A New Approach for Upgrading of Sewage Treatment Plants to Accommodate Excess Organic and Hydraulic Loads

Ibrahim Gar Al-Alm Rashed, Ahmed El-Morsy, Mohamed Ayoub




The communities with high population density suffer from limited land availability for construction of new sewage treatment plants or expansion of the existing plants, which suffer from receiving of excess hydraulic and/or organic loads. The undertaken work is devoted to investigate the feasibility of upgrading these plants using chemically enhanced primary treatment (CEPT) with hydraulic clari-flocculation. CEPT produces large amounts of primary sludge, which can be digested anaerobically to produce biogas. The results showed that a homogenous mixture of 67% alum and 33% sea-salt by weight can be used with dose of 40 mg/L as a suitable coagulant in addition to a range between 60-90 m/d of surface overflow rate as the optimum conditions for CEPT of sewage. These conditions result in removal efficiencies in the range between 52-70% of BOD5, 54-68% of COD and 76-88% of TSS. These results enable the primary sedimentation tank (PST) to accommodate double of its design capacity with very simple modifications in the raw sewage inlet to be chemically enhanced primary sedimentation tank (CEPST) according to the present study. In addition, CEPT maintains the operational conditions of activated sludge system in the recommended limits. Finally, CEPT for upgrading the present WWTP is definitely advantageous in reducing the capital costs by 30% and the treatment costs by 28%.


Keywords: Chemically enhanced primary treatment; hydraulic loads; organic loads; upgrading; wastewater treatment