Characteristics of nutrient removal and membrane fouling in a vertical membrane bioreactor

Abstract

Recent studies on wastewater treatment using MBR have focused on nutrient removal Although these MBRs have shown improved nitrogen removal, phosphorous has not been removed in significant amounts by these systems. Building upon such previous work, a vertical MBR composed of anoxic and oxic zones in one reactor has been fabricated and operated for about three years, which due to its physical structure, is expected to challenge current problems related both to the effective removal of pollutants from wastewater and the reduction of membrane fouling. From the study about the development of operating factors of the vertical MBR, it could be concluded that the optimum internal recycle rate and HRT were found to be 4Q and 8 hours, respectively. Under these conditions, the average removal efficiency of total nitrogen was 75% and total phosphorus was 71% at a COD/T-N ratio of 10, respectively. In the laboratory-scale vertical MBRs fed with various substrates (sodium acetate, propionic acid and glucose), total removal of particulate matter below detection level for suspended solids was possible and high removal efficiency of COD was (> 95%) observed regardless of operating conditions. In addition, it was found that the average removal efficiency of total nitrogen was 79% for all the MBRs. However, total phosphors removal efficiency decreased in order of the acetate fed MBR (87%), the propionic acid fed MBR (83%), and the glucose fed MBR (78%) at COD/T-N ratio of 10. When the condensate of food waste (CFW) was supplemented, phosphorus removal efficiency was improved and several kinds of PHAs were detected inside the cells. As based on the results of the lab-scale study, a pilot-scale vertical MBR treating municipal wastewater with a low COD/T-N ratio of 5.5 was operated for about two years. Removal efficiencies of total COD, T-N and T-P averaged 96%, 74% and 78%, respectively at 8 hours HRT and internal recycle rate of 400%. Subsequently, as the CFW was supplemented, th...