Aerobic sludge granulation facilitated by activated carbon for partial nitrification treatment of ammonia-rich wastewater

Although the use of partial nitrification, or nitritation, for nitrogen removal via nitrite is an energy-saving method for treating high-strength ammonia wastewater, its stable operation with sufficient enrichment of ammonia-oxidizing bacteria (AOB) is difficult to maintain in activated sludge systems. In this study, an aerobic granulation technique was developed for the effective and stable nitritation treatment of ammonia-rich inorganic influent. Granular activated carbon (GAC) or powdered activated carbon (PAC) was added to the bioreactor to enhance the granulation of slow-growing AOB. The results show that aerobic granules could be formed for partial nitrification through the selective discharge of small and slow-settling sludge flocs, with or without activated carbon addition. However, dosing GAC into the sludge greatly accelerated the granulation process and shortened the granulation period from about 6 weeks to less than 3 weeks with the formation of large and fast-settling granules. In contrast, dosing PAC led to the slower formation of smaller granules. Compared to activated sludge flocs, sludge granulation with selective sludge discharge was found to help halt ammonia oxidation to the level of partial nitrification rather than complete nitrification. Based on the molecular analysis, aerobic granulation resulted in AOB enrichment and the reduction of nitrite-oxidizing bacteria (NOB) in granules, which is highly favorable to a stable partial nitrification operation.

• Sludge granulation was achieved for nitritation treatment of ammonia wastewater.
• Initial GAC addition accelerated the formation of nitritation sludge granules.
• Granulation helped control ammonia oxidation at the partial nitrification level.
• AOB instead of NOB were enriched in nitrifying granular sludge.