Effects of COD / TN ratio and loading rates on performance of modified SBRs in simultaneous removal of organic matter and nitrogen from rubber latex processing wastewater

Abstract

Two modified sequencing batch reactors (SBRs), specially configured to consist of both oxic and anoxic zones, and be operated with only a single simultaneous oxic/anoxic phase in each treatment batch, were tested to evaluate their applicability in the treatment of rubber latex processing (RLP) wastewater. Reactor R1 was operated with a constant aeration, by contrast, reactor R2 was operated with an air flow varied from a lower rate in the early period of the reaction phase to a higher rate in the later period. The effects of the chemical oxygen demand (COD) to total nitrogen (TN) ratio and their loading rates on the performance of the modified SBRs in the simultaneous removal of organic matter and nitrogen from RLP wastewater were investigated. It was observed that the performance of the two reactors in removal of COD and ammonium nitrogen (ammonium-N) was similar, and did not remarkably change when varying the COD/TN ratio, as well as COD and TN loading rates in the ranges of 3.4 - 6.0 gCOD/gN, 0.8 - 1.7 kgCOD m-3d-1 and 0.15 - 0.34 kgNm-3d-1, respectively. The average COD removal efficiencies were over 95%. Ammonium-N was almost completely eliminated in both reactors (influent concentrations were 160 - 500 mg/L). The average ammonium-N removal efficiencies were over 99% with effluent concentrations of less than 1.0 mg/L. Nevertheless, the TN removal efficiencies of both reactors were significantly increased by increasing the COD/TN ratio from 3.4 to 6.0, and slightly decreased when increasing the TN loading rate from 0.15 to 0.34 kgNm-3d-1. The most effective COD/TN ratios were in the range of 5 - 6, at which the maximal TN removal efficiencies of Rl and R2 were 92% and 97%, respectively.