Passive vs Active DeChlorination

brass faucets,dripping water,fotolia,gardensMunicipal water decision makers now face the choice of which dechlorination method to employ in their water system maintenance program and emergency spill plan.  AWWA standards issued in 2010 now require that most field water discharge be dechlorinated before release into the local environment. This issue involves a choice between two fundamental approaches to water dechlorination, passive and active; the two primary categories all methods available fall into. The following discussion reviews important points to consider when choosing between passive or active treatment

The primary difference with these two approaches lies in how chlorine is neutralized.  Passive dechlorination involves bringing a portion of the water into contact with chemical which then mixes with the main flow of water which neutralizes chlorine as the chemical dissolves and disperses.  Active dechlorination involves preparing neutralization chemical for injection into waters through a mechanical device, causing neutralizing chemical to mix with water as it passes through the device.

Passive treatment can also be done by holding waters in open impoundment and letting chlorine oxidize and break down naturally, but time and space requirements make it impractical. 

The remainder of this discussion will explore mechanical devices used for dechlorination and will compare the practicalities of passive versus active equipment. 

Passive DeChlorinabuckets,households,pails,Photographstion

Passive dechlorination involves bringing a portion of the water into contact with chemical which then mixes with the main flow of water which neutralizes chlorine as the chemical dissolves and disperses. 

Passive treatment can also be done by holding waters in open impoundment, but this approach requires more time and space for water storage and dechlorination than is practical in the majority of situations.

This approach works adequately for low level residual chlorine at medium to high flow rates.

coils,gardening,hoses,irrigates,irrigation,photographs,tools,water hoses,watering,watersActive DeChlorination

Active devices rely on preparing neutralizing chemical as liquid solution for injection into discharged water.  A mechanical injection device draws water by vacuum from the solution supply and injects it into the main discharge stream as it passes through the device.  In most cases mixing is so thorough and chlorine neutralization so complete that the water can be released directly to the local environment without additional holding time.

Cost of Owenership

Passive Devices

Because of their relative simplicity passive devices have lower cost to manufacture and frequently less expensive than active devices.  Their performance range varies with each device and typically only neutralizes potable drinking water. If you are going to protect the environment, ascorbic acid tablet would be the choice of chemical however that will come with the highest cost in chemical.

Active Devices

More complex and higher tolerance, active devices are preferable when large volumes of water with high or low chlorine residual levels are involved.  Their primary strength is in achieving complete mixing within the tube of the injector device.  Active devices also offer the user to use the lowest in cost and most environmentally safe dechlorination chemical with a wider performance range than passive devices, and some models can be used for chlorination as well as dechlorination.

Which Method to Choose

Selecting a device should be based on three dominant areas of concern, 1)Total Cost of Ownership, 2)ease of use, 3)overall chemical consumption. For operators dealing only with low flows and residual levels passive dechlorination can be cost effective, given the availability of sufficient time and holding capacity for complete neutralization of residual chlorine to occur.  For the remainder of situations one is likely to encounter, active dechlorination offers many advantages.

First issue of importance is lower overall chemical consumption. 

Because active devices more closely meter chemical into the discharge stream less chemical is needed to treat the same volume of water as that needed for passive dechlorination.  Because of time constraints often faced in passive treatment it is frequently necessary to use more chemical than active treatment requires, to reduce chlorine residual to levels necessary for release, within the time constraints of the project.

Active devices are frequently easier to use because once set they meter a consistent volume of chemical into the discharge stream based on water flow rate. 

Passive treatment requires constant monitoring to assure chemical is replenished as it dissolves.  Tablet and granulated chemical can dissolve at variable rates over the period of treatment and must be continually replenished as chemical dissipates into solution. With active treatment one only needs to stage the quantity of chemical needed to complete each leg of discharge treatment, setup the equipment and wait for necessary volume of water to pass through the equipment. 

A number of firms manufacture and sell dechlorination devices.  For a more complete discussion of each and their capabilities download our free report, Making the Right Choice in Field Dechlorination.  It offers a complete comparison of each manufacturer’s equipment and discusses the performance range of each.

Making the right choice

While the different devices discussed in our free report Making the Right Choice in Field Dechlorination each have strong points, one manufacturer’s active dechlorination device offers the widest range of performance and chlorinates as well as dechlorinates.   The H2O Neutralizer from Measurement Technologies offers the widest range of performance of all devices currently available.  Built with a patented venturi induction design, the H2O Neutralizer has no moving parts and works based on the natural physics of flowing water.  Relying on the same principals as old fashioned vehicle carburetors to draw liquid from an external reservoir into the main discharge flow, the H2O Neutralizer requires no electrical or mechanical power to operate.

With a wider range of performance and the most consistent draw rate of all active treatment devices, the H2O Neutralizer has the lowest Total Cost of Ownership of any dechlorination device currently on the market.

To review what the H2O Neutralizer can do to meet your chlorination and dechlorination needs and get your free copy of Making the Right Choice in Field Dechlorination visit our website at and learn more about how our active dechlorination system can help you meet your needs.

Special offer - 30 Gal. of No-Chlor CTS with your Trade in...

Trade in any of the other devices reviewed in Making the Right Choice in Field Dechlorination, with your purchase of an H2O Neutralizer, and receive thirty gallons of No-Chlor Calcium Thiosulfate DeChlorination Solution free when we receive your trade-in.