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Maximizing Energy Efficiency in Wastewater Treatment: A Case Study at Milwaukee Metropolitan Sewerage District

Explore how MMSD is reducing energy costs and carbon footprint through bio-gas conversion, digester mixing, and high strength waste receiving. Learn about current projects and future opportunities for sustainability and cost savings.

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Maximizing Energy Efficiency in Wastewater Treatment: A Case Study at Milwaukee Metropolitan Sewerage District

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  1. Bio-Gas in the Wastewater SectorMilwaukee Metropolitan Sewerage District Kevin Shafer, PE Executive Director

  2. 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.

  3. 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

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

  5. SSWRF Digester Mixing • Existing mixing system not effective ~ 40% VSR. • Goal is to achieve 55% to 60% VSR. • Increase gas production ~ 325,000 ft3/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

  6. SSWRF Digester Mixing

  7. 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 ft3/da digester gas. • Value of additional gas > $50,000/yr • Minimum increase in digested biosolids

  8. SSWRF High Strength Waste Receiving

  9. Summary • Current Renewable Energy Projects • ~ 400,000 ft3/da digester gas • ~ 0.9 MW (7,884,000 kwh/yr) • ~ 1300 WI houses • Future Opportunities • Digester feed thickening • Others will be identified

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