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Wastewater Treatment Odor Control: Wet Scrubber Systems

Posted by Mike Baranski on Jul 5, 2017 8:10:41 PM
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Indispensable Wastewater Odor Control Technology

This article introduces the basics of how wet scrubber systems support wastewater treatment odor control, and offers a look at the best and most reliable method for directing odorous fumes to the scrubber systems.

While many of today’s wastewater treatment plants still utilize the same processes from generations ago, others have begun diversifying their water treatment technologies in an effort to improve not only water quality, but air quality as well.

At any facility where wastewater is centralized, contained, or broken down, offensive odors may exist and be created by the specific processes of the treatment plant. Primary and secondary treatment systems along with biosolids-processing-facilities are the largest producers of these fumes. As population densities grow and communities expand, wastewater odor control is becoming an increasingly prominent problem to solve for many waterworks facilities.

MORE THAN JUST A SMELL

During the early stages of treatment, the wastewater systems focus on settling or skimming large sediments and reducing biochemical oxygen demand (BOD) from within the wastewater. During BOD reduction, microbes or “bugs”, called sulfate-reducing-bacteria thrive on the sulfate ion, SO4, as their source of oxygen for respiration. This process gives off hydrogen sulfide (H2S) which most people recognize as the rotten-egg odor coming from treatment plants. 

Heavily Corroded Pipes

Hydrogen sulfide gas can cause more problems than just an offensive odor. It is corrosive to metals which can create issues with equipment and can complicate matters further along in the treatment process. 

Additionally, the United States Department of Labor - OSHA warns: 

"[H2S] is a highly flammable, explosive gas, and can cause possible life-threatening situations if not properly handled. In addition, hydrogen sulfide gas burns and produces other toxic vapors and gases, such as sulfur dioxide."

Heightened levels of H2S can also be toxic to workers or people exposed to amounts measuring greater than 100 ppm. 

Prolonged low-level exposure and/or rapid high-level exposure can result in "olfactory fatigue" which deadens our sense of smell, leaving us unaware of the poisonous gas. This risk alone should provide sufficient reason for implementing dependable air quality and odor control measures like wet air scrubbing into the wastewater treatment process. 

HOW WET SCRUBBERS WORK

For the purposes of vapor phase wastewater odor control, wet scrubber systems are typically located at the wet wells, headworks, grit chambers and biosolids treatment areas. These systems start by drawing large amounts of process-air from the fume source to the scrubber unit. The air is drawn under negative pressure to help ensure that contaminants are not released prior to reaching the scrubber itself. 

Properly installed coated-stainless-steel vent pipes are critical for carrying the corrosive exhaust fumes through the hoods and vents of the treatment facility to the wet scrubbing units. These can be short runs of 40 to 50 feet or can be hundreds of feet long across bridges and supports. 

Wet well lift station fitted with PermaShield PipeThe use of PermaShield Pipe (PSP®), a high grade stainless steel vent pipe with proprietary Fluoropolymer Barrier Coating on the inside, has proven to be the best and most reliable method for directing corrosive fumes to the wet scrubber systems.

Given the highly flammable nature of hydrogen sulfide gas, PSP® with it's zero flame spread rating, also dramatically improves the fire-safety of the system. 

Once the hazardous fumes are safely transported from their source, the wet scrubber systems convert the vaporous pollutants into a liquid/condensate solution. 

This is accomplished by spraying special chemical and water mists into the scrubber chambers, which solubilize targeted pollutants based on their chemical compounds. The resulting liquid/condensate is then purified. 

There are many different chemicals used in the scrubbing process to solubilize different vapors.

One of the chemicals used to remove hydrogen sulfide is sodium hydroxide. In a two-stage system, sodium hydroxide solubilizes H2S before passing it to a second round of cleansing. The second stage of the scrubber will recycle the effluent back through another scrubber chamber where sodium hypochlorite is added to remove the sodium hydroxide. 

Through this process, wet-air-scrubbing can remove one of the greatest dangers from wastewater treatment systems; flammable, toxic, and corrosive hydrogen sulfide gas (H2S).

In Summary

Wet air scrubbing is but one technology, and one aspect, of the never-ending process by which wastewater treatment plants work to purify both air and water before discharging the effluent back into our lakes, streams, and oceans to be safely used again.

Fab-Tech is proud to supply PermaShield Pipe® as a cost effective, durable, and dependable component for any stage, or any system, within this process. 

If you would like more information about PSP® wastewater treatment odor control duct, please feel free to download our general information guide below:

Corrosive Fume and Wastewater Odor Control Exhaust Duct Information Guide

OR

Click here to learn more about wastewater odor control in waterworks applications 

Topics: wastewater odor control, wet scrubber systems