Johannesburg’s water cycle

Johannesburg, built on a ridge, is one of the few cities in the world not located near a large water source.

This means that potable water for the region, which is purchased in bulk from Rand Water, has to be pumped up about 50 km from the region of the Vaal River.

The advantage of being on a ridge is that much of Johannesburg’s wastewater can flow by gravity to its treatment works.

Wastewater treated in Johannesburg Water’s treatment plants is discharged into one of two catchments: the Jukskei/Crocodile River catchment in the north; and the Klip/Vaal River catchment in the south. Both catchments are classed as sensitive to the discharge of waterborne pollutants.

Waste

Johannesburg Water has to ensure that all wastewater discharged into its sewers and conveyed to its treatment plants is treated to the highest standards before being discharged into the natural environment.

The purifying standards are enforced by the national Department of Water Affairs and Forestry (DWAF), and are among the highest in the world.

As part of the process to ensure that the wastewater is conveyed to treatment plants without leaking into the environment, Johannesburg Water cleans 144km of sewers and clears more than 3 000 sewer-blockages every month.

There are six wastewater treatment plants across the city, the largest being the Northern Works. It treats 400 million litres of wastewater every day from around 1,6 million people. This plant serves the area north of the Hillbrow ridge including Alexandra, Edenvale, Randburg, Sandton and parts of Midrand and Roodepoort. It is situated in the Diepsloot area.

The treated effluent from this plant is either discharged into the Jukskei River, used to irrigate Johannesburg Water’s farm lands, or pumped to the Kelvin Power Station for use as cooling water. This ensures that expensive high quality drinking water is not used for this purpose.

System Cycle

The Northern Works makes use of a sophisticated locally developed technology which uses natural biochemical processes. City scientists and engineers have, over many years, developed and refined a biological wastewater treatment process that removes organic pollutants as well as nitrogen and phosphorus.

The system is recognised internationally as the “Johannesburg Process”.

The quality is continuously controlled and monitored.

In addition, Johannesburg Water has found a use for the 100 000 dry tons of wastewater sludge produced yearly at the treatment works. Johannesburg Water produces a compost by-product – JO-GRO – made from the sludge and waste wood from the tree-felling industry. The technology to convert sludge into compost was adapted from technology used by many US cities.

JO-GRO is free of disease-carrying organisms and a good product in horticulture and agriculture. As well as containing the usual plant nutrients it contains trace nutrients and agents that suppress plant diseases and pests.

Monitoring Johannesburg’s water

Johannesburg Water has intensified its water monitoring in the greater Johannesburg area.  The following types of water are sampled and analysed in the company’s three laboratories at Cydna and at the Northern and Goudkoppies Wastewater Treatment Works, namely potable (drinking) water; wastewater and treated wastewater; industrial effluents; surface water; and groundwater.

Drinking water

Every month throughout Johannesburg about 500 samples are taken and analysed to ensure compliance with the SANS 241 standard.

Between 42 and 46 determinants are checked and more than 4 000 analyses carried out each month. These include aesthetic, mineral, chemical and microbiological parameters.

The results show excellent compliance with the highest category (Class 1) in this standard, which confirms that the drinking water in Johannesburg is some of the best in the world.

This water monitoring has increased since Johannesburg Water took over – previously only 150 samples were tested a month. In addition, the number of parameters tested has increased.

In one litre of Joburg water, there is typically 18 milligrams of calcium; eight milligrams magnesium; 10 milligrams of sodium; three milligrams of potassium; 11 milligrams of chloride; 12 milligrams of sulphate; 0,5 milligrams of nitrate; and 0,2 milligrams of fluoride; with a total alkalinity of 77; total dissolved solids 150; and 7.7 pH (pH units). This complies fully with SANS 241 Ed 6.1, Class 1 Drinking Water.

Wastewater and treated wastewater

Johannesburg Water owns and directly manages six wastewater treatment works, treating all the domestic sewage and industrial effluents discharged into its sewers. These works, which treat 930-million litres of sewerage daily, must comply with standards laid down by the national Department of Water Affairs and Forestry (DWAF).

The treatment works are intensively monitored on a daily basis to check the quality of the incoming wastewater, process performance and efficiency and the quality of final effluents and by products.

Over 2 200 samples are tested each month. In addition, certain key parameters are monitored on a continuous basis using on-line analysers. As part of the permit requirements, the upstream and downstream quality of the streams into which treated effluents are discharged are regularly monitored.

Bio-monitoring is also carried out to determine the effect of treated effluents on the habitat of these streams.

This intensive monitoring has assisted in these works improving overall compliance with DWAF requirements of 95 percent or more, as well as minimising the usage of power and chemicals.

Industrial effluents

There are approximately 90 industries in the city that discharge large quantities of problematic effluents to Johannesburg Water’s sewers. All industrial effluents from these factories are monitored to ensure that they do not contain dangerous or toxic chemicals (that is, they comply with the City’s by-laws) and to obtain data to enable the City to set tariffs for discharging pollutants into the sewer system.

Surface water

Although surface waters in Johannesburg are not used as a source of drinking water, all the streams and rivers in the city are regularly sampled by the City’s regional environmental health staff and monitored by its Water Quality Management Department and Johannesburg Water.

This is done to determine the effect of the treated effluents and to detect pollution caused by surface runoff, sewer overflows and illegal discharges. All these samples are analysed by Johannesburg Water’s Cydna Laboratory.

About 150 samples are analysed each month.

In addition, Johannesburg Water monitors by remote sensing a number of key places in its sewer network to detect sewer overflows and pump-station failures.

Groundwater

In order to determine the impact of the wastewater treatment works on underground water, 66 boreholes are monitored on a regular basis. A sample of each borehole is analysed monthly for 37 parameters.

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