Wastewater is extremely harmful to concrete and steel due to its propensity to form hydrogen sulfide gas. Hydrogen sulfide is corrosive and can also react to create sulfuric acid on the surface of wastewater containers, which rapidly damages them. Unfortunately, the old method of coating the interior of wastewater containers using coal tar epoxy has a number of drawbacks—the coating itself can also be damaged rapidly by acid or other chemicals in wastewater. If your treatment plant's wastewater reservoirs and lines are continually leaking due to corrosion, here's what you should know about new industrial coatings that offer more protection.
Why Is Wastewater Harmful to Concrete and Steel?
When a reservoir or sewer line isn't ventilated well, anaerobic bacteria begin to grow in the wastewater. Due to the presence of sulfur and carbon from the organic material in the wastewater, these bacteria are able to form hydrogen sulfide gas. Hydrogen sulfide gas is heavier than air, which would normally keep it at the waterline. However, since there's no air in the reservoir or sewer line, it's able to rise.
Once the hydrogen sulfide rises to the top of its container, it reacts with water to form sulfuric acid, and sulfuric acid will quickly erode both concrete and steel. Over time, this causes severe pitting and erosion. Eventually, the wastewater container will begin to leak, releasing wastewater into the local water table.
What Type of Industrial Coating Should Wastewater Treatment Plants Use?
The only way to prevent hydrogen sulfide gas from corroding wastewater containers is to apply an industrial coating to the inside of the container. Traditionally, coal tar epoxy was used for this purpose—it's very inexpensive.
Unfortunately, coal tar epoxy has a number of downsides. It can only be applied to dry surfaces and it requires a lengthy curing time before it can be immersed in wastewater. Wastewater reservoirs can't be used until the coal tar epoxy fully cures, which is a major inconvenience.
Coal tar epoxy is also carcinogenic, and maintenance workers at a wastewater treatment plant are sometimes exposed to it while performing inspections or making repairs. This can potentially create liability issues for a wastewater treatment plant if a worker develops cancer after repeated exposure to coal tar epoxy.
Finally, coal tar epoxy typically does not have a very long service life in wastewater applications. Sulfuric acid slowly eats away at the coating itself until the concrete underneath is exposed. Repeated exposure to sulfuric acid also causes the coating to become brittle. Thermal expansion and contraction of the concrete underneath can cause brittle coal tar epoxy to slowly flake off, which also exposes the concrete underneath to sulfuric acid.
Thankfully, new industrial coatings solve some of the major problems inherent with coal tar epoxy. Elastomeric coatings that are slightly alkaline are perfect for wastewater treatment facilities. Elastomeric industrial coatings are able to bend slightly, which prevents them from being damaged when the concrete underneath expands or contracts. The slight alkalinity neutralizes any sulfuric acid that forms on the surface, making these coatings much more resistant to sulfuric acid and wastewater that's slightly acidic.
Since these new industrial coatings last longer than traditional coal tar epoxy, wastewater treatment plants experience much less downtime when they apply these coatings to concrete or steel wastewater reservoirs. Waiting for coal tar epoxy to cure can significantly hamper wastewater treatment operations, especially if all of the coatings all start failing at once due to age and deterioration.
If you want to minimize operational downtime, contact an industrial coating contractor in your area that has experience working with wastewater treatment plants. The newer corrosion-resistant elastomeric coatings are more expensive than coal tar epoxy, but they have much greater resistance to the harmful effects of wastewater.
For more information, contact an industrial coating contractor in your area.
