Pakenham Sewage Treatment Plant Upgrade

The Pakenham STP upgrade for South East Water included the following works:

• Options study on screening type and performance including contacting every water authority in Victoria to discuss performance and on-site experience with screening issues and “lessons learnt”.
• Design, construction, modelling and reporting of physical modelling using a 1:10 scale model to optimise screen design and operation including baffle/flume design and flow splitting.
• Detailed design of an inlet works upgrade including a 100 L/s relift pump station, 350 L/s Raw Sewage Pump Station, and concept design of maceration at the pump station inlet;
• A 260 L/s capacity effluent reuse pumping station;
• Upgrades and modifications to the existing bioreactor; and,
• New bioreactor tanks including aeration, anoxic and swing zones.

Due to mixing complexities and the particularly aggressive/difficult nature of the incoming sewage, specialised investigation and testing was undertaken including:

• Computational fluid dynamic modelling (3D CFD) of the anoxic/swing zones to optimise mixer sizing, location and tank baffling arrangements.
• In-situ diffuser testing trialling a variety of diffuser materials over a 6 month period. The testing included progressive back pressure trending, cleaning effectiveness and material degradation tests.
• Physical modelling of the inlet works including band screens, step screens and the associated channels/pits.
• 2D effluent modelling of various clarifier energy dissipater inlet arrangements to optimise clarifier performance.

The additional design effort put in “up front” worked well, as South East Water was able to ensure project requirements were well documented and the system was easy and straight forward to initially commission.

Cost Savings: All significant upgrade components were analysed in detail over a range of options to determine the most appropriate option.  The tank height and depth were optimised for capital and operational expenditure.  The cost savings to South East Water were in excess of $1.5M.