Effect of Activated Sludge Retention Time, Operating Temperature, and Influent Phosphorus Deficiency on Floc Physicochemical Characteristics and UV Disinfection

Pilot-scale sequencing batch reactors (SBRs) were used to assess the effects of sludge retention time, temperature, and influent phosphorus level on floc physicochemical characteristics, effluent quality, and UV disinfection kinetics. Increasing the operating temperature from 12 to 22 °C caused an increase in the activated sludge flocs fractal dimension from 0.1 to 0.2, and improved the UV disinfection of final effluent. Influent phosphorus limitation, i.e., COD:N:P of 100:10:0.3, caused the formation of more spherical flocs with higher resistance to UV disinfection (by 1 log). However, influent phosphorus starvation, i.e., COD:N:P of 100:10:0.03, decreased the average floc size and sphericity, increased the final effluent turbidity, and lowered effluent UV dose demand. The findings provide useful information in terms of modifying wastewater treatment processes in the context of water reuse and improving UV disinfection efficiency.