Membrane Bioreactor Performance during Processing of a Low Carbon to Nitrogen Ratio Municipal Wastewater

Abstract

The performance of a pilot-scale hollow fiber submerged membrane bioreactor (MBR) for biological treatment of a low carbon/nitrogen ratio domestic wastewater was evaluated during 120 days of operation. The MBR system was operated under alternating aeration, periodic feeding and external organic carbon source addition in order to achieve the legislation disposal limits. Experiments were contacted under three carbon/nitrogen (COD/TKN) ratios, i.e. 3.66 ± 1.3, 4.37 ± 1.34 and 8.3 ± 1.03, where a low strength wastewater was treated in the absence and presence of raw wastewater or glycerol as external carbon source. At the end of the experimental period, biological oxygen demand (BOD5) and chemical oxygen demand (COD) removal was extremely high, reaching efficiencies and effluent concentrations of 99.2 ± 0.4 and 97.4 ± 2.4%, and 3.7 ± 1.1 and 14.7 ± 11.0 mg/L, respectively. Total Kjeldahl Nitrogen (TKN) and NH4+-N removal efficiencies were determined as 89.2 ± 3.9 and 97.0 ± 0.9%, with the corresponding effluent concentrations being equal of 7.9 ± 2.3 and 1.7 ± 0.5 mg/L, respectively. Denitrification was enhanced by adding glycerol, resulting in an effluent NO3−-N concentration of 1.9 ± 0.9 mg/L. The release of soluble microbial products (SMP) was favored over extracellular polymeric substances (EPS) under low COD/TKN ratio, although this trend was inverted under high COD/TKN ratio conditions. MBR effluent quality was found to be suitable for unlimited reuse.