Construction World December 2017

Category C: Professional Services: Consulting Engineers

CONSTRUCTION OF MODULE 2 AT THE WELGEDACHT WATER CARE WORKS Welgedacht WCW is a regional facility constructed for the treatment of wastewater from domestic and industrial sources from the Boksburg, Benoni, Daveyton, Springs and Brakpan areas within the Blesbokspruit catchment. Its finishes are good when measured against construction norms for this category of process plant and the architectural treatment of the buildings creates a modern, efficient visual effect.

two-stage Archimedean Screw Pump Lifting Station and a head of works comprising Screening and Grit removal, two Flow Balancing Tanks, two Primary Settling Tanks, secondary treatment consisting of two Fine-Bubble-Diffused-Air Aerated Biological Nutrient Removal Reactors, four Clarifiers, and tertiary treatment, two Chlorination tanks and De-Chlorination Channels. Primary sludge from PSTs is digested into mixed and heated Digesters with the digested sludge passing to a sludge holding tank (future digester presently unroofed) from where the sludge is for the present pumped to a land irrigation area for growing fodder crops. The plant utilises a treated effluent stream from the chlorination tank for all the wash water requirements on site, except where potable water is required, which is provided separately from a borehole on site. The discharge outlet was constructed

The site itself is quite remote and from outside, the view is somewhat obstructed on three of four boundaries by railway lines, one of which is on a 8 m high embankment which makes the treatment plant less conspicuous from the public’s sight. The project sought to maximise the use of natural materials particularly for the earthworks and civil and building works. Welgedacht WCW is a regional facility constructed for the treatment of wastewater from domestic and industrial sources from the Boksburg, Benoni, Daveyton, Springs and Brakpan areas within the Blesbokspruit catchment. Module 2 was designed to augment the treatment capacity of the existing Module 1 Plant with a second module of 50 M ℓ /d. The Head of Works was sized to accommodate a further 50 M ℓ /d plant extension while the outlet from the facility to the Blesbokspruit, incorporating

de-chlorination channels, has been sized for the present and future facilities or 135 M ℓ /d. The approach to flow routing through Module 2 Plant differs markedly from Module 1, where isolating unit operations and processes for maintenance is in many cases difficult or impossible. Module 2 consists of two 25 M ℓ /d process trains in parallel with cross linkages and/or by-passes to allow for access to process structures for maintenance and repairs. The Module 2 process also differs from Module 1 in as much as sewage sludge is separated from the liquid phase in primary settling tanks (PSTs) and pumped to an anaerobic sludge digestion plant. This is motivated by the recent dramatic increase in the cost of power and the possibility for using digester gas for on-site power generation in future. The main structures of Module 2 are a

to combine Module 1, 2 and a future Module 3 into one discharge point as required by DWS.

PROJECT INFORMATION

• Company entering: Royal HaskoningDHV • Client: East Rand Water Care Company (ERWAT) • Contract value: R455 550 378 • Start date: June 2012 • End date: August 2016 • Project team: Royal HaskoningDHV – Palace Technologies JV • Main contractor: Group Five Civil Engineering

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