Integration of a membrane bioreactor coupled with reverse osmosis for advanced treatment of municipal wastewater

This work investigated the evaluation of a pilot-scale membrane bioreactor (MBR) system in combination with a reverse osmosis (RO) unit. The MBR treatment with biomass concentration (MLSS) of 5 mg/L provided a high level of treatment for primary municipal wastewater. The removal of SS reached 99.99% resulting in a MBR effluent with SS levels below 1 mg/L. This demonstrated excellent solids separation achieved by the UF membrane. Similar removal levels were achieved for turbidity (99.72%). The average COD removal was 97.3% resulting in an effluent with COD ranging between 8–32 mg/L. However, relatively low total nitrogen removal (TN) was achieved with a most likely mechanism for nitrogen removal nitrogen assimilation in the biomass. Heavy metal removals were very high: Pb and Ni were removed completely, indicating that these two metals were in particulate form, while Cr and Cu were removed by 89% and 49%, respectively. Combination of MBR and RO provided a superb quality effluent devoid of heavy metals and with very low organic matter concentration (DOC level below 4 mg/L). Yet, TN removal was not complete, resulting in a TN concentration around or less than 20 mg/L.