Restoring the water balance at Setumo Dam

At Setumo Dam, the situation was so severe that the cyanobacterial build-up had formed a series of layers from the surface to the bottom of the dam

BEFORE

Situated near Mahikeng, North West, Setumo Dam was constructed in 1997 to meet the water security and recreational needs of the surrounding community. In recent years, with the lack of effective rainfall, the water progressively turned a shade of green as cyanobacterial blooms took hold, killing off aquatic life and making abstraction and potable water treatment increasingly challenging.

By Alastair Currie

As in many parts of the world, the growth of these harmful algae blooms is fed by pollution. In Setumo’s case, this was caused by poorly treated sewage overflows from two nearby wastewater treatment works discharging into the Molopo River, which feeds the dam.

The situation reached a point where recreational use or abstraction for downstream potable treatment purposes became increasingly hazardous. The dam’s water quality greatly exceeded the levels deemed safe by the World Health Organization. The escalating organic loads at the water treatment plant also significantly increased the cost of chemical dosing. Additionally, there was a concern regarding the bad taste and odour of the treated water. Measuring around 1.6 km in length, this earth-fill dam has a surface area of some 447.3 ha (4 km2), with a total design capacity of around 19 600 000 m3. Given its size and the extent of cyanobacterial bloom, many deemed it untreatable.

A dramatic improvement in water quality was achieved at Setumo Dam following its treatment with LakeGuard

AFTER

Countering a parasitic threat

Cyanobacteria produce their own food via photosynthesis, which means they need sunlight to survive. In warm, nutrient-rich (high in phosphorus and nitrogen) environments, they can thrive – their cells doubling every 48 hours – progressively forming a scum that robs the water of essential light penetration and oxygen. At Setumo Dam, the situation was so severe that the cyanobacteria buildup had formed a series of layers from the surface to the bottom of the dam.

Rather than abandon the dam to its undeserved fate, Israeli company BlueGreen Water Technologies offered to fix the problem on a pro bono basis to prove the benefits of its proprietary solutions. These comprise LakeGuard™ Blue, and LakeGuard™ Oxy, the latter having been approved by the South African Department of Forestry, Fisheries and the Environment for use on public water bodies. Both products are certified internationally to meet the NSF/ ANSI/CAN 60 standard for drinking water.

The Setumo project went ahead as a joint venture in conjunction with the Department of Water and Sanitation, Sedibeng Water, and Rand Water Analytical Services. The results have been remarkable.

A surface killer

“The technology was developed using a well-established algaecide. However, the key difference is the proprietary coating, which enables LakeGuard to float on the surface where the cyanobacteria thrive, and that’s where the magic takes place,” explains Jurgens van Loggerenberg, director: Africa for BlueGreen Water Technologies.

“With a conventional algaecide, large quantities are required to cater for the volume of the water body – a percentage of which sinks down into the underlying sediment with minimal treatment benefit. This is not the case with LakeGuard,” Van Loggerenberg explains. LakeGuard Oxy’s active ingredient is sodium percarbonate, which slowly releases hydrogen peroxide. As it penetrates the cyanobacterial cells, they’re placed under major oxidative stress, prompting an autocatalytic cell death response within the population.

Using the prevailing wind direction to optimal effect, within three to four days, some 90 t of LakeGuard had been released on to the surface of Setumo Dam using a custom-designed dispensing bag The growth of cyanobacterial blooms at Setumo Dam was caused by poorly treated sewage overflows, which made downstream potable water treatment increasingly challenging

Restoring the balance

One of the project challenges at Setumo was to determine the best LakeGuard application approach. Beyond fishermen’s kayaks, there were no other boats of sufficient scale to disperse the algaecide.

Taking a similar approach to crop spraying, the solution was to use a helicopter with a custom-designed dispensing bag suspended underneath the aircraft. Using the prevailing wind direction to optimal effect, some 90 t of LakeGuard had been released onto the surface of Setumo within three to four days.

To put this in perspective, 20 kg of product is typically used on a 2 ha irrigation dam. This provides an indication of the scale at Setumo, which is one of BlueGreen Water Technologies’ largest projects to date globally.

“After around a month, the water quality had transformed so dramatically that you could see clearly to the bottom of the dam. The bird population has also recovered – a clear indication of an improving system. Plus, the water treatment plant is under far less pressure, with a resultant marked improvement in drinking water quality,” says Van Loggerenberg

The return of the ‘good’ algae

Once the cyanobacterial population has been eradicated, the ecological balance begins to return, enabling the formation of ‘good’ green algae that form as a natural barrier. These beneficial algae help to suppress cyanobacterial blooms from reoccurring. However, were a resurgence to occur, only a relatively small maintenance dose of LakeGuard (around 1 t) would be required, usually applied in winter.

The key to preventing a resurgence is to ensure that the wastewater treatment plants discharging into the dam adhere to acceptable effluent discharge requirements.

“The Setumo project has positively impacted more than half a million lives and serves as an excellent case study for similar interventions across Africa. We need to ensure that we protect our water resources and, to achieve this, we need buy-in from all stakeholders,” Van Loggerenberg concludes.