A water treatment additive is contributing to corrosion in Australian sewers, according to a paper published last week in the journal Science.
Researchers from the University of Queensland conducted sampling in South East Queensland over a period of two years, as well as an extensive industry survey across Australia and a comprehensive model-based scenario analysis of the various sources of sulfide. They concluded that the addition of aluminum sulfate during the drinking water treatment process contributes substantially to the sulfate load in sewage and indirectly serves as the primary source of sulfide.
In sewage, sulfide is generated from sulfate and organic waste and can be stripped as hydrogen sulfide gas into the sewer atmosphere. This, in turn, oxidises with air to form sulfuric acid, which is extremely powerful in corroding concrete -- the most common material used in large sewer pipes, the researchers explained in an article for The Conversation.
The researchers claim that in some cases the lifetime of concrete pipes is being reduced by up to 90 percent because of sulfide-induced corrosion. This costs billions of dollars every year. They also said, however, that a simple change in the chemicals used to treat water could reduce much of that corrosion.
Water treatment plants should switch to sulfate-free coagulants to avoid this unintended consequence of drinking water production, they argued, adding that there would be only marginal additional treatment costs and potentially significant overall savings across the whole water system by reducing corrosion.