Management of domestic wastewater for reuse in irrigation

Abstract

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 crop evapotranspiration requirements. Nitrification of ammonia in the effluent by soil microorganisms caused a reduced soil pH early in the growing season, but this was reversed as the season continued. For most of the growth season plant nitrogen demand ensured a low soil nitrogen concentration, but towards the end of plant growth the continuous nitrogen supplied in the effluent exceeded crop requirements with a result that nitrate accumulated in the soil. The applied effluent also had a high phosphorus concentration but there was only a slight accumulation 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 main 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 practices for re-use are discussed.