With the expansion of flower cultivation area and the improvement of quality requirements, the requirements for cleaning and sterilizing of water quality are also higher. The pathogens transmitted by irrigation water mainly include fungi, bacteria, viruses and nematodes. Although not all microorganisms pose a hazard to plants, when these microorganisms enter the plant, they may cause the plant to become sick until death. Therefore, the sterilization operation is to remove and kill these pathogens. From the point of view of economic cost, the more thorough the sterilization, the higher the cost. Since the pathogen does not necessarily cause disease under certain low concentrations, the irrigation water does not necessarily need 100% sterilization. However, in order to ensure that the flowers are not affected by foreign pathogens due to irrigation, the irrigation water must solve the sterilization problem.
First, the main sterilization technology Currently available sterilization technology mainly includes heat treatment, ozone treatment, ultraviolet radiation, slow sand filtration, membrane filtration, ion sterilization.
1. Heat treatment This treatment method is to exchange the irrigation water at 95 Â° C for more than 30 s. Before entering the heat exchanger, the pH should be reduced to below 4.5 to avoid accumulation of calcium on the heat exchanger. The wall material of the exchanger is mainly stainless steel or titanium alloy. Heating energy Take natural gas as an example. It takes about 2 to 4 cubic meters of natural gas per cubic meter of hot water. Currently, flower growers in the Netherlands mainly use this technology for sterilization.
2. Ozone treatment Since ozone has three oxygen molecules, it has a strong oxidizing power to the cell membrane. When used in a closed room, 10 g of ozone is required per cubic meter of irrigation water. The pH of the water before use is less than 4.0, and it can be supplied for irrigation for 1 hour after use. Water is filtered through carbon to prevent ozone from escaping into the greenhouse or staying in the water to produce toxicity.
3. UV treatment This method is the most popular and reliable, and will be described in detail below. The main purpose is to irradiate the water through ultraviolet light at a dose of 100 to 300 ml/cm 2 .
4. Slow sand filtration This method is used to filter drinking water in many countries. The results show that the fungus can be filtered out with 0.35-0.5mm fine sand, and the filtration rate of bacteria is 95%-99%. The slow operation of the bacteria is the main problem of this technology, and the virus cannot be filtered out.
5. Membrane Filtration Method This method utilizes a filter membrane with a very small pore size to separate the entry of fungi, bacteria or nematodes, using a pore size of 0.05 to 0.25 Î¼m. The main application problem is that the aperture is easily blocked.
6. Ion sterilization method This technology is still in the research stage. The main problem is that the sterilized irrigation water does not easily remove residual ions and is toxic to plants.
At present, the sterilization of greenhouse irrigation water in the Netherlands and North America is mainly based on heat treatment, ozone treatment and ultraviolet sterilization. When selecting irrigation and sterilizing equipment, in addition to considering the relationship between flower crops and pathogens, the planning and design of the sterilization system must also consider the supply and storage of water sources, and the cost of use is a decisive factor. In addition, the question to be considered is whether 100% complete sterilization is required. If the flower crop is resistant to the disease, it does not need to be completely sterilized to reduce costs.
Second, the introduction of ultraviolet light sterilization technology Because of the virus disease in domestic flower cultivation (especially greenhouse flower cultivation), the use of ultraviolet sterilization is the most reliable technology, so it is described in detail here.
1. Principle of action Ultraviolet light is a certain band of light, also known as an electromagnetic wave. Energy is determined by frequency or wavelength. Ultraviolet rays are usually classified into three categories: ultraviolet A (long-wave ultraviolet), ultraviolet B (medium-wave ultraviolet), and ultraviolet C (short-wave ultraviolet). Since UV C has the shortest wavelength and highest energy, it is most suitable for sterilization.
The way UV rays deal with pathogens is to use their energy to penetrate the cell membrane and block the DNA of the molecule. Since the DNA structure is exposed to ultraviolet light, all genetic data no longer exists and can no longer be read, thus causing the cells to lose their function or die, thus losing the ability to reproduce.
There are two determinants of the amount of radiation that cause the cells to lose their vitality: the intensity (or density) absorbed by the irrigation water when it is exposed to ultraviolet light. The second is the time of action of irrigation water in the treatment room. The product of the two is called the dose, and the unit is mJ/cm 2 .
2. Sterilization technology The use of UV sterilization operations is based on two factors: the intensity and time of the dose used. Factors affecting bactericidal performance during actual operations also require consideration of the cleanliness of the water. Since the particles in the water absorb ultraviolet energy and affect the sterilizing ability, impurities in the water must be filtered out before the sterilization operation.
The pathogens in the water should be subjected to sufficient dose to have a bactericidal effect. In order to enable the radiation source to be delivered to the water, the following factors must be considered in use: the radiant energy of the ultraviolet light source, the distance between the light source and the irrigation water, and the ultraviolet light energy. The ability to transfer in the water. The energy required to kill pathogens is not the same. Generally, the bacteria commonly found in households only need 70ml/cm2. To kill the pathogens causing plant diseases, the required dose is roughly 100ml/cm2 for mold or bacteria. The virus needs to reach 250ml/cm2.
5. Design of ultraviolet disinfection equipment (1) Sterilization work room: The work room is usually made of stainless steel material. Ultraviolet light is usually generated by high-pressure quartz lamp. Ultraviolet sensor must be installed in the treatment room to continuously monitor the light energy. At present, there are three types of common sterilization chamber structures: one is the axial type, that is, the germicidal lamp is located at the center, and water flows through the cylinder. The second is concentric type, that is, water flows through the circular tube, and the germicidal lamp is located on the circumferential wall. The third is a flat film type, that is, water flows through the flat plate surface, and the flat plate is equipped with an ultraviolet lamp tube. In order to ensure that the irrigation water is sterilized by ultraviolet light, a turbulence device must be provided in the sterilization chamber to uniformly expose the flowing water to ultraviolet light. In order to avoid the accumulation of impurities in the lamp and the sensor to affect the performance, the work room should be cleaned regularly.
(2) Controller: In order to ensure the sterilization performance, the sterilization process must be monitored. The hours of use of the UV lamp should be continuously recorded to determine that the service life is not exceeded.
4. Frequently Asked Questions for Using Water to Treat Water Quality Using UV sterilization, you should be able to kill germs with proper planning and proper use. However, sometimes using ultraviolet light for water treatment, there will be some problems. The reasons for failure can be summarized as follows:
(1) The light source energy is too small: improper design is the main reason, and the selected lamp can not provide enough energy.
(2) Lamp aging: The total time of use of the lamp exceeds the service life.
(3) The water volume is too large or the flow rate is too fast: the irrigation water is exposed to ultraviolet light for too short or insufficient strength, resulting in insufficient total energy.
(4) Accumulated impurities in the lamp: The energy that the ultraviolet rays escape is blocked due to the accumulation of impurities.
(5) Too much impurities in the water: The impurities absorb the ultraviolet energy, causing insufficient energy in the water to kill the virus.
(6) The water flow treatment is not comprehensive: all the irrigation water does not completely pass the ultraviolet light, and some of the water originates from the bypass passage into the container that has been sterilized, and mixes with each other to cause pollution.
All of the above problems should be taken in a timely manner to prevent the sterilization of irrigation water sources from affecting the production of flower crops.
With the expansion of flower cultivation area and the improvement of quality requirements, the requirements for cleaning and sterilizing of water quality are also higher. In order to ensure that the flowers are not invaded by foreign pathogens due to irrigation, the irrigation water must be solved whether it is sprayed directly during cultivation or recycled. Although China's flower industry has not paid enough attention to water quality sterilization, for the future development, irrigation water source sterilization will become a problem that flower cultivation (especially facility cultivation) must face.
Author unit: Jiangxi Yichun College Agricultural College
Source: "Agricultural New Technology"
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