When it Comes to CSOs, What’s at the End of the Line Makes All the Difference

Posted by Accu-Tab News Team
September 17, 2019

Two Pipes Photo

Is your municipality studying ways to upgrade or combine your current combined sewer overflow (CSO) facilities to comply with the Clean Water Act? 

One of the most important components of any CSO comes at the end of the line, where overflow waterborne pollutants encounter the chemical or mechanical processes that will make them safe for discharge. Choosing the right treatment system for your CSO needs to be aligned with: safe operation and low maintenance, reasonable capital and operating costs and effective treatment.    

What follows is a brief review of the top current wastewater treatment methods that meet effluent guidelines:

Accu-Tab® Cal-Hypo and CleanSlate® Dechlorination Systems – Accu-Tab and CleanSlate systems offer a two-phase approach to treating CSO wastewater before discharge. The Accu-Tab system features specially engineered chlorinators with controlled release of 68 nominal Family of Chlorinators Photo UPDATEDpercent three-inch calcium hypochlorite (cal-hypo) tablets. When stored properly, these tablets have a prolonged shelf-life to deliver a more effective solution for intermittent use. The Accu-Tab system eliminates the hassles of added training and SCBA requirements that come with chlorine gas cylinders. In comparison to liquid bleach, spill risks are vastly minimized thanks to solid chemicals, meaning no dual containment is necessary. Cal-hypo tablets also have reduced toxic fumes that can be common with liquid bleach. The equipment used to accurately dose Accu-Tab tablets has few moving parts, meaning preventative maintenance is kept to a minimum.

Once the chlorination stage is complete, CleanSlate dechlorination tablets, consisting of 90 percent active ingredients including sodium sullfite and sodium thiosulfite, allow for discharge of water that meets NPDES, Clean Water Act and Tier II Stormwater standards. The CleanSlate dechlorination system uses analogous equipment to the Accu-Tab system for ease of operation and maintenance.

Chlorine Gas – Though a chlorine gas system is economically enticing based upon its 100 percent chlorine strength, the added safety liabilities must be considered. Since most CSO treatment facilities are typically unmanned, a chlorine gas cylinder leak could go undetected for days at a time. This is particularly concerning since many facilities are located on riverfronts that may have community recreation or businesses nearby. When utilizing gas, trained staff members must wear respirators whenever they need to adjust or replenish cylinders. A separate dechlorination unit is also required here after the chlorination process.

Sodium Hypochlorite (Liquid Bleach) – Safety concerns must also be taken into consideration when considering sodium hypochlorite systems. Large volumes of bleach will require secondary containment and could cause an OSHA recordable if a spill were to occur. With sporadic delivery and intermittent use, liquid bleach has the potential to degrade while it sits unused, leading to unpredictable chlorine delivery when reliable doses are needed most. Like any chlorine-based disinfection method, a separate dechlorination system is required as well.

UV Disinfection – UV has an extremely high kill rate of pathogens, yet implementation of this disinfection system can come at a high price. First, UV systems are one of the most costly to install. Then, unclean water inherent in CSO operations can cause UV bulbs to cloud and lose effectiveness rapidly, causing repeated maintenance. Finally, operating costs associated with UV disinfection should be closely scrutinized due to the fact that the system’s parts frequently need replaced and it takes large amounts of electricity to effectively run.

Want to learn more about the Accu-Tab and Cleanslate CSO advantages? Contact an Accu-Tab specialist today or check out our Municipal Water/Wastewater and Industrial Applications brochure.


Topics: Wastewater, CSO


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