Advanced primary treatment: An alternative to biological secondary treatment. The city of Los Angeles hyperion treatment plant experience

Abstract

Advanced primary treatment (APT) is a process, in which chemicals are added to raw sewage to enhance total suspended solids (TSS) and biochemical oxygen demand (BOD5) removals by coagulation and flocculation. The City of Los Angeles Hyperion Treatment Plant (HTP) is the largest APT plant in the USA, servicing over 4 million people within an area of 1500 km2 and currently treating an average of 15 m3/s (350 MGD). HTP began using APT in 1986; current chemical doses to the raw sewage are 10 mg/l of FeCl3 and 0.15 mg/l of an extremely high molecular weight anionic polymer. The 1992 annual average influent TSS and BOD5 concentrations were both 330 mg/l and the APT removed an average 83% TSS and 51% BOD5 at an average surface overflow rate of 75 m/day (1900 gals/ft2,day). This paper discusses the overall performance of APT. The process is more cost effective than conventional primary treatment and its use can significantly reduce the size of the following secondary treatment process. APT is especially suitable for developing countries because of its low capital and operating costs.