Durbanville wine route: Wastewater used to good effect?

by | Feb 26, 2020 | News

Since using the City of Cape Town’s cost-effective and nutrient-rich treated wastewater for irrigation, grape wine producers in Durbanville have seen a significant increase in their yields. But could infrastructure problems at the plant impede on producers’ viability? Anton Pretorius investigates.

In 2004, the City of Cape Town established the Potsdam wastewater treatment plant in Milnerton.

Drought and water scarcity has had a serious impact on agriculture, and specifically South Africa’s wine industry.

Due to the low trust in South African water service providers, farmers are willing to pay for a privately managed scheme for water reuse. Many wine grape producers in the Western Cape have looked towards treated wastewater as an alternative water source for irrigation. Several studies have found treated wastewater to be acceptable for agricultural use, and farmers are attracted by its few usage restrictions and cost-effectiveness.

In 2004, the City of Cape Town established the Potsdam wastewater treatment plant in Milnerton. Through an intricate network of pipes, Potsdam now supplies most of the wine farms and estates situated along the Durbanville wine route with effluent water for irrigation. The increasing demand for effluent water among farmers and producers has prompted the City to double the plant’s capacity. The next six years will see capacity go from 47 million litres per day to 100 million litres per day.

Potsdam supplies most of the wine farms and estates situated along the Durbanville wine route with effluent water for irrigation

Higher yields, better production

Pierre Blake, owner of Boterberg, a farm near Philadelphia that delivers quality wine grapes for Distell, relies on Potsdam treated wastewater for additional irrigation. The water isn’t used for his mass-production grapes, but rather for quality, lower-yielding vineyards. “The wastewater irrigation is applied optimally for our higher-quality grapes,” he says. “We irrigate about twice or three times before harvest.” It’s critical that the vineyards are irrigated with the treated effluent water at the right time. “Too much too early and you’re back to mass-production. The water must be applied strategically.”

Wastewater also has a significant impact on labour. “When you irrigate the right amount of water to these high-quality grapes and vineyards, the vineyards develop a certain growth and you require more hands in the vineyard to do head suckering.” Head suckering is a viticulture practice that entails the removal of unwanted shoots from the canopy of head-trained vines, especially the water shoots.

The treated effluent water has made a remarkable difference to Pierre’s crop and yield. Initially, when the vineyards were planted in 1998/99, Pierre managed to get around five or six tonnes per hectare. “I would say it has doubled our yield. Since we’ve started using the treated effluent water, we’ve seen an increase of between eight and 12 tonnes per hectare – it’s the difference between a profit and a loss.”

Irrigating his vineyards with treated wastewater has allowed Pierre’s farm to remain viable. “We’ve had two or three years of poor rainfall in our area. As it became drier, the treated wastewater has become essential to our operation. Without that water, we won’t be able to farm anymore.”

But the water isn’t a guarantee for a great harvest. “It’s more about the availability of the water, and your ability to manage your crops. You can give or withhold water at certain times for optimal production. It’s more about water management.”

Daniel Keulder, winemaker at Nitida Wines, says roughly 80% of his vineyards are under irrigation from the treated wastewater. While he has found the water to have made a significant improvement in the vineyard and to his yield – due to its availability and cost-effectiveness – he says there are some risks associated. “We’ve had some issues from the Potsdam wastewater treatment plant. Because of a lack of infrastructure maintenance on the pipes and systems, the water flow is often interrupted.”

He adds that despite the problems, it’s still cheaper than most water schemes currently available, costing around R2.20 per kilolitre (compared to normal drinking water that costs around R50 per kilolitre). “When it works properly, the system is wonderful to have.”

Treated wastewater has resulted in a 20% increase in the region’s grape production.

Infrastructure impedes progress

André Thompson, manager at Durbanville Pipeline Joint Venture (DPJV), says while the treated wastewater has resulted in a 20% increase in the region’s grape production, there’s been recent reports of “poor service” from the Potsdam wastewater treatment plant. “The drought and lack of water has caused infrastructural problems at Potsdam. Last year, repair and maintenance took several months to complete, which has really impeded the process. And this year, it doesn’t look likely to improve.”

The plant has also experienced severe water shortages. “Where the plant usually receives up to 50 megalitres of water per day, [in recent years] it only received 15 megalitres per day.” This is particularly problematic because the availability of the wastewater – not the water itself – is the big drawcard of the scheme. “The accessibility of the wastewater for irrigation is the sole reason for the increase in production among producers in the Durbanville region,” André says. “Without access, the scheme is not helping farmers, and they’re back to square one. From infrastructure to management to the lack of water quality, it’s all very problematic at the moment.”

Problems with the plant’s infrastructure are more common during summer, when the rainfall is low and people don’t flush their toilets as often. “We see blocked filters and damaged pumps,” André says. “Eskom’s loadshedding is also wreaking havoc on the plant’s infrastructure, and nothing is functioning optimally.”

But it’s not all doom and gloom. “They are currently busy with upgrades to the infrastructure of the plant. However, it can take anywhere from three to five years to complete.”

The scientists agree

Irrigation expert Dr. Philip Myburgh, of the Agricultural Research Council of South Africa, agrees that it’s not the water, but rather the availability of the treated wastewater that’s responsible for improving producers’ yields and production. “It’s not magic water,” he says.

Philip has been conducting intensive field tests to determine the effect of effluent wastewater on the soil over a period of 10 years. “There’s no evidence to suggest that the soil has weakened as a result of the wastewater,” he says. “The quality of the water is within limits for agricultural purposes. The only risk farmers face is when the City doesn’t manage the water quality properly, or when they don’t do proper maintenance on the works. So it’s not exactly a given.”

Karla Hoogendijk – a BSc Agric student at Stellenbosch University completing her Masters’ degree in Soil Sciences – has also been conducting long-term trials in commercial vineyards in the coastal region of the Western Cape. Her thesis, ‘Soil and grapevine responses to irrigation with treated municipal and winery wastewaters,’ studied Cabernet Sauvignon and Sauvignon Blanc grapevines that were irrigated using treated municipal wastewater from the Potsdam wastewater treatment works for 11 years.

Karla found that irrigation using treated municipal wastewater increased soil pH and electrical conductivity. She also observed an accumulation of chloride in the topsoil, probably due to the chlorine-disinfection process that’s part of the treatment at the wastewater facility.

“Appreciable amounts of sodium and potassium also accumulated in the topsoil due to wastewater irrigation,” Karla noted. “However, this did not result in enhanced uptake by grapevines. The irrigation however, did reduce water constraints throughout the growing season. Consequently, the grapevines produced stronger vegetative growth and higher yields compared to rainfed grapevines.”

Her study concluded that, with proper management, grapevines can be irrigated successfully using treated municipal wastewater.

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