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TACOMA DUAL DIGESTION . A Tail of Adoption and Adaptation. THE INVESTIGATION. Studies began in 1984 for improvements to the biosolids system in conjunction with a planned installation of HPO secondary treatment. Only Class A options were considered. Anaerobic Digestion Dual Digestion.

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TACOMA DUAL DIGESTION

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TACOMA DUAL DIGESTION

A Tail of Adoption and Adaptation


THE INVESTIGATION

  • Studies began in 1984 for improvements to the biosolids system in conjunction with a planned installation of HPO secondary treatment.

  • Only Class A options were considered.

    • Anaerobic Digestion

    • Dual Digestion


ECONOMIC EVALUATIONCost Analysis in 1985 Dollars


NON ECONOMIC FACTOR MATRIX


NON ECONOMIC FACTOR EXPLANATION

  • Reliability

    • Anaerobic Digestion well known and reliable

    • Dual Digestion system simple and reliance on autothermal process considered more reliable

  • Gas production

    • Dual Digestion produced greater gas yield potential for energy capture

    • Anaerobic Digestion did not produce enough gas to warrant gas utilization facilities

  • Reliability and Stability

    • Dual Digestion received best rating due to the aerobic conditioning step

  • Product Acceptability

    • Dual Digestion received the high rating due to reliable PFRP process

  • Ease of Construction rated as similar for both alternatives


Dewatering Alternatives(1985 Dollars)


Construction and Implementation

  • Construction Completed 1988

  • Facility start up 1989

    • PFRP Equivalency letter

  • Implementation of TAGRO Program 1992

    • Introduction of TAGRO Mix Blended Product

    • Implementation of Home Delivery Program (for a fee)

    • Continuation of Successful Liquid Program

  • Introduction of Mulch and Potting Soil 2003

  • Introduction of Bagged Product 2005


Dual Digestion Issues

  • Process was not totally autothermal

    • Some digester gas was required for preheating

  • Anticipated BOD loading never materialized

    • Food processors left town

  • Plugging problems with the sludge to sludge heat exchanger

    • Back flushing and grinding was required

  • Odor issues were significant

    • Off gases had to be piped into the O2 decks


Biosolids Recycling Issues

  • Initial Product was very odorous

    • Required a change in operational procedures for the anaerobic digesters and in application timing

  • No significant local market for Biosolids cake

  • Shrinking market for liquid biosolids

  • Required the creation of a new product and development of a new market


Development of the TAGRO Program

  • Give away program began in the 50s

    • small portion of annual production was dried in drying beds and given away

    • Promoted for use in home gardens

  • Agricultural application was the primary use

    • Mostly liquid

    • Some farmers picked up dried product

  • Class A (PFRP) process seen as perpetuating existing program

  • Facility plan relied on agricultural application

    • Begin with continuation of liquid program

    • Develop cake program

  • Reality Intrudes


Adaptation In A Dynamic World

  • Odor issues force changes in the liquid program

    • Reduction from 10% solids to 5-7% solids

    • Application timing adjusted to avoid applying in warm weather and on or near holidays

  • Cake program had market and logistical issues

    • Limited market for cake further reduced by regional controversies

    • Ram eject trailers not properly designed for high density loads (like biosolids)

    • Eventually sold the trailers

  • Rapid urbanization reduced the market and increased the hauling distance for liquid customers

    • Developed forest application program

    • Entered into composting contract with private firm

    • Created new product specifically designed for home garden use


New Markets New Headaches

  • Blended Products required specification for blending agents

    • Sand

    • Sawdust

  • Marketing to the home gardener required:

    • Cultural Revolution

    • Significant commitment to retail marketing

    • Development of credible experts

    • Fanning the flames of the word of mouth conflagration

    • Developing a pricing philosophy and a price structure

    • Attention to Customer Service

  • Marketing to commercial landscapers required:

    • Flexible billing procedures

    • Flexible delivery procedures

    • Attention to customer service


Continuous Improvement

  • Diversification of product Line enhances stability

    • Potting Soil

    • Mulch

    • Green Roof Growing Medium

    • Rain Garden Mix

  • Development of retail outlets

    • Improved distribution

    • Greater market penetration

  • Improvements in Billing and Customer Service

    • Credit Cards


TAGRO Resources

  • Personnel

    • 9 drivers

    • 2 sales representatives

    • 1 program manager

  • Equipment

    • 2 loaders

    • 5 dump trucks

    • 3 soil shredders (various sizes)

    • 1 bagger

    • 3-5 very old liquid distributors

    • 3 6000 gallon tankers


Laboratory Testing

  • Mandated DOE Regulatory Testing

    • Metals every two months

    • Fecals every two months

  • Optional Testing

    • Agricultural sampling every quarter

      • Nutrients

      • C:N ratio

      • Moisture content


DOE Permit Status

  • Obtained PFRP equivalency 1989

    • Multiple thermophilic steps

    • Long term data (salmonella, enteric viruses)


Lessons Learnedand Confirmed

  • Markets and regulations are constantly changing: Evolve

  • Flexibility is your friend

  • Never underestimate the creativity of an operator

  • You will never learn to fly if you if you don’t jump off the cliff


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