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Optimising Sludge Dewatering – Benefits from Shared Water Services

Explore the optimization strategies implemented in the Porirua wastewater network serving urban areas, with significant future growth and modern facilities ensuring effective treatment and disposal of sludge. Learn about dewatering improvements and operational enhancements enhancing overall system performance and compliance.

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Optimising Sludge Dewatering – Benefits from Shared Water Services

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  1. Optimising Sludge Dewatering – Benefits from Shared Water Services

  2. Porirua wastewater network Serves all urban PCC • PukeruaBay to Keneperu Includes northern WCC • Tawa, Churton Park, etc Currently about 82,000 popn. • Significant future growth

  3. Porirua WWTP

  4. Maximum pumped inflow currently 1,130 l/s Milliscreens (4 no.) hydraulic capacity 1,590 l/s Screenings to landfill Emergency bypass 1,500 l/s capacity Process flow Centrifuges (2 no.) Sludge to landfill Screened bypass Flows >950 l/s Waste Activated Sludge to Gravity Thickening tanks Aeration basin 950l/s capacity 3 x DWF to full treatment Wet weather bypass Gravity thickeners Centrifuge dewatering Sludge to landfill Aeration Basin Return Activated Sludge to Aeration Basin Outlet weir Clarifier 1&2 Return Activated Sludge pump stations (3 no.) Clarifier 1 460 l/s capacity Clarifier 3 620 l/s capacity Clarifier 2 460 l/s capacity Treated effluent UV treatment 1,000 l/s capacity UV bypass 1,500 l/s capacity To Rukutane Outfall 1,500 l/s capacity

  5. Forming Wellington Water Capacity Infrastructure Services • WCC & HCC formed in 2004 • UHCC joined 2008 • PCC joined Nov 2013 PCC in-house operation Treatment plant and pump station operations Wellington Water formed Sept 2014 • GW Bulk Water & Capacity

  6. WWTP Issues Identified Range of operational issues at the plant: Poor dewatering system performance Poor WAS/RAS control

  7. Sludge Disposal Challenges Landfill odour complaints Abatement notice June 2015 Mixing ratio issues Consent minimum 5:1 Waste volumes decreasing Delivery timing “Fresh” bins required Landfill operating hours Limit of 600 wet tonnes/month

  8. Dewatering Issues Centrifuge performance – Cake: 13%DS; 33% capture rate Polymer system dosing limitations O&M process documentation Bin removal by 3rd party during Landfill operating hours Existing Powder Polymer Left: Jar Test showing poor floc structure Right: ‘Dirty’ Centrate

  9. Polymer Trials Jar-tested a range of polymers Full-scale testing of emulsion polymer: Vastly improved floc structure Capture rate >80% , cake quality >18%DS

  10. Emulsion polymer Powdered polymer Dewatering Improvements: Emulsion Polymer

  11. Emulsion polymer Powdered polymer Value for Money Chemical cost analysis versus increased solids disposal to landfill

  12. Other Dewatering System Improvements Forklift for bin handling Control system modifications PRV’s on polymer dosing pumps

  13. RAS / WAS upgrade Clarifier 3 added in 2012 • Modern design • Common RAS/WAS station System balance issues Sludge blanket control Variable thickener feed RAS/WAS upgrade 2015 Dedicated pump stations

  14. Progress in 2016 Focus on MLSS in aeration basin Dewatering system limited by landfill operation Minimal centrifuge redundancy Playing ‘catch-up’ on solids removal from site Thermal dryer investigation

  15. Current work Projects include: Further thickener optimisation Operator training Aquen trial Biosolids treatment options

  16. Summary Working with landfill operation Benefits of wider operations pool Value for money achieved

  17. Acknowledgements WWTP operators GEA Westfalia IXOM suppliers Add graphic – photo from trials - Amy?

  18. Contact: mike.binns@wellingtonwater.co.nz

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