Algal blooms not toxic

2018-12-18 06:00

False Bay residents do not have to worry about the algal blooms along the False Bay coastline as they are harmless.

The City of Cape Town advises residents that 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 it 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).

According to a statement released by the City, algal blooms are a normal and common occurrence off the coastline of Cape Town, and South Africa more broadly. The statement clearly explains that the phenomenon is mostly caused by ocean upwelling events that brings 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.

“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,” reads the statement.

Xanthea Limberg, Mayco member for informal settlements, water and waste services and energy, says 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 241:2015) 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 our augmentation programme and as such, temporary drops in production are not expected to have a very significant impact on the overall water supply,” she says.

Limberg says the City has for several years been attempting to upgrade the plant but this has been delayed by five tender appeals, including a High Court appeal, and a land claim.

“Encouragingly, most of the upgrade work has been approved by Council in the past few months, and it is expected that work will begin in the first half of 2019. We still, however, require residents to obey the laws which state that nothing should be flushed down the toilet or thrown into manholes which could interfere with the free flow of sewage, such as rags, litter, rubble, cooking oil and fat, and anything other than grey water and toilet paper,’’she adds.

The commissioning of the new plant is anticipated by December 2023. Soon thereafter, a further expansion will be implemented to cater for continuing urban growth in the area. Work will see construction of a membrane bioreactor (MBR), sludge dewatering facilities, new inlet works, pump stations, primary settling tanks and maturation ponds where effluent is purified before discharge.

“Importantly, it must be noted that the City does not discharge untreated sewage into the river. The plant currently operates within the design capacity in terms of flow rates. However, it is over its capacity in terms of nutrient load due to the population growth in the area which is serviced by the plant. The City is implementing a number of initiatives such as the addition of polymers for treatment to settle the nutrients while the expansion is underway. The City’s sampling and testing frequency has been increased to a weekly schedule, and will include input from the community on agreed sampling locations. These results are being shared with the National Department of Water and Sanitation, and with the CSIR,” concludes Limberg.


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