Organics Workshop- Mixed Organic Streams as Feedstock & Products: Andrew Carpenter, Northern Tilth makes the case for utilizing biosolids as a way to reduce waste and put nutrients back into the earth.
Organic NOrganic C(energy source)MicrobialactivityNO3-N assimilationN MineralizationOrganic Matter Transformations in SoilMature Soil Organic Matter(Soil Humus)C assimilationPlant-availablenitrogen in a slow-release form• Improving soil fertility throughthe addition of organic matter-based residuals is a primary tenetof sustainable agriculture– Healthy soil ecosystem– Long-term pool of soil nutrients– Reduced erosion– Feeding soil not just crops
The Value in BiosolidsOrganic MatterIn Soil•Food for soil microbes•Builds Soil Tilth•Erosion Resistance•Water-holding capacity•Ability to retain nutrientsMacro-Nutrients•Nitrogen (5%)•Phosphorus (2%)•CalciumMicro-Nutrients•Zinc•Copper•MolybdenumNutrientsFor Energy Recovery•Energy in the chemical bonds of organicmatter•9,300,000 Btu/metric ton of biosolidsavailable through anaerobic digestionOrganic Matter
6.5 Million Dry Metric Tons of Municipal WastewaterSolids Generated Annually in the U.S.Level of Treatment•60% Class B•40% Class AData excerpted from National Biosolids Regulations, Quality, End Use and Disposal Survey, 2007 (2004 data)
Overall Trends in Wastewater SolidsManagementThe amount being recycled to soils versus theamount going to landfills or to incinerationappears to have been steady from the mid1990s through 2004
Greater Lawrence Sanitary District, MassachusettsBenefits•Digester Gas is used as fuel for the dryer•Solid market for the biopellets•Selling for between $15 - $25 per ton (worth closer to $50 per ton fornitrogen and phosphorus replacement alone)•Value has increased with the recent rise in fertlizer prices•General distribution no site-specific permitting
Triclocarban: Anexample of a personalcare product in biosolidsInfluentEffluentBiologically DegradedCompounds CO2 and H2OWastewaterWastewater SolidsSolubleCompoundsNutrients OrganicMatterInsoluble, non-volatile compoundsTriclocarban in anti-bacterialsoap 15,000 ppmTriclocarbanTriclocarban inbiosolids 30 ppm(450 X lowerconcentration thanin the soap)
Opportunities in the Future• Assumptions– 30% of U.S. wastewater solids are landfilled, and half of the 15%of solids incinerated have no associated energy recovery 2.4million dry Mg/year not utilized– All of this would instead go to anaerobic digestion and theanaerobically digested biosolids would be land applied– 75% volatile solids on a dry wt. basis– 60% volatile solids reduction during anaerobic digestion– 75% of nitrogen eventually available for plant uptake– 0.485 gallons of fuel oil used per kg of nitrogen fertilizer produced– 40% plant availability of phosphorus in biosolids• 650,000,000 m3 of natural gas use avoided• 90,000 Mg/year of nitrogen fertilizer use avoided– Additional savings of 44,000,000 gallons of fuel oil• 42,000 Mg/year of phosphorus fertilizer (as P2O5)use avoided
Combined Scenarios(each scenario includes thickening, de-watering and transport)-50000500010000150002000025000CO2Equivalence(Mg/year)transportEnergy recoveryCold wet climate800oC25% solidsDigested solidsNo recovery65% heat30% elect.1% fugitiveLandfillIncineration1Incineration2900oC30% solidsundigestedEnergy recoveryCementreplacementClassAAlkalineLandApClass A usingrecycled limesource such asCKDAnaerobicdig.Landap
Concluding Remarksandrew@northerntilth.com• Use It or Lose It!