Ammonium sorption and regeneration using Mg-modified zeolites: A study on the interferences of competing ions from aquaculture effluent

Abstract

Aquaculture effluents consist of dilute nutrients such as ammonium (NH4+) is harmful to the environment and toxic to aquatic species. This research investigated the practicality of modified zeolites for aquaculture effluent treatment and ammonium recovery. Zeolites (Mordenite and Zeolite-Y) were modified by calcination and/or chemical modification with MgCl2 solution resulting in H-zeolites and Mg-zeolites, respectively. The presence of competing cations (Na+, Mg2+, Ca2+, and K+) provides an obstacle for the ion exchange process between zeolites and NH4+. Mg-modified zeolites can handle the interference of competing cations better than H-modified zeolites with the trend for cation selectivity for Mg-mordenite is K+ > Na+ > > NH4+ > Ca2+ > Mg2+. The optimum zeolite dosage for both Mg-modified zeolites was 9 g/L. Both Mg-modified zeolites showed better fit of Freundlich isotherm and pseudo-second order kinetic model. By conducting thermodynamic studies, the NH4+ sorption for both Mg-modified zeolites were found out to be an exothermic process. Mg-zeolite Y showed better NH4+ removal efficiency compared to Mg-mordenite for real aquaculture effluent treatment. This showed that Mg-zeolite Y exhibited higher NH4+ selectivity and was more practical in handling the complex aquaculture effluent. A two-step sorption process using 9 g/L Mg-zeolite Y was proposed which led to an increased NH4+ removal efficiency of 64.18%. A 10-cycles regeneration study concluded that Mg-zeolite Y have good reusability potential. A simple cost analysis showed an 89% reduction in cost by comparing between fresh zeolites every cycle and reusing both zeolites and regeneration solution for 10 cycles.