Effects of Varying Substrate to Inoculum Ratio for Anaerobic Co-Digestion of Fecal Sludge with Organic Waste

Abstract

Sanitation is a recognized basic human right by World Health Organization nevertheless; 1.7 billion people worldwide still lack access to latrines or other forms of basic sanitation. Additionally, it is a severe issue when fecal sludge is dumped in the open and released untreated into the environment, open fields, and aquatic bodies. Hence, there is a need to devise a solution that can assist individuals in accessing sanitation services effectively, while also exploring the potential of biogas production as a sustainable energy source in the process. To deal with this problem we set our focus to study anaerobic digestion of fecal sludge to provide a possible sustainable treatment method to improve sanitation conditions. The anaerobic digestion of fecal sludge was studied through Bio Methane Potential (BMP) test applied at different ratios i.e. 0.25, 0.5, 1, 2 and 4. Along with that BMP was operated for both Mono-digestion and Co-digestion of fecal sludge. In this study, biogas production and reduction of parameters of interest were analyzed for a period of 25 days. The fecal sludge samples were collected from pits connected to household and septic tanks connected to a restaurant to have a comparison of fecal sludge from domestic area and commercial area.

The highest gas yield was observed for Substrate to Inoculum Ratio (SIR) 0.25 for both mono- digestion of fecal sludge from pits and co-digestion of fecal sludge from pits with food waste

with a value of 45.20 ± 1.13 ml/g VS of substrate and 121.09 ± 3.10 ml/g VS of substrate respectively. Mono-digestion of fecal sludge from septic tank has the highest biogas production in SIR 0.5 with a value of 104.7 ± 1.27 ml/g VS of substrate. This shows that the fecal sludge from the septic tanks (commercial vicinity) has more potential in terms of Biogas production. The co-digestion of fecal sludge from pits with food waste produced 1.5-3 times more gas as compared to the mono-digestion of fecal sludge from pits. The maximum removal of Total Solids (TS) and Volatile Solids (VS) was achieved at SIR 0.25 for mono-digestion and co-digestion of fecal sludge from pits but for mono-digestion of fecal sludge from septic tank, it was achieved at SIR 0.5. The maximum removal of Chemical Oxygen Demand (COD) was achieved at SIR 0.25 for mono and co-digestion of fecal sludge from pits and at SIR 0.5 for mono-digestion of fecal sludge from septic tanks. As other researchers have noted comparable tendencies, it is rather typical to detect differences in the generation of biogas and removal percentages of COD, sCOD, TS, VS, etc. in different substrates.