Adjusting the chlorine level by adjusting current in the Bac Terminator

Authors: S.S. Bjerregard and P. Fogh. Date: February 2011 Contact: Adept Water Technologies mail@adeptwatertech.com

Key words: drinking water, chlorine, current, voltage, cost, Bac Terminator, bacteria, disinfection

Chlorine adjustment vs. current – summary

BacTerminator is a unit used for disinfection of e.g. drinking water without adding any chemicals to the water. The principle underlying BacTerminator disinfection is electrolysis, turning salt in the water into hypochlorous acid, hypochlorite and chlorine and thereby effectively eliminating bacteria and other microorganisms.

Control of the chlorine in the BacTerminator is often desired. This can easily be achieved by adjusting the current.

The amount of chlorine produced also depends on the amount of salt (NaCl) in the water. Theory

Primary electrode processes goes here..

Deduction that chlorine production is proportional to the current goes here…

The sum of the resistance in the system goes here (anode voltage drop, conductivity of media, cathode voltage drop) – two of them are constant, one variable.

How much power is used to produce free chlorine?

This study investigated the current and voltage required to reach a given chlorine production. Since chlorine production depends on the salt (NaCl) content in the water, with different chlorine contents were tested.

The study resulted in a set of tables detailing the current and the voltage which must be applied to the BacTerminator to reach a certain level of chlorine production.

Results

Tabels 1 and 2 provide an overview of how current and voltage need to be adjusted in order to produce 1 ppm free chlorine.

Low current and voltage are required to produce 1 ppm free chlorine in water with high conductivity and chloride content. High current and voltage are needed to produce 1 ppm of free chlorine if the conductivity and chloride content are low. This is because the resistance of the electrolysis chamber depends on the conductivity of the water. At low conductivity the resistance is high, and a high current and voltage are therefore needed to produce chlorine. High current and voltage mean higher costs. How to minimise the cost of using the BacTerminator is discussed here:. In general the Bac Terminator is a more cost efficient disinfection method than chemical disinfection.

A remark on the salt composition, the effect on the chloride fraction

Table 1. Power (watts) needed to achieve 1 ppm free chlorine in 1 m3 Water. The values were obtained by linear extrapolation of measured values.

200 μS/cm    400 μS/cm    600 μS/cm    1000 μS/cm  1500 μS/cm   2000 μS/cm

10 mg/L Cl-165614882555233337325188
20 mg/L Cl-47560385964310831306
50 mg/L Cl-94131148204170198
75 mg/L Cl- 77919490104
100 mg/L Cl- 8070726863
125 mg/L Cl-  50585653
175 mg/L Cl-  24454748
250 mg/L Cl-   302838
300 mg/L Cl-    3050
How to measure free chlorine

The chlorine content of water samples was measured after running them through the Bac Terminator. The water samples differed in conductivity and chloride content. For each sample, several measurements were made at different currents and voltages.

Methods, equipment, and reagents for determination of chlorine were obtained from Hach Lange. The standard reference instrument used for colorimetric measurement was the DR2800. Chlorine was determined with the LCK310 cuvettes.

1) Krasner S W. (2009) The formation of and control of emerging disinfection by-products of health concern. Phil. Trans. R. Soc. A 367:4077-4095