Investigation and efficiency estimation of a hydrocyclone for the treatment of primary municipal wastewater

Conventional wastewater treatment is widely recognized for its high energy consumption. Several wastewater treatment plants (WWTPs) in Europe and elsewhere are aging. As a result, many WWTPs do not meet performance requirements due to the expansion of sewerage networks and the rise of wastewater flow rates. This study examines if the use of hydrocyclones for early removal of suspended solids present in municipal wastewater, upstream of the secondary treatment, can result in decreased energy demands and enhanced operational efficiency compared to a conventional WWTP. Hydrocyclones are crucial solids-liquid separation apparatuses in industry. In this study a hydrocyclone with maximum hydraulic capacity of 50 m3/d, was installed downstream of the primary clarification at the WWTP of Chania, Greece. An efficiency estimation method was employed to assess the effectiveness of hydrocyclone and predict the total suspended solids (TSS) effluent concentration as function of the influent TSS concentrations and surface overflow rate (SOR) values. It was shown that the hydrocyclone achieved a TSS removal rate ranging from 9 % to 48 %, with an average of 33 %, resulting to effluent TSS concentrations varying from 74 to 285 mg/L. The average biological oxygen demand (BOD5) removal rate of the hydrocyclone was 19 %, with a range of 6 %-42 %, achieving effluent BOD5 concentrations between 154 and 395 mg/L. The hydrocyclone chemical oxygen demand (COD) removal rates were estimated to vary from 2 % to 39 %, with an average of 13 %, and the effluent COD concentrations from 252 to 782 mg/L. Finally, a numerical model was proposed, which fitted the experiment data satisfactory. The implementation of the hydrocyclone system in the WWTP significantly reduces the volume of aeration tanks (9-48 %), oxygen demand (8-42 %), electricity consumption of the aeration tank (17-50 %), and secondary sludge production (11-61 %). The use of hydrocyclones to remove TSS from municipal wastewater was demonstrated to be efficient, with minimal capital and operating costs.