THE LESSONS OF TWENTY-TWO YEARS OF BIOSOLIDS RECYCLING BY THE CITY OF PHILADELPHIA WATER DEPARTMENT: DIVERSIFICATION AND CONTINUAL IMPROVEMENT

The City of Philadelphia Water Department (PWD) is a regional water and wastewater utility serving 2.3 million residents of Philadelphia and portions of four adjoining counties. PWD stabilizes wastewater solids in anaerobic digesters, operates a centralized dewatering station with ten large capacity centrifuges, and uses a 72-acre facility for aerated static pile composting. PWD has recycled its biosolids for twenty-two years, having ended ocean disposal in 1980 in response to federal policy, and in that time has handled 4 million tons of biosolids in a diversified program. Since 1984, 837,000 tons have been used for reclamation, 679,000 tons for agricultural applications, 172,000 tons for public works, and 350,000 tons for commercial marketing. In addition, 1,450,000 tons of biosolids were co-disposed with trash in municipal solid waste landfills.Based on extensive experience, PWD recommends that large wastewater utilities develop flexible and diverse outlets for their biosolids products and plan for continual improvements to their products and programs. In planning for sound biosolids recycling programs, wastewater utilities can draw from several of PWD's findings.Biosolids generation increases as wastewater manages strive for maximum system performance.Reduction in pollutant metals reach a plateau as industrial pretreatment becomes uniformly effective and water system corrosion is put under control.Anaerobic digesters can produce a biosolids of acceptable odors and pathogens when welloperated.Aerated static-pile composting is a flexible, low capital cost technology and produces a product with commercial value.Diversity of products and outlets is a successful approach to developing dependable and cost-effective biosolids management programReclamation of mined lands can handle large volumes of biosolids.Agricultural application of biosolids is a low-cost recycling program.Co-disposal of biosolids in landfills helps offset weather and other variables.Public support for recycling requires continual attention and can never be presumed.Management efficiencies and competition among outlets can significantly reduce costs.Continual improvement is a successful paradigm for managing biosolids programs.Participation in national, regional and local biosolids affairs serves utility interests.