This paper presents the results of full scale experimental investigations into the fate of phosphorus in the Hyperion Treatment Plant, City of Los Angeles, CA, USA. For almost three decades, the activated sludge process, operated at standard rate has exhibited enhanced biological phosphate removal accompanied by initial anaerobic phosphate release and subsequent aerobic phosphate uptake. In 1989 when high rate treatment was initiated the enhanced phosphate removal and accompanying initial anaerobic phosphate release decreased and finally was eliminated. Phosphorus in the secondary effluent increased from 0.4 to 3.1 mg/l as the MCRT decreased from 3.1 to 1.5 days. Of added interest was the accompanying decrease in struvite (MgNH4PO4.6H2O(s)) build-up in the sludge dewatering processes downstream of the anaerobic digesters.

The City of Los Angeles has developed a diversified sludge management program since cessation of the ocean disposal of sludge in November 1987. At the heart of this program is the centrifugal dewatering of digested sludge at the Hyperion Wastewater Treatment Plant. The experience gained from the dewatering process includes: centrifuge startup problem solving, optimization of the dewatering process, polymer testing, struvite monitoring and control, and waste activated sludge dewatering parameter development.

The City of Los Angeles USA Hyperion Treatment Plant (HTP) implemented high rate air activated sludge operations in November 1989. Using this process, the secondary treatment organic loading (F/M) was increased from 0.5 to 1.0 kg BOD/kg MLVSS/day and the MCRT reduced from 3.1 days to 1.5 days, thereby enabling the secondary treated flow to be increased from 150 mgd to 200mgd (6.6 to 8.8 m3/s). Excellent secondary effluent quality (BOD5 = 15 mg/l, carbonaceous BOD5 = 6 mg/l, SS = 6 mg/l) is currently obtained using rectangular secondary clarifiers operated at surface overflow rates of 1,100 gal/day/ft2 (43 m3/m2/day) and low MLSS concentrations (950 mg/l). The enhanced biological phosphorus removal that was obtained when operating at a 3 day MCRT was eliminated in the change to high rate operation and struvite (MgNH4PO4(c)) build-up in the anaerobic digesters has been eliminated. Nocardia scum formation, with its odor generating potential and other associated operating problems, has also been eliminated by high rate operation.

The current federal sludge regulations for the first time place limitations on the concentration of pathogens or indicator organisms in sludge and sludge products destined for distribution and marketing and land application. However, there is a general lack of data for assessing the impacts of these new limits on the wastewater industry. To understand better the extent of the compliance problem and the factors that may enable publicly owned treatment works (POTWs) using anaerobic digestion to comply with the new criteria, a survey of treatment plants around the U.S. was undertaken. In addition to data on fecal coliform densities in raw and digested sludge, information was collected on the design and operating characteristics of the 54 digestion facilities that participated in the survey. Based on the analysis of survey responses, it appears that the pathogen reduction criteria under the regulations are not unreasonable and should be achievable by most conventional anaerobic digestion facilities.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res., 66, 255 (1994).

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.