Enhanced nitrogen removal in single-stage sequencing batch rotating biological contactors

Abstract

The Rotating Biological Contactor (RBC), recognized for its energy efficiency, eliminates the need for aeration and sludge return in wastewater treatment. This study evaluates a Biocage-modified RBC, aimed at enhancing biomass retention and optimizing treatment efficacy. We compare continuous (C-DRBC) and sequential batch influent modes (SB-DRBC) concerning denitrification effectiveness. The continuous mode shows limited total nitrogen (TN) removal at 32.8 %, constrained by higher dissolved oxygen levels in the biofilm, which impede stable denitrification. Conversely, the SB-DRBC, operating at a hydraulic retention time of 6 h and a rotation speed of 3 rpm, substantially increases TN removal to 64.1 %. This enhancement is attributed to the development of an anoxic zone within the biofilm, conducive to denitrification. The biofilm's uptake of polyhydroxyalkanoates and glycogen metabolism by glycogen-accumulating organisms further augments nitrogen removal. Microbial analyses indicate a predominance of denitrifying bacteria such as Paracoccus, Thauera, and Azoarcus in the SB-DRBC mode. Reducing rotational speed fosters larger anoxic zones, thus elevating denitrification efficiency. These findings advocate the SB-DRBC approach as a formidable strategy for achieving efficient nitrogen removal and energy conservation in wastewater treatment.