Application of Reverse Osmosis Treated Water in Beer Production

The water quality indicators of raw water, coarse filtered purified water and treated water measured at different times are shown in Table 1.

Table 1: Quality indicators of raw water, purified water and treated water Unit: German degrees

It can be seen that the total hardness of the raw water is between 17 and 23 degrees, and the pH value is between 7.2 and 7.6. The temporary hardness and permanent hardness fluctuate greatly at different times, which does not meet the requirements of brewing water and cannot be directly used for beer brewing; the treated water made by reverse osmosis membrane has too low pH value, low total hardness and too few ions in the water, which causes the activity of amylase and protease to decrease, the non-biological stability of beer is poor, and the taste is light, etc. during the beer brewing process, and it cannot be directly used for brewing water.

Therefore, the reverse osmosis treated water needs to be mixed with the purified water after coarse filtration. The mixing ratio can be determined according to the requirements of brewing water, and then used for brewing production. The quality indicators of the mixed water are shown in Table 2.

Table 2: Mixed water quality indicators Unit: German degrees

It can be seen that after the treated water and purified water are mixed in proportion according to the needs, the hardness is 3~5 German degrees, the alkalinity is 1~1.5 German degrees, the pH value is 6.4~7.0, and the quality of brewing water is relatively stable, which reduces the impact of the fluctuation of brewing water quality on the quality of beer and can basically meet the requirements of brewing water; adding a small amount of acid during saccharification can adjust the pH value of the saccharified mash to meet the requirements and improve the taste quality of beer. At the same time, it was found that even after the treated water and purified water were mixed, the calcium ion content in the brewing water was still relatively low and could not meet the needs of production. Therefore, a certain amount of calcium ions should be added during saccharification to reach 60~90mg/l to ensure the activity of protease and amylase and the non-biological stability of beer. In addition, reverse osmosis water can be sterilized by ultraviolet light to remove bacteria, viruses, and microorganisms in the water, and made into sterile water for fermentation tanks, CIP cleaning of sake tanks and beer dilution water, and can also be used for the last clean water spray of bottle washing machines.

Cleaning and sterilization

1. The pretreatment process design of the reverse osmosis system has removed the pollutants brought in the raw water to the greatest extent possible, but it cannot remove all of them, so the pollution of the reverse osmosis system is very common. Fortunately, most pollutants can be removed by regular chemical cleaning. As long as the pretreatment works properly and there are no uncontrollable reasons, such as changes in the raw water quality or unavoidable microbial contamination, the cleaning frequency can be kept as low as possible. Sometimes operating errors can lead to membrane contamination, such as too high recovery rate or abnormal dosing system. The water output will decrease when the membrane is contaminated, the desalination rate will decrease, and the pressure difference between the inlet and the concentrated water will increase.

Membrane cleaning can make some acid and alkali agents (under pH2-12 conditions), and the membrane cleaning solution temperature is up to 45°C. Many pollutants, especially slime, accumulate over time and are compressed and thickened, which makes it very difficult to clean. Therefore, the cleaning cycle should not be too long.

2. Chemical cleaning standards: If the symptoms meet the following characteristics, the membrane element should be cleaned immediately.

· The standardized water output is reduced by 10-15%.

· The desalination rate decreased by 0.5%.

· The pressure difference ΔP increased by 15% (compared with the initial pressure difference value of 24-48 hours).

3. Cleaning medicine box and other equipment

The chemical cleaning medicine box is usually made of PE or FRP and can withstand the pH range of 1-12. The cleaning temperature should be as high as possible, such as 35-40℃. Chemical cleaning should not be carried out below 15℃ because the cleaning efficiency is very low. Sometimes cooling is also required to prevent overheating, so heating and cooling devices are required to control the temperature of the cleaning solution. The volume of the cleaning medicine box should be large enough, and the pipe volume of the pressure vessel and the system should be considered. If it is difficult to calculate the pipe volume, it can be calculated as 20% of the volume of the pressure vessel. When cleaning, suitable pumps, corresponding valves, flow meters, and pressure gauges need to be installed.

Figure 3: Reverse Osmosis Membrane

4. Cleaning procedure

1) Inject RO product water into the cleaning water tank. The amount of cleaning liquid should meet the needs of the pressure vessel and pipeline volume. Add the calculated amount of medicine to the cleaning water tank, turn on the cleaning pump, and fully stir the mixed liquid in a closed loop.

2) Try to drain the water in the RO host to avoid diluting the liquid.

3) It is best to heat the cleaning liquid according to the requirements of the membrane manufacturer to improve the cleaning efficiency.

4) Inject the preheated liquid into the pipeline, squeeze out the residual water in the pipeline at low pressure and low flow, and drain the discharged water until the liquid appears in the concentrated water or circulating pipeline (indicated by the cleaning liquid temperature or pH value).

5) The cleaning liquid circulates between the RO host and the cleaning device and maintains the temperature. Pay attention to the turbidity of the liquid to determine the proportion of its effective ingredients. Especially during alkaline washing, if the turbidity and color of the liquid change significantly, the original liquid should be discharged and the liquid should be re-prepared. During the pickling process, the pH value should be tested. When dissolving inorganic salts, acid solution is consumed. If the pH value rises by 0.5 units, acid needs to be added.

6) After the circulation, turn off the cleaning pump to soak the membrane element. Sometimes soaking for 1 hour is enough, but for complex pollution, soaking for 10-15 hours is very effective. To maintain the temperature during soaking, a small flow rate can be used for circulation.

7) Recirculate for 30-60 minutes to flush away the loose pollutants on the membrane surface. If the pollution is heavy, flushing with a cleaning flow rate of 50% will help. Excessive pressure drop during cleaning will cause problems. It is recommended that the pressure drop of a single membrane is less than 1.4 bar, and the pressure drop of multiple membranes is less than 4.1 bar. The cleaning flow direction should be the same as the flow direction during operation.

8) Discharge the cleaning solution, take samples and analyze the type and content of pollutants in the solution, which is helpful to determine the cleaning effect and the cause of pollution.

9) The membrane system can be flushed with reverse osmosis water or clean water. To prevent precipitation, the minimum flushing water temperature is 20℃.

10) After cleaning, the system is restarted, but the initial water must be drained until the conductivity and pH value of the produced water return to normal. If the system needs another chemical cleaning, the water in the system must be drained. Note that if the system is shut down for more than 24 hours after cleaning, it should be soaked in protective liquid (1% sodium bisulfite solution). If it is a multi-stage system, it is best to clean it in stages. You can use the same cleaning pump to clean them separately, or you can configure multiple cleaning pumps.

5. Sterilization If the reverse osmosis system is found to be contaminated by microbial mucosa, such as microbial mucosa or humus, the system should be sterilized after cleaning. The procedure is the same as chemical cleaning except that high-flow circulation is not required.

Commonly used bactericides include hydrogen peroxide and peracetic acid. Peracetic acid solution with a concentration of 400ppm can be used to sterilize the reverse osmosis system. The system sterilization effect of peracetic acid solution is much better than that of hydrogen peroxide. Be very careful when operating and do not exceed a concentration of 0.2%. It is recommended to use it intermittently to avoid damage to the membrane due to continuous use. When using peracetic acid, pH adjustment is usually not required.(Cr. BREW&BEVERAGE TECHNOLOGY EQUIPMENT