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Self-sustaining biosolids drying

Self-sustaining biosolids drying

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    The Class AA product is a source of organic material and nitrogen that is sold in bulk to central Florida's fertilizer industry. The pellets can also be sold as fuel for biomass incinerators. Photos: West Palm Beach Solid Waste Authority

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    Capable of turning 600 wet tons of sludge into 60 tons of marketable fertilizer every day, Palm Beach County's Resource Recovery Facility is processing 400 wet tons daily. Solid waste and wastewater treatment managers plan to add another 900 scfm by capturing gas from a second landfill.

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    Palm Beach County's North County Resource Recovery Facility is centrally located, lowering the hauling costs and vehicle emissions between five wastewater treatment plants and the landfill, which owned enough land to house a biosolids drying and pelletizing facility.

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    The compression system runs 24 hours a day, six days per week, recirculating gas to a continuous pilot that automatically switches back to flaring when the pelletization facility isn't operating.

By Victoria Ludwig

FEDERAL REGULATIONS FOR MANAGING BIOSOLIDS

The EPA Office of Water's Part 503 Biosolids Rule (40 CFR, Part 503) regulates the surface disposal of biosolids. The rule imposes numerical standards for 10 metals and operational standards for microbial organisms in biosolids.

Although drying and selling biosolids isn't new, using landfill gas to power dryers is. Since U.S. EPA's Landfill Methane Outreach Program began keeping track in 1997, wastewater and solid waste managers in eight locations across the country have overcome logistical and regulatory barriers to build a mutually beneficial partnership.

In August 2010, Florida's Palm Beach County celebrated its first anniversary as the latest addition to that list.

The county's five wastewater utilities had been land-applying biosolids for two decades, but the practice was in decline because of negative public perception and regulator concern over nutrient runoff into the Lake Okeechobee, Everglades, and Indian River Lagoon water basins. The ground's so saturated during South Florida's rainy season that spreaders bog down in muddy fields.

Wastewater managers wanted a more environmentally sound, longer-term solution to biosolids disposal that complies with U.S. EPA Office of Water Part 503 limits on pollutants and pathogens. (See info box on page 47.) So they approached their cohort at the county's solid waste authority about building a drying and pelletizing operation that would:

Provide an alternative to land application. As defined by the Florida Department of Environmental Protection, Class AA biosolids can be distributed and marketed like other commercial fertilizers.

Repurpose an existing energy source. Converting the methane at a landfill, specifically the 41-million-cubic-yard capacity Class I landfill at the county's North County Resource Recovery Facility, rather than flaring it off would reduce dependence on natural gas, reducing operating costs and making the project more economically feasible. A site was available right next to the landfill, which would lower the cost of transporting the gas it generates to the pelletization facility.

Generate an environmentally sound saleable product. The partners would sell the pelletized biosolids to fertilizer manufacturers in central Florida, where they are used as an additive to provide nitrogen and organic matter primarily on pastureland.

Solid waste managers agreed such a facility would provide a long-term, environmentally sound solution without exacerbating water pollution. Engineering consulting firm CDM was hired to permit, design, and build the $25 million pelletization facility, helping to obtain more than $3.25 million in federal and state grants from EPA's State and Tribal Grants program and the South Florida Water Management District.

Using historical data on gas quality and quantity, EPA's free Excel-based Landfill Gas Emissions Model (Land-GEM) software, and their own observations, the managers decided the 1,500 standard cubic feet/minute (scfm) of gas they were flaring would provide enough British thermal units (Btus) to power two 300 ton/day Baker-Rullman Mfg. Inc. dryers.