Performance evaluation of lab-scale aerobic and anaerobic digestion systems for treatment of domestic wastewater

Abstract

The study focuses on the development of an authentic, unsophisticated and cost effective wastewater treatment process. Keeping in view the current water crisis, the basic aim is to reuse treated domestic wastewater for irrigational purposes. This study was designed to investigate the performance of a dual digestion system and a single stage anaerobic digestion system for the treatment of domestic wastewater. Experiments were carried out in two phases. In phase I, three experiments were conducted at different temperatures (35, 45 and 55°C) but same hydraulic retention time (48 hours aerobic and 6 days anaerobic). Phase II experiments were conducted in a single stage lab scale reactor, treated anaerobically at different temperatures (35, 45 and 55°C) but same hydraulic retention times (25 days). All the experiments were evaluated at the different stages of experiment using physico-chemical analysis and microbiological analysis of the samples. The microbial diversity of wastewater was also studied to determine the types of microbes present in it. The untreated wastewater contained greater number of pathogens including the genuses Klebsiella, Proteus, Bacillus, Enterobacter, Shigella, Pseudomonas, Staphylococcus, Salmonella and the specie E.coli. A significant decrease in the physico- chemical parameters such as phosphates, nitrates, nitrites, TSS, TDS and alkalinity was observed in all the experiments indicating considerable improvement in the quality of water. The treatment of domestic wastewater proved to be efficient at 35 and 45°C with a remarkable reduction in COD (94%) and BOD (93%), but at thermophilic temperature (55°C) reduction in COD and BOD was 54 and 55% respectively. The results of MPN also showed a marked reduction in coliforms especially under thermophilic temperatures, while the removal efficiency of pathogens was lower under mesophilic temperature than thermophilic temperatures. Mesophilic anaerobic digestion (MAD) showed the best results and hence, can be employed for pilot scale studies. However, again major reduction in the pathogenic count was observed at thermophilic temperatures under anaerobic conditions.