Western Treatment Plant Werribee

Western Treatment Plant (Werribee) - 12 October 2009 • • • • • • • • • • • • • • • • • • • • • • •

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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

• clark Energy (AGL) runs the generators - they buy the methane from the treatment plant and the treatment plant buys back the electricity • 60-70% of the power needs of the plant are met by methane production • 52 GWh p.a. • able to hold gas for 8 hours to allow for electricity production at peak times (electricity worth more then) - there are some issues with distributing the electricity safely • they flare the excess methane (turns it into 25 times less harmful CO2) - up to 1/3 of the gas is flared currently • undercover dredging -> biosolids -> drying pans -> dump (stockpile) • aerators - facultative zone? - anaerobic to aearobic bacteria • 8 MW generators + 2 MW added in 6 months • lagoons are a harsh environment for metal - hydrogen sulphide • activated sludge plant - remove nitogen - aerobic and anoxic site - nitrifying bacteria (urine) nitrites -> nitrates. denitrafying bacteria in adjacent pond -> nitrogen released to atmosphere. High carbon required to maintain the bacteria leads to the 'brown colour'. Clarifier used -> heavy sludge sinks • 31,000 tonnes of Nitrogen is allowed to be released into Port Phillip Bay (supports food for marine life) • sterilization - ponds are shallow, zoolankton, algae (nitrogen feeders) and sunlight kills pathogens • currently dams are recording 40% of their 100 year average - dire situation. • If you drew a line between Kew and CBD, everything west of that goes to Western Treatment Plant (rest goes to Eastern Treatment plant) Pond 1 - anaerobic zone 1-2 days, solids settle -> methane. Covered with membrane -> 20,000 m3 of methane / day. 70% moves to aerobic zone. 30% activated sludge basin (pond 5). in aerobic for 5 days. activated sludge basin - excess bacteria from pond 1 used to encourage additional nitrification of sewage carbon matherial (pond 1) for activated sludge basin denitrification pond 4 back to pond 1 increase oxygen level and reduce odour emissions sewage works its way through the 10 ponds of each lagoon in a zig zag motion e.g. pond 1 has outlet to pond 2 at top, pond 2 outlet to pond 3 at bottom... clarifiers at pond 4 pond 5 is activated sludge basin ponds 5-10 algae and zooplankton from pond 10 it goes to port phillip bay Better description of how the lagoons work by visiting http://education.melbournewater.com.au/content/sewage_and_recycling/ western_treatment_plant/western_treatment_plant_explorer/ western_treatment_plant_explorer.asp# and running the explorer, clicking skip and then clicking on lagoon 55 east. http://www.melbournewater.com.au/content/sewerage/western_treatment_plant/ western_treatment_plant.asp?bhcp=1