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Small scale water treatment for Kenya horticulture


Using clean irrigation water improves the quality of your crop and your crop yield. Furthermore, the usage of good quality water is of high importance for your post harvest water. It lengthens the vase life considerably. However, on our continent water is most of the time not available in quantities that are needed for a healthy crop, not to speak of obtaining water that is of a constant quality.

Water is a many sided product. Substances dissolve in water, and countless (micro) organisms grow in water. The treatment of the different sorts of water demands different technologies. Furthermore, each local situation requires its own individual solution. In this article we tried to outline the possibilities for the provision of water for small scale projects. Obviously, one of your goals is an optimum crop yield. Costs, quality and availability have always to be taken into account. Whether you will harvest rainwater or want to go that extra mile. At all times, water efficiency is highly important.

Availability, costs and required quality will always be on the bases of the decision what water provision to rely on. What are the possibilities for your water provision?

Rainwater
Rainwater is excellent to use as irrigation water or post harvest water for small scale water projects. It is easily collected in basins, but unpredictable weather circumstances make it difficult to rely on it as your only source of water. Furthermore, water deteriorates quickly. To ensure a stable quality of your water, you still have to conserve and treat before use. Filtration is most widely used

Lake or river water
When you have the luxury to be stationed in the vicinity of a lake or river, you can consider using that water. Transport costs will be low, but the quality of the water will vary fairly. As a consequence, the water will need treatment depending on the contamination of the water (and features of the lake): innumerable organisms grow in water.

To lake and river water filtering and disinfection technologies have to be applied or chemicals have to be added to destroy unwanted organisms that can ruin your crop. Treatment will be necessary to conserve and maximize the crop yield. As the quality of the feed water varies tremendously, samples have to be taken continuously and the appropriate treatment has to be adjusted according to the results of the analysis every time, which makes it very time consuming. Often multimedia filtration and UV disinfection shall be a necessary treatment for this water.

Borehole water (well water)
To overcome the dry season or when there is a shortage of water you can also use borehole water. This will ensure that you always have an adequate supply of both irrigation and post harvest water. Another advantage is that it is of a constant high quality. For this, you use borehole water. As this water is often too saline for irrigation purposes, you need to treat it with reverse osmosis (RO) membrane filtration. With this desalination step, most of the substances present in the water are separated by membrane filtration. To prevent the membranes from fouling a pre filtration has to be applied. The optimum pre filtration set up depends on the specific feed water quality and the situation at the project location (climate, local skills etc). E.g. cyclone / multimedia / cartridge filtration.

A borehole must be made by a professional drilling company. Depending on layers they can determine exact place and depth. The quality of the bore hole water is leading for the design of a reverse osmosis system. The choice of components depends directly on the different ions and impurities in the water. Furthermore the desired quantity and quality are main items of an inventory that should be made before a well informed choice can be made.

The treatment of the different sorts of water demands different technologies and products. To name but a few: filtration, desalination (reverse osmosis), (UV) disinfection. Solutions are possible, from low to high tech, but of course financial boundaries have to be known.

 

Amiran Amiran2

 

Reverse Osmosis
The reverse osmosis technology has proven itself over the last 25 years and is a reliable, simple, solution. The retention of most elements (e.g. Na, Cl, HCO3) is approximately 99 . The high quality water makes it possible to recirculate the water and thus saving on water use, but of course this depends on the method of growing your crop. The water that is produced however, is environment-friendly and is of high quality that is optimized for a maximum crop yield. The well water ensures that you have ample supply of water, year round.

As the initial investment costs of a reverse osmosis installation are rather substantial, implementing reverses osmosis in your business asks inventiveness. Of course, one should consider perspectives. Which quality does one try to achieve? What expectations does one have for the quality of their crop and the vase life? What expectations of expansions are ahead? Reverse osmosis solutions have a capacity from 1 m3 per hour up to >1000 m3 per hour but the smallest capacity can even be too small for some small scale projects. So once you know that the scale of your projects will stay small, you could consider a cooperation with other farmers that do want to have a maximum return on their water investments.

Multimedia Filtration
Contrary to a regular sand filter, the multimedia filters are being built up with different layers from fine to coarse. The different layers increase the capacity and enhances the quality. The grainsizes of these different layers are to be determined by experienced suppliers. They have al large dirt and waste retaining capacity and therefore also called deep filtration. Simple and constant action with good results with which you can filter out as much as possible dirt. By a backwashing process all dirt captures are washed out of the filter media.

UV Disinfection
This is a chemical free disinfection method. Ultraviolet (UV) light is a very effective method of water disinfection for e.g. rain water. In farms of a higher technical level it is often used to disinfect drain water (run-off) of soilless cultures before re-use. Water for horticultural purposes has to be "scrubbed" free of plant pathogens, including bacteria, fungus spores, viruses and/or nematodes. Some plant viruses are very difficult to kill and some fungi produce 'survival structures' designed to withstand all sorts of difficult conditions.

 
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