Wastewater treatment works extension completed

27th March 2009 By: Fatima Gabru

The liquid phase commissioning of the R170-million extension of the Waterval wastewater treatment plant successfully took place towards the end of 2008, diversified engineering company SSI Engineers & Environmental Consultant water sector senior engineer Cliff Geddie tells Engineering News.

The Waterval project is for the Ekurhuleni metropolitan municipality’s utility company, East Rand Water (Erwat).

The civil, structural and building works for the Erwat project were awarded in May, 2005, with the joint venture consulting engineers for the project being BCP Engineers and Palace Consulting Engineers. SSI took over BCP at the end of 2007, without changing any of the BCP staff on the project.

The scope of the project was to increase the capacity of the Waterval wastewater treatment works from 100 Mℓ/d to 150 Mℓ/d. This was achieved by constructing a new screening and degritting facility and a 50-Mℓ/d biological nutrient removal activated sludge plant. Measures for diverting excess stormwater to a temporary holding dam for later treatment were also provided.

The civil and structural component was completed at a cost of about R100-million, while the electromechanical component cost about R56-million.

The plant, located at the confluence of the Klipspruit and the Rietspruit, allows for gravity flow from Alberton in an outfall sewer following the Kliprivier and from the southern portions of Germiston, Boksburg and Benoni, which drain along the Natalspruit and Rietspruit valleys.

The planning and design of the sludge treatment faci- lities were initially delayed pending the release of the Department of Water Affair’s Guidelines for the Selection of Management Options and the Requirements for the Agricultural use of Sludge, as well as lack of funding. “With these constraints now removed, tenders have been invited for additional anaerobic sludge digesters as well as for sludge dewatering facilities for the entire plant,” adds Geddie.

The final component of the project will include the up- grading of existing sludge digestion facilities. For operational reasons, this is only planned to begin after the new sludge treatment facilities come on line.

Preliminary planning for incorporating cogeneration at the site, as well as a proposal for the recovery of nutrients from the filtrate produced by the sludge presses, has been compiled by the consulting engineers.

“These aspects will receive further attention once the contracts for the new sludge stabilisation and dewatering facilities are finalised,” he comments.

Geddie says a significant amount of the electricity require- ments of the plant could be generated on site. Further, the waste heat from the generation of the electricity would be used in the digestion process.

He says that the Waterval project was initially constrained by the lack of finance and envi- ronmental approvals.

“The design was for a 50-Mℓ/d activated sludge plant. At one stage consideration was given to building a 25-Mℓ/d plant instead, but when a Municipal infrastructure grant was approved, the scope reverted to the original 50-Mℓ/d capa- city,” he adds.

A significant challenge on the project was the coordina- tion of information and amendments to information between the process, mecha- nical, electrical, instrumen- tation, civil, structural and building disciplines at the design stage. In addition, contractor design information had to be incorporated where applicable, he comments.

The existing plant had been operating at well past its hydraulic design capacity and the new extension has resolved the problem with regard to the liquid phase of the system.

A benefit of the project is that one of the constraints to further urban development in the drainage basin has been resolved, adds Geddie.

He adds that SSI is currently busy with the early stages for two further projects for Erwat, which, he says, is one of the country’s more successful water agency’s that plans well in advance.

“Erwat is proactive in acquiring finance for critical upgrades and new projects, which is essential in the provision of services to the country’s growing demands,” he concludes.