The mesophilic-thermophilic digestion process is a new two-step concept for treating municipal wasterwater sludges. The first step operates under mesophilic process conditions (digestion with anaerobic microorganisms that thrive at 90 to 100F). The second step operates under thermophilic process conditions (digestion with anaerobic microorganisms that thrive at 120 to 130F). Results at the Rockaway Pollution Control Plant in New York City indicate that the physical characteristics of mesophilic-thermophilic sludge are changed to the extent that the economics of dewatering are significantly improved. The evaluation at Blue Plains concludes that: (1) a limited expansion of digester capacity is required to handle the entire sludge stream; (2) digester gas would be available for sale to outside interests after internal heating requirements were satisfied; and (3) the cost of sludge handling could be reduced by $24 to $31 per million gallons of influent flow (from $72/MG to $41-48/MG). The analysis also indicates that the improved characteristics of the mesophilic-thermophilic digested sludge could reduce chemical conditioning requirements so that the cost would be almost $7/MG less than mesophilic digestion and almost $4/MG less than thermophilic digestion. Under the present circumstances, the thermophilic digestion option would require the least capital expenditure and would be the most expedient, cost-effective solution to the sludge management problems at Blue Plains.

July 1981. SL. Series. CRDP Project Historic Shelflist record.