Biological removal of nitrogen from industrial wastewater was investigated by a novel O/A (oxic/anoxic) type process with natural zeolite circulation. This process consists of ammonium ion removal by zeolites and subsequent biological regeneration of zeolites. Two types of raw wastewater with high strength ammonia nitrogen (300–400 mg/L) from a fertilizer industry and a tannery industry, separately, were prepared for laboratory scale experiments. After ammonia ion removal from the influent wastewater by zeolite in the anoxic reactor, nitrifying bacteria, either attached to the zeolite or suspended in solution, participated in the conversion of ammonia to nitrite and nitrate in the following oxic reactor. Zeolites saturated with ammonia nitrogen were continuously regenerated and circulated in the proposed process without the use of chemical regenerants such as NaCl. Experimental results showed an 88–92% removal of ammonia nitrogen and high settleability in the final clarifier for both examples of wastewater. The results support that the proposed biological reactors with zeolite powder circulation are very effective in treating high strength nitrogen bearing wastewater.

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