High-rate composting-vermicomposting of water hyacinth (Eichhornia crassipes,Mart. Solms)

In an attempt to develop a system with which the aquatic weed water hyacinth (Eichhornia crassipes, Mart. Solms) can be economically processed to generate vermicompost in large quantities, the weed was first composted by a 'high-rate' method and then subjected to vermicomposting in reactors operating at much larger densities of earthworm than recommended hitherto: 50, 62.5, 75, 87.5, 100, 112.5, 125, 137.5, and 150 adults of Eudrilus eugeniae Kinberg per litre of digester volume. The composting step was accomplished in 20 days and the composted weed was found to be vermicomposted three times as rapidly as uncomposted water hyacinth [Bioresource Technology 76 (2001) 177]. The studies substantiated the feasibility of high-rate composting-vermicomposting systems, as all reactors yielded consistent vermicast output during seven months of operation. There was no earthworm mortality during the first four months in spite of the high animal densities in the reactors. In the subsequent three months a total of 79 worms died out of 1650, representing less than 1.6% mortality per month. The results also indicated that an increase in the surface-to-volume ratio of the reactors might further improve their efficiency.     

Vermicomposting of the leaf litter of acacia (Acacia auriculiformis): Possible roles of reactor geometry,polyphenols, and lignin

Vermicomposting of the pre-composted leaf litter of acacia (Acacia auriculiformis) was studied in reactors of identical volume but with surface area: height ratios varying from 4 to 250. In separate sets of experiments with these reactors, epigeic earthworm species Eudrilus eugeniae and anecic earthworm species Lampito mauritii were employed at densities of 75 and 150 adult animals per litre of reactor volume.The results reveal that greater the surface area: volume ratio of the reactor, higher is the vermicast output in terms of vermicast output per animal; the more densely populated reactors were comparatively under-productive.Even as the vermicast production remained consistently high in all the reactors, there was significant earthworm mortality throughout the course of the experiments and the worms who survived, steadily lost weight with time. A detailed investigation of the possible causes revealed that, whereas the C:N ratio of acacia compost was comparable with that of other substrates; the polyphenols and lignin content were much higher. Studies by other authors on leaf litter consumption by earthworms in natural or man-made forests have indicated that leaf litter rich in polyphenols and lignin are not preferred by most species of earthworm. This may perhaps be the reason for the high rate of mortality and weight loss in earthworms forced to feed upon acacia in the experiments conducted by the authors.     

Towards maximising output from vermireactors fed with cowdung spiked paper waste

Paper waste, spiked with varying proportions of cowdung, was vermicomposted in 'low-rate' and 'high-rate' reactors. The former type of reactors had earthworm populations and feed loading rates similar to ones recommended by previous workers. The 'high-rate' reactors were operated with 12.5 times higher earthworm densities and feed loading rates. All the reactors were studied for six months to assess the vermicast output, survivability, growth and reproduction of the earthworms hence the sustainability of the reactors--for long-term, continuous operation. The studies revealed the viability of the high-rate vermireactor concept. The high-rate reactors consistently produced over 6.5 times more castings per unit digester volume with no adverse effect on the earthworm population, as reflected by (a) absence of mortality, (b) consistent growth in worm zoomass, and (c) normal rate of reproduction. The studies also revealed that an increase in the cowdung fraction in the feed from 14.3% to 20% (4:1 paper:cowdung blends to 6:1 blends) had little positive impact on the vermicast output or earthworm health. This indicated that spiking of paper feed with approximately 14% cowdung, or perhaps an even smaller fraction, might be adequate to support earthworms in the paper-fed vermireactors.     

Neem leaves as a source of fertilizer-cum-pesticide vermicompost

Vermicomposting of neem (Azadirachta indica A. Juss) was accomplished in "high-rate" reactors operated at the earthworm (Eudrilus eugeniae) densities of 62.5 and 75 animals per litre of reactor volume. Contrary to the fears that neem--a powerful nematicide--might not be palatable to the annelids, the earthworms fed voraciously on the neem compost, converting upto 7% of the feed into vermicompost per day. Indeed the worms grew faster and reproduced more rapidly in the neem-fed vermireactors than in the reactors fed with mango leaf litter earlier studied by the authors (Gajalakshmi et al., 2003). Another set of experiments on the growth, flowering, and fruition of brinjal (Solanum melongena) plants with and without fertilization with vermicompost, revealed that the vermicompost had a significantly beneficial impact.     

Vermiconversion of paper waste by earthworm born and grown in the waste-fed reactors compared to the pioneers raised to adulthood on cowdung feed

The performance of four species of earthworm--Eudrilus eugeniae, Kinberg, Drawida willsi Michaelsen, Lampito mauritii, Kinberg and Perionyx excavatus, Perrier--born and grown in vermireactors fed with paper waste was studied over six months, in terms of vermicast output per unit feed, production of offspring, and increase in worm zoomass. These were compared with the performance of the previous generation which had been raised to adulthood on cowdung as principal feed before shifting them to vermireactors operating on cowdung-spiked paper waste. The results indicated that except with D. willsi of which the second generation performed only a shade better than the first, there was significant improvement in vermicast output, animal growth, and reproduction in the second generation compared to the first. The results indicated that cowdung-spiked paper waste can be an adequate food for successive generations of earthworms and that reactors can be operated indefinitely on this feed. The results also indicated that the earthworm generations born and raised in vermireactors operated on this feed become better vermiconverters of this feed than the parent earthworms.     

Development of a modified vermireactor for efficient vermicomposting: a laboratory study

Waste has become an index of growth. Utilization of waste materials for productivity purposes is important for both economic and environmental reasons. Vermicomposting is an important aspect as it converts waste to wealth. In this context, a modified vermireactor in place of the conventional vermireactor for efficient vermicomposting has been developed.

In the conventional low- and high-rate vermireactors, the space for vermicomposting is reduced due to the thick layer of vermibed at the bottom of the reactor, thus a small amount of worm casts is produced. In the modified vermireactors there was only a thick moist cloth at the bottom in place of the thick vermibed which allowed a comparatively large quantity of organic waste to be vermicomposted as compared to conventional vermireactors. Laboratory studies showed that the modified vermireactor performed better than the conventional vermireactor in average vermicast produced and mg castings l⁻¹ (digester volume) day⁻¹. The study further showed that only the volume of the vermireactor was responsible for the high yield of worm casts.     

Recovery of methane-rich gas from solid-feed anaerobic digestion of ipomoea (Ipomoea carnea)

Studies are presented on new types of anaerobic digesters in which chopped or dry crushed Ipomoea carnea was fed without any other pretreatment, in an attempt to develop commercially viable means of utilizing the otherwise very harmful plant. Two types of solid-feed anaerobic digesters (SFADs) were studied. The first type had a single vessel in which the bottom 35% portion was separated from the top portion by a perforated PVC disk. The weed was charged from the top and inoculated with anaerobically digested cowdung-water slurry. The fermentation of the weed in the reactor led to the formation of volatile fatty acids (VFAs) plus some biogas. The leachate, rich in the VFAs, was passed through the perforated PVC sheet and collected in the lower portion of the vessel. The other type of reactors had two vessels, the first one was fully charged with the weed and the second received the VFA leachate. With both types were attached upflow anaerobic filters (UAFs) which converted the leachate into combustible biogas consisting of approximately 70% methane. All SFADs developed very consistent performance in terms of biogas yield within 17 weeks of start. The two-compartment reactors yielded significantly more biogas than the single-compartment reactors of corresponding total volume, and the reactors with which anaerobic filters (AF) were attached yielded more biogas than the ones without AF. The best performing units generated 2.41m(3) of biogas per m(3) of digester volume, as compared to 0.1-0.2m(3) of biogas, m(-3)d(-1), obtainable with conventional digesters. This indicates the viability of this technology. The spent weed can be vermicomposted directly to obtain good soil-conditioner cum fertilizer; earthworm Eudrilus eugeniae produced 540mg vermicast per animal every day, achieving near total conversion of feed to vermicast in 20 days. The proposed systems, thus, makes it possible to accomplish total utilization of ipomoea.     

Potential of two epigeic and two anecic earthworm species in vermicomposting of water hyacinth

The potential of two epigeic species (Eudrilus eugeniae Kinberg, and Perionyx excavatus Perrier) and two anecic species (Lampito mauritii Kinberg and Drawida willsi Michaelson) of earthworms was assessed in terms of efficiency and sustainability of vermicomposting water hyacinth (Eichhornia crassipes, Mart. Solm.). In different vermireactors, each run in duplicate with one of the four species of earthworms, and 75 g of 6:1 water hyacinth:cowdung as feed, vermicasts were produced with steadily increasing output in all the reactors. E. eugeniae was by far the most efficient producer of vermicasts, followed by the other epigeic P. excavatus. The two anecics came next, with D. willsi being the least effective which could generate only about half the quantity of vermicasts achieved in a corresponding time by E. eugeniae. In all the reactors, the earthworms grew well, increasing their weights by more than 250%. The maximum net gain of weight (average 30.7 g) was by E. eugeniae, followed by P. excavatus, L. mauritii and D. willsi. This trend, which followed the efficiency of vermicast production, was also shown in terms of reproductive ability as measured by the number of offspring produced by the four species.     

Potential utilization of guar gum industrial waste in vermicompost production

Recycling of guar gum industrial waste through vermitechnology was studied under laboratory conditions by using composting earthworm Perionyx excavatus (Perrier). Three different combination of guar gum industrial waste namely guar gum industrial waste:cow dung:saw dust in 40:30:30 ratio (T1), guar gum industrial waste:cow dung:saw dust in 60:20:20 ratio (T2), and guar gum industrial waste:cow dung:saw dust in 75:15:10 ratio (T3) were used for vermicomposting experiments. Chemical changes during vermicomposting were measured and comparatively T2 showed great increase (from its initial level) for total N (25.4%), phosphorus (72.8%) and potassium (20.9%) than the other treatments. T2 also showed higher vermicomposting coefficient (VC), higher mean biomass for P. excavatus (146.68 mg) and higher cocoon production (about 21.9% and 645.5% more than the T1 and T3, respectively). Maximum earthworm mortality during vermicomposting was recorded with T3 treatment while zero mortality was recorded for T2 treatment after 150 days. Overall, T2 treatment appeared to be an ideal combination for enhancing maximum biopotential of earthworms to management guar gum industrial waste as well as for earthworm biomass and cocoon production.     

Feasibility of utilization of horse dung spiked filter cake in vermicomposters using exotic earthworm Eisenia foetida

This contribution reports the potential of vermicomposting technology in the management of horse dung (HD) spiked sugar mill filter cake (SMFC) using an epigeic earthworm Eisenia foetida under laboratory conditions. A total of six vermicomposters filled with different ratios of HD and SMFC were maintained for this study. The growth and fecundity of E. foetida was monitored for 12 weeks. Maximum growth was recorded in 90% HD+10% SMFC feed mixture containing vermicomposter. Earthworms' biomass gain and reproduction was favorably up to 50% HD+50% SMFC feed composition. Maximum cocoons were also recorded in 90% HD+10% SMFC feed mixtures, however increasing proportions of SMFC in different vermicomposters affected the growth and fecundity of worms. A significant decrease in C:N ratio and increase in total kjeldahl nitrogen, total available phosphorus and calcium contents was recorded. The heavy metals content was higher in the vermicompost obtained in all the reactors than initial feed substrates. Based on investigations it is concluded that vermicomposting could be an alternative technology for the management of filter cake if it is mixed in 1:1 ratio with horse dung.     

Vermicomposting of different forms of water hyacinth by the earthworm Eudrilus eugeniae,Kinberg

Six-month long trials were conducted on different vermireactors fed with one of the following forms of water hyacinth: (a) fresh whole plants, (b) dried whole plants, (c) chopped pieces of fresh plants, (d) 'spent' weed taken from reactors after extracting volatile fatty acids (VFAs), (e) precomposted fresh weed and (f) precomposted spent weed. The first four forms were studied with and without cowdung. The experiments revealed three clear trends (i) of the various forms of the weed assessed, the precomposted forms were the most favoured as feed by Eudrilus eugeniae, Kinberg, while the fresh whole form was the least favoured, (ii) the different forms of spent weed were favoured over the corresponding forms of fresh weed, and (iii) blending of cowdung (approximately 14% of the feed mass) with different forms of water hyacinth had a significant positive impact on vermicast output, growth in worm zoomass, and production of offspring relative to the corresponding unblended feed. In all reactors, the 'parent' earthworms steadily grew in size over the six-month span, and produced offspring. There was no mortality. The experiments thus confirm that water hyacinth can be sustainably vermicomposted in any of the forms with E. eugeniae.     

Bioconversion of filter mud using vermicomposting employing two exotic and one local earthworm species

Three different earthworm species Eisenia fetida, Eudrilus eugeniae and Perionyx excavatus in individual (Monocultures) and combinations (Polycultures) were utilized to compare the suitability of worm species for vermicomposting of filter mud as well as the quality of the end product. The filter mud blended with saw dust can be directly converted into good quality fertilizer (vermicompost). Eight different reactors including three monocultures and four polycultures of E. fetida, E. eugeniae and P. excavatus and one control were used for the experiment. Vermicomposting resulted in significant reduction in C/N ratio, pH, total organic matter (TOC) but increase in electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP) and macronutrients (K, Ca and Na). Oxygen uptake rate (OUR) dropped up to 1.64–1.95 mg/g (volatile solids) VS/day for monoculture reactors and 1.45–1.78 mg/g VS/day for polycultures reactors, respectively, after 45 days of vermicomposting. Cocoon production and the earthworm biomass increased as vermicomposting progressed. On an overall the mono as well as polyculture reactors produced high quality stable compost free from pathogens and no specific differentiation could be inferred between the reactors.     

Microbial and decomposition efficiencies of monoculture and polyculture vermireactors,based on epigeic and anecic earthworms

Efforts have been made to evaluate the microbial and decomposition efficiency of three different vermireactors: (i) polyculture (introducing equal numbers of anecic and epigeic earthworms), (ii) monoculture (anecic) and (iii) monoculture (epigeic), designed by using earthworms of two different ecological categories i.e. anecic (Lampito mauritii Kinberg) and epigeic (Eisenia fetida (Savigny)). The microbial load of vermireactors was measured through substrate-induced respiration rate (SIR), microbial biomass N content and rate of dehydrogenase activity, while mineralization rate was evaluated measuring some chemical parameters of the substrate. Earthworms caused a decrease (as compared to initial value) in pH (41.9–80.7%), organic C (10.3–14.2%) and C:N ratio (41.9–80.7%) and an increase in total N (29.1–58.8%), NH₄-N (876.1–1485.7%), NO₃-N (29081.8–56792.6%), available P (16–19.4%) and exchangeable K (9.8–13.5%) contents of the substrate. The mineralization efficiency of the reactors was in the order: polyculture (epigeic + anecic) > monoculture (anecic) > monoculture (epigeic). The polyculture reactor showed the maximum rate of SIR (2.91 ± 0.2 mg CO₂ g⁻¹ substrate), microbial biomass N (3108.1 ± 289.2 mg N g⁻¹ substrate), and dehydrogenase activity (2453.3 ± 379.8 μg g⁻¹ substrate 24 h), while in the monoculture (epigeic) the lowest values of the same parameters were observed. It is concluded that the observed differences among reactors were due to different feeding behaviour and niche structures of epigeic and anecic earthworms. Data suggests that burrowing earthworms in waste-decomposing-system not only enhance the microbial efficiencies, but at the same time also accelerate the organic matter mineralization in a vermireactor. However, most of the previous studies were based on monoculture reactors (using epigeic earthworms) which have been recommended for waste decomposition operations, but this study revealed that polyculture vermicomposting (adding of burrowing worms with epigeic earthworms in vermicomposting system) might be beneficial for rapid decomposition of organic wastes.     

Vermicomposting of Taro (Colocasia esculenta) with two epigeic earthworm species

The bioconversion potential of two epigeic species (Eisenia foetida Sav. and Eudrilus eugeniae Kinberg) of earthworms was assessed in terms of efficiency and sustainability of vermicomposting of Taro (Colocasia esculenta (Linn) Schott in Schott and Endl). In different vermireactors, each run in triplicates with one of the two species of earthworms, and 60 g of 6:1 Colocasia:cowdung as feed, vermicasts were produced with steadily increasing output in all the reactors. E. eugeniae was found to be more efficient producer of vermicasts than E. foetida. In all reactors, the earthworms grew well, increasing their weights and number.     

Evaluation by respirometry of the loading capacity of a high rate vermicompost bed for treating sewage sludge

This study examines high rate vermicomposting of sewage sludge using high stocking densities of earthworms. To examine the loading capacity, two vermicompost beds were established in identical 0.84 m diameter reactors, one loaded at an average rate of 10 kg-wet-sludge-mixture m(-2) day(-1) (0.5 kg-carbon m(-2) day(-1)), the other loaded at 20 kg-wet-sludge-mixture m(-2) day(-1) (1 kg-carbon m(-2) day(-1)). The sludge mixture was from a commercial vermicomposting company (Vermitech) and contained 80-90% sludge and 10-20% green waste and clay. The beds were operated in fed-batch mode for 38 days, and then monitored for a further 12 days without any further sludge loading. Earthworms (Eisenia fetida) were added once or twice weekly over the 38 days loading period to gradually decrease the ratio of sludge loading rate to total earthworm biomass. By adding earthworm incrementally, the feeding rate ranged from 3.9 to 1.25 kg-wet-sludge kg-earthworm(-1) day(-1) for the full load experiment and 2-0.62 kg-wet-sludge kg-earthworm(-1) day(-1) for the half load experiment. The extent of degradation was estimated by fitting a 1st order model to the CO2 production rate from the beds. Based on the 1st order model, 53+/-20% (95% CI) and 68+/-4% of the organic carbon was converted to CO2 -C in the full load and half load experiments respectively. The CO2 production rate in the half load experiment became stable and repeatable when the total earthworm biomass reached 5.4 kg, corresponding to a feed rate of 1.04 kg-wet-sludge-mixture kg-earthworm(-1) day(-1). In contrast, the rate of CO2 production was still climbing and traces of methane were evident in the full load experiment at the end of the 38 day loading period. The experiments indicate that high rate vermicomposting beds are sustainable providing the feeding rate does not exceed approximately 1 kg-wet-sludge kg-earthworm(-1) day(-1).     

Nutrient changes and biodynamics of epigeic earthworm Perionyx excavatus (Perrier) during recycling of some agriculture wastes

Potential of an oriental composting earthworm: Perionyx excavatus (Perrier) to decompose waste resources generated from agricultural practices (crop residues, farm yard manure, and cattle dung) was studied for 150days under laboratory conditions. At the end of experiment, all vermibeds showed significant decrease in their organic C content ( approximately 21-29%), while increase in total N ( approximately 91-144%), available P ( approximately 63-105%), and exchangeable K ( approximately 45-90%). P. excavatus showed maximum individual live weight (662.05mg) after 120days in MIXED (mixed crop residues+cow dung in 1:1) substrate. The maximum growth rate (mg worm(-1)day(-1)) was between 3.79+/-0.08 and 2.35+/-0.16 on different substrates. The mean number of cocoon production was between 394.3+/-23.2 and 690.7+/-23.2 for different experimental beddings. MIXED bedding showed maximum reproduction rate (0.23+/-0.004 cocoons worm(-1) day(-1)), whereas farmyard manure bedding (FYM) showed least value (0.15+/-0.002 cocoons worm(-1)day(-1)). During vermicomposting, the total mortality in worms' population was recorded between 0% (in MIXED) and 21.7% (in Jowar straw (Sorghum vulgare)+millet straw (Pennisenum typhoides)+sheep manure in 1:1:2 ratio (JMS)). The waste decomposition and earthworm production was associated strongly with the quality of the substrate, especially with their chemical as well as biological composition.     

Evaluation of three composting systems for the management of spent coffee grounds

This study was conducted to evaluate the optimum composting approach for the management of spent coffee grounds from the restaurant and ready-to-serve coffee industry. Three composting systems were assessed, including in-vessel composting, vermicomposting bins, and aerated static pile bin composting, over study periods ranging from 47 to 98 days. Total carbon content was reduced by 5-7% in the spent coffee ground treatments across the three composting systems. Nitrogen and other mineral nutrient contents were conserved or enhanced from the initial to the final composts in all the composting systems assessed. Earthworm growth and survival (15-80%) was reduced in all the treatments but mortality rates were lower in coffee treatments with cardboard additions. A decline in earthworm mortality with cardboard additions was the result of reduced exposure to organic compounds and chemicals released through the decomposition of spent coffee grounds.     

Chemical and microbiological changes during vermicomposting of coffee pulp using exotic (<Emphasis Type="Italic">Eudrilus eugeniae</Emphasis>) and native earthworm (<Emphasis Type="Italic">Perionyx ceylanesis</Emphasis>) species

Coffee pulp is the main solid residue from the wet processing of coffee berries. Due to presence of anti-physiological and anti-nutritional factors, coffee pulp is not considered as adequate substrate for bioconversion process by coffee farmers. Recent stringent measures by Pollution Control authorities, made it mandatory to treat all the solid and liquid waste emanating from the coffee farms. A study was conducted to evaluate the efficiency of an exotic (Eudrilus eugeniae) and a native earthworm (Perionyx ceylanesis) from coffee farm for decomposition of coffee pulp into valuable vermicompost. Exotic earthworms were found to degrade the coffee pulp faster (112 days) as compared to the native worms (165 days) and the vermicomposting efficiency (77.9%) and vermicompost yield (389 kg) were found to significantly higher with native worms. The multiplication rate of earthworms (280%) and worm yield (3.78 kg) recorded significantly higher with the exotic earthworms. The percentage of nitrogen, phosphorous, potassium, calcium and magnesium in vermicompost was found to increase while C:N ratio, pH and total organic carbon declined as a function of the vermicomposting. The plant nutrients, nitrogen (80.6%), phosphorus (292%) and potassium (550%) content found to increase significantly in the vermicompost produced using native earthworms as compared to the initial values, while the calcium (85.7%) and magnesium (210%) content found to increase significantly in compost produced utilizing exotic worms. Vermicompost and vermicasts from native earthworms recorded significantly higher functional microbial group’s population as compared to the exotic worms. The study reveals that coffee pulp can be very well used as substrate for vermicomposting using exotic (Eudrilus eugeniae) and native earthworm (Perionyx ceylanesis).     

Changes in microbial community structure and function during vermicomposting of pig slurry

Most studies investigating the effects of earthworms on microorganisms have focused on the changes before and after vermicomposting rather than those that occur throughout the process. In the present study, we designed continuous feeding reactors in which new layers of pig slurry (1.5 and 3 kg) were added sequentially to form an age gradient inside the reactors in order to evaluate the impact of the earthworm species Eisenia fetida on microbial community structure and function. The activity of earthworms greatly reduced the bacterial and fungal biomass and microbial diversity relative to the control values. However, the pronounced presence of earthworms in the younger layers stimulated microbial activity and as such increased carbon mineralization probably due to the fact that the microorganisms may have been less resource-limited as a result of earthworm activity, as indicated by the ratio of monounsaturated to saturated PLFAs.     

Pilot-scale vermireactors for sewage sludge stabilization and metal remediation process: Comparison with small-scale vermireactors

Most of the previous studies on vermicomposting have been conducted as lab trials at small-scale (SS) using small quantity of waste mixtures. Efforts were made in this study to stabilize the sewage sludge amended with sugarcane trash using pilot-scale (PS) vermicomposting operation. Results of PS vermireactors were compared with SS trials in terms of quality of ready vermicompost and earthworm production rates. Results thus suggest a clear-cut difference between SS and PS in terms of waste mineralization rate and earthworm production. The waste mineralization rate in PS was significantly lower than SS (P < 0.05). Total N and available P were higher in end product from SS, while exchangeable cations (Ca²⁺ and K⁺) showed reverse behavior during the process of waste stabilization. There was significant difference between PS and SS for metal remediation rate in end materials. The growth and reproduction pattern of Eisenia fetida was completely different in PS as compared to lab trials, i.e. SS. Probably, the distinct earthworm stocking density and microclimate conditions in SS and PS were responsible for observed differences in results of waste mineralization rate and earthworm growth. This study suggests that SS laboratory trials may differ in PS field operations due to distinct behavior of earthworm in field conditions. It is concluded that SS laboratory trials should be tested in field at large-scale in order to measure the feasibility of technology for large-scale waste decomposition operations in open conditions.