THE EFFECT OF CHEMICAL OXIDANTS ON EFFLUENT CONSTITUENTS FOR DRIP IRRIGATION

One of the main problems concerning drip irrigation by effluents is the clogging of drippers and emitters, which, due to their small diameters, are extremely vulnerable to clogging by effluent constituents. Earlier observations revealed that this phenomenon can be reduced if effluents are treated with oxidants. In order to realize the role of oxidants in these processes, and to obtain meaningful and reproducible results, synthetic effluents rather than authentic effluents were used. However, the synthetic effluents were composed so as to provide the best possible resemblance to natural effluents, and the effects of Cl-2 and ClO2 on their constituents were studied. The demand of these effluents for Cl-2 was 5-8 mg l(-1) and for ClO2 3-4 mg l(-1). Two mg l(-1) of either oxidant caused a very fast bacteria inactivation that reached four orders of magnitude after 1 min. However, with respect to algae, concentrations up to 20 mg l(-1) of either oxidant did not affect the number of algae cells, although they caused a remarkable decrease in algal viability as expressed by its chlorophyll content and replication ability. Both oxidants have demonstrated a notable aggregation effect on the effluents. The conclusions of the results described above were examined in a pilot system. Continued chlorination by 5-10 mg l(-1) Cl-2 applied directly to the drippers was not very effective. The reason for this was the presence of clogging agents, ''immune'' to low Cl-2 concentrations, produced as early as in the reservoir, and carried down to the drippers by the effluent stream. Batch treatment combined with settling was much more efficient, and reduced the clogging significantly, because in this case the Cl-2 reacted not only as a disinfectant, but also as a coagulant due to the oxidation of humic constituents.