Oxygen transfer and plant-wide energy assessment of primary screening in WRRFs

Primary screening is gaining interest as a method to achieve removal performances comparable to primary clarification while reducing the footprint and increasing operational elasticity. Aeration efficiency indicators in a pilot sequential batch reactor (SBR) and a full scale water resource recovery facility (WRRF) were investigated after the implementation of rotating belt filters/screens (RBF). To compare the impact between screened (350 μm) and nonscreened primary influent, two identical treatment lines were monitored using off-gas and respirometric measurements. The study provides the first result on improved oxygen transfer efficiency due to primary screening. Consistent aeration efficiency improvements of 27% and 20% between screened and nonscreened were obtained at pilot and full scale, respectively. Changes in aeration efficiency and carbon redirection were integrated into a set of models to investigate the primary screening impact on the WRRF energy balance. While the plant-wide assessment for different scenarios improved the energy balance up to 15%, a detailed comparative analysis between various treatment schemes gained insight into the advantages and limitations of the energetic sustainability of primary screening. PRACTITIONER POINTS: Aeration efficiency improved 27% at pilot scale Aeration efficiency improved 20% at full scale. Use of primary screening can improve the energy balance up to 15 Assessment of advantages and limitations of primary screening.