(Nakirijja E. 2023) Effect of thermophilic composting on the microbial and physiochemical properties of sludge.

Abstract

Fecal sludge (FS) disposal in urban environment still remains a big challenge because the material retains unstable biosolids heavy laden with pathogenic organisms while its further biological treatment is limited by its low carbon to nitrogen (C/N) ration. This study assessed the potentials and performance of combined treatment of FS and Banana Pseudo Stems (BPS) through co-composting. The forced aeration and thermophilic process was tested for its ability to eliminate pathogens while BPS were introduced to step up the C/N ration but also improve the agronomic value of the resultant compost. To this end, the specific study objectives were; to characterize FS and BPS for composting; test the different mixtures of FS + BPS for compost quality and assess pathogen reduction as a result of the composting process. Dewatered FS was combined with BPS in mixing ratios of 0:1, 2:1 and 3:1 by volume and was composted until there was no change in total volatile solids which was at 9 weeks (≈56 days) using three duplicate composting units (1.2 m3). For process stability monitoring, solid samples were taken analyzed for pH, total volatile solids (TVS) and total solids (TS) every week. The compost temperature was continuously monitored by a digital thermocouple inserted into the composting biomass. Volume reduction, temperature trend and TVS dynamics were chosen as compost maturity indicators. Results showed that composting method maintained an average temperature of 52◦C which contributed to microbial elimination. The final compost had no detectable Salmonella (0%), the E.Coli has reduced ( 52%-99%) while Entrococci reduction. At 2:1 and 3:1 (BPS:FS) ratios the E.coli reduction was 99% (2:1) , 97%(3:1) compared to 52% obtained in the control (0:1). The nutrient content in terms of total organic carbon, Total Khejahl nitrogen (TKN), Phosphorus (P) and Potassium (K). The final product contained TVS of about 19%. From the trials it can be concluded that thermophilic co-composting of FS with fibrous biomass such as BPS has capability to sanitized and stable the material while increasing its soil organic carbon and nutrients better than in the raw FS. However, given the limitations in the study scope, it is recommended that further studies be done with other biomass other BPS and also test out the bioavailability of nutrients of the compost.