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City of Lebanon Authority Wastewater Treatment Plant

Linear-mix digestion, biogas flex-storing, centrifuge dewatering, and biogas-fueled drying convert waste to fertilizer.

  • Aerial view of the wastewater facility—Gannett Fleming

    The regional wastewater facility can cost effectively serve 80,000 people.

  • Biogas storage area—Gannett Fleming

    The 221,000 cubic feet of stored biogas, produced by anaerobic digestion, fuels the biosolids dryer.

  • Alfa Laval centrifuge—Gannett Fleming

    High-solids centrifuges at 3,000 rpm concentrate digested solids to reduce the water content by 90 percent.

  • Biosolids building with dryer system—Gannett Fleming

    Auto-control biosolids drying process evaporates remaining water to produce a granular fertilizer.

City of Lebanon Authority

Lebanon, Pennsylvania 

Our Role
Process and Facilities Design, Construction Management, Commissioning, Training.

30 mgd
Construction Cost
$50 million
3 years
  • Treatment process reduces nitrogen loads to Chesapeake Bay 
  • Sludge drying system reuses biogas as a fuel 
  • $200,000 annual savings from energy recovery.

To continue attracting businesses to the Lebanon area, the City of Lebanon Authority knew its wastewater facilities and treatment capacity needed to be available for economic development and expansion. Its goal was to ensure its wastewater facilities would provide cost-effective service to the 80,000 people in the Lebanon metropolitan area and neighboring farmlands, as well as meet future needs as far out as 2032.  

Gannett Fleming met this challenge with creativity and innovation. As one aspect of a larger four-stage upgrade, Gannett Fleming designed a sludge drying system that reuses biogas as a fuel. The system improves the plant’s biosolids treatment and disposal process, reduces diesel fuel consumption, and benefits Lebanon farmlands.

What We Did

Gannett Fleming designed the plant’s nitrogen and phosphorus treatment processes to reduce nutrient loads to the Chesapeake Bay and improve water quality in accordance with federal regulations. We also managed the construction of the nutrient reduction upgrade that includes an innovative wastewater sludge drying system designed to reuse energy, sustain the environment, and save money. This sustainable solution eliminates biogas “flaring,” by using it as boiler fuel for the sludge drying process; this in turn helps to reduce greenhouse gases.

Drying the sludge evaporates its water content and reduces the weight of biosolids, or “sludge cake,” hauled by authority diesel-engine trucks and tractors by nearly 80 percent. The process lowers diesel fuel air emissions and translates to a 99 percent fossil-fuel cost savings. Also, the sludge drying system enhances agricultural production by beneficially reusing a nutrient-rich byproduct. Incorporating dried biosolids into farmland soil means fewer trips by farmers to buy fertilizer.

Key Features

  • New fixed-steel-arch primary digester, including a linear-motion-mixer with 96-inch-diameter mix element 
  • 100-foot-diameter secondary digester was fitted with a jet-mix-nozzle/pump system for high-rate digestion redundancy and to mix sludge prior to dewatering
  • New Biosolids Processing Building was constructed to house VeloDyne dry and neat liquid polymer mixing and metering feed systems
  • Digester biogas is used to fuel the dryer’s thermal-oil boiler, representing a holistic wastewater-to-energy cycle.

Sustainability Features & Outcomes

  • Improves Chesapeake Bay water quality through reduced nutrient loads
  • Creates nutrient-rich fertilizer benefitting Lebanon area farmlands
  • Promotes economic growth in the area by providing cost-effective wastewater services 
  • Decreases fossil fuel consumption through increased production of methane-rich biogas.

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