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 Extent of catchment Serves two city council areas Original discharge location Rukutane point Full treatment added in 1989

Porirua WWTP Plant commissioned 1989 A number of upgrades over the years: New milliscreens 20xx New centrifuges 2006 New clarifier 2012 New blowers 2013?

Process flow 3 x DWF to full treatment Wet weather bypass Emergency bypass 1,500 l/s capacity Aeration basin 950 l/s capacity Screened bypass Flows >950 l/s Waste Activated Sludge to Gravity Thickening tanks Centrifuges (2 no.) Sludge to landfill Aeration Basin Maximum pumped inflow currently 1,130 l/s Milliscreens (4 no.) hydraulic capacity 1,590 l/s Screenings to landfill Return Activated Sludge pump stations (3 no.) To Rukutane Outfall Clarifier 1 460 l/s capacity UV treatment 1,000 l/s capacity UV bypass Clarifier 2 Clarifier 3 620 l/s capacity Return Activated Sludge to Aeration Basin Treated effluent Outlet weir Clarifier 1&2 3 x DWF to full treatment Wet weather bypass Gravity thickeners Centrifuge dewatering Sludge to landfill Schematic process flow diagram Sludge system shown in brown WAS to gravity thickeners GT’s direct to centrifuges Centrifuges to modified skip bins Dewatered sludge to Spicer landfill

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 The plant had been operated in-house by PCC staff since commissioning Wellington council water services units merging since 2004 – HCC/WCC, then UHCC, then PCC Capacity had limited operational capability, other wastewater plants contracted out Wellington Water formed in September 2014 by merging GW bulk water unit with Capacity. GW bulk water operated the four regional potable water plants in-house, brought significant operations capability with them

WWTP Issues Identified Range of operational issues at the plant: Poor dewatering system performance 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 Around the time Wellington Water operations units were establishing Spicer Landfill was experiencing some serious challenges

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 Key staff turnover Main challenges were identified by ex-GW operations (Noel & Jeremy) as:

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 Good performance, given the ‘jerry-rig’ nature of the full-scale dosing trials (making up the emulsion polymer etc)

Dewatering Improvements: Emulsion Polymer Powdered polymer Emulsion polymer Obvious benefits in landfill costs

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 Shows importance of solids volume reduction prior to removal from site (i.e. drying) for more flexibility with disposal route

Current work Projects include: Further thickener optimisation Operator training Aquen trial Biosolids treatment options Operator training to better understand effects from poor performance of thickening and dewatering system

Summary Working with landfill operation Benefits of wider operations pool Value for money achieved VFM also provided a net increase in solids removal offsite

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

Contact: mike.binns@wellingtonwater.co.nz