Forcemain Systems Sulfide Control
Forcemain systems are typically high sulfide generators due to septicity conditions related to full pipe flow and a greater anaerobic slime layer (biofilm) thickness. Primary factors that influence sulfide loading generation in a forcemain include sewage temperature, BOD, retention time, pipe size and flow. Gaseous hydrogen sulfide (H2S) release at the forcemain discharge is usually the main concern related to odor and corrosion control needs; however, corrosion problems within the pipe can be of a concern (e.g. "crown cutting") at locations where air pockets can lead to concentrated H2S gas build up.
Some basic considerations for assessing an appropriate sulfide treatment method for forcemain systems include:
- Retention time / duration of control
- Pump station type / cycling (e.g. vfd; start/stop, etc).
- Forcemain injection tap points, if any (e.g. air relief valves)
- Existence of intermediate re-lift stations or in series pump stations
- Manifold forcemain systems
Treatment Methods
Several proven treatment methods exist that can be evaluated depending on retention time and sulfide loadings. As a general guide the following technology fit can be used:
Note:
(1) If a forcemain tap can be located within approximately 30 minute upstream of the discharge, H2O2 is a cost effective approach.
(2) PRI-SC requires intermediate dosing location for H2O2.
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