MANAGEMENT OF DOMESTIC WASTE-WATER FOR REUSE IN IRRIGATION

Treated effluent from an aerated lagoon and facultative pond system in southern Portugal, was used to irrigate fields planted to maize (Zea mays L.). The effluent was characterised with respect to its nitrogen and phosphorus content and applied by drip irrigation in response to c rop evapotranspiration requirements. Nitrification of ammonia in the e ffluent by soil microorganisms caused a reduced soil pH early in the g rowing season, but this was reversed as the season continued, For most of the growth season plant nitrogen demand ensured a low soil nitroge n concentration, but towards the end of plant growth the continuous ni trogen supplied in the effluent exceeded crop requirements with a resu lt that nitrate accumulated in the soil, The applied effluent also had a high phosphorus concentration but there was only a slight accumulat ion of this in the soil. The fertiliser value of the treated effluent was demonstrated by increased yields at physiological maturity and the N yield was within the range of expected values for this crop, The ma in removal mechanism for N during irrigation was crop uptake whereas P was removed primarily by soil processes. The advantages of wastewater reuse together with the importance of appropriate management practice s for re-use are discussed. Copyright (C) 1996 IAWQ. Published by Else vier Science Ltd.