Lesson 7 - Brewing Product Water Final Treatment SAQ

SAQ:

**The base product water entering the brewery has the following high-level composition:

• High levels of magnesium chloride.
• Low levels of bicarbonate.
• Summer levels of chlorine.
• A risk of THM.
• High levels of sodium sulphate.
• Trace levels of iron.

Explain what you would include in your final product water treatment plant to ensure that the water is:

• free of microbiological contaminants
• soft
• of low alkalinity
• free of THMs

Please note- you are not able to use reverse osmosis.

Response:

Chlorine can damage membrane and some ion exchangers, so the first task is to remove chlorine. However, it has also been noted that there is risk of THMs in the water, so the best solution would be to use an activated charcoal filter. This would remove both chlorine and organics, such as THMs.

The iron needs to be removed. Although it is possible to use phosphoric acid or oxygen to precipitate or filter out the oxidised iron or phosphate, the iron can be removed by cation exchange. A cation exchange removes the magnesium chloride and calcium or magnesium associated with bicarbonate, so the cation exchanger can be used to remove both.

Hardness due to bicarbonate can be removed by multiple methods, such as heating, lime addition and acid addition. However, cation exchange is the most effective means, as it removes the calcium and magnesium associated with bicarbonate hardness.

The required cation exchanger would be a SAC (strong acid cation) exchanger, as this can remove the magnesium chloride, as well as the calcium or magnesium associated with the bicarbonate and the iron.

Sulphates, chlorides and the actual bicarbonates are removed by anion exchange. For this particular task, a WBA (weak base anion) exchange will suffice. By putting the SAC and WBA in series (or as a mixed bed reactor), the two systems will remove all the magnesium, iron, sodium, chloride and sulphates from the water. A SBA (strong base anion) exchanger can remove carbonates, but the cation exchanger will have already removed the alkalinity caused by magnesium or calcium bicarbonate/carbonate.

The water leaving this system will have had all of the compounds listed above removed. However, it would need to be safeguarded against microbiological infection, as the chlorine has also been removed.

There a number of options, such as sterile filtration, ozonation, UV or chlorine dioxide. UV does not give residual protection, only point of contact and sterile filtration also does not give residual protection as the water could become infected post-filter. Ozone is expensive and so the best option may be to use chlorine dioxide, which is very effective and provides some residual protection.