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Innocent Ruwende Senior Reporter
Harare City Council will sell 1 000 cattle to finance the $1,2 million desludging of digesters and rehabilitation of the sludge heating system at Crowborough Sewerage Treatment Works.

In 2015, council was slapped with a $100 000 fine for violating the Environmental Management Act after it was found guilty of discharging raw sewage into water bodies.

The discharge of raw sewage into water bodies has also hit council hard in terms of the $3 million it requires monthly to procure water treatment chemical to treat the polluted water.

The local authority was found guilty of discharging about 3 885 mega litres of raw sewage into the city’s main water sources — Lake Chivero, Mukuvisi, Marimba, Ruwa and Nyatsime.

According to recent minutes of the Environmental Management Committee, acting director of Harare Water Engineer Mabhena Moyo reported that Crowborough Sewerage Treatment Works had three existing units of 18 mega litres design capacity each with four primary settling tanks for accumulation and removal of raw sewerage effluent.

“By design, this raw sludge was pumped to the sludge digesters where it was stabilised through a temperature controlled digestion process, before it could be disposed of through injection into the final effluent for pasture irrigation,” read the minutes.

“The sludge digestion process produced biogas, which was rich in methane gas and was used to fire boilers to heat water to a predetermined temperature.

“The heat was then transferred from heated water to sludge in heat exchangers to aid the digestion  process.”

He told the committee chaired by councillor Kudzai Kadzombe that digesters at Crowborough were currently clogged with grit and had since been de-commissioned, resulting in partially treated sewerage and the raw sludge from the primary settling tanks being discharged directly into the environment.

Eng Moyo said discharging raw sewerage directly into the environment was a health risk and of great environment concern as it not only attracted huge penalties from EMA, but also had unsustainable downstream effects of increasing potable water treatment costs at Morton Jaffray Treatment   Works.

“The sludge heating system mixing pumps, sludge injection pumps, sludge pipe work gas pipes and gas holding tanks were all non-functional due to corrosion and thus required rehabilitation for resuscitation of the sludge treatment process,” he said.

“On completion of the project, stabilised waste sludge would be produced and disposed of via pasture irrigation and pollution of the watercourse up to Lake Chivero would be minimised and potable water production costs  reduced.”