XVIII. Reverse Osmosis & Deionization - Reef Tank Prefilter
This article discusses Tap Water, Reverse Osmosis, Deionization & Alternatives
Reef keeping as a hobby nowadays has become common and the equipment and components available to maintain our ecosystems are readily available. Because of the modern ease of maintenance, it is possible to have aquariums in homes and offices with little consideration for specialty construction and alteration. Access to outlets and a willingness to move water from your tank to a drain and from the source to the tank are often the only considered factors when initially setting up our tanks. However, it is the very water we are moving is worth serious consideration when projecting for long-term success.
Tap Water
In the modern world, many municipalities or companies treat, supply and facilitate the capturing and recycling of water. In the treatment, process chemicals are added to the water to remove pathogens and impurities that lead to illness when consumed. This assures clean drinking water at command by simply turning on the tap. While many of these chemicals are regulated for human consumption, there is little consideration for the effects of drinking water on simple organisms that share traits and features with the pathogens we intend not to drink.
Chlorine and Chloramine are heavy metals added to drinking water as disinfectants. Organic nutrients like Phosphate and Nitrate are present in the groundwater that is sourced for treatment and is a result of fertilizer runoff, biological processes, and septic systems. Other elements such as Copper and Zinc can be leached from the plumbing within our home and silicates are so abundant in nature that they exist in water supplies before and after the water has been treated. While certain quantities of any of the above can have ill effects low levels tend to be acceptable and are monitored for human consumption.
The above-outlined contaminants present in drinking water have detrimental effects on our aquarium. Nitrate and Phosphate are well known for their stressful effects on coral and fish, and along with silicates the three fuel the explosive growth of nuisance algae and cyanobacteria. Copper, Chlorine, and Chloramine are all outright disruptive to the biological functions of invertebrates leading to death upon exposure in many cases. Through proper care and testing, we can assure that these levels stay undetectable in our aquariums as long as their presence in tap water is first addressed.
Reverse Osmosis
The most effective way of removing the majority of particulate contaminants. Silicates as addressed above and a very inclusive variety of salts and organic matter are filtered out producing water that is ninety-eight percent H2O containing very little contaminants. Reverse Osmosis units require plumbing to both a supply and a drain. It is possible to plumb these units yourself, or, many companies will install a reverse osmosis unit in your home.
Before reverse osmosis, water is passed first through a series of prefilters. A reverse osmosis membrane can filter hundreds of gallons if used without prefiltering this volume is drastically diminished and as a result, highly inadvisable. The number and configuration of prefilters are fairly broad and the reverse osmosis market offers a plethora of interchangeable options. The basic prefilter requirements are to remove as much as possible from the water without using the actual reverse osmosis membrane; Preserving the membrane efficiency for a longer period of time.
Tubes of tightly woven cotton or synthetic fibers are used as the first stage of prefiltering. These prefilters pass water through the fibers of the tube and into the hollow interior where it is passed through to the next stage. Emphasizing particulate remove these tubes are rated by the micron level they filter too. Commonly available in twenty, ten, five, and one micron, these filters are often used in conjunction with one another. Using a five-micron filter will allow all particles under five microns to pass through the system while capturing everything larger as well. Starting with a higher micron level and progressively stepping down serves to preserve the efficiency of each stage for a longer period of time. Care needs to be taken to assure that pressure within the system stays above sixty-five pounds per square inch (psi) for reverse osmosis if multiple micron filters are used a booster pump may be required to maintain this,
The second phase, though perhaps not the second stage of the system is to neutralize a portion of the smaller compounds below what a micron filter is capable of. Chlorine, chloramine and many dissolved metals require an ionic bind to pull them from suspension. To bind these dissolved compounds to another media so that the compound is removed from the water that is passed through the media. The most effective method of capturing these compounds on the ionic level is through carbon. Available in a block or granulated which dictates lifespan in gallonage. Granular Carbon offers more surface area at a higher rate of bypass meaning it is more suited for lower volume applications. Block carbon is capable of filtering a much higher volume with lower bypass at the cost of reducing system psi. Again a booster pump may be used to restore pressure to the desired levels.
Final filtration of the water is performed with a reverse osmosis membrane. A tightly coiled ribbon of perforated film is wrapped around a permeable core. Similar to the stages before water is passed over the exterior of the membrane and the force of incoming water pushes the water through the matrices of the membrane. Reverse osmosis membranes, however, filter down to a level of one one-thousandth of a micron. This removes virtually all contaminants from the water that remain after the initial prefiltering stages. During this stage, the pressure in the system must be regulated accurately to assure proper functionality of the membrane. If the pressure is too low water will not be sufficiently forced through the membrane to obtain the desired volume of filtered water and excessive wastewater will be created. Pressure too high will damage the membrane and the equipment possibly resulting in an explosion of the system, this is usually not an issue however as municipalities supply a line pressure right around sixty-five psi and we reduce it from there through filtering and booster pumps have maximum capabilities and restrictions.
Deionization
Organic and inorganic compounds display ionic polarity, attracting and binding to compounds of opposing polarities. To separate these compounds from the water column we can utilize anionic and cationic resins to attract positive and negative compounds respectively. Anionic resins are comprised of ions of a negative polarity, cationic - positive polarity. These resins are available individually, mixed, or in convenient color indicating mixes. In a similar fashion to reverse osmosis membranes care should be taken to prolong the life of the media employed to filter the water by prefiltering the water supplied to the deionization unit.
Because Deionization occurs at an ionic level, removing even colloids, the resulting water after deionization is considered ninety-nine percent pure H2O. Best employed as the final stage of a full reverse osmosis system deionization assures lab quality water production by filtering the remaining traces elements missed by reverse osmosis. Lab quality water may not be required, but, manufacturer recommendations are usually based on the provided substances reaction to water of lab quality and the most reliable results are derived from emulating the test conditions. When deionization is utilized in our homes it provides the best possible starting point for all of our water needs leading to the increased overall health of our systems and fewer continuous nuisances such as unexplainable algae or bacterial blooms. Whether considering deionizing the water after reverse osmosis or filtering the water with solely reverse osmosis the system should be plumbed to a drain to accommodate the generated grey water.
Alternatives
Greywater generated as a result of reverse osmosis is of varied concern. In some municipalities, this water is simply sent to sewage treatment plants, however on wells this grey water may be more of a concern. If you are concerned about reducing the wasted water there are several alternatives solutions to the standard reverse osmosis options. Overall reduction of grey water can be achieved by adding a second reverse osmosis membrane to process the waste created by the first membrane. Providing proper pressure is maintained this reclaiming process will reduce grey water to the drain. Adding a second reverse osmosis membrane will bring production to waste ratios to around four gallons of water per one gallon of pure lab quality water created.
If prior thought is given to plumbing your reverse osmosis system, many of these systems can be plumbed to the feed of your homes hot water system, the grey water is completely treated tap water that has become more concentrated in ionic concentration. While not suited for human consumption, conservation enthusiasts repurpose this water into their hot water tanks as it is however usable for dishes and laundry. It is possible to some degree to have a zero-waste reverse osmosis system if both duplications of membrane and plumbing to a secondary use such as hot water are employed. This method conserves the most water in the process of fulfilling our need for purified water and is highly recommended by this writer.
If all else fails and reverse osmosis/deionization is simply not feasible in your situation you may obtain filtered water from most local fish stores providing you bring your own container. Additionally, some companies manufacture premixed quantities of salt water or pure water for aquarium use. Lastly, there is the option of proprietary additives that either celate the toxic metals present in the tap water or otherwise neutralize a contaminant present by altering their composition. The above are suitable alternatives when the home operation of reverse osmosis or deionization unit is not possible but some form of water prefiltration should be employed and tap water should never be used as is for our tanks in any circumstance.