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Abstract Biochemical methane potential tests using water hyacinth (WH), pretreated water hyacinth (PWH), and Hydrilla verticillata (HV) as substrates using sewage media were explored. This study replaced the freshwater required to prepare the slurry for AD of organic solid waste with domestic sewage. Cow dung was used as the inoculum. WH (241.5 mL CH4/g VSadded), PWH (200.5 mL CH4/g VSadded), and HV (212 mL CH4/g VSadded) produced significant amounts of methane in the sewage medium. 16S-rRNA analysis showed that, in sewage, ~ 85% of the microbes were hydrolytic bacteria, and 7% were methanogens. This abundant quantity of hydrolytic microbes from sewage accelerated lignin degradation, achieving 28.32% and 38.34% degradation for WH and HV, respectively, within 14 days. Field emission-scanning electron microscopy images visually confirmed the enhanced substrate degradation in the presence of sewage. The net energy produced from the AD of WH and HV was significant (4664 J/g VSadded and 4109 J/g VSadded), but for PWH, it was negative, indicating that using sewage medium may be better than costly pretreatment techniques. This study demonstrated the potential of using sewage as an alternative to freshwater in AD, offering a sustainable solution for freshwater conservation and the possible utilisation of sewage for improved methane production, especially for substrates with lignin that are difficult to degrade.

Background Composting is one of the sustainable practices to convert sewage sludge into useful agricultural product because it is rich in organic matter, micro- and macronutrients, which is essential for plants growth and soil fauna to live. Therefore, the present study was to recycle the sewage sludge by rotary drum composter. Five sets of experiments (C/N 15, 20, 25, 30 including control) were carried out in the reactor, where sewage sludge was coupled with sawdust and cattle manure to attain the optimal feedstock. The process was monitored with respect to physico-chemical characteristics and stability parameters during 20 days of composting period. In addition, the kinetic parameters km and rm have been evaluated in the present work. Results Higher reductions in CO2 evolution and oxygen uptake rate (OUR) observed in C/N 30 showed the stability, resulting in the total biodegradable ingredients to be stabilized. Similarly, higher percentage reduction in carbon-nitrogen ratio was observed in C/N 30 followed by C/N 20, C/N 25, C/N 15 and control experiments, respectively, indicates maximum degradation was achieved; as it corroborate higher temperature regime occurred in C/N 30. The composting parameters such as moisture content, volatile solids, CO2 evolution, OUR and C/N ratio were reduced significantly (p.05). The kinetic model used illustrated the comparable variations in Michaelis constant (km) and maximum rate constant (rm) under varying proportions of the initial feedstock. The overall assessment of kinetic data for C/N 30 experiment showed enhancement of degradation during the composting process. Conclusions The results suggested that composting of sewage sludge with optimal proportion of cattle manure and saw dust, especially in C/N 30, can produce stable compost within 20 days of composting.

Purpose Composting of harvested Salvinia natans weed of Loktak lake of Manipur, India can protect the precious lake from the unwanted growth of the weeds but there is a need to assess the total amount and bioavailable forms of heavy metals and minerals of the final compost before application as a soil conditioner. Methods Studies were conducted on the transformations of the physico-chemical parameters and the total amount, bioavailable and leachable forms of heavy metals and minerals during agitated pile composting of S. natans with rice husk and cattle manure in five different combinations [trial 1 (5 S. natans: 4 cattle manure: 1 rice husk), trial 2 (6 S. natans: 3 cattle manure: 1 rice husk), trial 3 (7 S. natans: 2 cattle manure: 1 rice husk), trial 4 (8 S. natans: 1 cattle manure: 1 rice husk) and trial 5 (10 S. natans: 0 cattle manure: 0 rice husk)]. Results The highest temperature (52.2 C) was monitored in trial 2 having 30 % cattle manure during the process. Highest reduction of moisture content and volatile solid in trial 2 corroborated the temperature profile. Total concentrations of heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr), total concentration of nutrients (Na, K, Ca, and Mg) and the water-soluble forms of the nutrients were enhanced significantly. The water-soluble, plant-available and leachable metals decreased favorably with maximum reduction observed mostly in trial 2. The study also revealed that the total concentrations of Zn (211â254 mg/ kg), Ni (310â345 mg/kg) and Pb (805â891 mg/kg) of the final composts were higher than that of Cr (140â207 mg/ kg) but the water-soluble forms of Zn (3.6â4.7 % of total Zn), Ni (NIL) and Pb (0.7â1.0 % of total Pb) were lower than that of Cr (13.3â19.3 % of total Cr) indicating that Cr in the composts had higher toxicity potential. The leachable heavy metals were within the threshold limits prescribed for agricultural application. Conclusions Composting of S. natans biomass with appropriate proportion of cattle manure reduced the bioavailable and leachable forms of the heavy metals in the biomass.

Background Water hyacinth (Eichhornia crassipes) can cause a diversity of problems due to its fast spread and congested growth. The composting of water hyacinth can reduce the chemical fertilizer application to the agricultural field and problems related to its fast growth rate and also help in nutrient recycling. The present study was carried out on agitated pile composting of water hyacinth collected from four different areas (Bharalu River, Agriculture site, Boragaon landfill site and Industrial site). The nutrients and stability parameters were evaluated during the 30 days of agitated pile composting of water hyacinth mixed with cattle manure and sawdust. The stability of compost was evaluated using respiration techniques (CO2 evolution and oxygen uptake rate). Results Results showed that nutrients (Na, K, Ca, total nitrogen and phosphorus) were increased significantly in all agitated pile composting. Stability parameters such as CO2 evolution rate and oxygen uptake rate, biochemical chemical oxygen demand and chemical oxygen demand were reduced significantly during the process. Highest reduction of moisture content (35.2 %), volatile solid (40.5 %), ammonical nitrogen (75.6 %), biochemical oxygen demand (65.3 %), CO2 evolution rate (78.7 %), and oxygen uptake rate (74.4 %) were observed in the agitated pile of Bharalu River site as compared to other agitated piles. The higher increase of total nitrogen (83.5 %) and total phosphorus (76.0 %) was also observed in the agitated pile of Bharalu River site. Conclusion Addition of optimum amount of cattle manure was highly efficient for making compost of water hyacinth collected from four different sites. Highest content of nutrients was found in compost of water hyacinth collected from Bharalu River site due to availability of nutrients in sewage water. In the final compost of all trials, total coliform and fecal coliform were reduced significantly, which are pathogen indicators in the compost. The best compost quality was found in water hyacinth collected from Bharalu River site.

Background Water hyacinth (Eichhorniacrassipes) is one of the most uncompromising weeds in the whole world. Its adverse effects due to fast growth rate are main physical interference with fishing and navigation. Water hyacinth also causes eutrophication due to the large release of organic nutrients after its degradation, consequentially deterioration of water quality and also adversely affecting aquatic flora and fauna. Therefore, composting is one of the best methods for control and utilization of water hyacinth. Water hyacinth being the plant material is rich in cellulose, hemicellulose, and lignin content which hinders the rate of degradation during composting. The raw materials including water hyacinth along with sawdust and cattle manure in five different proportions trial 1 (10:0:0), trial 2 (8:1:1), trial 3 (7:2:1), trial 4 (6:3:1), and trial 5 (5:4:1) were composted using rotary drum composter. Results Final product of water hyacinth composting was flourishing of nutrients such as nitrogen, phosphorus, sodium, potassium, calcium, and magnesium. The lignin reduction in all the five trials was obtained between 10 and 40 %. The reduction in cellulose was observed ranging from 4 to 55 % in different trials. Similar as cellulose and lignin, hemicellulose was also reduced about 11â46 % in all five trials during the process. Conclusion The maximum reduction inorganic matter, lignin, cellulose and hemicellulose was observed in trial 4; whereas, the nutrient contents (nitrogen, phosphorus, Na, K, Ca, and Mg) were increased significantly during the process. On analyzing the FTIR results, trial 4 showed that aliphatic and polysaccharides have easily degraded and aromatic compounds have increased with composting time in trial 4

Background Disposal of vegetable waste in landfills and illegal sites leads to emission of greenhouse gases and leachate production, thereby imposing major environmental issues. As an alternative, this waste can be successfully recycled for its high nutrient content using composting process. Results Five trials were made with the ratio of 6:3:1 of trial 1 (50 kg), trial 2 (70 kg), trial 3 (90 kg), trial 4 (120 kg) and trial 5 (150 kg) by adding 10 kg of dry leaves in each of the trials as bulking agent. Due to active microbial population and high biodegradable organic matter in vegetable waste, early thermophilic phase was observed within 18â24 h of the composting process in all of the trials with a maximum of 61.4 C in trial 3. Total mesophilic heterotrophs were observed in the range of 7.1 9 1011 CFU g-1 and gradually reduced to 2.65 9 106 CFU g-1 at the end of 20 days, which was considered due to prolonged thermophilic phase maintained in trial 3. An average of 54â56 C temperature was maintained for 7 days in trial 3, with spore-forming population in the order of 3.82 9 109 CFU g-1 contributing to higher organic destruction. The populations of fungus, actinomycetes and streptomycetes were observed to reduce during thermophilic phase and remained in the order of 2.85 9 104 , 3.8 9 106 and 4.1 9 105 CFU g-1 , respectively, at the end of 20 days. CO2 evolution and OUR were in the order of 0.89 and 0.32 mg g-1 VS d-1 , respectively, in trial 3 denoting maximum degradation of organic matter and stabilization of compost. Indicator organisms were found well with the standard limits due to elevated temperature. Conclusions Combinations of waste materials played a major role in favoring microbial succession. Temperature in the compost system had major effect on the survival of the microbial populations. Elevated temperatures favored higher degradation of organic matter, thereby stabilizing the compost within proposed time of composting and also destructing the indicator pathogens.

Background Water hyacinth (Eichhornia crassipes) is one of the worst weeds in the world. Composting is one of the most economical ways for the treatment and final disposal of water hyacinth, because it combines material recycling and biomass disposal. A major restriction of land application of water hyacinth compost is the possible high heavy metal concentration in the final product. Zeolites may be useful as metal scavengers in metal-rich water hyacinth compost. The speciation of heavy metals (Zn, Cu, Mn, Fe, Pb, Ni, Cd and Cr) was done according to Tessierâs sequential extraction method during water hyacinth composting mixed with cattle manure, sawdust and natural zeolite. The water hyacinth, cattle manure and sawdust were taken in the 6:3:1 ratio with 5, 10 and 15 % natural zeolite, respectively. Results The temperature was measured in the range of 48.6â56.2 C in control and zeolite treatments. Higher reduction of exchangeable (F1) and oxidizable (F4) fractions of Zn was observed about 72.8 and 79.6 %, respectively, in zeolite 1 treatment but higher reduction of carbonate (F2) and reducible (F3) fractions was observed about 70 and 37 %, respectively, in zeolite 2 treatment. The F1, F2, F3 and F4 fractions of Cu and Fe were reduced in the control and all zeolite treatments. The F1, F2, F3 and F4 fractions of Mn were reduced significantly in the all zeolite treatments in comparison to control. The bioavailability factor (BF) of Zn, Cu, Mn, Fe, Ni, Cd and Cr was reduced significantly in zeolite treatments in comparison to control. There was no significant change observed with BF of Pb in zeolite treatments. The total concentration of Pb was higher than Zn, Cu, Mn, Ni and Cr but its BF was lowest among the all these metals. Conclusion Addition of optimum percentage of natural zeolite was successful for enhancing degradation of organic matter and reducing bioavailability of heavy metals during water hyacinth composting mixed with cattle manure and sawdust. The bioavailable fractions of heavy metals were effectively correlated with pH and TOC in control and zeolite 1 treatment as compared to zeolite 2 and 3 treatments.

Purpose Effective vermicomposting of Salvinia natans is a good alternative for protecting wetlands damaged by the weed due to the vast potential for use of the product vermicompost in agriculture, but the presence of toxic metals in the weeds may deter the usage. Methods Research was carried out on the physico-chemical and biological characteristics as well as bioavailability and leachability of nutrients and heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr) during vermicomposting of S. natans mixed with cattle manure and sawdust in five different combinations [trial 1 (eight S. natans: one cattle manure: one sawdust), trial 2 (seven S. natans: two cattle manure: one sawdust), trial 3 (six S. natans: three cattle manure: one sawdust), trial 4 (five S. natans: four cattle manure: one sawdust) and trial 5 (ten S. natans: 0 cattle manure: 0 sawdust)] for 45 days with Eisenia fetida earthworm. Results The highest growth of earthworms was in trial 4, having the highest (40 %) cattle manure. Trial 4 also indicated the highest reduction of volatile solids (38.6 %) and soluble BOD (82.3 %). The water-soluble forms of all nutrients were increased significantly. The highly bioavailable water-soluble and DTPA-extractable forms of heavy metals were reduced favourably after the process. The toxicity characteristic leaching procedure (TCLP) test indicated that leachable heavy metals of the vermicomposts were also reduced and were within the threshold limits for agricultural applications. Conclusions Eisenia fetida was very effective for reduction of bioavailable and leachable forms of selected heavy metals, and the TCLP test confirmed that the vermicompost was not hazardous for soil applications. The potential of the earthworms to increase the available nutrients, but mitigate the metal toxicity during vermicomposting of S. natans will be useful for sustainable land renovation practices.