pathogens, processing of faecal matter/faeces is necessary before this can be utilized as a fertilizer. Conversion of human excreta to good quality manure without any foul odour, flies and pathogen transmission is a challenging task.
* Corresponding author. Tel.: +91 9428398266. E-mail address: [email protected] (K.D. Yadav). 0956-053X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2009.09.034
Composting technology has been widely used for processing of source-separated human faeces (WHO, 2006; Niwagaba et al., 2009). To be effective, composting requires well-balanced conditions of moisture and aeration. In composting, pathogens are killed as a result of elevated temperatures and also competition with the favored thermophilic microbes (Faechem et al., 1983; Niwagaba et al., 2009). Several studies on composting of source-separated faeces have shown that a sufficiently high temperature for pathogen destruction is difficult to achieve, as temperatures normally increases by 10–15 °C above the ambient temperature (Bjorklund, 2002). Vermicomposting, on the other hand, is emerging as a most appropriate alternative to conventional aerobic composting. This process is not only rapid, easily controllable, cost effective, energy saving, and zero waste process, but also accomplishes most efficient recycling of organics and nutrients (Eastman et al., 2001). Vermicomposting is a viable low-cost technology system for the processing and treatment of organic solid wastes (Hand et al., 1988). It involves the joint action of earthworms and mesophilic microorganisms and does not involve a thermophilic stage. In contrast to traditional waste processing, vermicomposting results in the bioconversion of the waste into two useful products: the earthworm biomass and the vermicompost. Numerous studies have shown the ability of certain earthworm species such as Eisenia fetida (also known as brandling, red wiggler or manure worm), Eisenia andrei (red tiger), Lumbricus rubellus (red worms), to process a wide
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variety of organic matter such as animal excreta, sewage sludge, crop residual and agricultural wastes (Benitez et al., 1999; Bansal and Kapoor, 2000; Kaushik and Garg, 2004; Loh et al., 2005; Garg et al., 2006; Monroy et al., 2006; Suthar, 2008; Khwairakpam and Bhargava, 2009). Various physical/mechanical and biochemical processes are affected by earthworms. The physical processes include substrate aeration, mixing and actual grinding. The biochemical processes are affected by microbial decomposition of substrate in the intestines of the earthworms (Ndegwa et al., 2000). During this process, the important plant nutrients in the material are released and converted through microbial action into forms that are much more soluble and available to plants than those in the parent compounds (Ndegwa and Thompson, 2001). Eastman et al. (2001) have reported that vermicomposting technology is one of the best methods for reducing pathogen concentration in human faeces. While many studies have been reported in the literature on the use of vermicomposting for processing of different organic wastes, few studies reported its use in the processing of source-separated human faeces. Puri (2004) worked on the survivability and reproduction of E. fetida in human faeces and reported that their survival was possible only if the physical characteristics of faeces were changed along with the use of bulking material. Shalabi (2006) has attempted vermicomposting with partially degraded faecal matter by using two different earthworm species E. fetida and Dendrobena veneta at different temperatures. He concluded that faecal matter can be converted to mature compost by vermicomposting within 3 months if the temperature is kept between 20 and 30 °C. It was also found that CaCO3 addition to faecal matter resulted in a product with advanced maturity in terms of volatile solids, TOC and respiration activity. However, a lot more studies need to be conducted before the process can be applied for processing of human excreta. The objective of the present study was to assess the suitability of vermicomposting technology for processing of source-separated human faeces. For this, tests were conducted in three phases. In first two phases, conditions suitable for growth and reproduction of earthworm species E. fetida fed on human faeces were identified by providing soil and/or vermicompost as bulking/supporting medium. In the third phase a year-long study was conducted to assess the quality and quantity of vermicompost produced. 2. Materials and methods 2.1. Earthworms (E. fetida) Earthworm species E. fetida supplied by a Non-Governmental Organization (NGO) called ‘‘Baif” working in Gonda district, Uttar Pradesh, India was used in the present study. The NGO maintained the worm culture by feeding a mixture of partially degraded animal dung and plant residues such as leaves. The worm culture was subsequently developed outside the laboratory in specially made rectangular brick reactors of size 2000 1000 2000 mm. Proper drainage was provided by successive layers of blast slag, gravel and sand to avoid any water logging conditions. The reactors were covered with paddy sheds. Separate cultures that fed on partially degraded animal dung and human faeces were maintained by keeping optimum moisture levels. 2.2. Soil Earthworms normally prefer to perform most of their activities in the soil and hence are referred to as soil animals. It is with this background that soil is considered as an important supporting material for vermicomposting in this study. Soil collected from
Table 1 Characteristics of the soil used. Parameter
Value
pH Electrical conductivity, lmho/cm Water holding capacity, % Carbon, % Nitrogen, % % Sand (0.05–0.50 mm) % Silt (0.002–0.05 mm) % Clay (<0.002 mm) Bulk density, kg/m3
8.0 294 32 1.448 0.090 40 30 30 1120
an agricultural field from a village Barasirohi near Indian Institute of Technology, Kanpur was used in the study. Top 10 cm layer of soil was scrapped and objectionable materials in the soil were removed manually. It was then sifted and thoroughly mixed before used in different experiments. Some relevant characteristics of the soil used in the present study are presented in Table 1. 2.3. Bulking material Bulking material is needed for enrichment of the diversity of microbial population and enzymatic activities in addition to improving the physical environment for the sustenance in the experimental reactors. In the present study fresh and mature vermicompost was used as bulking/supporting material. It was collected from stock culture reactors. Partially degraded animal dung and human faeces were added to the reactors as feed to the earthworm species E. fetida to produce vermicompost. 2.4. Human faeces In the present study human faeces were collected from a nonflush, drop and store type of toilet from a village named Mandhana near IIT Kanpur. The toilet was designed to have separate seats for defecation and anal cleaning. Faeces were collected daily from 4 to 5 houses and thoroughly mixed before used for analysis, maintenance of earthworm stock, feeding in different experiments. The composition of human faeces is presented in Table 2. 2.5. Phase I: preliminary tests These tests were performed with an objective to assess the best conditions for earthworm biomass growth and reproduction by using different combinations of feed (faeces) and support materials (soil and/or vermicompost). The best combinations were used in further studies. The tests were conducted in the laboratory at room temperature (25 ± 2 °C) in transparent PVC reactors. The reactors (diameter 180 mm and depth 90 mm), with 0.025 m2 of exposed top surface area, were covered using perforated lids to provide proper air ventilation. One millimetre diameter perforations on the lid allowed exchange of gases but restricted the movement of worms out of the reactors. In these tests, six different combinations of up to four layers of feed and support materials were used. Details of the reactors with layer thickness used in each reactor are presented in Table 3. Three replicates were prepared for each combination. The soil was properly homogenized and moistened to the maximum water holding capacity prior to placing in the reactors. Experiments were conducted by applying a loading of 200 g of moist faeces (corresponding to a thickness of 15 mm) which was placed in the centre covering approximately 75% of the reactor surface area. Twenty mature earthworms having body weight of 0.25– 0.29 g were introduced in the reactors after 1 week of starting the reactors. A moisture content of 60–65% was maintained by regu-
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2.7. Phase III: bench scale experiment
Table 2 Characteristics of human faeces.
a
Parameter
Valuea
Moisture content, % Bulk density, kg/m3 pH Electrical conductivity, mmho/cm Volatile solids, mg/g dry weight Total carbon-C, mg/g dry weight Total organic carbon (TOC), mg/g dry weight Dissolved organic carbon (DOC), mg/g dry weight Total nitrogen (TN), mg/g dry weight C:N ratio Oxygen uptake rate, mg O2/g VS/h Phosphorous as P2O5, mg/g dry weight Potassium as K2O, mg/g dry weight Calcium, mg/g dry weight Magnesium, mg/g dry weight Sodium, mg/g dry weight Iron, mg/g dry weight Manganese, mg/g dry weight Zinc, mg/g dry weight Nickel, mg/g dry weight Total coliforms, MPN/g
80 ± 5 1200 ± 200 5.3 ± 0.2 60.0 ± 15.0 820 ± 50 425 ± 25 415 ± 15 25 ± 3 41.0 ± 4.0 10.5 ± 1.0 70.0 ± 5.0 11.0 ± 2.0 28.0 ± 1.7 32.0 ± 6.0 8.2 ± 1.5 8.5 ± 1.3 3.8 ± 0.9 0.27 ± 0.50 0.24 ± 0.04 0.009 ± 0.002 5.0 109
Values indicate mean ± standard deviation based on 48 samples.
larly sprinkling water over the entire period of the experiment. Reactors were manually examined after 15, 30, 45 and 60 days for survival and growth of earthworms by counting the number of cocoons and total biomass. 2.6. Phase II: scale-up tests The scale-up study was conducted with two promising combinations of SVFV and VFV. This study was conducted in open backyard of the Environmental Engineering Laboratory of IIT Kanpur during October 2004–January 2005 in brick reactors of dimension 300 300 600 mm at ambient temperature (5–30° C). The top surface of the reactors was covered with thick jute sheet. Details of the reactors with layer thickness are presented in Table 3. Thirty mature earthworms having approximately same body weight (0.25–0.29 g) were introduced in all the reactors after 1 week of starting the reactors. Experiments were conducted in duplicate and the loading of faeces was done monthly alternatively in two different half portion of the surface area for 4 months. All reactors were manually examined after 4 months for survival and growth of earthworms by counting the number of cocoons and mature earthworms. Vermicompost produced was also measured at the end of 4 months. Total weight of earthworms was estimated and average individual weight of the worms was calculated based on the number of earthworms present in reactor.
This experiment was conducted to study the quality and quantity of vermicompost produced from human faeces. Galvanized iron (GI) sheet reactor (300 mm length, 450 mm width and 300 mm depth) using VFV combination with 50 mm thick faeces layer sandwiched between 75 mm thick vermicompost layer was used in this study. The experiment was run continuously for 12 months at stocking density of 4.0 kg/m2 and feeding rate of 1.2–1.5 kg/m2/day. Feeding of fresh faeces was done at 7 days interval alternatively in two different half portion of the surface area. The experiment was run with four replicates. Some typical parameters, namely moisture content, pH, volatile solids, carbon content and nitrogen content were monitored after each feeding. The vermicompost produced was removed monthly and final vermicompost quality was assessed on termination of the reactor. 2.8. Chemical analysis For determination of pH and electrical conductivity of faeces, soil and compost, 1:10 suspension with de-ionized water was made. The water holding capacity was determined by submerging the material for 24 h in water and draining the excess water for 30 min. Moisture content was determined upon drying the samples to constant weight at 70 ± 2 °C for 24–72 h by using hot air oven. Organic matter content was obtained by burning the dried samples at 550 ± 5 °C. The analysis of pH, electrical conductivity, water holding capacity, moisture content and organic matter was done by methods as given in USDA and USCC (2002). The total carbon and nitrogen was determined by using Elemental Analyzer (Model: CE440, Leeman Labs Inc., USA) on dried samples. The metal analysis was done using atomic absorption spectrophotometer (Model: 220 FS, Varian, Australia) by digesting the samples (USEPA 3051 method modified for compost) in microwave digester (Model: V-800, Varshal Inc., USA). 2.9. Statistical analysis Various statistical analyses of the experimental data were performed using Microsoft Excel 2007. 3. Results and discussion 3.1. Preliminary tests The results of the preliminary tests are presented in Fig. 1. Earthworms became inactive within 15 min and died within an hour of introducing in faeces in the absence of any support media (Reactor F). Also, earthworms did not survive for more than 3 days
Table 3 Details of the reactors used in preliminary and scale-up tests.
a b
Reactor
Layer 1 (bottom-most layer)
Layer 2
Layer 3
Layer 4
Preliminary test SVFVa SVF VFV VF SF F Scale-up test
Soil(25)b Soil (25) Vermicompost (25) Vermicompost (25) Soil (25) Faeces (25)
Vermicompost (15) Vermicompost (15) Faeces (15) Faeces (15) Faeces (15) –
Faeces (15) Faeces (15) Vermicompost (15) – – –
Vermicompost (15) – – – – –
SVFV VFV
Soil (300) Vermicompost (300)
Vermicompost (75) Faeces (50)
Faeces (50) Vermicompost (75)
Vermicompost (75) –
S: soil; V: vermicompost; F: faeces. Numbers given in parentheses are thickness of each layer in mm.
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0 Days 15 Days 30 Days 45 Days 60 Days
175
Cocoons, Number
150 125 100 75 50 25 0
Total Biomass, g
25
0 Days 15 Days 30 Days 45 Days 60 Days
20
15
10
5
0 SVFV
SVF
VFV
VF
Reactors Fig. 1. Variation in total biomass growth and cocoons production in different reactors. (Earthworms did not survive in reactors S and SF and hence not shown in figure. Temperature: 25 ± 2 °C, relative humidity: 53 ± 2%.)
when the moisture was low in feed layer, soil supplied the moisture to the feed layer. Since soil is a good conducting material it also helped in controlling the temperature in the feed layer. Satvat and Tare (2004) also reported that soil layer positively influenced the survival of worms as it helped to maintain moisture in the vermicomposting and feed layer. Hundred percent earthworm’s mortality in reactors SF and F indicated that provision of support material such as compost/vermicompost either as separate layer beneath and/or above human faeces is necessary for survivability of earthworms. Fresh faeces have high amount of organic matter and high moisture content that promote formation of anaerobic conditions. In case of SF combination, due to movement of earthworms from inside to outside or vice-versa, the faeces spread to the entire surface of soil which resulted in anaerobic condition. Frederickson and Knight (1988) reported that in anaerobic conditions alcohol, ammonia, acetic acid and methane gas are produced which could be lethal to the earthworms. It was also observed that faeces were not accepted by earthworms until the conditions within feed became aerobic and/or the faeces were partially degraded. Neuhauser et al. (1988) reported that partial degradation, anaerobically or aerobically, of organic wastes is essential for survivability and growth of earthworms. Vermicompost as support material on above or beneath of fresh faeces helps (i) in preventing the faeces turning into anaerobic by absorbing the excess moisture, and (ii) in partial degradation by providing the active microbial biomass. Several researchers (Satchell, 1983; Mulongoy and Bedoret, 1989) reported that vermicompost helps in the degradation process by providing microbial biomass and enzymes. The individual weight of worms in different reactors varied between 0.30 and 0.58 g which is in the range of 0.30–1.26 g reported in the literature (Kaushik and Garg, 2004; Monroy et al., 2006). 3.2. Scale-up tests
in reactor SF where faeces were added above the soil layer. However, in all other reactors earthworms survived, grew and multiplied. It may be noted that the earthworms were introduced in all the reactors after 1 week of starting the reactors. It was realized that this period of precomposting helped (i) to eliminate anaerobic conditions, at least at the exterior of the feed, (ii) to reduce the concentration of mortality causing substances, and (iii) to make the feed acceptable to the earthworms. During this period, the feed pH increased from acidic to neutral, moisture content reduced by 20– 25%, and the levels of toxic volatile substances reduced significantly (data not shown). Gunadi et al. (2002), Garg et al. (2005, 2006) also reported that precomposting of waste was essential to avoid death of earthworm and to enhance the survivability of earthworms. Higher biomass growth of earthworms was found in reactors containing both soil and vermicompost. The total biomass growth was on an average 22–37% higher in reactors with soil bedding layer compared to those without soil layer. The total biomass (that is the weight of mature and unmature earthworms that are produced within the reactor) increased from 5.2 to 22.2 g within 60 days in SVFV combination. The biomass growth was higher in reactor SVFV compared to VFV. Similarly the biomass growth was higher in SVF compared to VF. This observation showed that provision of soil layer increases the biomass growth rate. This increase was possibly due to soil layer facilitating in maintaining a favorable environmental conditions inside the reactors by controlling the temperature and moisture. During the experiments, it was observed that soil layer works in two ways. When the moisture was higher, the soil helped in absorbing the excess moisture, and
Based on the preliminary tests, two combinations, SVFV and VFV, were selected for scale-up studies. Summary of results of these studies is reported in Table 4. In the scale-up studies, the individual weight of mature worms was similar (0.45 ± 0.01 g) in all reactors. The biomass growth and reproduction rate was higher in SVFV reactor compared to VFV reactor, similar to what was found in preliminary tests indicating the influence of soil layer on biomass growth. However, as can be seen from Table 4 soil did not affect the rate of vermicompost production as SVFV and VFV reactors showed similar levels. 3.3. Bench scale experiments As mentioned earlier bench scale experiments were conducted with VFV reactor for 1 year. Table 5 shows the characteristics of
Table 4 Summary of the results of the scale-up experiments after 4 months processing. Parameters
Total biomass (g) Earthworm, number Juvenile, number Cocoons, number Individual weight (g) Vermicompost quantity (g)
Reactor SVFV
VFV
120 ± 11.31 126 ± 11 280 ± 83 126 ± 17 0.45 ± 0.01 135 ± 21
94 ± 1.41 106 ± 23 212 ± 21 102 ± 25 0.45 ± 0.01 130 ± 14
Temperature: (5–30 °C); relative humidity: 50–70%; reactor surface area: 0.09 m2 number of earthworms introduced: 30; individual weight: 0.25–0.29 g, values are mean ± standard deviation.
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Table 5 Characteristics of vermicompost from human faeces. Parameter
Valuea
Faeces, kg dry weight loaded Vermicompost, kg dry weight produced Moisture content, % Bulk Density, kg/m3 Water holding capacity, % pH Electrical conductivity, mmho/cm Volatile solids, mg/g dry weight Total carbon-C, mg/g dry weight Total organic carbon (TOC), mg/g dry weight Dissolved organic carbon (DOC), mg/g dry weight Total nitrogen (TN), mg/g dry weight C:N ratio Oxygen uptake rate, mg O2/g VS/h Phosphorous as P2O5, mg/g dry weight Potassium as K2O, mg/g dry weight Calcium, mg/g dry weight Magnesium, mg/g dry weight Sodium, mg/g dry weight Iron, mg/g dry weight Manganese, mg/g dry weight Zinc, mg/g dry weight Nickel, mg/g dry weight Total coliforms, MPN/g
62 ± 5 25 ± 3 43 ± 5 720 ± 100 75 ± 5 8.0 ± 0.3 28.5 ± 3.0 340 ± 20 182 ± 12 175 ± 10 2.4 ± 0.43 28.0 ± 0.2 6.5 ± 0.5 0.15 ± 0.09 23.5 ± 2.5 65.0 ± 7.5 62.5 ± 11.5 19.5 ± 3.5 19.5 ± 7.0 8.0 ± 1.5 0.54 ± 0.16 0.48 ± 0.17 0.02 ± 0.006 <3.6
Temperature: (5–25 °C); relative humidity: 50–80%; reactor surface area: 0.135 m2; stocking density: 4.0 kg/m2; feed application rate: 1.2–1.5 kg/m2/day; replicates: 4. a Values indicate mean ± standard deviation based on 48 samples.
vermicompost produced from human faeces. Stocking density estimated on termination of the experiment was 3.2 ± 0.2 kg/m2 which was lower than the initial value of 4.0 kg/m2. This change in the stocking density showed that stocking density of 4.0 kg/m2 is not sustainable on a long-term basis. During the vermicomposting of the faeces, pH of the reactors started increasing and within a week it was above 9.0 (Fig. 2). After remaining constant for 2 weeks at that value, it started decreasing. The final pH of the vermicompost was 8.0 ± 0.31. The changes in pH are related to degradation of organics and formation of intermediate products such as ammonium ions and humic acids during the degradation process. Several authors have reported similar results (Short et al., 1999; Komilis and Ham, 2006). In the present study the volatile solids was reduced from 820 ± 50 mg/g to 340 ± 20 mg/g (58% reduction). Significant reduction in the volatile solids is one of the indicators used for compost maturity. Higher decrease in volatile solids means a more stable product indicating that earthworms play an important role in degradation of waste (Ramos et al., 2005; Shalabi, 2006).
10 9
pH
8 7 6 5 0
1
2
3
4
5
6
Week Temperature: 25±2OC; Relative Humidity: 53±2%; Replicates: 4 Fig. 2. Variation of pH during the vermicomposting of human faeces.
In the present study the total carbon was reduced from 425 ± 25 to 182 ± 12 mg/g while total organic carbon (TOC) content came down from 415 ± 15 to 175 ± 10 mg/g during vermicomposting. During processing of the faeces most of the organic carbon was oxidized and whatever carbon remained was not easily degradable. While the present study showed a TOC removal of 57%, different authors have reported TOC reduction values ranging between 26% and 66% during vermicomposting of wastes such as biosolids, sewage sludge and mixture of different organic waste with varying vermicomposting duration using different earthworm species (Elvira et al., 1998; Benitez et al., 1999; Nogales et al., 1999; Kaviraj and Sharma, 2003; Kaushik and Garg, 2004; Garg and Kaushik, 2005; Garg et al., 2005, 2006). The TOC reduction depends upon the degradable amount of organic carbon present in the waste. Dissolved organic carbon (DOC) was reduced from 25 ± 3 to 2.4 ± 0.43 mg/g during vermicomposting representing more than 90% reduction. DOC is the most easily degradable carbon fraction of the substrate because it gets easily dissolved in water. A higher reduction in the DOC is considered as an indicator of compost maturity. Ramos et al. (2005) reported soluble carbon less than 5 mg/g after 60 days of vermicomposting with different mixtures of biosolids with cow manure and oat straw. Several researchers (Elvira et al., 1998; Eggen and Vethe, 2001; Manna et al., 2003) reported DOC level of 3–15 mg/g after maturity of compost produced from different organic wastes. Nitrogen content in the vermicompost was 28 ± 0.2 mg/g compared to 41 ± 4 mg/g in the feed (faeces) corresponding to a loss of 32% on a dry weight basis. Though generally during biodegradation process nitrogen content increases due to mineralization of organic matter but in the present study the nitrogen was lost. As reported earlier, during the vermicomposting process pH increased to greater than 9 during the first 2 weeks and then remained constant at around 8. During the initial period nitrogen might have lost in the form of ammonia. Benitez et al. (1999) reported that 36% nitrogen content was lost during the vermicomposting of sewage sludge. Joseph, 1999 reported that composting microorganisms need 30 parts of carbon and 1 part of nitrogen in balanced diet. If the nitrogen content was very high then excess nitrogen will be lost in the form of smelly ammonia, and at low C/N ratio the nitrogen loss was high and it can be up to 60%. Martin and Dewes (1992) and Nogales et al. (1999) also reported similar results during vermicomposting. On the contrary, Garg et al. (2006) and Kaushik and Garg (2004) reported 1.8– 2.5 times higher nitrogen content during the vermicomposting of wastes. It is likely that the nitrogen content in the final compost depends upon the amount of nitrogen and C/N ratio of the feed. During vermicomposting, C/N ratio decreased from 10.5 to 6.5. Reduction in the C/N ratio was not in accordance with the reduction in carbon, presumably due to loss of nitrogen from the reactors during the degradation as mentioned earlier. A wide range of C/N ratio for mature compost has been reported in the literature (Benitez et al., 1999). This value depends upon the type of waste, and its degradation rate and the fate of carbon and nitrogen during the vermicomposting. This indicates that C/N ratio can not be used as maturity criterion for the vermicomposting if waste is rich in nitrogen. Oxygen uptake rate (OUR) or respiration rate is considered as one of the most reliable indicators for compost maturity. In the present study matured vermicompost had very low (0.15 mg/g) OUR compared to feed OUR of 70 mg/g. It is assumed that during the mineralization of waste, the microbial activity slows down and OUR gets reduced significantly. Several investigators (Paletksi and Young, 1995; Willson and Dalmat, 1996) have suggested that respiration activity is the most appropriate method to check the composting process stability.
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Total nutrient content in the vermicompost depends upon the characteristics of the raw material. On a dry weight basis, the nutrient content (excluding nitrogen) in the vermicompost was 2.1–2.4 times its value in the feed. Several researchers have reported higher content of N, P, K and micronutrients in vermicompost after processing. Tripathi and Bhardwaj (2004) reported that phosphorous and potassium contents were 1.36 and 2.14 times the initial concentration, respectively, after vermicomposting. In another study, total potassium concentration after the vermicomposting was reported to be 1.2–1.7 times the initial concentration (Garg et al., 2006). Though nutrients are required for assimilation of earthworms during the vermicomposting, the quantity required is very low compared to the total quantity present in the feed material. However, if expressed on a dry weight basis, the nutrients concentration showed an increase due to oxidation of organic matter during vermicomposting. Vermicompost production rate was found varying in the range 0.23–0.35 kg-cast/kg-worm/day with an average value of 0.30 kg-cast/kg-worm/day during the study. The vermicompost production rate generally depends on the characteristics of feed, environmental conditions and type of earthworm species. Gajalakshmi et al. (2001), Jain et al. (2003) reported that the vermicast production of 0.20–0.29 and 0.20–0.21 g-cast/g-worm/day for municipal solid waste and mixture of paper and cow dung, respectively. One of the important advantages of vermicomposting over composting is its ability to destroy pathogenic organisms. In the present study, no coliforms were detected in any of the mature vermicompost samples tested, while the faeces had an average coliform content of 5.0 109 MPN/g. In vermicomposting, killing of pathogens is prominently achieved through earthworm actions such as intestinal action, secretion of fluids and selective grazing (Bhawalkar, 1995; Dominguez and Edwards, 1997). 4. Conclusions The studies conducted have shown the potential of vermicomposting technology for processing source-separated human faeces. Precomposting of faeces in the presence of bulking material (vermicompost) is necessary to make the feed acceptable to earthworms. The presence of soil layer helped to increase earthworm biomass growth; it did not influence the vermicast production rate. Long-duration (1 year) study showed an acceptable earthworm stocking density of 3.2 kg/m2 and feeding rate of 1.2–1.5 kg/m2/day for processing of faeces. The vermicast production varied between 0.23 and 0.35 kg/kg-worm/day with an average value of 0.30 kg/kg-worm/day. The low levels of oxygen uptake rate and dissolved organic carbon indicated vermicompost maturity. Vermicomposting resulted in complete elimination of total coliforms. It was observed that C:N ratio can not be considered as a criterion for compost maturity for wastes with low C:N ratio. References Bansal, S., Kapoor, K.K., 2000. Vermicomposting of crop residue and cattle dung with Eisenia fetida. Bioresource Technology 73, 95–98. Benitez, E., Nogales, R., Elvira, C., Masciandaro, G., Ceccanti, B., 1999. Enzyme activities as indicators of the stabilization of sewage sludges composting with Eisenia fetida. Bioresource Technology 67, 297–303. Bhawalkar, U.S., 1995. Vermiculture Ecotechnology. Bhawalkar Earthworm Research Institute, Pune, India. p. 330. Bjorklund, A., 2002. The potential of using thermal composting for disinfection of separately collected faeces in Cuernacava, Mexico. Minor Field Studies No. 200. Swedish University of Agricultural Sciences, International Office. ISSN 14023237. Dominguez, J., Edwards, C.A., 1997. Effects of stocking rate and moisture content on the growth and maturation of Eisenia Andrei (Oligochaeta) in pig manure. Soil Biology and Biochemistry 29 (3–4), 743–746.
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