Desalination plants on and off

Operations at Strandfontein and Monwabisi desalination plants have intermittently been interrupted by algal blooms and the high turbidity of the sea water.

The Strandfontein plant was producing little to no water between November 1 and 7 and the Monwabisi plant could not operate for four days during the same time because of the high turbidity of the sea water, caused by bad weather (strong winds) and sea conditions (big swells).

After resuming production, both plants again stopped producing drinking water on Friday November 16
due to the occurrence of the algal bloom.

The algal bloom has dissipated in the False Bay area and the Strandfontein plant is in production again while the Monwabisi plant will be in production again soon.

The City of Cape Town said the blooms were natural occurrences, which were identified by the Department of Agriculture Forestry and Fisheries (DAFF) as Lepidodimium chloroforum and had no known toxins.

The department holds the mandate to monitor the occurrence of algal blooms and to issue any consumer warnings in the event of a toxic bloom or red tide.

According to a City media statement, the bloom phenomenon is mostly caused by ocean up welling events that bring colder, nutrient-rich water, and the accompanying dinoflagellate cells, into warmer surface waters. The combination of nutrients, warmth and sunlight cause the cells to bloom.

Algal blooms cause damage to the sensitive membrane filtration systems of the desalination plants, while the high turbidity affects the pre-treatment processes of the desalination plants, which can result in reduced production by the plant.

Halting operations temporarily was a precautionary approach while ongoing monitoring and technical assessments continue to ensure the optimal functioning of the plants.

The City only pays for water that is actually injected into the reticulation system and the contractors who have been appointed to run the desalination plants as part of the City’s Emergency Water Augmentation Scheme are contractually required to deliver water that meets South African National Standards (SANS 241:2015) requirements.

These standards are nationally set for drinking water quality.

The desalination plants have online monitoring equipment to check the quality of the desalination process and adherence to the SANS standard.

At this stage desalination is a relatively small component of the City’s augmentation programme and as such temporary drops in production were not expected to have a very significant impact on the overall water supply.