Study on ammonia generation from digested sludge by subcritical water treatment

Abstract

Organic sludge has recently attracted attention as a renewable energy source. While the organic matter contained in sludge can be utilized as various renewable energy sources, its nitrogen component has limited use. In this study, subcritical water treatment was conducted to recover ammonia from digested sludge. While ammonia recovered via stripping is limited to soluble components, subcritical water treatment can convert solid components and dissolved organic nitrogen sludge into ammonia. Digested sludge was treated at several reaction temperatures, reaction pressures, treatment times, and oxygen ratios to determine the ammonia generation rate. Among the conditions tested in this study, an ammonium generation rate of 84.0% was obtained at 400 °C, 10 MPa, a treatment time of 5 min, and at an oxygen ratio of 1.2.