Accumulation of Chemical Oxygen Demand in Membrane Bioreactors at Pilot-Scale and Full-Scale Conditions

Abstract

The accumulation of high-molecular-weight organic compounds is a common phenomenon in membrane bioreactors (MBRs). It is currently not known to what extent accumulation occurs in full-scale plants because relevant tests were mostly performed in experimental plants. To overcome the lack of practical experience, a measurement campaign was carried out including four municipal wastewater treatment plants and two pilot plants [one MBR and one conventional wastewater treatment plant (WWTP)]. The results clearly showed that accumulation depends on sludge retention time (SRT), temperature, sludge volume index (SVI), and the fraction of volatile suspended solids (VSS). As a result of biological processes, the chemical oxygen demand (COD) accumulation may increase for a limited period of time and amounts