EFFECTS OF DOMESTIC WASTE-WATER SPRAY IRRIGATION ON DENITRIFICATION RATES

Spray irrigation of domestic wastewater has potential as an effective on-site wastewater treatment and disposal method for soils that have l imited renovation capacity. Nitrogen removal via denitrification from spray irrigation can fluctuate due to the alternating aerobic and anae robic conditions caused by irrigation frequency. The objectives of thi s study were (i) to determine the effect of domestic wastewater applic ation rates and frequencies within a 24-h period on nitrous oxide (N2O -N) emissions from soil columns measured by the acetylene block techni que, and (ii) to determine the influence of wastewater irrigation on t he denitrification capacity of the soil. Treatments used two effluent application rates (1.25 and 2.5 cm wk(-1)) and three daily irrigation frequencies (1, 2, and 3 times d(-1)) and a no-effluent control. Incre ased effluent application and splitting the effluent into two or three applications d(-1) increased levels of N2O-N emissions as compared wi th the control, Single daily doses of effluent produced low levels of N2O-N emissions over the 24-h measuring period, whereas more frequent applications produced rapid increases in N2O-N emissions directly afte r effluent application. Gaseous losses of N averaged 5.3 and 26.2% of the applied N at the 1.25 and 2.5 cm wk(-1) effluent loading rates, re spectively, The denitrifying capacity of the soils was limited by both N and C. Maintaining effluent in the upper, more microbially active p art of the soil column through split applications was important to N r emoval via denitrification.