A novel process, natural freezing, was developed to remove ammonia from wastewater in this study. A series of experiments were carried out to examine the ammonia removal and ice productivity in laboratory in Dalian, the effect of operating conditions such as solution concentration, pH, ice content formed, and Na~+ concentration were conducted. The results showed that the natural freezing method could effectively remove ammonia from wastewater; about 80% ammonia was removed at about 500 mg/L initial ammonia concentration, while the fraction of ice formed was about 50% controlling the pH at 7. When the freezing process was carried out under natural temperature conditions, the obvious advantage was the savings in energy. Unlike mechanical freezing process, natural freezing usually did not require complex facilities and thus is simple and less expensive to operate. Therefore, the natural freezing method was characterized by low pollution, simple facility, low energy consumption, and it is feasible in most of regions north of China because of the long winter and low temperature conditions. This study could introduce the fundamental principle and research development of the natural freezing method.
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