This paper describes the progress up to June 2000 for thermophilic digestion of wastewater sludge at the Los Angeles, California, Bureau of Sanitation's Terminal Island Treatment Plant. The development of the microorganism culture has followed a course similar to that seen at other successful plants for establishment of a stable, wellbalanced thermophilic culture in a large digester, but at an accelerated pace. This study began with rapid heating, increasing the temperature of the 4500 m 3 (1.2 mil. gal) digester to the target temperature of 55°C at approximately 3°C/d. A method of feeding to maximize the rate of culture development was used as feeding accelerated to approximately 400 m 3 /d (0.1 mgd). An initial rise of acid concentration (primarily acetate) was seen. Within two weeks, acid concentration declined and stabilized, indicating that acidogenic and methanogenic microbial communities came into balance. Coliform data indicate that digester disinfection was stably effective from the middle of April. The salmonella tests done to date satisfy the U.S. Environmental Protection Agency (U.S. EPA) class A specifi cation. Testing with helminth ova and enteric viruses before and after the digester shows satisfaction of class A standard for those organisms. The present combination of low volatile fatty acids and low hydrogen sulfi de is good news for odor control. The data show increases in volatile solids destruction and estimated gas production, compared with the previous mesophilic operation; however, large uncertainties have been calculated from the data. As the digester is now operating successfully at the current feed rate, there seems to be no barriers to processing the entire sludge production of the plant. Other results indicate that the U.S. EPA requirements for exceptional quality class A biosolids are likely to be achieved. Water Environ. Res., 74, 494 (2002).
The City of Los Angeles Hyperion Treatment Plant (HTP) has conducted a multiphase study of thermophilic anaerobic digestion to meet federal (Part 503 Biosolids Rule) and local (Kern County ordinance) requirements for Exceptional Quality Class A biosolids. The study consisted of five Phases of full-scale testing.
Results from several recent studies of UV disinfection of reclaimed wastewater led to the conclusion that disinfection effectiveness is likely to be reduced at low flow velocities. Considerations from basic hydraulics make this likely because the formation of boundary layers along welled surfaces in lamp banks reduces the UV dose absorbed by most of the water. Boundary layers grow thicker with decreasing mean flow velocity through the lamp bank. This analysis of disinfection is supported by two reports of hydraulic tests and a study that changed flow rates to change the estimated dose per bank of lamps and found that the proportion of viruses killed in each bank was independent of flow velocity over the observed range. Additional laboratory and computational work is suggested to test this hypothesis. If. as expected. results confirm the hypothesis. then arrays of small vanes, similar to those used in aeronautical engineering, may provide a useful countermeasure.This recommendationcan be tested by the same methods used to test the hypothesis. Water Environ. Res., 71, 114 (1999).
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