The Western Treatment Plant (WTP) treats approximately 52 per cent of Melbourne’s sewage, a total of approximately 485 million litres/day using a sequential activated sludge-lagoon (AS-lagoon) process. WTP employs two AS-lagoon systems (25W and 55E) from which the treated water is transferred to the head of the road storage pond (HORS) where it is disinfected prior to use as recycled water. The HORS can be supplied with treated water from either 25W, 55E, or a mixture of water from both systems. Melbourne Water currently supplies recycled water from WTP for various on-site and off-site uses and is working towards future schemes to meet the State Government’s target of 20 per cent water recycling by 2010.
The salt level (1,800 μS cm-1) is a limiting factor to the long term sustainable use of the recycled water and requires ongoing management; the State Government has committed to reducing this salt level by 40 per cent. Trials have demonstrated that microfiltration (MF) or ultrafiltration (UF) can be used to pre-treat the effluent from the WTP prior to salt reduction via reverse osmosis (RO), however, it was observed that membrane fouling was a potential problem.
Since the effluent from WTP contains algae and algal products from the lagoon process, as well as some residual products from the AS process, the resultant membrane fouling may be more problematic and differ from that arising from separate AS and lagoon processes. Membrane fouling leads to a decline in membrane permeability and thus reduces throughput and water recovery.
The aim of this project is to develop an effective and practical strategy to overcome the MF and UF fouling problem which will support the future design and operation of a membrane salt reduction plant (MSRP) at WTP with high water recovery.