Achieving energy self-sufficiency in wastewater treatment plants (WWTPs) is an important goal, and anaerobic digesters (AD) play a significant role by producing biogas. Because the AD is part of a complex, interconnected system rather than a standalone unit, its optimization requires an understanding of interactions between mainstream and sidestream processes. This study applied Sumo4N, a modified activated sludge model, to investigate these interactions. To comprehensively evaluate system behavior, a total of 654 scenarios were developed. Of these, 544 scenarios tested variations in operational parameters, and the results were analyzed using response surface methodology to visualize interactions. An additional 100 scenarios examined the effects of virtually retrofitting reject water treatment with biological processes under altered operating strategies. Methane yield per COD removal, and the ammonia concentration of reject water were influenced by influent COD load in the mainstream and by food waste addition for co-digestion. Coagulant dosage for phosphorus removal also affected methane yield. Although retrofitting with biological processes improved effluent quality, it substantially increased greenhouse gas (GHG) emissions, providing limited overall benefit when water quality, energy use, and GHG emissions were considered collectively.
Lee et al. (Sat,) studied this question.