15 April 2009

By Keotshepile wa Mogotsi and Sipho None

POOR effluent quality, lack of capacity, sensitive location and discharge point are just some of the challenges that Mogale City’s Percy Steward Wastewater Treatment Works has faced in its years of operation.

But these problems are slowly being overcome through a major upgrade of the works, announced in the mayor’s State of the City address on 4 April 2008.

At a briefing at the works’ offices, the municipal manager, Dan Mashitisho, took pride in the successes of the project so far, and applauded wastewater treatment works officials and service providers for the well-orchestrated job. “It has been a resounding success and it needs to be recorded properly. Environmentally, this was a nightmare and we would like to see this going further,” said a joyful Mashitisho.

For years, the works, in Delporton near the Jack Taylor Airstrip, has been perceived to have a 25ml/day treatment capacity, based on a chemical oxygen demand (COD) loading of 600 mg/l, which is the design norm for sewage that is primarily domestic in origin.

In his speech in 2008, Executive Mayor Koketso Calvin Seerane said: “We have commenced on a project to upgrade the Percy Stewart Wastewater Treatment Plant. The intention is to improve its performance so that it complies with its licensing requirements …

“There are three interventions we are working on: the first involves the upgrading of the plant, which includes mechanical, electrical and instrumentation works; the second involves the application of our by-laws to reduce the high load on the plant; and the third concerns itself with design and construction of a new plant.

“The first two interventions will assist us to minimise the problem, and even stop it. The third intervention will create more capacity for us to handle the rapid growth experienced by our city.”

Holistic solution Mashitisho echoed these words at the briefing, saying the municipality was looking at a holistic solution for the plant. “To alleviate further problems for the plant which has been an albatross around the neck of the municipality, the proposed plan should create a climate for economic development and be environmental friendly.

“We are looking forward to see the Percy Steward Wastewater Treatment Works being operational and maintenance-driven and sustainable. And we should also keep to the indicated timelines.”

Leon Naudé, the principal engineer at SSI, the appointed engineering and environmental consultants, reported that the perceived capacity was based on a COD loading of 600 mg/l, which is the design norm for sewage that is primarily domestic in origin.

However, the current and more realistic COD loading was 1000 mg/l, which included low cost housing and industrial. He said this perception reduced the plant capacity to 15 Ml/day and resulted in a lack of proper maintenance, which had further decreased the treatment capacity to about 5 Ml/day.

Dennis Mokotedi, the infrastructure executive manager, said his team did not know the degree of the problem at the plant, other than the affluent discharge.

“We did not know the degree of the problem other than the fact that the affluent discharge was not complaint with the National Water Act,” Mokotedi said. “All what we did was based on the findings that resulted on our analysis of the situation at the waterworks treatment.”

Mechanical and electrical refurbishment of the plant cost the municipality at least R14-million.

Extension To accommodate emerging housing developments, Mokotedi said the 10mg/l extension of the plant, estimated to cost R100-million, was expected to be resumed in January 2010.

Naudé said two of the major challenges his team faced was that it had to work around the clock during the extension and that the plant was on uneven and rocky ground. However, he cautioned that no panic buttons should be pressed as the team had designed a scientific engineering plan to improve the performance of the plant.

The extension will include, among others, inlets with screens and degretters, primary settling tanks, a balancing tank, activated sludge reactors, clarifiers and chlorine contact chambers. The project will also have an economic development slant, and skills transfer opportunities to benefit local people.

Based on the 2001 census figures and adjusted for annual growth, the plant is servicing more than 22 000 households and 78 000 people. This includes low and high income residential areas.