Biological nutrient removal in bench-scale membrane bioreactor and full-scale sequencing batch reactor under various configurations and conditions

Abstract

Advantages such as excellent effluent quality, flexibility in operation, smaller plant size, and low biomass production give MBR a superior edge over conventional biological treatment processes. MBR can be operated at hydraulic retention times (HRTs) as low as 1 hour and solids residence times (SRTs) as high as 70 100 days making the MBR a flexible system over conventional systems. Mixed liquor suspended solids (MLSS) or biomass concentrations of 35,000 mg/L can be maintained in the aeration tank resulting in high organic matter biodegradation rates for short HRTs of 1 3 hours. With stricter nutrient discharge requirements, the question is whether the many advantages of MBR can be harnessed for biological nutrient removal by using various anaerobic, anoxic, and oxic manipulations. An important issue is whether the MBR operating at high SRTs or low HRTs may hinder biological phosphorus removal. Very few studies focused on the impact of SRTs on biological phosphorus removal. Longer SRTs are expected to hinder phosphorus removal since less mixed liquor is wasted in the process. Models on biological nutrient removal are needed to be calibrated for long SRTs and short HRTs. More important information is emerging and biological phosphorus removal is dependent on competition between glycogen accumulating organisms (GAOs) and phosphate accumulating organisms (PAOs) for poly-hydoxy-butyrates (PHBs) under anaerobic conditions. When the minimum pH in the anaerobic tank was higher than 7.5, the PHB uptake reached the maximum. Carbon-to-phosphorus (C/P) ratio was demonstrated to be a factor in biological phosphorus uptake such that for C/P ratios < 32, phosphorus removal efficiency is directly proportional to the C/P ratio. For C/P ratio greater than 32, phosphorus removal efficiency may be maintained at over 90%, and effluent phosphorus concentration may be less than 0.5 mg/L in a