THE EFFECT OF CHEMICAL OXIDANTS ON EFFLUENT CONSTITUENTS FOR DRIP IRRIGATION

One of the main problems concerning drip irrigation by effluents is th e clogging of drippers and emitters, which, due to their small diamete rs, are extremely vulnerable to clogging by effluent constituents. Ear lier observations revealed that this phenomenon can be reduced if effl uents are treated with oxidants. In order to realize the role of oxida nts in these processes, and to obtain meaningful and reproducible resu lts, synthetic effluents rather than authentic effluents were used. Ho wever, the synthetic effluents were composed so as to provide the best possible resemblance to natural effluents, and the effects of Cl-2 an d ClO2 on their constituents were studied. The demand of these effluen ts for Cl-2 was 5-8 mg l(-1) and for ClO2 3-4 mg l(-1). Two mg l(-1) o f 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 replicatio n ability. Both oxidants have demonstrated a notable aggregation effec t on the effluents. The conclusions of the results described above wer e 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 reas on for this was the presence of clogging agents, ''immune'' to low Cl- 2 concentrations, produced as early as in the reservoir, and carried d own to the drippers by the effluent stream. Batch treatment combined w ith settling was much more efficient, and reduced the clogging signifi cantly, because in this case the Cl-2 reacted not only as a disinfecta nt, but also as a coagulant due to the oxidation of humic constituents .