Brewing Water Treatment | Chlorination

One single milliliter of fresh water holds more than one million bacterial cells. This shocking fact shows how important is the disinfection of water, not only for consumption but also for brewing. Despite UV Light, ultrafiltration, and ozonation, chlorination is the most used process to disinfect water and this article will approach it. I hope you enjoy it!

Chlorine Adding

Free chlorine can be added to water by gas bubble or by adding sodium or calcium hypochlorite. In both ways, it will hydrolyze forming hypochlorous acid (HOCl).

The hypochlorous acid is a weak acid and will disassociate forming hypochlorite ion (OCl-).?

This reaction rate is controlled by pH. At pH below 7.6 HOCl will be predominant.

Hypochlorous acid (HOCl) has stronger germicidal power, causing lower pH better for disinfection (optimal range is 5.5 to 7.5).

How does the Disinfection work?

Chlorine is a good pathogen killer because it attacks the chemical bonds in their molecules. When chlorine comes in contact with compounds, for example, enzymes, one or more hydrogen atoms are exchanged by Cl, which causes the entire molecule to change shape, killing the microorganism or at least preventing it from reproducing.

The Hypochlorous acid (HOCl) has no electrical charge (neutral) while the hypochlorite ions (OCl-) are negative. As the cell wall is negatively charged, it can be penetrated by HOCl which will disassociate into hydrochloric acid (HCl) and an atom of oxygen (O). Oxygen is also a strong disinfectant because can oxidize proteins and lipids, breaking the cell wall.?

Effectiveness

The measure that evaluates the effectiveness of the disinfection process is the “CT” value. CT is “Concentration X?Time”, in ppm and minutes respectively. This means that when doubling the concentration, only half of the time is needed to achieve the same level of effectiveness.

Chloramine

Chloramines are the result of reactions between chlorine and ammonia compounds, forming monochloramine, dichloramine, or trichloramine.

Hypochlorite can react with organic compounds forming carcinogenic compounds known as disinfection by-products (DBPs). DBPs are undesirable in fresh water and are controlled by many environmental regulations. Chloramine is preferred to chlorine because it does not form DBP. In many cases, ammonia is added to the water after chlorine, inducing chloramin formation.

The disadvantage of the use of chloramine is it has a lower odor threshold (3 – 5 ppm) than chlorine (5 – 20 ppm) and it is responsible for the odor in swimming pools.

Chlorophenol

Chlorine must be removed from the water before brewing because chlorine can bind with phenols producing chlorophenol. This compound is responsible for a very unpleasant off-flavor of “band-aid”, besides being toxic. Even a small quantity of chlorine is enough to create chlorophenol and possibly doom the whole batch.

Stainless Steel Corrosion

The equipment and tanks in a brewery are normally built in austenitic stainless steel AISI 304, 304L, or 316L. These alloys have good corrosion resistance due to the presence of a high content of chrome, which forms a passive layer protecting the material. In the presence of chlorine, pitting corrosion can be induced in the shell of the tank, damaging the equipment. Even stainless steel AISI 304 (the most common material in breweries) can deal with chlorine in lower concentrations and temperatures but when is necessary to store hot chlorinated water (or higher chlorine content) the brewery must evaluate using a more noble materials, such as AISI 316L.

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In the next article, we will approach the chlorine removal methods!