| Thioguard® Why has
the H2S increased?
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.
|
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| 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. |
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| 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. |
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| Without metals to control bacterial growth, oxygen is more quickly
depleted. At <0.1 mg/l dissolved oxygen anaerobic bacteria reduce sulfates to sulfide |
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| 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. |
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Sewage has changed. If your odor and corrosion control program hasn't improved...expect
more unhappy customers.
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