Sewage Wastewater Chlorine Tablet Precautions

Brent Hardbass, PE

English: Calcium hypochlorite formula

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Calcium hypochlorite is generally the approved septic wastewater chlorine tablets. It is very important that you do not confuse isocyanurates with calcium hypochlorite. Isocyanurates are generally used for swimming pool chlorination, not wastewater disinfection. You should never use isocyanurates for sewage wastewater disinfection or septic tank chlorination.

We can break down wastewater treatment systems into two categories; high and low wastewater flow rates. A high flow system is normally a large residential wastewater treatment system or commercial wastewater treatment system. The high flow systems generally use a product similar to NORWECO’s Bio-sanitizer disinfection tablets. The Bio-sanitizer tablets dissolve faster than the low flow chlorine tablets. Low flow systems require specially designed tablets, which are similar to the NORWECO Blue Crystal sanitizing tablets.

Low flow systems or systems that do not have flow equalization (FE) generally use of Blue Crystal type chlorine tablet. These tablets are specially design to work under these low flow conditions. The base material is still calcium hypochlorite, with a different tablet-bonding agent. If you are looking for low flow chlorination tablets, then we recommend NORWECO’s Blue Crystal disinfection tablets.

Commercial wastewater treatment systems, generally, have higher flow rates. The calcium hypochlorite tablets used in this application are designed for these higher flows. Commercial systems can flow in excess of 300 gallons per minute flows. NORWECO produces a specially designed calcium hypochlorite tablet that is known as “bio-sanitizer disinfecting tablets.” In both the high flow and low flow applications, the tablet size is the same (2 5/8 inch diameter, and 3/16 of an inch thick). Standard chlorine-tablet-feeder-tubes, generally 3 inches in diameter, readily accept this size of tablet. We recommend the NORWECO biodynamic tablet feeder LF series, as the best on the market.

Chlorine tablet handling precautions: Chlorine tablet vapors and the calcium hypochlorite tablets can be very toxic to your hands, face and lungs. In addition, these calcium hypochlorite tablets react quite violently with grease, oils and other petroleum products. In addition, dechlorination tablets and other types of chlorine can react quite violently with the calcium hypochlorite tablets.

Whenever you handle calcium hypochlorite tablets, you should use a protective face shield and rubber gloves. Be especially careful when you first open the tablet storage container. Large amounts of chlorine-based gases release when you first open the container. Never, breathe these gases in. The gases can damage your lungs, your face and other mucous membranes, such as your eyes. Handle calcium hypochlorite tablets caution.

How much chlorine should you expect to use?: A standard three bedroom 2-bath home should use about 12 chlorine tablets every four months. This assumes that a three bedroom two bath home has six persons living in it. A significantly higher tablet usage rate could indicate excessive wastewater flow, caused by a leaking faucet or toilet. Also, jerry-rigged and/or poorly designed chlorine tablet feeders could be the cause. First, check for water leaks, and then consider replacing your wastewater chlorine tablet feeder. For example, a jerry-rigged tablet feeder could be made with a 4 inch Tee with a vertical three-inch PVC tube. In this case, the chlorine tablets could be in constant contact with the wastewater. The tablets in it dissolve more quickly because the bottom tablet is partially submerged in the water. A good replacement consideration would be the NORWECO biodynamic LF series feeder.

The price you pay per chlorine tablet can vary greatly from vendor to vendor. Shopping online for your chlorine tablets is a very good option. For example, you can easily spend $100 or more, if you have a larger wastewater treatment system. If you can save 20% or more on the price that you pay per tablet, you can save thousands of dollars per year. It pays to shop for the best price.

In conclusion, calcium hypochlorite tablets should be the only type tablets you use in your wastewater treatment system. Make sure you take the proper precautions, if you maintain the system yourself. Use personal protective equipment at all times when handling the chlorine tablets. Make sure you store your chlorine tablets and clean, dry areas away from all petroleum products and other chlorine. Keep an eye on your chlorine tablet consumption. If you are using too much chlorine for the size of your wastewater treatment system, you should consider looking for water leaks in your system and/or replacing your wastewater tablet feeder with a NORWECO biodynamic LF series feeder or equivalent. Please feel free to leave a comment and tell us how you like this article.

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My Creative Site design edit

Sewage Wastewater Chlorine Tablet Feeder Design Considerations

By: Bruce Hardboss, PE


This article discusses minimum sewage wastewater chlorine-tablet-feeder design considerations.  As a wastewater engineer, I routinely see application of wastewater tablet feeders for chlorination designs that are not well thought out.  This article will highlight the NORWECO tablet feeder designs since we feel that the NORWECO tablet feeders are the best on the market.  The principles that we present are recommendations for you to implement in your design.

Feeder Tube

Tablet feeders generally have some sort if tube which is filled with the chlorine tablets.  The tube is easily removed for re-filling.  As noted in the figure below, the tube is slotted on the bottom, which allows the wastewater to contact the chlorine tablets, dissolving them, and thusly chlorinated in the wastewater stream.  The tube feeder product that you select should have a removable tube, such as the NORWECO design.

Tiered flow

The second design consideration should include some sort of tiered flow.  As in the figure above, as the flow is increased the width and depth of the tiered flow should also be increased.  This allows for, under low flow conditions, wetting of only the first tablet in the tablet tube.  This tiered flow design significantly reduces the rate that the tablets are expended.  In addition, under low flow conditions better chlorination due to contact with the first tablet is achieved.  The tablet feeder that you select should have a tiered flow design.

Tiered Flow Considerations


Tablet feeder that you select should also have a minimum warranty of 20-years.  Tablet feeders that come with a 20-year warranty, generally, are made from superior materials that resist corrosion, cracking and deterioration.  So if the tablet feeder that you select does not have a 10-year warranty.  I would suspect that the materials used are substandard.


The NORWECO tablet feeders also come within a unique feature.  At the base of the tablet feeder holding tube, 4 inch PVC piping can be glued or sealed on the top of the tablet feeder.  This feature allows you to bury the tablet feeder deeper than the standard riser tubes.  The PVC piping thickness can be increased to schedule 80, which allows for superior protection of the feeder riser tubes from the surrounding soil.  Alternatively, the NORWECO IT series tablet feeders include plastic direct burial risers, which are generally used in commercial applications. As we increase daily wastewater flow-rates, the tablet feeders increase the number of tablet feeder tubes, as noted in the figure below:

Increased Number of Chlorine Tubes With Increased Flow Rates


NORWECO’s Direct Burial ITR-S Series Tablet Feeder


As you shop around for your next tablet feeder, we strongly recommend the NORWECO line of products.  NORWECO is been in operation for over 100 years.  NORWECO’s products are seasoned, and continuously improved.  If you are considering purchasing or installing a tablet feeder in your present system, then please consider the designs options that we have presented in this article.  If you are interested in our NORWECO products, please click on any one of the images in this article, or merely go to the NORWECO products page on this website.  Our recommendations are written by a registered professional engineer with a strong background in wastewater engineering.

If you have any questions, then please feel free to contact us at

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