Ammonium removal and recovery from greywater using the combination of ion exchange and air stripping: The utilization of NaOH for the regeneration of natural zeolites

Abstract

Greywater could take up a major portion of domestic wastewater, thus, recycling and reuse of greywater positively promote sustainable water to cope with water shortage and demand. In this study, ammonium adsorption from greywater via natural zeolites and ammonium recovery using NaCl and NaOH were comparatively investigated. Column tests were performed for ammonium adsorption as well as natural zeolite regeneration. Ammonium adsorption was terminated after Ct/C0 = 10 %. Following adsorption, regeneration phase was carried out using 25 L of regenerant for 2.5 h. In the treatment with NaOH as the regenerant solution, accumulated ammonia was subsequently eliminated by air stripping using a newly developed water spray reactor. It was found that no significant ammonium exchange capacity was observed between treatments which was (3.23 ± 0.03) and (3.24 ± 0.03) mg-NH4+ per g zeolites for NaCl and NaOH, respectively. The average regeneration efficiency by NaCl was (95.7 ± 1.2)%, whereas (94.4 ± 9.5)% was obtained from that of NaOH regeneration. In general, the amount of NaCl needed for traditional regeneration was 181 g to recover 1 g of ammonium whereas the combination of air stripping with NaOH only required 12 g NaOH. Theoretically, the conventional method by utilizing NaCl for regeneration burdens the chemical expenses as much as ~50 % more expensive than that of using NaOH with the combination of air stripping technique. Furthermore, unlike ion exchange loop stripping method, no supplementary NaOH and pH adjustment was done within 10 times of regeneration cycles which enabled a simple operation and an efficient utilization of NaOH. Ammonia removal efficiency using water spray reactor was relatively stable, effective and satisfying (>97 %) compared to that of using a stripping vessel.