Aerobic granular sludge: Cultivation parameters and removal mechanisms

Stability of aerobic granular sludge in a pilot scale sequencing batch reactor enhanced by granular particle size control

Aerobic granulation was successfully achieved in a pilot scale sequencing batch reactor within 40 days. Then, stability of different particle size granules was explored according to their activity and resistance to ultrasonic crushing. Different particle size granules (0.3-0.6 mm, 0.6-1 mm, 1-1.43 mm, 1.43-2 mm, 2-3 mm and 3-4 mm) were exposed under different ultrasonic power separately. It was found that the granules with 2-3 mm always had the maximum granulation rates after ultrasonic crushing. Meanwhile, activity data showed that the 2-3 mm granules had the lowest specific oxygen utilization rates, which indicated that they were easier to maintain stability as the increase of their particle sizes was the slowest. So, 500 mL mixed liquid of the reactor were taken out and sieved to obtain the 2-3 mm granules, which were subsequently returned to the reactor to increase their proportion. Through the manual regulation, the proportion of 2-3 mm granules kept increasing which gradually became dominant in the reactor. Under the strategy of 86 days of operation, the aerobic granules were regular and compact, which had good removal effects of the real wastewater. The results indicated that the stability of the system could be greatly enhanced by the method, which provided a new strategy to maintain the granular stability.

Different bioreactors for treating secondary effluent from recycled paper mill

Secondary effluent from paper mill was characterized by poor biodegradability and containing recalcitrant compounds. In this study, four bioreactors, including a sequencing batch biofilm reactor (SBBR), a stirred-tank reactor (STR) and two submerged aeration reactors (SAR) were used to treat secondary effluent from a recycled paper mill respectively. The results indicated that chemical oxygen demand (COD) was increased by SAR2 treatment and COD removal efficiency for SBBR, SAR1 and STR was 39.7%, 15.7% and 30.9% respectively. It is suggested that recalcitrant compounds were removed by SBBR, SAR1 and STR respectively. Total nitrogen (TN) and total phosphorus (TP) of wastewater were increased by treatments of each bioreactor, which suggested that endogenous respiration of biomass occurred during the treatment. Microbial analysis of sludge from different bioreactors suggested that the removal of recalcitrant compounds in SBBR and STR might be related to the presence of unique microorganisms in each reactor.