Enhanced formation of aerobic granular sludge with yellow earth as nucleating agent in a sequencing batch reactor

Enhanced formation of aerobic granulation was investigated by adding yellow earth as a nucleating agent in a sequencing batch reactor with a constant setting time of 10 min. As a result, granules with an average diameter over 1 mm were obtained on the 4th day. The mature granules behaved better than the seed sludge in the water content, specific gravity, sludge volume index, settling velocity, and specific oxygen uptake rate. The yellow earth stimulated the secretion of extracellular polymeric substances, especially proteins. Both chemical oxygen demand and ammonia nitrogen had a removal rate over 90%, and more than 80% of the total inorganic nitrogen was removed even under aeration conditions due to simultaneous denitrification. The enhancement effects of the yellow earth might be based on the unique physicochemical characteristics and short settling time. A settling time of 10 min or more turned out not to be a prerequisite for a rapid granulation process.