Algal blooms not toxic

2018-12-18 06:01

Naturally occurring, non-toxic algal blooms along False Bay coastline are not toxic, the City of Cape Town confirmed last week.

Residents are advised that, contrary to what is being reported by some news outlets, the naturally occurring algal blooms along the False Bay coastline are not toxic and have nothing to do with inland or wastewater quality.

The particular species of algal bloom occurring along the coastline was identified by the National Department of Agriculture, Forestry and Fisheries (DAFF) as Lepidodimium chloroforum and has no known toxins. DAFF holds the mandate to monitor the occurrence of algal blooms as well as for issuing any consumer warnings in the event of a toxic bloom – red tide. Algal blooms are a normal and common occurrence off the coastline of Cape Town, and South Africa more broadly.

The phenomenon is mostly caused by ocean upwelling events that bring colder, nutrient-rich water, and the accompanying dinoflagellate cells, into warmer surface waters. The combination of nutrients, warmth and sunlight causes the cells to bloom.

“It must also be noted that there are organisations that are creating the impression that the City’s desalination plants have not been working at all due to some functional failure or cover-up by the City. This is simply not true,” the City says in a statement.

The operations of the desalination plants in Strandfontein and Monwabisi have at times been affected by algal blooms and the high turbidity of the seawater. The algal blooms occur naturally and the high turbidity in the ocean is normally caused by bad weather and sea conditions (strong winds and big swells). 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 is thus a precautionary approach while ongoing monitoring and technical assessments continue to ensure the optimal functioning of the plants. The Strandfontein plant was producing little to no water over the period Thursday 1 to Wednesday 7 November due to the high turbidity of the seawater. The Monwabisi plant could not operate for four days during the same period. After resuming production, both plants again stopped producing drinking water on Friday 16 November due to the occurrence of the algal bloom but are fully functional otherwise.

“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. It must be noted that the City only pays for water that is actually injected into the reticulation system, hence the temporary suspension is not for the City’s account, as claimed,” the statement says.

The contractors who have been appointed to run the desalination plants as part of the City’s Water Emergency Augmentation Scheme are contractually required to deliver water that meets South African National Standards (SANS) requirements. These are the standards set nationally for drinking water quality. The City has a proud record of always meeting these standards. The desalination plants have online monitoring equipment to check the quality of the desalination process and adherence to the SANS standard. Desalination, at this stage, is a relatively small component of the augmentation programme and as such temporary drops in production are not expected to have a very significant impact on the overall water supply.

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