Effects of Hydraulic Loading Rate on the Removal of Pollutants from an Integrated Biological Settling Tank

Based on the designing concepts of rotating biological disk and settling tank, a hybrid biological purification and settling tank was developed to achieve simultaneous removal of turbidity causing materials, organic matters, NH4+-N, and TP. Experimental results showed that under certain rotary speed and water quality conditions, the removal rates of both turbidity and organic matters and NH4+-N were relatively stable first and then started to decrease with the increase of hydraulic loading rate. The highest value was achieved at 0.036 g·(m2·d)-1 and 0.064 g·(m2·d)-1 respectively. Compared with turbidity and TOC and NH4+-N, the removal rate of TP was greatly influenced by hydraulic loading rate. The average TP removal was the worst at 0.064 g·(m2·d)-1. Appropriately decreasing or increasing the hydraulic load was helpful to the phosphorus removal process. Further study showed that nitrification and dephosphorization processes competed for the limited carbon source and DO in the water phase. Along the flow direction, the surface of the disc populations of microorganisms with good coordination and distribution along the characteristics ensured that the process still had certain decontamination effect under the condition of unfavorable hydraulic load, which indicated that the biological settling tank had a capacity in resisting organic loading rate shock and could be used in enhancing pollutant removal in treating micro-polluted water.