Membrane bioreactor process for removing biodegradable organic matter and disinfection by-product precursors from water: Modeling and process efficiency

The membrane bioreactor (MBR) process combines biodegradation and adsorption for removing dissolved constituents and microfiltration (MF) for removing suspended solids. The MBR process is a promising new technology for treating potable water sources having high disinfection by-product (DBP) formation or with high biodegradable organic matter (BOM) levels. This research evaluated an MBR process combined with pre-ozonation for removing BOM and lowering halogenated by-product formation in potable water. Additionally, a mathematical model was developed to predict MBR process efficiency.; Ozonation studies were first conducted to determine the magnitude of ozone by-product formation and to evaluate suitable BOM surrogates for mathematical modeling. A comprehensive series of tests were conducted using a bench-scale and mini-pilot-scale MBR process treating pre-ozonated water that exhibited high assimilable organic carbon (AOC) formation potential and high trihalomethane (THM) formation potential. These tests evaluated the MBR process efficiency for removing total aldehydes, dissolved organic carbon (DOC), biodegradable organic carbon (BDOC), AOC, and THM precursors at different powdered activated carbon (PAC) doses, varying hydraulic residence times (HRTs), and at different pH levels. A mathematical model was developed that predicted substrate removal in the MBR process. The combined adsorption/biofilm model was calibrated using parameter constants measured in adsorption isotherm, adsorption rate, and biokinetic studies. The calibrated model was verified for predicting total aldehyde, DOC, BDOC, and AOC removal using data measured in MBR experiments. The calibrated model was then used to predict MBR process performance under a wide range of hypothetical large-scale operating conditions.; In conclusion, the MBR process is a promising technology for treating potable water sources having high THM formation or with high BDOC levels. This study has demonstrated that operating strategy has a substantial impact on membrane flux and, ultimately, on process economics and viability. The scale of studies conducted in this work provided a proof of concept and a preliminary assessment of operating strategies to minimize membrane fouling and maximize BOM removal.