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TACOMA DUAL DIGESTION

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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  1. TACOMA DUAL DIGESTION A Tail of Adoption and Adaptation

  2. 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

  3. ECONOMIC EVALUATIONCost Analysis in 1985 Dollars

  4. NON ECONOMIC FACTOR MATRIX

  5. 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

  6. Dewatering Alternatives(1985 Dollars)

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. DOE Permit Status • Obtained PFRP equivalency 1989 • Multiple thermophilic steps • Long term data (salmonella, enteric viruses)

  17. 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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