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  • By Chris Enloe-Instrument & Supply, Inc. And Shannon Jones, P.E.-Utilities Engineer City of Fayetteville

    Biosolids Management Utilizing Solar and Thermal Processes

  • What are biosolids?  Biosolids are the treated finished product from the

    wastewater treatment process.  Billions of bacteria and other microbes thrive in the

    wastewater facility environment where they consume the organic content from the wastewater stream and continually multiply.

     To maintain optimum conditions and remove the nutrients absorbed by the microbes, a fraction of the microbial population is regularly removed. Referred to as Waste Activated Sludge (WAS).

     When treated and processed, sewage sludge becomes biosolids which can be safely recycled and applied as fertilizer to sustainably improve and maintain productive soils and stimulate plant growth.

  • Fayetteville History  In 2003, Fayetteville was forced to abandon land

    application of waste sludge  Landfill disposal was readily available and inexpensive  By 2008, several area landfills no longer accepted AR

    solids  Landfill costs for those that would still take solids

    skyrocketed almost 600%  Fayetteville wanted a long-term, dependable, and

    more sustainable solution

  • Why consider drying?  Takes waste out of landfill  Big volume reduction  Beneficially useful product  Self reliant  If energy is managed, can be lower operating cost

    AND smaller carbon footprint

  • Class A vs. Class B  40 CFR, Part 503  Class A biosolids contain no detectible levels of

    pathogens. Class A biosolids meet strict vector attraction reduction requirements and low level metals contents, and generally have unrestricted use.

     Class B biosolids are treated but still contain detectible levels of pathogens. There are buffer requirements, public access, and crop harvesting restrictions for virtually all forms of Class B biosolids.

  • Alternatives Considered

  • Specific Options Compared

  • Option Selected  Combined application of both Solar and Thermal

    Drying  Results in lower capital and operating cost – long term

  • Combination Drying

    Bound

    Free

    WAS

  • Drying Sludge Provides Big Volume Reduction

    Before – 100 lbs. Wet After – 20 lbs. Dry

  • Beneficially Useful Product Class A Product for Distribution/Sale  Stockpile storage - low cost, long life

  • Spreadable – bulk fertilizer

  • 1 Air flap 2 Exhaust fans 3 Ceiling fans

    4 Electric Mole 5 Inside sensor 6 Outside sensors

    7 PLC

    1

    4

    3 2 5

    First Step-Solar Houses 6 7

  • Thermo-System Active Solar Dryer

    Fayetteville, AR Biosolids Management Site

  • Typical Solar House Drying Cycle

    De-watered biosolids are trucked to the site from either WWTP

  • Solids are emptied into the “Unload Basin”

  • Solids are then loaded into the spreader or hauled directly into the houses with the skid-steer loader

  • Solids are then spread as evenly as possible inside the houses

  • Then the ‘moles’ are turned loose to do their thing!

  • Mole Video

  • After a variable weather-dependent drying period, the final product is ready for the next step

  • 1 Sludge goes from hopper to drying chamber. 2 Steam to condenser. 3 Dry product to silo. 4 Heated by thermal fluid from heat exchanger.

    1

    2

    3

    4

    Second Step – Thermal Dryer

  • Inlet Conveyor

  • Loading product into Thermal Building

  • Feed Conveyor Discharges into Feed Hopper

  • Feed Hopper – before initial use

  • Feed Hopper – initial fill

  • Screw Conveyors Transport Solids to the Dryer

  • Fenton Fenix Batch Dryer - Indirect Heat

  • Internal Rotating Assembly

  • Heat Exchanger – 15,000,000 BTUs

  • Natural Gas - >20,000 cfh capacity

  • Surge Bin – allows product to cool

  • Finished product ready for hauling/storage

  • Bulk Storage Silo

  • Performance Solar Houses  Target 50% solids before

    transferring to Thermal Dryer

     Initial results before thermal dryer completion (summer months)

     >80% Solids (Class B)  5:1 Volume Reduction  5:1 Weight Reduction

    Thermal Dryer  >90% Solids (Class A)  5:1 Volume Reduction  5:1 Weight Reduction

    ~60% Reduction in Costs vs. Landfill

  • Biosolids Management Site

  • Project Contributors  City of Fayetteville (Design & Construction Management)  CH2M HILL (Wastewater Operations)  CDM Smith (Biosolids Management Study)  McClelland Consulting Engineers (Geotech/Foundation Design)  Instrument & Supply (Manufacturer’s Representative)  Parkson / Thermo-System (Solar Equipment)  Fenton Environmental Technologies (Thermal Equipment)

  • Questions?

    Slide Number 1 What are biosolids? Fayetteville History Why consider drying? Class A vs. Class B Alternatives Considered Specific Options Compared Option Selected Combination Drying Drying Sludge Provides Big Volume Reduction Beneficially Useful Product �Class A Product for Distribution/Sale Slide Number 12 First Step-Solar Houses Slide Number 14 Typical Solar House Drying Cycle Slide Number 16 Slide Number 17 Slide Number 18 Slide Number 19 Slide Number 20 Slide Number 21 Slide Number 22 Slide Number 23 Slide Number 24 1 Sludge goes from hopper to drying chamber. �2 Steam to condenser. �3 Dry product to silo. �4 Heated by thermal fluid from heat exchanger. Inlet Conveyor Loading product into Thermal Building Feed Conveyor Discharges into Feed Hopper Feed Hopper – before initial use Feed Hopper – initial fill Screw Conveyors Transport Solids to the Dryer Fenton Fenix�Batch Dryer - Indirect Heat Internal Rotating Assembly Heat Exchanger – 15,000,000 BTUs Natural Gas - >20,000 cfh capacity Surge Bin – allows product to cool Finished product ready for hauling/storage Bulk Storage Silo Performance Slide Number 40 Biosolids Management Site Project Contributors Questions?