The City of Los Angeles Hyperion Treatment Plant (HTP) has conducted a multiphase study of thermophilic digestion to meet a newly stringent pathogen standard in the counties where it sends its biosolids for land application. The original plan was that Phase III of the studies would be a test of a batch process that was guaranteed to meet the time/temperature requirement of Alternative 1 of 40 CFR 503, the Federal sludge regulation. However, operational problems delayed the startup of this process. Consequently, Phase III became a full-scale test of a continuous two-stage thermophilic anaerobic digestion process. These tests were conducted in August and September, 2002. Thermophilic digestion was at average digester temperatures in the first and second stage of 128.1 -131.7 0 F (53.4 -55.4 0 C) and 122.0 -127.8 0 F (50 -53.2 0 C), respectively, and at an overall mean HRT of about 12 days. Almost full compliance with the Class A pathogen requirements was demonstrated in biosolids at the Truck Loading Facility and the farm for biosolids land application. Salmonella sp. in raw sludge were completely removed and these pathogens were non-detect in all samples taken at the farm. Kern County requires testing for both Salmonella sp. and fecal coliforms. Reactivation and/or growth of fecal coliforms in biosolids after the digesters, as was previously observed during Phase I (late 2001) and Phase II (early 2002) tests, did not occur during Phase III. This can possibly be attributed to two modifications implemented in the Phase III process. First, insulation of the post-digestion train prevented cooling of biosolids during post-digestion processing, i.e., biosolids temperatures from the digester outflow to the Truck Loading Facility decreased only by approximately 1 0 F. Second, the full conversion of HTP to thermophilic treatment prevented the risk of contamination by mesophilic plant operations. Further studies in the laboratory with biosolids from the Truck Loading Facility and the farm demonstrated that no reactivation and/or growth of fecal coliform occurred when the biosolids were stored for up to six days at 75 0 F. The Phase IV Class A Biosolids program at HTP (October 2002) will test the timetemperature relationship for batch treatment (Alternative 1 of 40 CFR 503). Experiments were conducted during this write-up and the results will also be presented at the conference.

It has been shown in the literature that the introduction of Fats, Oils, and Grease (FOG) into Anaerobic Digesters holds many benefits, namely the increase in efficiency of the digester, an increase in digester gas production, and the diversion of organic matter from landfills (Wimmer 2010). Several municipalities in Southern California, such as in Riverside, Rialto, and Oxnard have been involved in FOG digestion. As a result, the City of Los Angeles' Hyperion Treatment Plant started its own FOG digestion pilot project in 2010. The pilot injected FOG into one 2.5 million gallon thermophilic digester. The plant partnered with Baker Commodities, a grease rendering company, to bring 5,000 gallons of FOG initially and ramped up after that. Most critical digester parameters were monitored and results were analyzed. Although the digester was loaded 15% in Volatile Solids the effect was 30% increase in gas production, which demonstrated a "supercharging" or increase in efficiency effect in the digester.

Several experiments were conducted to investigate the cause of fecal coliform recurrence in biosolids after thermophilic anaerobic digestion. Fecal coliform recurrence has been observed at the City of Los Angeles Hyperion Treatment Plant (HTP) during pilot-scale experiments with a designated thermophilic battery of six digesters, while other digesters were still at a mesophilic temperature. The main results of the present investigation were:-QA/QC plant inspections indicated that the designated thermophilic battery and its post-digestion train likely were isolated from mesophilic operations, but contamination by mesophilically digested biosolids could not entirely be excluded. -High-pressure effluent and Mannich polymer did not contain fecal coliforms, hence, their additions to the post-digestion train could be ruled out as contamination sources. -Laboratory simulations could not confirm the suspected role of dewatering centrifuges in the recurrence of fecal coliforms observed at HTP. -Regrowth tests in the laboratory and the field demonstrated that the minimum temperature for preventing fecal coliform recurrence was about 50 0 C.Based on these results, it was postulated the fecal coliform recurrence observed during the pilot-scale tests could probably be attributed to a combination of contamination by mesophilically digested biosolids and a large drop of the biosolids temperature during post-digestion processing.

Anaerobic digestion of high-strength organic wastes, such as Fats, Oils, and Grease (FOG) has become increasingly popular among wastewater treatment facilities in Southern California [1]. In 2010, the City of Los Angeles’ Hyperion Treatment Plant started running its own FOG Digestion Pilot Project. The project injects processed grease trap wastewater (FOG) into one of 16 anaerobic digesters at the facility. A partnership was formed between the Hyperion Treatment Plant (HTP) and Baker Commodities, Inc., a Grease rendering company located in the City of Vernon. They provide processed grease trap wastewater (FOG) to the pilot project. The plan was to load the digester with increasing amounts of FOG and observe the impact. The parameters monitored in the digester during the test are volatile acids, pH, alkalinity, temperature, and gas production in the digester. The pilot project’s objective was to obtain a 10 to 20% increase in gas production. So far those expectations have been exceeded.

No abstract