Two practical trials by Wageningen University & Research have provided more insight into the usefulness of filtration of the drain water of a greenhouse horticulture company. The advantages are a cleaner system and better operation of the disinfection installation. Filtration is always tailor-made; the effect depends on the farm situation and cultivation.
At a cucumber company, the own approach with a belt filter was compared with a filter line consisting of a screen filter of 25 microns plus a ring filter of 10 microns. The aim of the trial was to remove as many suspended particles as possible from dirty water. This makes the ozone installation more effective.
Researchers measured the particles before and after the old and new systems. Visually, the water was much cleaner with the finer filtration, and this was also apparent from the measurements. As a result, the badge times for the ozone treatment became shorter and the capacity higher. This also saves on electricity costs. The grower was satisfied with the water quality.
In order to be able to fully reuse the rinse water, it was collected in a buffer tank and then placed on a heavy belt filter with a small pump. It then slowly sinks through cloth and filter cake. That works very well, according to measurements. The canvas was twice as heavy as normal. It was determined that the fabric filter must be oversized in relation to the water flow. It is also important where exactly in the system the filtering takes place. If the filter line is placed directly after the waste drain tank, the maximum effectiveness in ozone decontamination is achieved.
The second practical trial took place at a phalaenopsis farm. Due to the nature of the substrate used, there are many suspended particles in the return water. In addition, the distance between the waste drain tank and the water technical area on this farm is large. The pipe between them is prone to clogging. The company already used a SAF filter. This approach has been compared with a filter line, consisting of a gauze filter followed by a 3 micron fiber filter.
The main goal was to improve the transparency of the water so that the UV installation works better. That didn’t quite work out. The company uses EDDHA as a chelate. This cannot be completely removed with filtration, although it is a major determinant of UV transmission. Yet there was a difference between the two methods of filtering. The test was too short to determine whether the long pipe was less clogged.
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