Effect of coupling primary sedimentation tank (PST) and microscreen (MS) to remove particulate organic carbon (POC): a study to mitigate energy demand in municipal wastewater treatment plants

Abstract

Particulate Chemical Oxygen Demand (COD) removal is one of the first and foremost steps in a wastewater treatment plant (WWTP). It is a highly essential step that supports subsequent biological steps to achieve discharge limits. However, the energy demand for subsequent biological steps is significant due to the requirement of physical processes such as aeration. As a part of the project: WWTP of the future, it was expected that by coupling primary sedimentation tank (PST) and microscreen (MS) as advanced primary treatment (APT), around 60 to 70% removal of total COD and more than 90% of total suspended solids could be achieved which can replace such energy-intensive steps. To achieve this, a pilot plant set up including two different types of rotatory drum sieves (8 and 20 μm) was coupled with a PST in the WWTP Büsnau, Stuttgart, Germany, and the efficiency of APT was undergone for deeper investigations. The results showed that applying APT processes is an innovative and robust approach for removing more solids in municipal WWTPs so that retrofitting treatment plants comes true with a marginal footprint. However, the long-term performance of the APT system demonstrated that the system’s ability to remove solids is highly limited by MS capacity and strength of produced flocs/filter-cakes inside the MS against shear forces, which makes it easier for flocs to be detained by MS. Therefore, additional auxiliary steps like flocculation are recommended to be synchronized with APT system to enhance its efficiency. Additionally, applying a middle mesh size sieve, for instance, a 15 μm, along with changing the backwashing regime, could be considered the next alternative.