MechChem Africa

Within the context of the ongoing water crisis in the Western Cape, MechChem Africa talks to Xylem’s water reuse specialist, Lucinda Jooste, who presents the argument that, while the current situation is dire, it also offers an opportunity to put in place lasting solutions to overcome increasing water scarcity.

Lucinda Jooste has been with Xylem South Africa since 2012 where, in recent times, she has become increasingly involved with water reclamation projects. These projects offer potential applications for Wedeco’s MiPROTM advanced oxidation process (AOP) technologies, which incorporate modern UV- and ozone-based treatments into the wastewater recycling streams; as well asLeopold’sas Leopold’s OxeliaTM ozone-enhanced biologically active filtration system.

She begins by pointing out that, as a whole, South Africa has always been dry. “Droughts are nothing new. They have been part of our history for centuries,” she says. Pointing to rainfall statistics from 1904 to 2015 and highlighting repeated drought cycles, over various periods, including the current Western Cape drought cycle, which began back in 2011.

Xylem Wedeco SMOOzone treatment using Xylem’s Wedeco SMOevo system is commonly used for municipal water and wastewater treatment.

“Climate change, increase in population growth, planning and management issues are contributing factors that can impact the intensity and frequency of drought cycles And, while likely to continue, this is not limited to the Western Cape or to South Africa. All over the globe, water scarcity is increasing as is evident in places across the globe such as California, Texas, Florida and Arizona in the US to name but a few” Jooste tells MechChem Africa.

“All of these states are strong advocates for water reclamation and, following a recent visit to Arizona for the Annual WateReuse Symposium in September 2017, it was fascinating to see what is possible when water reclamation forms part of planning to increase water supply to a water scarce region,” she adds.

Comparing Arizona to Cape Town, Jooste says that with a population of 6.93-million people spread over an area of nearly 300 000 km2, an average temperature of 39 °C and rainfall averaging only 203 mm per year, Arizona is dependant mainly on ground water of which a large portion is replenished with reclaimed water, while at the same time also making use of tertiary treated effluent for non-potable applications such as irrigation in order to offset potable water usage. “Arizona places a huge emphasis on water reclamation,” Jooste notes.

Cape Town has half the population and over double the rainfall and it services a population density of 1 530 people per km2 – compared to Arizona’s 18 – yet, as in the rest of South Africa, 77% of Cape Town’s water comes from surface sources: rivers, dams and lakes. Nationally, the utilisation of return flows is only 14% and this is mostly prevalent in regions outside of the Western Cape.

Jooste cites a 2017 report published by Green Cape, which noted that 98% of South Africa’s surface water resources are already allocated and a water deficit of seven to 22% per annum is anticipated nationally by 2030 if we continue on the current water usage trend.

“This level of pressure on existing resources requires thinking out of the box and identifying alternative resources, such as reclaimed domestic and industrial wastewater and far better management of storm water,” she suggests, adding that it is clearly not sustainable to depend only on surface water.

She adds that groundwater, which has long played a part in South Africa’s reserves, is not well legislated and managed. “We take the water out, but we don’t focus on replenishing it – and reclaimed water is an ideal resource for replenishing groundwater reserves,” she argues.

“Any water that is no longer fit for its original purpose can be reclaimed if put through the appropriate treatment steps to achieve the required quality standards for its new intended application,” Jooste says. “It always boils down to the source and the fit-for-use end requirement, ie, where treatment water quality starts and where it needs to finish,” she adds.

She describes three main types of water reuse: non-potable reuse NPR; indirect potable reuse (IPR); and direct potable reuse (DPR).

“NPR involves the treatment of domestic or industrial effluent to tertiary standards. While not suitable for drinking, this water is ideal for agricultural irrigation or for watering golf courses, for example, which in return offsets valuable potable water supply, which means that less water has to be expensively treated to potable standards. “Xylem offer’s UV solutions that can be used to ensure that water from NPR treatment trains is safe for using in this way.

“The City of Cape Town is already doing good work in this regard by supplying treated effluent via an independent pipeline network and at set draw off points for non-potable applications such as irrigation.

“But there can be no compromise for drinking water,” Jooste continues.

Potable reuse refers to the extensive treatment of wastewater in order to produce water that is safe for human consumption. Treatment technologies such as ozone, BAC, UV and AOP offered within the Xylem portfolio are used in conjunction with membrane technologies to ensure water of highest safety and quality.

IPR involves treating effluent to a high quality potable standard, using advanced treatment processes and then discharging it into an environmental buffer such as a dam, groundwater source, drinking water plant etc. prior to it being used. Existing return flows (i.e. where treated effluent is discharged into rivers and then abstracted downstream for treatment in a drinking water plant) is a good illustration of how this works although in this case it would be classified as non-intentional reuse. The implementation of IPR systems will make provision for even better water quality and higher safety measurements as it is applied for intentional reuse applications

Direct potable reuse (DPR) involves taking wastewater through even more stringent stages of advanced treatment, then blending it with water from natural sources before passing it directly into the domestic water reticulation network. “Psychologically, DPR is perceived as less safe, but in actual fact, because the entire treatment and distribution cylcecycle takes place in a closed system, the safety and quality of the water can be even better controlled, while also avoiding post-treatment contamination by environmental sources,” Jooste says.

“It is important to note that in either case, the quality of water delivered from IPR or DPR reclamation processes will be of an even higher water quality than that currently produced by conventional water treatment systems,” she adds.

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