July 2006

Techniques For Cleaning Water

Water quality is an important topic for growers, though not all of them are aware of the numerous ways to treat water problems. Before diving in with a basic solution, it is a good idea to test the water first, as the treatment methods vary depending on both the problem and the body of water.

Testing is a useful tool to find the source of a water dilemma and determine which treatment(s) should be used to remedy the situation. Each water source presents its own set of problems, and growers must remember that ponds, rivers, lakes, wells, municipal or cisterns all have different water-quality issues. Some pose bacterial problems, while others have high mineral content. Therefore, a technology that works on a municipal water source might not work the same way on a well or pond.

There are numerous solutions to water quality problems. The remedies include UV light, ozone, copper ionization, filtration and reverse osmosis. It is difficult to sum up every technology in a few sentences, though each one has its own clear advantages and disadvantages. A quick overview of each solution, including its pros and cons, is an excellent introduction into the world of water quality.

Available Technologies

UV light is a good choice for controlling bacteria. It is desirable because it does not add anything to the water. However, UV systems require the use of pretreated water to prevent quartz sleeves from scaling, which can create maintenance headaches. Things like iron, hardness minerals and high turbidity can create scaling on the sleeves. This reduces the UV transmission to the water, thus affecting the technology’s ability to control bacteria. Flow rates also have a negative affect on UV systems. If the system is not sized correctly, then a high flow rate can hinder its performance.

Ozone is another up and coming technology in the greenhouse industry. This particular method of bacterial control has been around since time began. Lightning is a natural example of mother nature creating ozone to clean out the air. For more than a century, man-made ozone systems have been used in water treatment to control bacteria. For an ozone system to work well it must be installed correctly, which is easier to achieve when salespeople and manufacturers have experience in the horticulture industry. The greatest advantage of ozone is that it is useful for oxidizing iron, manganese and organics for filtration, and it can also control a host of bacteria and pathogens. The biggest disadvantage is that the system is very sensitive to accurate load factoring and unit size, without which the appropriate dose will not be applied.

Copper ionization has been used for decades to control bacteria. Centuries ago Egyptians and pioneers used copper and silver to reduce bacteria in their water sources. Applying a small electrical charge to a copper electrode has remarkable effects on bacteria and algae growth. The best thing about copper ionization is that it is easy to install and use. The problem with this technology is that, similar to UV, the water needs to be pretreated. Without initial water treatment, the copper will bind to the iron and manganese, thus causing scale and loss of output. Flow rates are also a problem in terms of achieving proper dosages and satisfactory results. With copper ionization, proper sizing is a must, regardless of the manufacturer.

Among the water treatment technologies, filtration is the one most misunderstood. Many think that a simple cartridge filter will perform the same duties as an iron filter or one made to reduce hardness minerals. Cartridge filters are useful tools for removing sediment but will only stop particles that coincide with the rating of the cartridge. There are many other types of filtration media available. Some are used as stand alone products that require only backwashing, while others need proper oxidizers or regenerates to work properly. The filters that do not require anything but backwashing are advantageous because they are easy to use. The disadvantage is that a certain amount of oxygen must be present in the water, which is not always available from the raw source. In addition, this type of system can be expensive, depending on the filtering medium. The flow rates needed in many operations make the capital cost high for the initial investment, and if oxidizers are necessary, then chemical costs and other equipment will make the technology even more expensive.

Reverse osmosis (RO) technology might be overkill for some greenhouse growers. The high quality water that is attained by using RO is excellent for growing plants, but cost can be a factor. RO also requires from pretreatment. If the influent water contains hardness minerals or iron, then the membranes will clog prematurely and will not last as long, adding to the cost and maintenance. A softener can be used to remove low levels of iron (<5 ppm) and hardness so water can be prepared for RO systems. Another disadvantage of RO is that it takes four gallons of water to obtain one usable gallon. One way to combat this issue is to blend raw water with RO. However, there are systems and technologies becoming available that do not waste as much water.

Do Your Research

Above are some examples of technologies that can be used to improve water quality for greenhouse growers. Since water chemistry is so complex and the technologies are so ambiguous, it is difficult to set specific parameters that would work for every water source and application. Furthermore, each system needs to be designed and constructed properly to achieve the desired results and benefits.

Before purchasing any water treatment products, first test the water to get to the bottom of the problem, and then consider the water source to properly remedy any water quality issues.