Effects of membrane relaxation rate on performance of pilot-scale membrane aerated biofilm reactors treating domestic wastewater.

The membranes of a Membrane Aerated Biofilm Reactor (MABR) function as bubble-less air diffusers and bio-carriers. Recent bench-scale experiments reported that the shape of membranes influenced the oxygen transfer and utilization rates, which in turn affected the pollutant removal performance of the MABR. In this study, two pilot-scale MABRs using multi-layer hollow fiber membranes with the relaxation rates of 0.1-1.8% (MABR 1) and 1.0-2.8% (MABR 2) were used for the treatment of organics and nitrogen in real medium-strength domestic wastewater. Higher-relaxation-rate membranes have loose and more curved fiber bunch that may allow biofilm to grow more easily and let air diffuse more efficiently. MABR 2 had achieved better performance than MABR 1 at 12- and 6-h Hydraulic Retention Time (HRT), with respectively 0.7-4.3%, 17.7-18.1%, and 5.5-9.0% higher removal efficiencies for Chemical Oxygen Demand (COD), Ammonia Nitrogen (NH), and Total Nitrogen (TN). The highest COD, NH, and TN removal efficiencies were 94.7%, 81.1%, and 57.1%, respectively, at 12 h HRT in MABR 2. The addition of Polyvinyl Alcohol (PVA) gel beads carrying denitrifying bacteria had enhanced the denitrification in both the reactors. Increments of 5.0-9.0% and 6.6-12.3% were reported for TN removal efficiencies of MABR 1 and 2 combined with PVA gel, sequentially.