Nebo Township Water Treatment Plant

Our Solution

Dowdens were successful in the tendering process due to:

• The proximity of Dowdens head office in Mackay and long term presence in the region.
• Dowdens in-house engineering capabilities and proven track record of delivering high-quality water/wastewater treatment infrastructure.
• High level of detail provided in the preliminary engineering proposal.
• Tailoring a specific solution to suit the client’s needs.

The new plant increases the Towns water treatment capacity from 400kL/day to 2ML/day with a peak output of 90kL/Hr (26L/s). A superior level of water treatment is achieved using filtration, softening and Chlorine / UV disinfection processes.

The Nebo Water Treatment Plant consists of raw water tanks (2 of ), glass media filters (6 of ), ion exchange vessels (3 of ), a 10kL brine tank (1 of ), ultraviolet disinfection units (2 of ),
chemical dosing systems (NaOH and chlorine gas) and associated tanks, pumps and water quality monitoring instrumentation.

Raw water is produced by the existing borefield, made of 6 separate bores, and transferred to the site via an isolated borefield network. The raw water is then stored on-site in the raw
water tanks, which act as a buffer (1 – 2 hours) for the main water treatment plant process, the Filter Feed System, which consists of the glass media filters, the ion exchange vessels and the ultraviolet disinfection units.

The raw water is pumped to the glass media filters to reduce the turbidity of the raw water by removing most of the suspended particles that are greater than 1 micron. The GMF filtrate is then partially softened, by utilising a modulating control valve installed in the IX by-pass, to a target treated total hardness level.

If required, prior to the ultraviolet sterilisation units, the IX filtrate can be dosed with diluted sodium hydroxide to increase the final treated water pH prior to storage in the 2 ML treated water tank.

The IX filtrate, now partially softened (and potentially pH corrected), is disinfected via a large low-pressure UV unit that monitors the instantaneous UVI and modulates the duty units
output based on the known flow to ensure the minimal level of disinfection is achieved.

The now sterilised water produced by the main water treatment process is disinfected with super-chlorinated water produced by a proportionally controlled chlorine gas dosing
system. This is the final process step before the treated water enters the 2 ML treated water tank.

The water stored in the 2 ML treated water tank is constantly recirculated with the residual free chlorine levels monitored and automatically topped up as required.

Plant completely Automated

The new WTP is completely automated and user-adjustable via the CITECT SCADA Computer System. Operators receive alarms remotely and can log into the plant and take control without the need to set foot on site. If operators need to attend the site they can open/close the main access gate through an application on their phone via the 3G Enabled Security System. The system logs the date/time of entry and the operator who was present.

Dowdens coordinated the design, build and commissioning of the WTP from project inception through to final handover. This included, but was not limited to:

• Preliminary and detailed design including 50, 75 & 100% Design Review Meetings;
• Combined Safety in Design / HAZOP Workshop;
• Preliminary civil works establishing the site including importing and compacting fill to achieve design levels.
• Under boring Airstrip Road for installation of raw water pipeline;
• Installation of all underground services;
• Pouring of slabs;
• Construction of the following buildings:
  • Block Render Site Office & Workshop
  • Main WTP Steel Building
  • Block Salt Storage / Brine Building
  • Block Chlorine Building
  • Steel Pump Station Roof Structure
• Installation of process equipment;
• Installation of all interconnecting pipework;
• Electrical installation of control panel and field instrumentation/equipment;
• Commissioning of instruments / equipment / PLC program and SCADA.
• Successful completion of ‘Proof of Performance’ testing and all necessary operator training.