Estimate of N2O release from pit-toilets

The use of pit-toilets has severely contaminated the groundwater with nitrate ions in Mulbagal town, Karnataka, India. This paper examines the potential of nitrate ions in the pit-toilet effluents to transform to N2O and to escape to atmosphere from 16 wards of Mulbagal town. Anaerobic conditions prevailing in the pit-toilet convert 25 % of the available N to ammonium ions. Only 3-33 % of ammonium ions transform to nitrate ions in the pit-toilet and escape with the effluent. During migration to aquifer, only 4.5 % of available nitrate concentration in the effluent transforms to N-2 and N2O gases in the 1.5-m-thick saturated zone underlying the pit-toilet; 36-55 % of the gases comprise N2O and the remainder of N-2. Further only 18 % of N2O formed escapes to atmosphere, while the remainder is retained in soil solution. Calculations show that 9.88 x 10(13) molecules of N2O/cm(2) would be cumulatively released from 16 wards of Mulbagal town, over an area of 4.9 km(2).