System for ammonia removal from anaerobic digestion and associated ammonium sulfate production: Simulation and design considerations

A side-stream ammonia stripping system coupled with a full-scale anaerobic digestion plant is considered. The system is based on an ammonia stripping unit (thin film evaporator, TFE), a Venturi scrubber and a reactive absorption column. A portion of the sludge treated in the digesters is continuously withdrawn and transferred to the TFE, where ammonia is stripped through a biogas stream. The ammonia rich biogas is then treated with a sulfuric acid/water solution in the Venturi scrubber and in the absorption column, with production of an ammonium sulfate solution, which is stored in a tank until utilization as a fertilizer. The aim of this paper is to provide a comprehensive engineering framework supporting the design of a full-scale ammonia stripping system with associated ammonium sulfate production, to be coupled with pre-existing anaerobic digestion plants. On the one hand, an analytical equation is proposed for the simulation of ammonia desorption and the design of the ammonia stripping unit as a function of the selected operating conditions of flowrate, temperature and pH. On the other hand, corrosion issues affecting the storage tank are studied. Corrosion tests, carried out on a selected paint system, demonstrate no development of coating degradation or disbonding, even if local damage occurs in the film. Thus, guidelines to avoid corrosion are given.