Enhanced two-phase anaerobic co-digestion of organic wastes using acidogenesis optimization and anaerobic membrane bioreactor

Abstract

Anaerobic digestion using various organic wastes could be promising environmental technology because it can provide not only waste treatment also bioenergy production. Due to low efficiency and effluent quality of conventional anaerobic digestion, several new or modified systems for improving performance have been developed, and post treatment is inevitably applied for water reuse. Good performance using phase-separation technology has been reported because of providing optimal environments for each major group of microorganisms and their associated biological reactions. In a two-phase process, overall process efficiency is determined by acidogenic phase since it includes hydrolysis, referred to the overall rate-limiting step, so optimization of acidogenic phase is necessary. Having all merits of anaerobic digestion, anaerobic membrane bioreactors (AnMBRs) can offer high quality effluent, but the major obstacle for wide application of AnMBRs is fouling problem which is directly related to the operational cost. In contrast to aerobic MBRs, fouling characteristics of AnMBRs has not been studied a lot. Therefore, this study was performed to improve the methane production rate and effluent quality by modified two-phase anaerobic digestion system consisted of optimized acidogenic fermentation and AnMBRs. Additionally, characteristics of membrane fouling in submerged AnMBRs were evaluated though ultrafiltration of sludge in AnMBR at various HRTs. Firstly, anaerobic batch tests were conducted to find out optimum co-substrate condition for maximum acidification. Three kinds of substrates, livestock wastewater, sewage sludge and food waste leachate, were used and an optimized substrate condition was determined by maximum VFA increase and SCOD increase simultaneously using statistical analysis. Suggested optimum mixing ratio of livestock wastewater, sewage sludge and food waste leachate was 0.4 : 1.0 : 1.1, respectively on COD basis. Secondly, response surface me...