EFFECTS OF MEMBRANE FILTRATION ON ORGANIC-MATTER AND VIABLE BACTERIA IN RECIRCULATING NUTRIENT SOLUTIONS IN GREENHOUSES

Cucumbers were grown in nutrient film systems with (A) recirculation o f solution and (B) membrane filtration and recirculation of solution. Samples of the nutrient solutions were taken during May-August. Nutrie nt solution in circulation without membrane filtration contained on av erage 23 ppm TOC (total organic carbon), while the filtered nutrient s olution contained 15 ppm TOC. Spectrophotometric analysis of the sampl es showed a clear correlation of absorbance at 295 nm with TOC. The sp ectrometric data are compatible with tannin- and lignin-like material as the main organic residues in the nutrient solution. Membrane-filter ed nutrient solutions were rapidly reinfected with bacteria, and filte red and non-filtered nutrient solutions flowing to the plants did not differ with regard to the number of bacteria.