Simultaneous regeneration of exhausted zeolite and nitrogen recovery using an air stripping method at alkaline pH

Abstract

Ammonium nitrogen recovery using natural zeolite from the permeates of anaerobic membrane bioreactors was investigated with batch and continuous experiments. Regeneration of exhausted zeolite was compared between mechanical shaking and air stripping, and experimental results showed the superiority of air stripping over the shaking. Liquid circulation and air flow rates were optimized in a continuous zeolite-packed column with a separate recovery system consisting of a regeneration chamber and a stripping column. The liquid circulation rate had significant effect neither on the regeneration efficiency ( RE ) nor the ammonia transfer efficiency ( ATE ), while the ATE significantly increased with increasing air flow rate. The effect of pH on ammonia recovery was also tested and the results showed that both RE and ATE significantly improved at alkaline pH. When pH increased from 9.5 to 12, the RE increased from 9.2% to 84% and the ATE increased from 54% to 92%. The results emphasized that the pH should be higher than 11 for efficient regeneration and recovery of ammonia. The preliminary economic analysis showed the superiority of the alkaline regeneration–air stripping process over the high pH regeneration and the conventional regeneration.