The amount of sludge generated from urban centers is increasing more and more, so wastewater treatment plants are being constructed. Recycling of sludge by application to agricultural land can alleviate the disposal pressure, and, at the same time, utilize the plant nutrients in the waste. Organic nitrogen in sludge is mineralized to inorganic forms such as nitrate and ammonium that can be taken up by plants. The inorganic forms of nitrogen, especially nitrates, can easily be leached because of its negative charge. Not only do nitrates cause eutrophication, but, at high concentration in drinking water, can also cause chemical suffocation disease in babies. This work is meant to quantify nitrate and ammonium nitrogen leached from soil treated with sludge. In order to obtain information on the composition of leachate from sludge, Kandiustults and a lysimeter study were used. Municipal and industrial sludge were applied to completely random design plots at different rates: 125, 250 and 375 kg N/ha. Each control lysimeter was treated with chemical fertilizer (N-P2O5-K2O : 20-10-10) at the rate of 125 kg N/ha. After the Chinese kale (Brassica oleracea L.) was planted in each lysimeter, leachate was collected every week and analyzed for NO3 and NH4+. The experiment was conducted at Kasetsart University, Bangkhen Campus, Bangkok, Thailand. Average nitrogen leach in the form of NO3 was 25 times more concentrated than the NH4+. Nitrate concentrations in the leachate exceeded the drinking water standard. Nitrate and ammonium leaching were measured to be between 1.50-3.00 % and 0.03-0.14% of the total treated nitrogen, respectively. Total nitrogen losses found in this study were 44.88%, 77.24% and 77.91% of the total nitrogen applied by chemical fertilizer, Huay Kwang sludge and Bangpa In sludge, respectively.

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