1. Optimising Sludge Dewatering – Benefits from Shared Water Services

2. 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

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

4. 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

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
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

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
Around the time Wellington Water operations units were establishing Spicer Landfill was experiencing some serious challenges

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

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

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

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

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

15. 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

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

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

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