Lesson 8 - Water Final SAQ

1.  

SAQ:

***Your brewery is based on a working farm. You can source water directly from a large lake on the farm. Explain how you would treat the water to ensure that it is suitable for brewing product water. List all your assumptions.

Response:

The water is sourced from surface water and is based on a working farm. Based on this, you can assume that you would expect agricultural run-off into the water. Therefore, there are likely to be high levels of nitrates and other organic contamination, including high microbiological levels. Turbidity is also likely to be high, with significant solid material in the water (leaves, sticks, plants, animal life, litter, etc). Lakes are usually fairly stagnant, so there is a chance of algae (especially with the higher nitrate levels) and the colour is unlikely to be clear. The water may have high levels of dissolved oxygen as there is a large surface area to absorb oxygen. Photosynthesis from plants and algae is likely to occur in the water, generating oxygen. Iron and manganese levels are likely to be low, as will the levels of all the other minerals (compared to ground water). Surface water is usually softer than ground water.

Based on these assumptions, the following water treatment should be in place:

The water could be pumped into a large reservoir for storage. Some settling time should be allowed for large contaminants. This will also allow sunlight to break down some of the organic contaminants.

The water from the lake or the reservoir will be fed through a series of screens of different sized mesh, to remove large solid particles and objects from the water. The water is deemed low in Fe, so aeration is not necessary. Chemical treatment will follow to coagulate and precipitate out solid particles, including bacteria, viruses and protozoa. The water will be filtered through a sand filter to remove turbidity, algae and microbiological contamination. The trapped bacteria will help breakdown organic material in the water as it filters through the sand bed and then through a microfiltration unit to remove any remaining bacteria and suspended solids. The water will then go through an activated carbon filter to remove any other organic contaminates, such as THMs. We would not expect any chlorine in this water, so there would be no need for de-chlorination.

We have assumed that the water is soft, with low alkalinity and low mineral content. There is thus little need for a cation exchanger, or other methods of water softening. However, we have noted that the nitrate levels are high, thus there may be a need for anion exchange – specifically a Weak Base Anion exchanger, which exchange hydroxide ions for nitrate. The water should then be sterilised using chlorine dioxide. Ozone or UV could also be used.

At this point, the water will be potable. We have mentioned that the water is soft. It has been through an anion exchanger, so the mineral content is likely to be very low at this point. The water’s pH should now be adjusted.

Mineralisation will need to occur, specifically the addition of calcium (water was soft) and chlorides and sulphates (anion exchanger removed them) before mashing in. Not all treatment options have been covered. You could also mention (depending on assumptions) aeration and iron/manganese removal, cation exchange, reverse osmosis, other membrane filtration and other methods to reduce alkalinity (heat, lime, acid).