Use of Tetrazolium Salt INT for Estimation of Biological Activity of Activated Sludge Cultivated in SBR Process

The tetrazolium salt 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride (INT) was used as a tool for estimating the activity of the electron transport system (ETS) in activated sludge in a 40 L sequencing batch reactor (SBR) and domestic sewage as the organic substrate. The activity of INT-ETS during one SBR cycle, and the effect of the ammonia concentration and the concentration of organic matter influent on the INT-ETS activity were investigated. The results show that: the use of INT is reliable in estimating of biological activity of activated sludge of SBR system; Biological activity of organic matter biodegradation, nitrification and denitrification process in SBR system reduce orderly. Obviously, INT-ETS activity reduces from 232.59 mg/(g·h) to 190.65 mg/(g·h) at first and then decreases to 113.88 mg/(g·h) when influent concentration of COD and NH₄+-N is 300 mg/L and 40 mg/L respectively. In addition, various influent Nitrogen (NH₄+-N are 14.5 mg/L and 42.0 mg/L) and organic shock loading (COD are 293 mg/L and 685 mg/L) experimentations cure prove that operational conditions have no obvious effect on INT-ETS variation rule. However, the time of the appearance of feature points marking different reaction phase is influenced.