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 EVALUATION Cost Analysis in 1985 Dollars AlternativeCapital Cost Annual O&M Structure Salvage Total Present Worth Rank Dual Digestion$17.0 M$0.063 M$ 0$17.56 M 1 Anaerobic Digestion$19.1 M$0.045M$0$19.57 M 2

NON ECONOMIC FACTOR MATRIX AlternativeReliabilityGas Production Reliability /Stability Odor Potential Product Acceptability Ease of Construction Dual Digestion+Higher gas yield BestlowerBetter Acceptance Neutral Anaerobic Digestion NeutralLower gas yield WorstHigherAcceptanceNeutral

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) AlternativesCapital Cost O&M Costs Total Present Worth Rank Filter Press (Plate and Frame?) $52.9M$0.4M$56.8M 3 Centrifuge$19.7M$0.36M$23.1M 2 Belt Filter Press $4.5M$0.56M$9.9M 1

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 – 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 Learned and 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