Hot microbubble injection in thin liquid film layers for ammonia separation from ammonia rich-wastewater

With 140MT of ammonia produced per annum, over 2% of the world's total energy output is used for ammonia production. Consequently, the remediation and recovery problem is daunting. Ammonia is a pernicious pollutant with an extremely high affinity for water. Less than 2mgL−1 is harmful to flora and fauna but most waste streams contain between 500 mgL−1–5000mgL−1. Physico-chemical processes recover ammonia but are not highly effective in terms of efficiencies for such dilute solutions. Hot microbubble stripping is investigated here. It involves their injection into thin liquid layers for selective vaporization with limited sensible heating of the substrate liquid phase. The method results in several phenomena not previously observed in literature: (i) 100% separation efficiency in 30 min of processing time as opposed to 95% efficiency in 30 h for the benchmark of industrial stripping; (ii) stripping of ammonia at a pH less than 9, i.e. without addition of alkaline pH modifiers and with air as a carrier gas; (iii) using cold microbubbles to strip ammonia is effective, just slower. The process is enhanced due to high mass transfer coefficients: 1000–3000 times faster than conventional stripping. This effect is explained by a new non-equilibrium chemical thermodynamics evaporation – condensation model based on Langmuir's vapour pressure prediction from the kinetic theory of gases that explains the first order kinetics, its magnitude, and the very strong temperature dependence.