Optimising Sludge Dewatering Benefits from Shared Water Services
Optimising Sludge Dewatering – Benefits from Shared Water Services
Porirua wastewater network Serves all urban PCC • Pukerua Bay to Keneperu Includes northern WCC • Tawa, Churton Park, etc Currently about 82, 000 popn. • Significant future growth
Porirua WWTP
Process flow 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 Centrifuges (2 no. ) Sludge to landfill Screened bypass Flows >950 l/s 3 x DWF to full treatment Wet weather bypass Gravity thickeners Centrifuge dewatering Sludge to landfill Waste Activated Sludge to Gravity Thickening tanks Aeration basin 950 l/s capacity 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 2 460 l/s capacity UV treatment 1, 000 l/s capacity To Rukutane Outfall 1, 500 l/s capacity Treated effluent UV bypass 1, 500 l/s capacity Clarifier 3 620 l/s capacity
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
WWTP Issues Identified Range of operational issues at the plant: 1. Poor dewatering system performance 2. Poor WAS/RAS control
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
Dewatering Issues 1. 2. 3. 4. Centrifuge performance – Cake: 13%DS; 33% capture rate Polymer system dosing limitations O&M process documentation Bin removal by 3 rd party during Landfill operating hours Existing Powder Polymer Left: Jar Test showing poor floc structure Right: ‘Dirty’ Centrate
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
Dewatering Improvements: Emulsion Polymer Powdered polymer Emulsion polymer
Value for Money Chemical cost analysis versus increased solids disposal to landfill Powdered polymer Emulsion polymer
Other Dewatering System Improvements Forklift for bin handling Control system modifications PRV’s on polymer dosing pumps
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
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
Current work Projects include: • Further thickener optimisation • Operator training • Aquen trial • Biosolids treatment options
Summary Working with landfill operation Benefits of wider operations pool Value for money achieved
Acknowledgements WWTP operators GEA Westfalia IXOM suppliers Add graphic – photo from trials - Amy?
Contact: mike. binns@wellingtonwater. co. nz
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