Effects of Domestic Wastewater Spray Irrigation on Denitrification Rates

Abstract

AbstractSpray irrigation of domestic wastewater has potential as an effective on‐site wastewater treatment and disposal method for soils that have limited renovation capacity. Nitrogen removal via denitrification from spray irrigation can fluctuate due to the alternating aerobic and anaerobic conditions caused by irrigation frequency. The objectives of this study were (i) to determine the effect of domestic wastewater application rates and frequencies within a 24‐h period on nitrous oxide (N2O‐N) emissions from soil columns measured by the acetylene block technique, and (ii) to determine the influence of wastewater irrigation on the 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. Increased effluent application and splitting the effluent into two or three applications d−1 increased levels of N2O‐N emissions as compared with 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 after 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, respectively. The denitrifying capacity of the soils was limited by both N and C. Maintaining effluent in the upper, more microbially active part of the soil column through split applications was important to N removal via denitrification.