20 years ago, odor and corrosion were considered nuisance issues.  Today, they have become serious problems that adversely impact our quality of life.

So.....what changed?

Most municipalities testing for sulfides observed a steady rise from the early 1980’s to mid 90’s. These changes were subtle, yet very significant to odor and corrosion.

Many municipalities did not measure sulfides, but increases of 1500% were not uncommon where tested. (data courtesy of the City of LA, CA)

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 ...
   

• legislative changes impacting sewage biochemistry.

To protect public health the EPA enacted the 1983 Categorical Pretreatment Act. This legislation severely reduced metals limits for industrial dischargers.

Analysis of influent metals clearly shows the change in chemistry caused by pretreatment.

In the absence of metals bacterial activity increases. At dissolved oxygen above 1 mg/l aerobes reduce organic matter via oxidation.

Very little sulfide is produced at this stage.

Without metals to control bacterial growth, oxygen is more quickly depleted. At <0.1 mg/l dissolved oxygen anaerobic bacteria reduce sulfates to sulfide.

Although reducing metals was necessary to protect public health, as the graph (left) shows, pretreatment has contributed significantly to increased odors and accelerated corrosion.

The primary reasons hydrogen sulfide levels have risen are pretreatment and longer retention times.

Sewage has changed. If your odor and corrosion control program hasn't improved...expect more unhappy customers.