Evaluation of organic acids as scrubbing agents for ammonia recovery from wastewater through Aspen Plus® simulations

Abstract

This study evaluates the effectiveness of organic acids, specifically citric acid, lactic acid, and malic acid, as scrubbing agents for ammonia (NH3) recovery from waste air streams. The acid scrubbing process was modeled using Aspen Plus® and validated against sulfuric acid scrubbing process data available in the literature. The effects of various system variables, such as temperature, gas liquid ratio (G/L) pressure, acid and NH3 concentrations, on the scrubbing efficiency as well as outlet ammonium ion mass flow rate was investigated. Results showed that reducing temperature, acid reflux ratio, G/L ratio, and inlet NH3 concentration while increasing pressure and inlet acid concentration can improve scrubbing efficiency. Citric acid exhibited the highest ammonia removal rate, the lowest acid consumption, and the least change in scrubbing efficiency when changing inlet ammonia concentration, followed by malic acid and lactic acid. These findings suggest that citric acid is a promising alternative to sulfuric acid as a scrubbing agent for NH3 recovery in wastewater treatment plants. This study needs to further incorporate the dissociation reactions equations of organic acids to provide accurate results. Additionally, the simulation's simplification in the design of the scrubber system introduces uncertainties in the results.