Study on Bioconversion of Household Waste and Faecal Sludge through Various Composting Process

Abstract

This research work is concerned on the preparation, characterization, analysis and comparison of three types of compost, namely, (a) organic solid waste compost, (b) cocompost of faecal sludge and organic solid waste and (c) vermicompost of faecal sludge and organic solid waste ensuring SRDI (Soil Resource and Development Institute) standard. To this purpose, solid waste was collected from the waste management plant established in the campus of Khulna University of Engineering & Technology (KUET), while the faecal sludge was collected from the septic tank of the KUET campus. Dried faecal sludge and organic solid waste were mixed at a ratio of 1:3 to prepare co-compost using passively aeration method. For vermicompost, Eisenia fetida, earthworm species was used. A 56 days cycle of composting period was considered for maturation. During composting cycle moisture and temperature plays an important role. So, temperature of different composts was monitored carefully in this period. The peak temperature of all composts was obtained within 7-8 days. Highest temperature of the composts was recorded as 51°C for organic solid waste compost, 47°C for co-compost, 38°C for faecal sludge vermicompost and 40°C for solid waste vermicompost. After that temperature starts to decrease and finally merged with the ambient temperature. Initially all compost samples consists of 3.00 kgs of sample except faecal sludge and solid waste co-compost. To maintain the 1:3 ratio of faecal sludge nad solid waste, 1 kg dry faecal sludge was mixed with 3.00 kg solid waste sample. The mass reduction is greater for solid waste than faecal sludge. In case of solid waste compost the mass reduction is about 70% (70.26% for solid waste compost and 70.43 for solid waste vermicompost). Whereas the mass reduction of faecal sludge vermicompost and faecal sludge-solid waste co-compost is 41.53% and 58.82% respectively. Loss of moisture cintent is above 80% for solid waste compost, solid waste vermicompost and faecal sludge and faecal sludge solid waste vermicompost. But in case of faecal sludge vermicompost moisture reduction is 61.12%. Similar condition is observed for voletile solids. The fixed solid reduction percentage is 4.47%, 6.43%, 11.99% and 4.94% for solid waste compost, solid waste vermicompost, faecal sludge vermicompost and faecal sludge solid waste co-compost. Initially composts were slight acidic except the co-compost of faecal sludge and organic solid waste (8.3). at final condition all prepared composts were a little alkaline (pH was above 7). Moisture content, total organic carbon and TVS decreased during composting process. A reverse scenario was observed in case of fixed solids and total kjeldhal nitrogen content. C/N ratio is an important indication of compost quality and maturity. According to SRDI, C/N ratio of a finely matured organic fertilizer should be within 20. In this experiment, C/N ratio of different composts were found as 10.29 for solid waste compost, 10.08 for solid waste vermicompost, 12.25 for faecal sludge vermicompost and 10.67 for co-compost of faecal sludge and organic solid waste. So, the C/N ratio values were within the SRDI recommended values. A remarkable progress was observed in case of pathogen destruction. At maturation stage the number of faecal coliform decreased by 50 times with respect to the initial condition. Phosphorus content of vermicompost (1.34% for solid awste vermicompost and 1.22% for faecal sludge vermicompost) was higher than the organic solid waste compost (0.86%) and co-compost (0.96%). Faecal sludge vermicompost was recorded to have higher potassium content than solid waste compost (0.8%), solid waste vermicompost (0.75%) and co-compost (0.76%). But according to SRDI standard the potassium content of organic fertilizer should be within 1-3%. Therefore, only faecal sludge vermicompost satisfied the SRDI standard value for total potassium content.