Greater Pretoria Metropolitan Council Embark on BOT Project For The Processing And Disposal of Waste Water Sludge (Engineer News Water and Sewage Feature)

In line with the Governments committed intention to finance capital projects through the private sector using BOT/BOOT techniques, the Greater Pretoria Metropolitan Council (GPMC) is in the process of finalising enquiries for a 20 year BOOT project for the processing and disposal of approximately 36 000 tons per annum of waste water sludge generated from their seven plants.

The processing and disposal of Municipal Waste Water Sludge has increased in importance since the establishment of secondary treatment standards by the Department of Water Affairs and Forestry and the Department of Health. The GPMC is responsible for seven major Water Care Works in the region and the present primary and waste activated sludges generated are about 100 tons of dry solids per day. At an estimated growth rate of 3% the estimated production of wastewater sludge will be about 200 t dry solids per day in 20 years.

The seven Water Care Works in the GPMC region are Baviaanspoort, Daspoort, the Rooiwal Complex, Zeekoegat, Sunderland Ridge, Rietgat and Sandspruit. The sludge produced at the seven works is either aerobically or anaerobically stabilised before disposal. At Daspoort, Baviaanspoort, Rooiwal and Zeekoegat the stabilised sludge is applied to land. At Sunderland Ridge all the sludge is dewatered by a belt press and is then placed on sludge drying beds before it is disinfected and bagged for agricultural use. At the Sandspruit Works sludge is also dewatered mechanically, placed on sludge drying beds and then stockpiled on site, while at Rietgat the sludge is dried on sludge drying beds before being stockpiled on site.

The GPMC is responsible for bulk conveyance of sewage and wastewater purification for the whole GPMC. Due to the expertise required to operate and maintain sludge handling, processing and disposal facilities and to market the final product for beneficial use, the GPMC has identified the need for municipal services delivery programmes for the handling and disposal of raw and/or partially stabilised sludge from the seven water care works in the GPMC area.

Consulting Engineers, Meiring, Turner and Hoffman, acknowledged experts in the design of wastewater treatment plants have been retained by GPMC to prepare the technical specifications as a basis for the Design and Build to be carried out by the successful tenderer. Engineering and construction contract consultants, Binnington Copeland & Associates (Pty) Ltd., experts in the commercial and contractual field of BOT and BOOT type projects have been retained to prepare the pre-qualification and main enquiry documentation and to assist with the commercial adjudication of submitted bids. Comments Johan Pansegrouw, Executive Director, water and environment:

“Private participation in municipal schemes is seen as a way to develop services for which capital may not presently be available as well as empowering previously disadvantaged groups, in line with government directives@.

Chris Binnington, Managing Director of Binnington Copeland & Associates (Pty) Ltd, says:

“ABOT/BOOT projects are particularly suited to those types of projects where a readily identifiable revenue stream can be made available by the Employer. Such projects typically involve toll-roads and power generation and are now to be increasingly found in the sphere of water treatment and wastewater disposal”.

Binnington advises that pre-qualification for this project has already taken place and the main enquiry document should be issued during April. The documents will be structured in such a way that the normal high cost of bidding a BOT/BOOT project occasioned by the multiplicity of parallel designs during the tender phase, will be controlled by having a series of milestones for preliminary design review by the employer and its consultants.

Beneficial Use of Sludge

Sludge should be seen as a resource and not a waste product and, as such, it should be put to beneficial use. Sludge should be disposed of in the most economical and environmentally acceptable way possible.

In view of its organic and plant nutrient content, wastewater sludge is regarded as a soil conditioner and fertiliser for agricultural and horticultural purposes. Since wastewater sludge is produced during the treatment of domestic and industrial wastewaters, originating from residential as well as from trade and industry, it contains pathogenic organisms, various metals as well as inorganic and organic chemicals. Therefore, in utilising the wastewater sludge, careful consideration must be given to its potentially hazardous properties in order to protect human and animal health and the environment in general.