Stripping and recovery of ammonia from centrate of anaerobically digested biosolids at elevated temperatures

Abstract

The process of air stripping/absorption was studied at pilot scale at temperatures ranging between 23 and 75°C using ammonia in artificial and natural centrate. The process was more effective at high temperatures and became pH insensitive beyond a critical pH, which was found to drop as the operating temperature increased. Thus, at high temperatures, shorter packing height and lower pH are required to achieve the same ammonia removal. The Onda correlations predicted well the mass‐transfer properties of 25 mm (1 in.) and 32 mm (1.25 in.) nominal size packing in the ranges of 40 to 60°C and 53 to 61°C, respectively. The Norman/Sherwood–Holloway correlations predicted well the mass‐transfer properties for the former and poorly underpredieted the latter packing. The Onda correlations are recommended for preliminary design of stripping/absorption systems within the preceding temperature ranges.