Evaluation of leachate impact on domestic sewage co-treatment in aerobic granular sludge systems

Abstract

Aerobic granular sludge (AGS) technology has been consolidated for sewage treatment. However, studies about the co-treatment of landfill leachate in municipal wastewater treatment plants (MWWTPs) with AGS systems are still incipient. The engineering and microbiological aspects of leachate co-treatment with sewage in step-feeding (R1) and conventional (R2) AGS systems were evaluated. Initially, synthetic sewage with a gradual increase in the organic load for granule formation was used (Periods I and II). Subsequently, co-treatment with leachate pre-treated by coagulation-flocculation was carried out with 5% (Period III) and 10% (Period IV) concentrations. Finally, methanol supplementation was conducted as an attempt to improve nutrients removal performance (Period V). Based on the results obtained, the co-treatment in granular reactors was feasible. The best conditions were obtained in R1 during Period V with methanol supplementation. Step-feeding produced a more compact and resistant aerobic granular biomass, resulting in better operational stability. Moreover, this strategy favored denitrification, especially during methanol supplementation, minimizing one of the main problems reported regarding leachate co-treatment in AGS systems. As a result, higher total nitrogen (TN) removals were obtained. At the end of the last period, in R1, Chemical Oxygen Dissolved (COD), TN, and Dissolved Organic Carbon (DOC) removals were 93%, and phosphorus removal was 54%, reaching values higher or similar to other AGS investigations with sewage, leachate, or co-treatment. Therefore, the strategies investigated unprecedentedly contribute to consolidating the domestic sewage co-treatment with leachate in AGS systems and providing a good perspective for other industrial wastewaters.