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City of Lancaster, Pennsylvania Biosolids Management Solution: New Facilities, New Processing and New Disposal/Use

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The City of Lancaster, Pennsylvania's advanced wastewater treatment facility (AWWTF) produces approximately 30,000 wet tons per year of dewatered wastewater solids. Up until recent months, the primary and secondary solids have been landfilled without any stabilization method.

In 2004, the City selected CDM to develop a plan to stabilize solids to meet Pennsylvania Department of Environmental Protection regulatory requirements. Equally as important, the plan had to provide practices and facilities that address neighborhood complaints about solids-related odors. The selected plan involved lime stabilization that produces Class B biosolids and an odor control system that provides complete enclosure of all new facilities.

Planning for the new facilities included developing criteria and comparing various alkaline stabilization technologies. Alternatives were evaluated based on cost and non-cost factors, including odor, operation and maintenance requirements, redundancy, operational performance, Class A/B flexibility, product acceptance potential and end use reliability, operational responsibility, and permit compliance responsibility. Evaluation of alternatives was accomplished by CDM and City operations and engineering staff through a series of workshops. A dual-train lime stabilization facility to be operated by the city was selected for design. Hauling and disposal of the stabilized biosolids was contracted with a service provider.

Modifications were made to the existing abandoned composting building to accommodate the new lime stabilization facilities and to the site to accommodate a new scrubber and biofilter for odor control. All new lime stabilization facilities were constructed inside the existing composting building. The new odor control facilities were placed outside, adjacent to the existing building.

The lime stabilization process consists of mixing raw belt-press dewatered sludge and lime in pug-mill mixers to produce stabilized biosolids. The lime storage silo was constructed on the roof of the existing composting building, and the lime is discharged through the roof to a lime conveyance system. Truck loading and storage bays were also constructed inside the existing composting building. Odor control for the new lime stabilization facilities and the existing belt filter press room includes a wet scrubber for ammonia and lime dust removal and an enclosed 2- stage biofilter to treat the remaining odorous compounds. Because the facility is in a valley with homes nearby, the biofilter discharges to a high velocity dilution stack system. A topical chemical spray system was also constructed to allow blanketing of the loaded trailers for odor control during storage and transport. In addition, new electrical and instrumentation systems were constructed to allow for monitoring and control of the lime stabilization and odor control facilities.

The new biosolids processing system has been recently completed and has been operating since April 2008. Proposals for the disposal contract for the City's lime stabilized biosolids are due in March 2009. Landfill disposal, land application and composting are expected proposed disposal options.

Keywords: Biofilter; beneficial use; lime stabilization; scrubber

Document Type: Research Article


Publication date: 2009-01-01

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