Development of an Integrated Direct Membrane Filtration (DMF) and Anaerobic Membrane Bioreactor (AnMBR) System for Dilute Municipal Wastewater Treatment

The total electricity consumption due to municipal wastewater treatment in the US accounts for 1.3% of total demand. Also, a significant portion of biodegradable constituents in wastewater is converted into biomass, which needs further processing. On the one hand, an excessive amount of energy and chemicals are being used to treat wastewater, but on the other hand, resources (such as nitrogen and phosphorus, energy, and water) in wastewater are being discharged or removed rather than recovered. From this perspective, new wastewater treatment technologies are sorely needed to facilitate resource recovery from wastewater for a better, more sustainable future. Anaerobic membrane bioreactor (AnMBR) technology has often been appointed to being capable of such treatment performances due to their small footprint and high-quality effluent, suitable for resource recovery applications provided by ultrafiltration membranes. The utilization of membranes also enables the decoupling of sludge retention time (SRT) and reduces the hydraulic retention time (HRT) significantly compared to conventional anaerobic digestion systems, which can improve the overall throughput immensely. However, the widespread applications of this process are limited due to WW being dilute in nature. In this research, a novel WW treatment concept was tested for achieving a higher throughput and enabling increased energy recovery from dilute municipal wastewater. To achieve this, a direct membrane filtration (DMF) process utilizing a crossflow ultrafiltration membrane configuration was assessed, improved, and integrated with an AnMBR. In the first design, DMF process was operated in a batch mode in order to achieve a concentration factor of 10 (CF10) (CF = initial feed volume/final concentrate volume) at an initial flux of 75 LMH. This initial testing revealed that DMF of dilute WW caused severe fouling at a 30.6 mbar/h rate and the process was only operated around 30 hours before reaching to a 1 bar trans membrane pressure (TMP). Severe fouling also caused a rapid flux decline and a final flux of 15 LMH was observed. Therefore, an improved configuration with a concentrically baffled settling tank (CBST) was designed, and semi continuous operations were tested. The results showed only 0.63 mbar/h fouling rate during 180-hour CF10 operation without any flux decline at 50 LMH. Also, only 15% influent tCOD lost to the permeate while 69% was concentrated and fed into the AnMBR for energy recovery. The high strength concentrate increased the overall AnMBR removal efficiency from 78% to 96% and the biogas production 9.7 times compared to the startup period. The corresponding 15.54 kWh/m3 energy recovery was determined to be enough to offset the background energy demand for the DMF-AnMBR process and for influent heating at 10°C to 35°C when a permeate heat pump technology was incorporated