Physicochemical Treatment of Municipal Wastewater : From Direct Membrane Filtration to Adsorption of Organic Micropollutants

Abstract: Pharmaceutical residues and other organic micropollutants are transported via municipal wastewater to wastewater treatment plants (WWTPs). However, current treatment processes are not designed to remove organic micropollutants, and several such compounds have been found in recipients, where they can have negative effects on aquatic organisms. Additional processes are therefore required to reduce the release of organic micropollutants to the environment.Additional treatment is likely to increase the energy demand at WWTPs. However, municipal wastewater contains organic matter that can be used for energy production in the form of biogas. Using physicochemical treatment methods would allow more of the organic content to be separated from the wastewater, increasing biogas production compared to conventional treatment with activated sludge.This dissertation discusses the potential and limitations of physicochemical wastewater treatment on pilot scale by chemically enhanced primary treatment (CEPT) with microsieving, direct membrane filtration (DMF) and adsorption with activated carbon.The results of pilot-scale tests showed that optimized CEPT with microsieving was very important for the high retention of particles, organic content and phosphorus, and for higher flux in subsequent DMF. However, the fouling of the membranes was severe, which prevented long-term operation. Biomethane produced from the sludge after microsieving could potentially produce enough energy to cover ~60% of the electricity required for such a treatment train (CEPT with microsieving and DMF). Supplementary biological treatment downstream of the treatment train could be used to reduce the remaining oxygen demand, and thus also reduce the dissolved organic content. The removal of organic micropollutants by CEPT with microsieving and DMF was small. However, by subsequent filtration through granular activated carbon, a high removal could be achieved. The carbon filter could only be operated for 4 days due to the fouling of the membranes, and longer filtration times are suggested in future research.Laboratory-scale tests using powdered activated carbon showed that the tighter filtration used in the pre-treatment, the more organic micropollutants could be adsorbed. Ultrafiltration was better than microfiltration, which was better than microsieving. This was related to lower concentrations of dissolved organic matter in the effluents the finer the filter used. The adsorption was highest in the effluent from a full-scale WWTP using biological treatment. This effluent had the lowest concentration of dissolved organic matter of all effluents. Finally, it was observed that granular activated carbon could be used to remove organic micropollutants after the WWTP and that the removals were similar to that by using powdered activated carbon.