Q&A with Ron Bianchetti: Finding the Source of Costly Sewer Corrosion
Most urban wastewater contains chemicals that can form one of the most corrosive substances known to man: sulfuric acid. A recent study asks a new question: Where do these contaminants originate?
Does this study actually present a new view on sewer pipe corrosion?
Sulfuric acid (H2SO4) sewer pipe corrosion is an ongoing problem throughout the world. The problem isn’t new, but this study takes an interesting view on the use of sulfates on the drinking water side. About 80% of urban drinking water gets either flushed or run into the sewer system. Any sulfates present in drinking water can eventually—on the sewer side—become a constituent in the production of hydrogen sulfate, which contributes to corrosion of the sewer pipes. Hydrogen sulfide and sulfuric acid corrosion issues have typically been mitigated at the sewer level, but nobody has backed up and asked: Is hydrogen sulfide being developed in the sewer itself, or is there some other source?
Why are sulfate coagulants added during drinking water treatment?
Sulfate-based flocculent chemicals are used by some (but not all) water authorities to remove solids from source water. Because these chemicals are bipolar, their molecules attract dirt and sediment particles suspended in the water. When sufficient mass is attracted to the flocculent chemical substance, the mass settles to the bottom of the basin. What you’re left with on top is clear water. The flocculent doesn’t clarify the water completely. This is just the first course cut that readies the water for the next step, such as carbon filtering.
Do you know the estimated cost of sewer infrastructure corrosion?
Suffice it to say, it easily runs into the billions of dollars annually just in the U.S. (For more on this topic, see Corrosion Costs & Recommended Practices for the Water Industry.)
Do you agree that the industry needs to find water treatment alternatives?
Yes, I would agree that we need to rethink the use of aluminum sulfate-type products in the water system, so that we don’t have this carryover of sulfates that will contribute significantly to sewer system corrosion. Choosing another type of chemical for first-step drinking water treatment may significantly reduce the risk of concrete sewer corrosion.
The research, titled “Reducing sewer corrosion through integrated urban water management” by Ilje Pikaar et al., appeared in the August 15, 2014 issue of the journal Science. The researchers at University of Queensland’s Advanced Water Management Centre conducted an extensive industry survey of water plants and sewers across Australia, and found that aluminum sulfate—used as a coagulant in treating drinking water—was the primary source of sulfate-based corrosion in sewer systems. The paper proposes that the industry switch to sulfate-free coagulants as a viable cost alternative compared to the large potential savings in corrosion costs.