ISHS Acta Horticulturae 119: III International Symposium on Water supply and Irrigation in the open and under Protected Cultivation
PRETREATMENT TO REVERSE OSMOSIS |
| Author: | G. Klomp |
| Abstract:
Due to the salinity of groundwater and surfacewater in Holland, about 200 market gardeners are owner now of a desalination apparatus. Most of these are of the R.O. (reverse osmosis) type. This means that the water is forced through a membrane, which refuses the salt molecules to pass. The increasing salt concentration on the pressureside causes an increasing back pressure called osmotic pressure. Because of the increasing concentration of nearly all dissolved solids, most of the organic matter and some of the salts, there is a tendendy towards precipitation on the surface of the membrane. This precipitation and clogging can be prevented by applying a high flow velocity along the membrane. This can be caused by a recirculation-pump at the cost of high energy consumption and expensive open membrane structure, like tubular and flat membranes. So the need has been evident for the design of a simple, cheap and small pretreatment system. The pretreatment installation has to remove the polluting organic matter, such as algae, colloids, bacteria, as sludge of high concentration. The choice between a number of known processes for the removal of pollutants from water depends on some specific demands. These demands are: a small plant, reliable, simple, cheap, low-sludge volume-concentrated, low energy consumption. After a number of experiments the choice has been made in favour of the process of flocculation and coagulation of the colloids. To remove the flocs preference was given to the flotation process. Flotation is a process in which a flow of small bubbles of air, adhering to the flocs, transports the flocs to the surface of the water. The foamy sludge has a high dry matter content (4–6%). The developed process is able to produce clean water, comparable with tap water in the west of Holland derived from surface water. Turbidity figures are from experiments involving Rhine water and badly polluted ditch water. | |
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