May 30, 2002
By Lucille Davie
JO'BURGERS don't know it, but by going about their everyday business, they are helping produce a high quality fertilizer called JOGRO - thanks to a new method for treating the city's waste.
At the Olifantsvlei Waste Water Treatment Facility, some 20 kilometres south of the city centre, Johannesburg Water (JW), the city's water and sanitation utility, produces this fertilizer in an advanced treatment plant.
This plant has for many years produced compost from the city's solid waste material, but in December JW introduced a new treatment method, and some time in the future Joburgers will be able to use JOGRO to fertilize their roses and petunias.
JW treats some 850 million litres of sewage daily in six treatment plants around the city. "Considering the volumes treated and the treatment standards applied, we operate arguably some of the most advanced waste water treatment facilities in the world," says the utility. High standards are enforced by the national Department of Water Affairs and JW has no trouble meeting these standards.
Besides the "high quality of effluent" discharged into the nearby Klipspruit River, Olifantsvlei thickens, dewaters and composts 100 tons of sludge it receives each day, in one of the largest composting facilities in the world.
The sludge is mixed with wood and wood chips produced on site from waste wood. This is then stacked into windrows or movable racks under a roofed area, and the piles are periodically aerated.
The composting process takes between 21 and 30 days, during which the pathogenic organisms are destroyed. After this the fertilizer undergoes a further maturation period of between 60 and 90 days when temperatures reach around 65 degrees Celsius. In the process turners are used to mix, invert and aerate the fertilizer.
The end product is JOGRO, particularly well suited to reinforcing the humus content and water-retaining properties of soil. Its high levels of nitrogen and phosphorus contribute to improving crop yields. Its trace nutrients help in suppressing plant diseases and pests.
It complies with the national guidelines issued by the departments of health, agriculture, and water affairs and forestry, which regulate the levels of pathogens and heavy metals allowed in fertilizer.
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