Definition osmosis
reverse osmosis system
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In principle, a reverse osmosis system is a very fine filter. With a certain minimum water pressure, usually 4 bar, tap water is pressed against the osmosis membrane. The membrane lets almost only water molecules through and holds back all particles dissolved in the water, i.e. ions, molecules, etc., which are larger than water H2O. About 95% of all other ingredients in the water are retained.
A fine filter is located in front of the osmosis membrane to roughly pre-clean the water. If the tap water is chlorinated, an activated carbon filter should be used in addition to the fine filter, otherwise the membrane can be destroyed.
To ensure that the membrane does not become clogged after a short time, it must be flushed regularly before and after operation. An osmosis system has an outlet for the ultrapure water and an outlet for the waste water. An osmosis system is set in such a way that 4 liters of waste water are produced for the production of 1 liter of ultrapure water. A total of 5 liters of water are therefore required to produce 1 liter of reverse osmosis water.
Osmosis systems are connected to a washing machine connection or a normal water tap.
In aquaristics, osmosis systems are used when
- the tap water for the fish is too hard
- the tap water is too polluted with pollutants, e.g. B. copper, nitrate, phosphate, etc.
About 95% of the pollutants are retained. The water can then be adjusted to the requirements of the fish. It can e.g. B. soft water for red neons can be generated. With seawater, the salt content can be better adjusted.
The decisive factor for the purchase of an osmosis system is often the nitrate value, which in German drinking water often reaches values at which a water change with this drinking water is almost pointless.
The water produced is usually not filled directly into the aquarium, but in suitable containers? temporarily stored and processed if necessary.
Usually a simple no-name system is sufficient, which is available cheaply. Depending on the water pressure, such systems produce between 90 and 120 liters of reverse osmosis water per day. Inexpensive systems cost around €100.
Providers are e.g. B. Zajac or possibly a cheap pet shop. Even expensive systems work on the same principle and do not produce better water. Only if more water is required per day are systems with correspondingly high-performance membranes required, which are correspondingly more expensive.
Installing an osmosis system is easy. A water connection that is otherwise not used and a water drain are required, because only part of the tap water is used. Because an osmosis system works with high pressure, only the hoses supplied should be used.
The difference between osmosis water and distilled water
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To produce distilled water, the source water is boiled. The resulting water vapor is cooled.
Osmosis water is pressed through a very fine-meshed, mechanical filter at high pressure.
The water produced is no different from each other. Distilled water should no longer contain any impurities. The prerequisite for this is that the distillation has been done correctly. In most cases, however, no protective gas etc. is used. There is hardly any real distilled water nowadays, also because of the high energy costs. Distilled water for car batteries etc. is obtained with the help of multi-stage osmosis systems or ion exchangers. Therefore, commercially available distilled water such as osmosis water still contains foreign substances.
There is still deionized water that is produced with ion exchangers or deionizers. Deionized water may still contain organic matter, while reverse osmosis water contains only trace amounts of inorganic and organic matter small enough to slip through the membrane.
For use as aquarium water, all of this water must first be prepared. For this purpose, the water produced is brought to the desired hardness with hardening salt or mixed with tap water in order to set the desired water values.
A Brief History of Reverse Osmosis
Osmosis systems were developed in the 1960s. As with many high-tech products, NASA was the client. NASA needed a drinking water recycling system for manned spaceflight.
Today, osmosis systems are mainly used in large-scale seawater desalination. Other areas of application are:
- Food industry for concentrating fruit juices
- medicine, e.g. B. in dialysis
- waste water recycling, e.g. B. in galvanic plants
- inexpensive drinking water treatment, e.g. B. Major projects in India, Brazil
- Bottled water industry, especially in Mexico and USA by Pepsi-Cola and others
In the US, reverse osmosis water is sold in supermarkets. Osmosis water is delivered to the house in large balloons for the so-called water cooler. These are also in many offices. You can buy reverse osmosis water in any supermarket for a few cents per liter.
Operation of an osmosis system
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Normally, an osmosis system is screwed to the wall near a water tap. In principle, the system could also be assembled and disassembled before and after use. However, this is cumbersome.
An osmosis system has three hoses. A hose is connected to the water pipe. It is usually a 3/4 inch connection. This corresponds to a tap for connecting a washing machine. If a washing machine is already in operation on the tap, you can easily expand this connection with a T-piece and an additional tap in front of the actual washing machine tap.
After turning on the tap, permeate, ie the filtered osmosis water, comes out of a hose. Wastewater comes out of the other hose. The waste water is led into a sink. For this purpose, the corresponding end of the hose z. B. placed in a bathtub, shower tray or in a water basin.
The higher the line pressure, the faster an osmosis system works and the better the ratio between waste water and osmosis water. As a rule, osmosis systems work optimally at a pressure of 5 bar.
The faucet can be fully opened. However, this is not necessary. The line pressure builds up in front of the diaphragm even if the flow rate is low. The pressure does not increase when the faucet is opened wide. A water tap or valve represents a flow resistance. The smaller the flow, the lower the losses. With the small amounts of water that flow through an osmosis system, the currents remain so small that the flow resistance can be neglected in almost every position of the tap. The full pressure potential is retained without flow losses.
Osmosis systems are operated with cold water. Although the performance of the system increases with temperature, the membrane is sensitive to temperature. Temperatures that are too high destroy the membrane. It also makes no sense ecologically and economically to use hot water to produce osmosis water more quickly.
The membrane must not dry out. But that doesn’t mean that the system has to run constantly. If the hoses are tied up immediately after using the system, water will always remain in the system. In conventional systems, the hoses are attached at the top so that the system can never run completely empty. The two hoses can also be connected to a hose with a larger diameter. The system is then completely closed. However, the hoses may only be connected in the depressurized state.
The hoses can also be sealed with valves like those normally used on the air hoses.
To be on the safe side, the system should be put into operation once a month. The system can also be stored lying flat in a bowl so that it does not run empty.
The system only runs if osmosis water is really to be produced.
If the flow decreases noticeably, the pre-filter must be changed. Any existing carbon filter will be replaced after approx. 6 months.
Maintenance work is not necessary. Only the membrane needs to be rinsed before and after use. To do this, the flushing valve is opened fully. After flushing, the valve is closed without any effort.
The residual water should not be fed back into the pre-filter. Substances that are not wanted in the aquarium are in the residual water. If there is too much of these substances in the water, the membrane becomes clogged.
Electricity costs do not arise. Water costs vary from region to region. It must be taken into account that there is 3 to 4 times the amount of waste water or residual water for the desired amount of osmosis water. If possible, waste water and rainwater can also be used. The water must be collected in a barrel and pumped to the osmosis system with a booster pump.
Osmosis water can be drunk and used as water for coffee or tea. To kill any bacteria that may be present, the water should be boiled briefly. Diet usually provides enough minerals when eating a healthy diet. The sweated-out minerals are only absorbed more quickly through liquids during heavy physical exertion.
Consumables are the membrane, the fine filter and, if available, the activated carbon filter.
Osmosis systems can last 6 years or more if the pre-filter and carbon filter are regularly flushed and changed.
Operating costs of an osmosis system
Running costs of an osmosis system are:
- Rinse water costs
- Cost of osmosis water
- waste water costs
- Carbon filter cost
- Costs for pre- and fine filters
Sample calculation:
- 200 liters of reverse osmosis water are required per month.
- The system works with 20% efficiency.
- 1000 liters = 1 m3 of water are required per month.
- Flushing is 15 minutes every 2 weeks.
- 100 liters of flushing water are required per month.
- 1.1 m3 of water are required per month.
- At a price of €2.90 per 1 m^3 of water including waste water, the monthly water costs are €3.19.
- If needed, a new carbon filter is required every 6 months for around €25.
- A new fine filter is required every 2 years for around €25.
- Material costs for the filters are €5.20 per month.
- The total monthly cost is €8.39.
As a comparison, the corresponding costs for an ion exchanger with a capacity of 16,000 liters of hardness and a starting water with 16 °dGH:
- The ion exchanger has a yield of 1000 liters of deionized water before it needs to be regenerated.
- 200 liters of water per month cost €0.58, at a price of €2.90 per 1 m3 including waste water.
- Every 5 months, 1.75 liters of technical hydrochloric acid for €6.08, 280 grams of caustic soda biscuits for around €1.82 and around 101 liters of water are required for rinsing and preparing the regeneration solutions.
- The regeneration solutions are collected, neutralized by pouring them together and poured down the drain.
- The regeneration costs €8.19 including water every 5 months.
- The monthly cost…