H2S: Historical Increase

25 years ago, corrosion and odor of wastewater were considered nuisance issues. Today, the increase of hydrogen sulfate has become a serious problem that can adversely impact our quality of life.

What changed?

Most municipalities (testing for sulfides) observed a steady rise from the early 1980s to mid 1990s. These changes were subtle, yet very significant to odor and corrosion. Many municipalities had never tested for sulfides, but increases of 1500% were not uncommon, where they were measured. A variety of factors have contributed to increased sulfides:

- Longer retention times caused by urban sprawl and centralized treatment strategies
- Low flow plumbing fixtures and other water conservation measures
- Legislative changes impacting waste- water chemistry and biochemistry
- Phosphate based detergents replaced by Sulfate based detergents

To protect public health, and the environment, the EPA enacted the 1983 Categorical Pretreatment Act. This legislation severely reduced metals limits from industrial discharges. Analysis of influent metals clearly shows the change in chemistry caused by pretreatment.

In the absence of metals, bacterial activity increases. At dissolved oxygen concentrations above 1 mg/L, aerobes reduce organic matter via oxidation. Very little sulfide is produced at this stage.

Although reducing metals was necessary to protect public health, pretreatment has contributed significantly to increased odors and accelerated sulfide related corrosion.

Sewage has changed. Odor complaints have increased and infrastructure failures have become prevalent.

Without metals to control bacterial growth,
oxygen is more quickly depleted.

At < 0.1 mg/L dissolved oxygen, anaerobic
bacteria reduce sulfates to sulfides.






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