When a liquid (raw water) is passed through a Reverse Osmosis (RO) membrane with a lower concentration vs a greater liquid concentration, the process of osmosis begins. Eventually, the concentrations of both liquids will be equal. For example, osmosis is how plants uptake water – outside the roots there is a higher concentration of water than inside the roots, and the water start moving into the roots to create equality of liquids or balance.
The Reverse osmosis (RO) system pressurizes the greater concentrated liquid, forcing the liquid through the membrane, where the liquid is lesser concentrated. Therefore the term, reverse osmosis is used. Through this process the membrane traps impurities and particles as small as 0.0009 microns and permeate – spread the impurities throughout the outside of the membrane and effluent – discharged it into the wastewater line, thus producing purified clean water which is free from impurities. The most basic RO process is to remove impurities and filter them out of the water.
The water source for irrigation may contain minerals and or impurities/contaminants. RO water system can assist in providing measurable and constant quality. Thus, controlling nutrients becomes easier, and we don’t have to bother worrying what is in the water source for the irrigation process. The contaminants such as herbicides, pesticides, heavy metals, chlorine, magnesium, calcium, manganese, and iron, can react with other nutrients, causing problems growing organic foods and on the other side of the spectrum can conflict with the effectiveness of the fertilizer mix.
The controlled addition of nutrients combined with high quality purified water, provides the grower with the tools to calculate and determine the concentrations needed for optimum quality and growth which translates into marketable/sellable product. Therefore, the irrigated water contains only those nutrient and minerals that are an advantage to the plant. The use of purified water eliminates TDS (total dissolved solids), which denies conductivity to elements present in the water with an electrical charge. These electrical charged (EC) elements might negate the use of the added nutrients. Pure water will neither conduct electricity, nor will it have a TDS or an EC reading.
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RO can be quite complexed to implement, cost considerations being the most objectionable. Additionally, wastewater is one of the fundamental downsides of this technology. In RO designs, there are two types of membranes, each having its limits and uses. The cellulose triacetate membrane doesn’t offer the rejection rate of TFC (or thin-film composite) membranes. However, TFC membranes can be broken down faster through chlorine, causing the system to fail prematurely. Therefore, it is recommended that a carbon pretreatment is used to remove chlorine.
If pretreatment of the influent water is not taken into consideration, the membranes may disintegrate faster than expected. If the pretreatment issue is not addressed, it may also bring up additional labor and maintenance costs. In the absence of pretreatment, membranes become clogged i.e., requiring the need to be cleaned and or replaced them sooner than their designed and expected use. When used in conjunction with softened water, membranes last longer because other minerals are removed before they enter the RO the system. The additional installation of a softener causes for an added system and labor costs. The benefits derived while utilizing it in combination with an RO system must be calculated as an offset of the higher cost of replacing the membranes, the downtime of the water treatment system, and water.
Another factor that needs to be taken into consideration is that when RO is being used, wastewater is created. In general, based on the size and pressure of the unit, producing 1 gallon of RO water requires 4 gallons of water. In areas where the use of water is restricted, this may not be the best water treatment. The market has already introduced a lot of newer systems that produce less waste and are far more efficient. However, for the quantity of water required for irrigation, it will be a while before these RO systems are widely used.
Since RO water does not contain minerals, nevertheless it still can be very corrosive and aggressive, especially to metal piping. RO water should never be passed through copper or galvanized pipes because over time, the water will destroy it. The foggers, misters, drippers, tubing, and pipes should be able to stand up to RO water.
System Costs and Sizes
The size of an RO water system varies significantly with respect to the manufacturer. When looking at cost, a number of factors may be taken into consideration; for example, how much water is required daily? However, the majority of the systems are rated on the number of gallons per day (GPD), and or per minute (GPM) that the system may produce. Without a pressure pump, residential systems may produce anywhere from 15-100 GP; the rejection rates are acceptable, and the cost ranges from $200-600. A system with a pressure pump may produce 100-175 GPD for $800-1,000, but because of the extra pressure, their rejection rates are even greater.
The customer should not be locked into the system’s size offered by the manufacturer.
The customer needs to discuss with the manufacturer his/her water source, production capacity, intent of use and budget constraints, to get the most out of the proposed RO system.
The prices of industrial, home, and commercial reverse osmosis systems may escalate, but so does the need for large storage tanks, high-pressure pumps, and the volume of water being produced. These systems may produce large volume of water staring with 1,000 gallons per day to more than 100,000 GPM. The costs vary from manufacturer to manufacturers and application to application. It needs to be taken into consideration that large amounts of processed water needed which leads to the need for storage tanks and its effect on the overall cost.
Most growers would benefit from almost any type of water treatment that gets rid of impurities. By removing contaminants that facilitate microbial growth, will bring a significant difference of growing goods, with the impact being seen from reduced root problems like fungal diseases or Pythium that are introduced as a result of waterborne bacteria. Most of the growers target their water treatment strategies in propagation areas.
Any grower will find RO to be a great asset, especially as nutrient solutions could be calculated and controlled for an array of crops and being duplicated for consistency. While RO is often an expensive initial investment, it can offer a fast return on investment if correctly incorporated.