Sewer systems globally are corroding at an alarming rate and costing governments billions of dollars to replace, according to researchers at the University of Queensland.
The main cause for this corrosion is the presence of sulfide in sewage, which forms following the addition of sulfate compounds.
Sulfate is added to drinking water to purify it and it’s also found naturally in source water used for drinking water production and in sewage waste materials.
In oxygen-less environments, such as sewers, it turns to sulfide and, ultimately, to corrosive sulfuric acid.
Some water utilities have tried to remove sulfide after it forms but at great expense and with little success.
Dr Ilje Pikaar and colleagues at the University of Queensland did an industry survey and sampling campaign across Australia.
They suggest aluminum sulfate added as a purifier to drinking water treatment contributes about half of the sulfate levels in the sewers in Australia.
In their simulations, replacing aluminum sulfate with sulfate-free compounds at the drinking water treatment stage dramatically reduces concrete corrosion by 35% after 10 hours and 60% over longer durations.
The researchers say this sewer corrosion problem is largely a result of fragmented urban water management practices, which separate water supply from water sanitation, two seemingly independent systems which should really be considered together.
This research appears in the journal Science.
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