Lesson 6 - Brewing Product Water Final Treatment
This lesson deals with the various physical and chemical procedures that we can use to treat all water supplied to the brewery. It also examines the processes used to make water potable (if the water supplied to the brewery is not already potable).
We will also explore all additional treatment processes that we can use to prepare water to the correct quality specifications, making it fit for use as brewing product water.
Weakly Basic Anion (WBA)
WBA resins have amines as the functional group and exchange hydroxyl ions for the anions of strong acids such as nitric, sulphuric and hydrochloric acid. However, they will not remove the anions of weak acids, carbon dioxide or silica which are more stable in solution.
They are used where strong acid anions predominate and silica reduction is not required. The equation below illustrates the removal of strong acid anions by WBA ion exchange:
resin-OH + (strong acid anion)- → resin-strong acid anion + H2O
The main advantages of this exchanger type are its high capacity and the effective utilisation of chemicals. If used before strongly basic resins for full demineralisation, WBA resins can remove sulphates and chlorides more economically and effectively than using a strongly basic resin alone. They are also regenerated more efficiently than strongly basic resins.
Regeneration takes place with sodium hydroxide according to the equation below:
resin-NO3 + OH- → resin-OH + NO3
The ability of the WBA resins to remove nitrate means they are suited to treating surface water contaminated by fertilisers. Although the water guidelines recommend nitrate levels to be below 50 mg/L, it is preferable to have nitrate levels below 10 mg/L in brewing product water. This is to reduce the total amount of nitrate that could be reduced to nitrites, which can be poisonous to yeast cells and a putative carcinogen. Nitrates are also easily removed using strongly basic anion resins with chloride as the exchange ion. Ion exchange resins designed specifically for nitrate removal are also available.
Because they do not remove carbonate, WBA resins are the least used of all the resin types for brewing. They can cause a slight increase in pH because the hydroxyl exchange ion neutralises the H+ liberated from the acid anion that they remove but carbonate is left in solution. Some pH adjustment of the treated water therefore may be necessary depending on the carbonate levels in the feed water