Bio-Gas in the Wastewater Sector Milwaukee Metropolitan Sewerage District Kevin Shafer, PE Executive Director

Current MMSD Energy Situation Summary Energy costs are significant to MMSD. MMSD has significant carbon footprint. Natural gas is most significant energy source: Financially BTUs Carbon footprint Reductions in energy use can save money.

Purchased Energy Energy Budget (2011): ~$13M 16% of O&M budget By Cost: 70% gas, 30% electricity By BTU: 90% gas, 10% electricity Total BTUs purchased at WRFs is ~10,000 Wisconsin residential homes

South Shore WRF Biogas BioGas converted to electrical power by Engine Generators. Air Used in Secondary Treatment Heat Used in Digestion Process Biosolids can be Transferred via 11-mile Pipeline.

 Existing mixing system not effective ~ 40% VSR.  Goal is to achieve 55% to 60% VSR.  Increase gas production ~ 325,000 ft 3 /da Additional ~ 1.4 MW on-peak power generated Value of increased gas production ~ $300,000/yr Additional heat recovery from engines for digesters  Reduce biosolids mass ~ 18%  Increase effective capacity of digesters  Mixing technologies to be evaluated in design  Pump and nozzle (good mixing, higher energy)  Linear motion (fair mixing, less energy)  Bid October 2012 Complete 2016 SSWRF Digester Mixing

SSWRF High Strength Waste Receiving  Digester capacity increased with mixing project.  Industrial wastes fed to digesters to make gas.  Revenue for taking industrial wastes  Airport deicing waste has been fed for ~ 10 years.  HSW Receiving Facilities include:  Receiving station (AgriLife loadout station)  Storage (Modify existing tank)  Grinders and pumping (New)  Goal is > 60,000 ft 3 /da digester gas.  Value of additional gas > $50,000/yr  Minimum increase in digested biosolids

SSWRF High Strength Waste Receiving

Summary  Current Renewable Energy Projects  ~ 400,000 ft 3 /da digester gas  ~ 0.9 MW (7,884,000 kwh/yr)  ~ 1300 WI houses  Future Opportunities  Digester feed thickening  Others will be identified