Novel process concept alternatives for improved removal of micropollutants in wastewater treatment

Conventional activated sludge treatment plants have limited capability to remove micropollutants from municipal wastewater, and as a consequence, concentrations of micropollutants in water bodies are increasing. This creates concerns due to their potentially harmful effects on the aquatic environment, as well as needs to improve or replace the traditional wastewater treatment processes with novel process concepts. In this study, two novel process concept alternatives for enhanced removal of micropollutants are examined. The experiments were done in pilot scale with real wastewater of a small municipality. In the first concept, a membrane bioreactor process (MBR) without phosphorus precipitation was combined with high permeability nanofiltration (NF), and in the other, the MBR with the precipitation of phosphorus was combined with advanced oxidation implemented by pulsed corona discharge (PCD). The results showed that the MBR processes were insufficient for removing unreadily biodegradable micropollutants, such as carbamazepine and diclofenac. However, combining the nanofiltration or PCD oxidation step with the MBR enabled significant enhancement in the removal of micropollutants. Over 84% removal was reached with nanofiltration (NF270) for most of the studied micropollutants, except caffeine and hydrochlorothiazide. The performance of PCD oxidation (oxidation energy 0.2 kWh/m3) in the removal of micropollutants exceeded the one of nanofiltration; over 90% removal of most of the studied micropollutants was reached, and the pollutants were degraded below 0.1 µg/L concentration. Thus, the total removal of micropollutants was better in the concept combining MBR and oxidation treatment. However, the concept combining MBR and nanofiltration provided better overall removal of organic compounds (removal of COD and DOC > 99%), and it also enabled the recovery of phosphorus as a concentrated solution.