[Aerobic granular sludge for simultaneous COD and nitrogen removal at high carbon and nitrogen loading rates]

In a 4 L reactor, aerobic granular sludge was cultured with piggery wastewater with glucose and ammonium sulfate as the additional carbon and nitrogen sources, respectively. No exotic activated sludge was inoculated, and activated carbon powder was used to immobilize the indigenous microorganisms of wastewater in the set-up period. The reaction was conducted under controlled conditions of progressively increasing COD and NH4(+)-N loading rates, decreasing settlement time, and enhancing aeration. The resulted aerobic granular sludge was capable of simultaneous COD and nitrogen removal. The performance (COD and NH4(+)-N removal efficiencies) and characteristics of aerobic granules at high loading rates were investigated. The mature aerobic granular sludge was brown-yellow, and took an irregular spherical shape with a diameter of 0.5-3.5 mm. Under the COD loading rates of 4.80-12.6 kg x (m3 x d)(-1) and NH4(+)-N loading rates of 0.217-0.503 kg x (m3 x d)(-1), the removal efficiencies of COD and NH:4(+)-N were greater than 94% and 98%, respectively. When the COD and NH4(+)-N loading rates reached 15.7 kg x (m3 x d)(-1) and 0.723 kg x (m3 x d) (-1), respectively, the floc sludge grew quickly, and the granules disaggregated. The removal efficiency of NH4(+)-N decreased to 81.6% in four days. Yet the removal efficiency of NH4(+)-N returned to higher than 98% when the sludge was partially removed and the loading rates were reduced. The aerobic granules cultured in this study exhibited excellent abilities of simultaneous COD and nitrogen removal, and resistance to simultaneous shock of high COD and NH4(+)-N loading rates.