A report on biochemical action of the secondary settling tank (SST)in Beishiqiao wastewater treatment plant,Xi'an

摘要

This study firstly reported the concentration change of dissolved pollutant in the Secondary Settling Tank(SST)of Beishiqiao Wastewater Treatment Plant and the possible biochemical action happened in the SST was discussed.The samples were collected stochastically from the inlet and outlet of the SST and the measurement results showed that the concentration change of some routine dissolved contaminant(such as SCOD,NO3-N,PO43--p)took place besides the suspended solid in the SST of Beishiqiao WWTP.Firstly,the pH values of the effluent were higher than that of influent entirely however it seemed that denltrification did not occur because the concentration of nitrate and nitrite took on a bit elevation,which conflicted with the theory of current denitrification.Secondly,the concentrations of phosphate in the effluent were higher than that in the influent in 75％of these samples,which led to 25％effluent concentration exceeding the standard limit(1.0mg/L).All phenomena above may attribute to complicated biochemical action(maybe phosphorus-rich sludge releasing phosphorus or hydrolyze under anaerobic condition or nitrification partially)in the SST and need further research.