STARTUP AND STABILIZATION OF THERMOPHILIC DIGESTION AT TERMINAL ISLAND TREATMENT PLANT

This paper describes the progress up to June 27, 2000, of the project for thermophilic digestion of wastewater sludge at the Bureau of Sanitation's Terminal Island T reatment Plant. This is the Bureau's first use of thermophilic digestion since its Hyperion Treatment Plant used it in the Seventies. The present study has been conducted with rapid heating, using recent experience showing how to feed to maximize the rate of culture development as feeding accelerated to the present level near 100,000 gallons per day. The development of the culture has followed a course similar to that seen at other successful thermophilic plants. An initial rise of acid concentration (primarily acetate) was seen as the acidogen activity initially exceeded the activity of the methanogens, and a later decline and approximate stabilization of the acid concentration as the activities of the microbial communities came into balance. Balance was achieved in less than two weeks. The chemical parameters have been largely stable since early in the startup period, indicating that a biological community has been established that has been able to increase in numbers to meet the increases in the feed rate. Likewise, coliform data indicate that disinfection was stably effective from the middle of April, and the present combination of low volatile fatty acids and low hydrogen sulfide is good news for odor control. The Salmonella tests done to date satisfy the USEPA Class A specification, as expected from previous research showing that Salmonella are rarely detectable when the coliform count meets the Class A standard. We expect testing for enteric viruses and helminth ova to verify compliance with the other pathogen specifications of the Class A standard for biosolids, since it is known that the concentrations of these organisms are usually low or undetectable in untreated sludge, and that they are rapidly killed by thermophilic temperatures. Work to verify compliance with the rest of the pathogen standard alternative is in progress; we know that the 38% VS reduction standard for reducing vector attraction is being met; and the thermophilic samples tested for heavy metal pollutants so far were as good or better than the plant's 1999 averages for mesophilic sludge in showing acceptable concentrations of all of the metals. Together, these imply that all three requirements for exceptional quality certification are likely to be achieved. As the digester is now operating successfully at the current feed rate, there appear to be no barriers to carrying out our plan to process the whole sludge production of the plant. We are extremely satisfied with the progress of this project.