Page 23 - Thola Issue 17

WASTE WATER TREATMENT WORKS
The good
The city treats over half a billion litres of waste water a day via twenty-seven waste water treatment works. Twenty- five works treat to river discharge standards and two sea pipelines discharge effluent four kilometres out at sea. The impact of the sea outfalls is negligible. However, it is expected that a project to produce methane at the Southern Wastewater Treatment Works within the next three years will reduce waste loads to sea, produce energy-rich methane gas, and produce fertiliser for agricultural use.
An extensive staff comprising chemical engineers and qualified process controllers, operate the works. The staff have managed to secure Green Drop awards for excellence for 11 of the waste water treatment works.
The bad
South African sewers are not designed to accommodate rain water associated with the intensive storms we are so used to. The costs of designing sewers
that can accommodate rain water would be prohibitively expensive due to their excessive size. One in five domestic households illegally discharge storm water into the sewers, flooding the system, increasing pumping costs, costs in clearing blockages caused by sand and grit, and creating short-term overflows into the rivers.
Mitigation
A proposal was submitted to the City Manager’s restructuring official to
address the situation. It required that
a levy be raised on all households allowing rain water into the sewer. This would cost the average person allowing storm water into the sewer a minimum of R3 000 per year on their water bill. The revenue generated will be used to recruit inspectors who would advise
the public on alternatives to the illegal connections. The pictures below show the sort of technology that is used to detect properties with storm water connections to the sewer.
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WASTE WATER NETWORKS (SEWER PIPES AND PUMP STATIONS)
The good
The City has over 7 500 km of main trunk sewer and 280 sewerage pump stations to convey waste water throughout the City. This keeps poor water quality out of the rivers and dams. A staff of over 500 people and sub-contractors maintain this infrastructure.
The bad
Again, ratepayers allow rain water into the sewers, which causes problems. In addition, the public abuse the sewerage system; it is designed only for human excretions, wash water and toilet paper. Anything other than this material causes sewer blockages.
A significant percentage of sewer blockages occur due to disposal of
fat from households and restaurants. This does not make sense since fat and oil are good materials which can be converted into engine grease, low grade soap, biodiesel, glycerine and methane.
Recently, the theft of metal infrastructure has plagued the city, causing serious water pollution.
Mitigation
A proposal was submitted to the City Manager’s restructuring official to address the situation. It was proposed that a levy be raised on restaurants
to finance city officials, who would
be able to advise on managing fat in their establishments. Serious offenders would be prosecuted.
LEFT: Smoke is blown up the sewer using a motorised fan.
RIGHT: If the sewer is connected to a storm water drain, smoke is blown out of the drain.
ABOVE: A neglected fat trap. Would you eat in this restaurant based in Hillcrest?
thola: VOLUME 17. 2014/15