Warkworth wastewater treatment peak flow upgrade update
Veolia Systems has won the contract to supply a peak flow treatment system, which will be installed and commissioned before December 2008, as required by the new resource consent.
Also associated with the upgrade will be a Timbertank (ex Tindall’s Bay reservoir), which is required as the buffer tank for the plant, and a new ultraviolet disinfection unit, to operate in parallel with the existing one.
Currently, when high flows are received (due to the high inflow and infiltration of stormwater into the wastewater system) for a lengthy period of time (not just a short, sharp shower), the aerators are turned off and solids allowed to settle. The wastewater is still processed through the entire plant, including ultraviolet treatment, except in an extreme event when the present ultraviolet unit does not take the flow and is bypassed.
The peak flow treatment system is designed to operate when the treatment plant receives high flows during heavy rain events and will mean that the existing system can continue to operate in parallel. The system will be ready to go when the rain event occurs, and starts up very quickly. The effluent quality produced by the Actiflo is not as good as the normal effluent—it uses a chemical process, rather than a biological one, meaning that there is still a lot of dissolved organic material in the effluent.
The key drivers in Warkworth’s case are to protect downstream shellfish farms and bathers and therefore efficient ultraviolet light disinfection (to destroy bugs, bacteria and viruses) of all the effluent is required. In order to achieve this effluent needs to have good clarity and low solids content (light can’t get through solids to destroy bugs). The Actiflo achieves this.
As far as infiltration and inflow of stormwater is concerned, Rodney District Council’s number one priority is to sort out Warkworth’s problems and the council is actively progressing with the program of identifying problems (on public and private systems) and making sure they are fixed.
Mahurangi Wastewater Strategy
Harrison Grierson has been commissioned to assist Rodney District Council with the Mahurangi Wastewater Strategy. The first stage of the process underway is to collect and refresh all the information that needs to be pulled into the strategy such as population projections, growth areas, transport issues, Mahurangi Action Plan, marinas, technology, monitoring etc. NIWA are to prepare quantitative microbial health risk assessments using the Monte Carlo model (used for Christchurch) for Warkworth and Snell–Algies receiving environments based on scenarios that Harrison Grierson will establish as options for future servicing. Obviously, reuse of as much of the wastewater is desirable but modelling must be based on the worst case.
For more information, or to provide feedback, contact
Jo Floyd wastewater consent engineer
Rodney District Council
DD 09 427 3395 Ph 09 426 5169 Fax 09 426 0219
See also letter to the Mahurangi Magazine