What Can Biosolids Do for You? Shifting towards Solids as an Energy Resource Eric Auerbach, ARCADIS Thomas Kunetz, Metropolitan Water Reclamation District of Greater Chicago Rob Van Evra, City of Columbus Division of Sewerage and Drainage Dave Comeford, Buffalo Sewer Authority MWEA Conference, Boyne, MI June 24 th, 2014
A Shift in Thinking Wastewater treatment plants are not waste disposal facilities, but rather water resource recovery facilities that produce clean water, recover nutrients, and have the potential to reduce the nation s dependence upon fossil fuel through the production and use of renewable energy. -WEF Position Statement, Oct 2011 Wastewater Treatment Plant (WWTP) Water Resource Recovery Facility (WRRF)
Different Levels of Solids/Energy Management Advanced Maximize Biogas Generation Combined Heat and Power (CHP) Generation Optimal Utilization of Waste Heat Produce Usable Products from Final Solids Approaching Energy Neutrality Traditional Typical Biogas Generation Burn Biogas for Heating and/or Incineration Flare Excess Biogas in Summer Final Solids Disposed as Waste Large Energy Consumption and Cost
Three Utilities Looking to be More Advanced City of Columbus Division of Sewerage and Drainage (Columbus DOSD) Metropolitan Water Reclamation District of Greater Chicago (MWRD) Buffalo Sewer Authority (BSA)
Thinking About Solids as Energy Coal Boiler Sludge Incinerator
Heating Value of Sludge Heating Value Substance [mmbtu/ton dry solids] Raw Primary Sludge 1 20-25 Waste Activated Sludge 1 17-20 Digested Primary Sludge 1 8-12 Bituminous Coal 21-28 Lignite 14 1. Metcalf and Eddy, 1991 Raw Sludge is energetically equivalent to standard coal Digested Sludge is equivalent to lignite or low grade coal
Thinking About Energy at a WRRF Chemical Energy In Solids Water Content Volatile Content and Digestibility Energy Content of Volatiles Biogas Treatment Contaminant Removal Pipeline Gas Production Vehicle Fuel Production Electrical Generation Electric Production Efficiency O&M and Availability Partial Load Performance Varying Forms of Waste Heat Heat Utilization Seasonal Plant Heat Demands Steam vs Hot Water Heat for Solids Drying Recovery from Incinerators
Quantitative Model Planning Step Sludge Digester Gas? Plant Heating Boilers Solids Drying Cogeneration Natural Gas Plant Heat Demand Plant Electric Demand Power Plant
Case Study 1 City of Columbus Division of Sewerage and Drainage Columbus, OH
Columbus Treatment Plants Southerly (SWWTP) Avg Flow = 100 MGD Solids Production = 80 dtpd Jackson Pike (JPWWTP) Avg Flow = 80 MGD Solids Production = 65 dtpd
Wide Variety of Solids Treatment Options Southerly Dual Phase Meso Digesters Completed in 2010 Solids Disposal Mostly in Incinerators Some to Compost Facility Landfilling Available Jackson Pike Single Phase Meso Digesters Only Digested 25% of WAS 3 rd Party Solids Offtake Contract Solids Disposal Mostly in Incinerators Some to Land Application Landfilling and Compost Available Biogas Utilization at Both Plants Mostly in Incinerators Boiler Heating Flares
Driver for Energy/Solids Planning Solids Master Planning in 2008 Mayor s Climate Protection Agreement - reduce regional GHG emissions to 7% lower than 1990 WWTPs identified as target improvement areas beneficial reuse of digester gas Quantitative mass/energy flow model developed with The Ohio State Center for Resiliency
Percentage of Baseline Modeling Questions Posed Digesters Single / Dual Phase Meso / Thermophillic WAS lysis Solids Disposal Incineration Land Application Compost Land Fill Biogas Utilization Sell Raw Gas Cogeneration Flares Example of Results 160% 140% 120% SWWTP Optimized Baseline Results Baseline Min Total Cost - 100% INC, 0% COMP, 0% LANDF Min Variable Cost - 45% INC, 55% COMP, 0% LANDF Min Energy/GHG - 27% INC, 46% COM, 27% LANDF 100% 80% 60% 40% 20% 0% Cost ($) Energy (MJ) GHG FF (MT CO2)
Recommendations Pilot WAS lysis for digestion at JPWWTP De-emphasize incineration and expand land app/compost Look to sell raw DG or clean to NG quality Plan for a CNG facility in the future
What Are they Doing Now? Trending towards less incineration More solids to compost facility Expanded land application Only seasonal incineration as needed Expand biogas utilization Currently used for incineration and plant heating More gas available as incineration trends down 3 rd party solicitation for biogas utilization in progress
Case Study 2 Metropolitan Water Reclamation District (MWRD) Chicago, IL
Stickney Water Reclamation Plant (SWRP) Lake Michigan Chicago Stickney Avg influent flow = 750 MGD Receives sludge from another 250 MGD plant (via pipeline) Solids Production = 430 dtpd Biosolids drying facility located on site 3 rd party operator
Driver for Energy/Solids Planning Potential for major increase in biogas production Planned Capital Improvements Replace Imhoff tanks with Primary Settling Tanks Upgrade Sludge Thickening Facilities Potential to double future biogas Current = 3.4 million cf/d Future Projection = 6.7 million cf/d MWRD wants to prepare to utilize this influx of additional biogas
Questions Posed Where should the biogas go? Cogeneration Onsite Solids Drying What type of prime mover? Engines Gas Turbines Steam Turbines How to size cogeneration? Large swings in seasonal heat demands Should supplemental natural gas be used Iterative gas supply/heat demand calculation
Quantitative Modeling Step Developed Energy Flow Model tool Interactive user interface Tracks energy flow through plant processes Gives quantitative results to facilitate decision making Digester Gas? Plant Heating Boilers Solids Drying Facility Cogeneration Natural Gas Plant Heat Demand Plant Electric Demand Power Plant
Energy Flow Model Outputs = Annualized Cost, GHG Reduction, Energy Efficiency
-$1,314,000 -$124,830 Annualized Scenario Cost [$] $1,910,461 $1,777,148 $2,052,632 $1,532,764 GHG Reduction [MT eco2] / Unused Energy [10 mmbtu] Example Energy Flow Model Results $3,000,000 Annualized Scenario Cost [$] GHG Reduction [MT eco2] Unused Energy [mmbtu] 150,000 $2,000,000 100,000 $1,000,000 50,000 $0 0 -$1,000,000-50,000 -$2,000,000 Natural Gas ($6/mmBtu) Electricity ($0.08/kWh) -100,000 Scenario Estimated net savings from cogeneration ~ $3 million/year Estimated GHG reduction ~ 30-60 thousand MT CO 2 /year (6-12 thousand cars removed from the road)
Recommendations - Biogas Utilization Send biogas to cogeneration Larger economic returns for cogeneration Engines or Steam Turbines as prime movers Heat recovery and plant heating systems important Fluctuation in energy prices heavily influenced economics Size cogeneration to use max (summer) biogas supply Supplement natural gas in winter to operate at full capacity
What Are they Doing Now? MWRD Energy priced bottomed out Bulk PPA for electric at ~ $0.055/kWh Natural gas prices at ~ $4-5/mmBtu 3 rd party solicitation for biogas utilization Includes gas utilization from Calumet WRP (another 300 mgd plant) Calumet WRP in progress Stickney WRP expected fall 2014
Case Study 3 Buffalo Sewer Authority (BSA) Buffalo, NY
Bird Island WWTP Avg influent flow = 180 MGD Solids Production = 65 dtpd Single Phase Mesophillic Digesters Solids Disposal in Incinerators Three MH incinerator units 60 dtpd capacity per incinerator
Driver for Energy/Solids Planning Regionalization of Incineration Facilities Capital Improvements to Incinerators Cake Receiving Facility New Burners and ID fans Increase Capacity and Efficiency Import Sludge from Outlying Communities Current Import = 15 dtpd Looking to take on more import sludge BSA wants to find the most economical way to operate their improved incinerator facilities.
Questions Posed What mix of solids to get autogenous burn? PS/WAS/Digested Addition of import sludge Where to send the sludge? Send to digesters to make biogas? Add directly to the incinerator? Is exhaust heat recovery viable? Waste heat recovery boilers Cogeneration with extraction steam turbine
Quantitative Modeling Step Used Energy Flow Model methodology Determine optimal way to route solids/energy resources
Energy Flow Model Outputs = Annualized Cost, GHG Reduction, Unused Energy
Recommendations Send plant generated sludge (PS/WAS) to digesters Centrifuging undigested solids energetically unfavorable Import sludge could go either way Energetically the same between digester or direct incineration Route import sludge based on ease of operations Autogenous burn will be difficult to achieve Significant operational changes needed (not just import addition) Heat value of volatiles very important (need sampling plan) Steam turbine CHP system viable Payback period of ~ 8 years Generate ~ 2 to 3 MW of electricity Extract steam to heat the entire plant
What are they Doing Now? - BSA Accepting Import Sludge at ~11 dtpd Looking to take on more sludge from other outlying communities Implementing incinerator heat recovery and steam turbine in fall 2014
Final Takeaways Plant Influent Solids = Energy, just like coal going to a boiler A quantitative model planning step is useful way to understand the energy interactions within your system and guide decision making Energy prices drive economic performance and can change significantly between the planning and implementation phase
Questions Eric Auerbach eric.auerbach@arcadis-us.com Special Thanks To: Rob Van Evra Thomas Kunetz Jarek Fink-Finowicki Dave Comerford James Keller