A pilot study on the removal of ammonia from aqueous solution using the integration of struvite synthesis and breakpoint chlorination

Document Type : Research Paper


1 Scientific Services, Research & Development Division, Erf 3475, Stoffberg street, Brits, 0250

2 Water Pollution Monitoring and Remediation Initiatives Research Group, School of Chemical and Minerals Engineering, North-West University, Potchefstroom 2531, South Africa

3 Magalies Water, Scientific Services, Research & Development Division, Erf 3475, Stoffberg street,Brits, 0250

4 North-West University, South Africa


Herein, a pilot study on the removal of ammonia from surface water using the integration of struvite precipitation and breakpoint chlorination is reported. A two staged pilot plant with a capacity of 1000 litres (1 m3) per run (LPR) was utilised, of which, stage one comprised struvite precipitation and stage two comprised breakpoint chlorination. Optimum conditions (i.e., stage 1) for struvite precipitation were 110 mg/L of Mg and P dosage (concentration), 150 rpm of mixing speed, 60 minutes of contact time, and lastly, 120 minutes of sedimentation while optimum condition for the breakpoint chlorination (i.e., stage 2) were 30 minutes of mixing, and 8:1 Cl2-NH4+ weight ratio. The synergistic effects of this hybrid system proved to be effective, with Stage 1 increasing the pH from 6.8 to 10.1, and a steep reduction in Mn (≥97.0%) and Fe (≥99.6%) concentrations and concomitantly deactivated E coli and TPC, i.e., ≥ 99% and ≥91%, respectively, while ammonia reduced from 5.4 mg/L to 2.7 mg/L-N (51.8 %). In Stage 2, i.e. breakpoint chlorination, ammonia was reduced from 2.7 mg/L to 0.02 mg/L-N whilst fully depleting residual microorganisms. Finally, the OPEX amounted to R4.85/kl ($0.31/m3), however, there is the potential of cost savings (≈53.2%) by replacing Kh2PO4 with waste phosphoric acid. Lastly, results from this techno-economic evaluation study showed great potential as compared to similar technologies hence making this approach a game-changer towards the prudent management of elevated levels of ammonia amongst other problematic contaminants.


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