ENHANCEMENT OF AEROBIC GRANULATION BY A NOVEL SLUDGE SELECTION STRATEGY TREATING LOW-STRENGTH WASTEWATER

摘要

Aerobic granular sludge process is known as a potential upgrading technology for wastewater treatment. However, start-up of aerobic granular sludge reactor is time-consuming, and frequently leads to deterioration treating low-strength wastewater. A novel sludge discharge strategy was proposed to enhance the granulation treating low-strength wastewater by sludge retention time (SRT) control strategy. After a short settling period, a variable discharge volume of effluent containing slow-settling flocs, which was predetermined by SRT, was withdrawn. The remainder of effluent was withdrawn after a long setting period. SRT in novel reactor (R1) was regulated and controlled at 12 days, while no specific SRT control strategy was applied in control group (R2). Results showed that granulation was achieved in R1 on day 50, while R2 failed to granulation. MLSS and SRT of R1 were stabilized at 11.6+/-0.24 g/L and 12+/-1.5 days, respectively, while in R2 they were 4.5+/-0.9 g/L and 4.2+/-0.5 days. Calcium carbonate particles with excellent settling ability were observed in R1. Bacteria then attached and grew on these particles to form mature granular structure. Results revealed that long SRT facilitated the growth of dense biomass with a slow growth rate, which enhanced biomass retention and aggregation in R1. High biomass concentration had accumulative effect on both carbon dioxide and calcium, which then formed calcium carbonate particles under alkaline condition in R1. Study stated that calcium carbonate nucleation enhanced biomass attachment, which were able to resist the detachment force and achieve complete granulation under unflavored condition.