Direct application of chemically enhanced primary treatment in a municipal wastewater treatment plant: A case study
Alicia Checa-Fernández, L.M. Ruíz, José María Torre-Marín, A. Muñoz-Ubina, J. Pérez, M.A. Gómez
Abstract
A feasible and efficient implementation of an Fe-based chemically enhanced primary treatment (CEPT) in a large conventional wastewater treatment plant (WWTP) was thoroughly evaluated. The influence of the velocity gradient and hydraulic retention time in the coagulation and flocculation stages, as well as the coagulant (FeCl 3 ) dosage, were evaluated at lab-scale. Standard Jar Tests were performed to simulate CEPT, and the results were compared with those obtained by primary settling without coagulant. The increase in FeCl 3 dosage and flocculation hydraulic retention time (HRT F ) increased the primary settling COD removal capacity between 6.6% and 18.1%, highlighting its effect on the easily biodegradable COD fraction. The COD removal capacity increased up to 16.8% when working with an HRT F of less than 4 min, facilitating CEPT direct application in conventional WWTPs, avoiding the need to incorporate flocculation chamber, with a corresponding decrease in the associated implementation cost. The presence of residual Fe in the primary settling effluent and an increase in the primary sludge volume were the main drawbacks of the process. The coagulation and flocculation velocity gradients or the coagulation hydraulic retention time did not significantly influence the process. • Coagulant dosage is the most influential variable, increasing COD and TSS removal. • Coagulation retention time and velocity gradient don´t significantly affect the process. • COD removal increases up to 16.8% for flocculation hydraulic retention < 4 min. • Efficient CEPT incorporation in conventional WWTP without the need for civil work. • The drawbacks are the residual Fe and the increase in the primary sludge volume.