Removal of nitrogen from swine manure wastewaters by ammonia stripping

Abstract

Laboratory-scale experiments were undertaken to investigate aeration and air stripping as methods for removing ammonia from swine wastewaters with high nitrogen concentrations. The effects of temperature, air to liquid flow ratio and pH were investigated using wastewaters with a range of solids concentrations and pH values. Five sets of aeration experiments were carried out using two identical 3 l reactors made of acrylic tubing. For the air-stripping experiments, two identical stripping towers were constructed out of acrylic tubing and packed with plastic rings. At a pH of 11·2, the aeration method took approximately 150 h to achieve 90% removal efficiency. This was achieved with temperatures of 22°C and a low air flow rate of 1·15-1·60 l/min. At a comparable pH (11·5), the best results for the air-stripping method achieved 90% removal with only 7 h of treatment. This result was obtained with wastewater temperatures at 22°C, as in the aeration experiment, but the air flow rate was much higher at 90 l/min. Results showed that at a pH of 9·5 and 10·5, ammonia removal efficiency was directly dependent upon the air and liquid influent temperatures. However, at a pH of 11·5 there was no appreciable improvement with a rise in air and influent temperatures. The results further showed that an influent with a low pH required a longer period of time to achieve the same treatment efficiency. A pH of 10·5 is recommended as the most efficient of those tested, as very high levels of nitrogen removal were obtained at that level without incurring problems of excess lime. The high ammonia removal efficiency of the air-stripping method indicates that it could provide an interim solution for current waste management problems in the swine industry.