Western Treatment Plant (Werribee) - 12 October 2009 • largest sewage plant by land size in the world - 11,000 hectares • first build in 1890 • the area chosen because it the lowest lying area, which allows for gravity feed • they used to use land filtration where sewage was placed over the land - flooded to a depth of 10 cm • delta soils • rain shadow (You Yangs) • rye grass • 2nd largest beef cattle industry; no dairy due to heavy metals getting into milk (Beryllium, Mercury, Zinc) • receives 420 million litres of sewage a day • 30% comes from industry, 50-60% from domestic and 10% from infiltration of rainwater/stormwater (illegal connections) • they have trade waste agreements now • salt from industry causes problems for water recycling - from cleaning products as well as salt used in industrial processes - 250 mg limit - they are looking at salt filtering • less water content now due to residential water conservation measures • 2 pumping stations 35000 litres/second - pumping stations 'chop up' the sewage • it takes 8 hours to make its way to the plant - they have a 'high tide' in the afternoon • EPA license means they shall have no odours off site • Odour controlled through 10 bio-gel columns that draw up hydrogen sulfide and then a tall chimney • Calcium nitrate in added into the system to prevent anearobic conditions which generates hydrogen sulphide • a lot of the odours residents report actually come from Geelong • biosolids are dredged out of ponds (plastic ends up there) and stockpiled in the middle of the site - they are still working out what to do with this stockpile • phyto-remediation trials are happening for dealing with the stockpile - however the technology comes out of Nthn hemisphere and they are not keen in introduce species - they want to find natives to do the job • the waste treatment plant has a 40 day turn around time (40 days for sewage to be processed by the plant and Class-A water to be released at other end) • disinfection plant on site ◦ takes class C water and turns it into class A water for community use (20% of input) for irrigation and schools - some suburbs have dual reticulation (purple pipes) but they are finding it hard to keep up with the demand ◦ storage dam under black tents - chlorine injection (concentrated chlorine) with the 'just right' dosage. 8 or more times more chlorine as used for drinking water ◦ UV sterilization • grass filtration may also be used in the future • $60 billion upgrades currently - wet weather upgrade • Each lagoon has 10 ponds each 200 x 1500 m, 6 m at deepest • underneath the membrane - anerobic bacteria break down the organic carbon • acidogenic bacteria break down short chain fatty acids • methanogenic bacteria bread down to CO2 and methane • 5% nitrogen, 5% sulphur hydroxide • black covers help heat up the pond which enhances the process as well as catching biogases - it is polyethylene foam with a protective plastic layer. gases collect between the foam and plastic layer and are drawn off to the biogas generator • 2 generators on site - with scrubbers to remove hydrogen sulphide