Vacuum evaporation coupled with anaerobic digestion for process intensification and ammonia recovery: Model development, validation and scenario analysis
Amr Mustafa Abdelrahman, Ali Khadir, Domenico Santoro, Eun-Kyung Jang, Ahmed Al-Omari, Chris Müller, Katherine Y. Bell, John Walton, Damien J. Batstone, George Nakhla
Abstract
• A mechanistic model was developed for vacuum evaporation. • The model predicted ammonia recovery with an NRMSE of less than 10%. • A pH increase is more effective for ammonia recovery than a temperature increase. • Vacuum evaporation integration with anaerobic digestion improved process economics. A mathematical model for vacuum evaporation process was developed, which was experimentally validated at different initial pHs and temperatures for ammonia removal from anaerobically digested sludge. Six scenarios were evaluated by combining vacuum evaporation process with anaerobic digestion using anaerobic digestion model 1. These scenarios included a control, a pretreatment by vacuum evaporation, a post-treatment by vacuum evaporation at pH 9, a post-treatment by conventional evaporation (100 °C), an intensification with vacuum-concentrated recycled digestate back to the digester, and a second intensification at pH 9. Results indicated that using the evaporator as post-treatment at pH 9 or for intensification at pH 9 were the most favorable options, recovering more than 76 % of the nitrogen present in influent sludge with no negative effect on methane production. An economic analysis showed that the intensification at pH 9 was cost-neutral, significantly higher than the net present value of the control scenario (–22 M$).