The first activated sludge plant built in 1932, followed by additional streams
in the 1950s and 1970s. Today the facility consists of three separate but
interconnected activated sludge plants catering for over 200 000 people. Each day it
treats 55 million litres of household and industrial wastewater.
The wastewater is drained from a 9 200 hectare area bounded by West Beach,
Seacliff, Coromandel Valley, Mitcham and Hindmarsh and reaches the treatment plant
via the Glenelg and West Beach Pumping stations.
The incoming wastewater from the drainage area passes through bar screens that
remove the large suspended matter. There are five automatically raked screens,
controlled by limiting upstream water level. The screenings are dropped into large
bins and collected daily for disposal at a landfill.
The screened wastewater then passes through grit removal tanks where sand, gravel
and other heavy inorganic heavy solids are removed and deposited in collection bins
also for disposal at a landfill. The degritted sewage is the preaerated to increase the
oxygen content and improve the performance of the primary sedimentation tanks.
There are seven rectangular primary sedimentation tanks, each 29.2 m long and
3.3 m deep. Suspended matter settles to the bottom as the wastewater travels very
slowly through these large tanks. Flight and chain scrapers that travel along the
floor of the tanks and drag the solids to hoppers from which it is pumped directly to
the digesters remove the settled sludge.
Floating material such as fats and greases are conveyed to one end of the tanks by
the returning sludge collectors and skimmed into manually operated tilting troughs.
The skimmings are then pumped, with the raw sludge, to the digestion tanks.
Primary effluent then flows to four activated sludge aeration tanks with aeration
provided by compressed air blown through fine bubble diffusers mounted near the tank
floor. The wastewater is aerated for several hours and then allowed to settle in final
sedimentation tanks. There are 12 circular final sedimentation tanks, four for each plant.
The tanks are equipped with rotary sludge collector mechanisms that sweep the settled
sludge to the centre of the cone-shaped tank bottom for continuous withdrawal. Most of
the separated activated sludge is returned to the aeration tanks and mixed with the
primary effluent to maintain a continuous cycle of treatment. The waste sludge is
transferred to the plant inlet and co-settled with the influent stream.
Some effluent is used for on-site irrigation of the grounds and as cooling and wash
down water. It is also distributed via a large diameter pipeline up Tapleys Hill and
Burbridge Roads for watering ovals, parks and golf courses. Consumers include the West
Beach Trust, Glenelg City Council, Glenelg Golf Club, West Torrens City Council, Kooyonga
Golf Club, Federal Airports Corporation and Lockleys Primary School. However, after
chlorination, the majority of the final effluent is discharged into Gulf St Vincent via
two 400 metre outfall pipes.
The sludge removed from the primary sedimentation tanks is stabilised anaerobically
in five digesters, two of which are equipped with floating covers for gas storage.
The digesters are mixed and heated to 36°C to maintain optimum conditions for anaerobic
digestion. Gas generated in the process is used as fuel for gas-fired engines, which hot
water for the heat exchangers that heat sludge in the digestion tanks. Burning digester
gas in three continuously operating power generators provides approximately 70% of the
plants power requirements. Each has a maximum power output of 600KW. Excess gas is
flared via the waste gas burner.
Digested sludge removed from the digesters is relatively stable due to the reduction
in volatile organic matter. This sludge is pumped to sludge-drying lagoons located at
the Bolivar WWTP.
