Assessing the need for COD fractionation in modelling impacts of source separation on wastewater treatment plants

Wastewater management challenges can be addressed through source separation strategies, such as urine or grey water separation. To quantify advantages and avoid operational issues, an understanding of the impact of source separation on municipal wastewater treatment plant (WWTP) operation and effluent discharge is necessary. This can be achieved using activated sludge models. A key question is whether detailed chemical oxygen demand (COD) fractionation of domestic wastewater sub-streams is needed or if a load-based approach suffices for simulations. Determining COD fractions of wastewater sub-streams is effort-intensive and uncertain, with unclear effects on simulation improvement. Therefore, a simulation study was conducted, in which urine, grey water, black water, and brown water were subsequently separated from the inflow of a WWTP model. Two distinct fractionation scenarios were investigated: (i) purely load-related separation and (ii) load-related separation with individual COD fractionation. The results indicate that most trends in all source separation scenarios are comparable between both fractionation scenarios for most parameters. Only the COD effluent concentrations for grey water separation showed opposing trends. Differentiated fractionation impacts precipitant consumption in grey and brown water scenarios. Thus, a purely load-related approach suffices to identify the main benefits or operational challenges of source separation on WWTPs.