The Philadelphia Water Department operates the world's largest sewage sludge composting plant – the Sludge Processing and Distribution Center (SPDC). This $80 million plant handles anaerobically digested sewage sludge generated by three regional sewage treatment plants treating 530 million gallons (2,000 million liters) of wastewater daily. SPDC was designed to compost sludge solids in an aerated static pile system of composting. During 1989, the SPDC composted the full 60,000 dry tons (56,000 dry metric tons) of sludge solids it received for processing. The Department has chosen, however, to not compost all incoming sludge solids in the future, but instead to maintain a diversified sludge utilization program. Five reasons have contributed to this decision:SPDC's practicable composting capacity is about two-fifths of its designed capacity.Facility managers have been compelled to consider limiting compost production as a key odor control strategy.Commercial markets for sludge compost have not grown in a one-to-one proportion to the increased production capacity at SPDC.Programs to use or dispose of uncomposted sludge solids are implementable and cost effective.Reliance on any single technology or end use is unacceptably risky.
The planned distribution of sludge products for calendar year 1990, by proportion of total solids and by product weight, consists of: 1) marketing of screened compost (33%), 36,000 metric tons; 2) stripmine reclamation with a cake/compost mix (20%), 45,000 metric tons; 3) landfill disposal of sludge cake (17%), 64,000 metric tons; 4) agricultural use of compost (15%), 40,000 metric tons; 5) agricultural use of sludge cake (10%), 27,000 metric tons; 6) land reclamation use of compost (3%), 10,000 metric tons; and 7) local application of compost (2%), 5,000 metric tons.
Bioaugmentation mitigates ammonia and hydrogen sulfide emissions during the mixture compost of dewatered sewage sludge and reed straw
