Resource: Engineering News    By: Schalk Burger
The effective monitoring of wastewater- derived contaminants in water abstracted for drinking is an important aspect of providing safe drinking water, says US engineering firm Hazen & Sawyer director of applied research Dr Ben Stanford.

“Humans are already part of an indirect water reuse system where one community’s wastewater is discharged into a river and becomes another downstream community’s drinking water. We are all exposed to contaminants introduced into watercourses by farms, industries, wildlife and people worldwide,” he notes.
The complexity of the chemistry of water contaminants at different stages of the water cycle results in no single technology being able to remove all the contaminants. Thus, a multiple barrier system is needed to ensure their reduction and removal, says Stanford.

Many medicines used by humans are excreted in urine, and subequently enter the wastewater system. Wastewater treatment plants most effectively treat biological contaminants in water and do not remove all chemical contaminants from water, which is then sent back into watercourses after treatment. However, most medicines present in drinking water are thousands of times below the levels of concern for human consumption.

“Removing contaminants from water drives the development of advanced technologies, but we must be aware of the kind of contaminants that are in the water and the true risk to humans,” he emphasises and points out that water receives disproportionate attention with regard to chemical contaminants.

Advanced oxidation technologies that produce hydroxyl radicals, an oxidant twice as powerful as chlorine, effectively remove many pharmaceutical and personal care products and disinfect the water. High- energy ultraviolet (UV) light can be effective in destroying some contaminants, such as N-nitrosodimethylamine, an organic chemical that is a known carcinogen, though in many cases the addition of hydrogen peroxide is necessary for contaminant destruction.

Reverse-osmosis techniques effectively remove most contaminants, but create a concentrated waste stream that contains the contaminants, and which must still be disposed of, says Stanford.

Ozone, another strong oxidant, can also be used before or after water enters the reverse-osmosis membranes to remove contaminants, he notes.

However, international trends in water reuse treatment often include the use of UV or oxidation and membrane-based technologies as part of a multibarrier treatment scheme. Alternative schemes such as ozone and granular activated carbon filters are being explored to disinfect the water and remove contaminants, residual odours, discolouration and by-products created by other treatment processes.

“An analysis must be completed on the use of different techniques and technologies to balance the energy needed to drive the processes with achieving public health goals through the removal of contaminants of concern. “The greater the effort invested in removing the contaminant, the greater the energy and costs, but also the greater the impact on removing contaminants,” notes Stanford.

There are several international best practices and benchmarks that utilities can use to determine effective methods of removing contaminants, but utilities must be aware of the different contaminants present in the water and have clearly defined public health goals before deploying technologies, he highlights.

Several prominent organisations recently weighed in on the issue of pharmaceuticals in water and recycled water, including the US Environmental Protection Agency, the World Health Organisation and the US National Water Resources Research Institute, says Stanford.

The South African Water Research Commission (WRC) is conducting research to deter- mine the pharmaceutical and personal care products present in South African waters and the typical amounts, in order to calculate the size of the risk, if any, adds Water Research Commission research manager Dr Jo Burgess.

Experts from water boards and universities are working together on numerous WRC projects to provide a clear picture of whether there is cause for concern, and what should be done to treat the water in the event that pharmaceutical and personal care products are detected, she says.
 



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