Study on granulation and performance of aerobic sludge induced by intermittent sludge application in ultra-high salt environment

Abstract

In the northern district of Alar city in the southern region, the presence of numerous textile printing and dyeing factories results in the generation of complex wastewater with high salinity due to the substantial water usage during the dyeing process. Consequently, it is of significant importance to investigate biological treatment technologies of degrading ultra-high salinity wastewater. Two sequencing batch reactors (SBRs) with a height-to-diameter ratio (RH/D) of 7.5 were inoculated with municipal activated sludge, and artificial simulated wastewater (with a salinity mass fraction of 10%, prepared by solid NaCl) was used as the influent. Two operating modes of intermittent sludge application (S1) and no sludge application (S2) were implemented. The analysis focused on the sludge morphology, pollutant removal performance, and the mechanism of maintaining granular structure stability during the granulation process of municipal sludge in ultra-high salinity wastewater. It was found that salt-tolerant aerobic granular sludge could eventually be formed through both intermittent sludge application and no sludge application, with granulation times of 43 days and 55 days, respectively. After the formation of salt-tolerant aerobic granular sludge, MLSS in S1 and S2 were approximately 4.5, 4.11 g/L, SVI30 were 20.8, 45.4 mL/g, and the corresponding granule sizes were 4 834.5, 3 686.2 µm, respectively, with the sludge morphology of oval-shaped. The protein secondary structure α-helix/(β-sheet+random coil) in the sludge granule EPS were about 0.685 (S1) and 0.699 (S2), and the hydrophobicity of the sludge granules was enhanced. The average removal rates of COD, TP, and NH4+-N in the wastewater by the intermittent sludge application reactor were 81.50%, 57.40%, and 93.30%, respectively, which were higher than the removal rates of pollutants in the no sludge application reactor. The intermittent sludge application was demonstrated to effectively shorten the time for sludge granulation, maintain the integrity of the granules, and strengthen the removal of pollutants, offering a new approach for the treatment of high-salinity wastewater.

Keywords

• salt-tolerant aerobic granular sludge
• sbr
• intermittent sludge application
• decontamination performance
• ultra-high salinity wastewater