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The Hyperion Treatment Plant, owned and operated by the City of Los Angeles, currently produces Class B biosolids, most of which is land applied in nearby Kern County. In order to meet a new County ordinance that will effectively ban the land application of Class B biosolids, Hyperion has been actively studying the means to produce Class A biosolids. Since June of 2000, the Hyperion Treatment Plant has successfully converted and operated six of its egg-shape digesters in thermophilic mode in order to gain experience and learn techniques in resolving any operational problems associated with the production of Class A biosolids.

The dewatering properties of sludge produced by thermophilic anaerobic digestion have been a concern in the biosolids industry. Hyperion conducted a full scale dewatering experiment of thermophilically digested sludge in order to evaluate its dewaterability. The results of the experiment will be used for further development of the Class A biosolids program.

The experiment was carried out using thermophilically digested sludge with an average detention time of 17 days, cationic liquid polymer, and one dedicated Alfa Laval Sharples DS-906 solid bowl centrifuge. A series of dewatering experiments was conducted at sludge feed flow rates of 500, 550, 600, 650, and 700 gpm. At each flow rates, Hyperion tried various combinations of polymer dosages ranging from 15 to 24 lbs/ton and torque settings ranging from 45 and 65% in order to find the best combination of good centrate quality and high cake solids.

Unexpectedly, thermophically digested biosolids were successfully dewatered to 32 percent solids with polymer dosages of 16, 16.5, and 17 pounds per ton at sludge feed flow rates of 600, 650, and 700 gpm respectively. In contrast, the polymer dosage had to be increased to about 23 pounds per ton to produce sludge cake of 30% percent solids when the blended sludge that is consisted of 25% thermophilic and 75% mesophilic sludge was dewatered.
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Document Type: Research Article

Publication date: 2002-01-01

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