Zutari – Lower Thukela Bulk Water Supply Scheme

Zutari for Lower Thukela Bulk Water Supply Scheme

Increasing demands from a growing population, combined with periodic droughts that are increasing in intensity, have left northern KwaZuluNatal’s water supply vulnerable.

The Lower Thukela Bulk Water Supply System was conceived decades ago but was shelved as a scheme because it had not been deemed necessary. However, with an impending drought in 2010, Umgeni Water needed to move quickly to implement the scheme.

The design of the scheme was challenging, as it needed to be executed within a short timeframe in order to meet the client’s delivery commitments. It also needed to be sufficiently robust so that the client would achieve a 95% assurance of supply to their customers. This required an unconventional design, considering the seasonal flooding of the river and the associated deterioration in river water quality.

The R1.6 billion scheme consists of an abstraction works from the Lower Thukela River, which needs to provide a steady supply of water from the river throughout the year, while also removing as much of the sediment load from the water as possible. The abstracted water is then pumped up to the water treatment works.

A weir was installed across the river to direct flow to the abstraction works, where the water will continually scour the riverbed to maintain a channel to the abstraction works. The removal of sediment is achieved through a sequence of boulder, pebble, gravel and sand traps.

The water treatment works uses three stages of sedimentation to further remove solid particles from the water. The water is then polished through rapid gravity sand filters and disinfected before being pumped from the water treatment works to a 30 Mℓ reservoir, from which it is distributed to the

PROJECT TEAM Client: Umgeni Water Consulting engineer: Zutari (previously Aurecon) Contractors: Group Five, Stefanutti Stocks Coastal, Veolia Water Solutions, Esor Franki

surrounding communities. Sediment collected on-site is then processed to landfill.

One of the key ecological functions of the Thukela River is the transportation of nutrient-rich sediment to the estuaries at the mouth of the river. Zutari modelled the river chemistry and sediment loads to demonstrate the optimum return flow of sediment from the works to the river in order to maintain the ecological service of the river, without impacting on the quality of the water in the river.

The scheme presently provides 55 Mℓ of treated flow per day, with the option to readily upgrade it in the future to 110 Mℓ/day.

WINNER

Zutari for Upgrade and Extension of Stellenbosch Wastewater Treatment Plant

PROJECT TEAM Client: Stellenbosch Municipality Consulting engineer: Zutari Civil contractor: CSV Construction Mechanical and electrical contractors: Veolia Water Solutions & Technologies South Africa

Effluent from the Stellenbosch Wastewater Treatment Works (WWTW) flows into the Eerste River, which is essential for the Cape Winelands’ agricultural and agritourism communities.

In 2011, the WWTW was operating over-capacity, dilapidated, struggling to meet effluent compliance, a hazard to the environment, and a nuisance to the surrounding community – ultimately placing the livelihood of the communities surrounding the Eerste River at risk.

Stellenbosch Municipality made the strategic and critical decision to upgrade the WWTW with the limited budget at hand. The main objectives were to increase capacity, improve the effluent quality and reduce the foul odour. Zutari (formerly Aurecon), as consulting engineer, undertook the planning and design of the treatment works in 2014, as well as site supervision when construction began in 2015.

The project comprised an upgrade of the plant to a full biological nutrient removal process that is capable of handling up to 35 Mℓ/day average dry weather flow, as well as ensuring compliance with the National Water Act. This upgrade comprised a new inlet works, a new 27 Mℓ/day membrane biological reactor (MBR) lane, the rejuvenation of the existing plant to an 8 Mℓ/day conventional activated sludge (CAS) plant with UV disinfection, and new sludge treatment facilities. The upgrade will cater for flows from the town up until 2035, allowing for further development and economic growth in the area.

The plant’s design included other innovative features, such as a sophisticated control system, odour eradication, energyefficient technologies and context-driven, sustainable design. The plant is fully automated with a state-of-the-art control system that ensures the process control and operating efficiency level is optimised.

The WWTW was also designed to be energy efficient by minimising pumping through the works and adopting energyefficient technologies like a fine bubble diffused aeration system in the MBR lane, which is 15% to 20% more energy efficient than traditional technologies. In addition, the facility was designed in such a manner that it can be easily retrofitted with a direct potable reuse facility and biogas-to-energy facility in the future.

The Stellenbosch WWTW was commissioned in March 2019 and is currently the largest MBR WWTW in South Africa. The incorporation of membrane technology has significantly improved the state of the Eerste River and the quality of water available for users.