Study Of Acrylonitrile Wastewater Treatment Using A/O~2Biological System

During the process of Acrylonitrile （AN） production an enormous number of wastewatercould be produced. Containing lots of refractory and toxic organic pollutants, the ANwastewater is difficult to be treated, and hence has attracted increasing scientists’ attention inrecent years. Moreover, in consideration of the acutely toxicity to humans at relatively lowlevels and potential threat to the environment and the development sustainability of society, tofind more efficient method to achieve the objective of meeting the standard beforedischarging AN wastewater, with no doubt, is necessary and meaningful to the human beings.In this work, anoxia biological process and two-stage biological contact oxidation （A/O²ï¼‰were combined as a biological treating system with the main purpose of the removal oforganic pollutants, NH₄⁺-N and NO₃^--N in AN wastewater. To estimate the treatment effect ofA/O²system and the fate and transformation of contaminants two batch experiments and acontinuous flow experiment were conducted.In the raw AN wastewater, the concentration of pollutants were as follows:839¹640mg/L of COD,43.3¹32mg/L of NH₄⁺-N,311.7⁴10mg/L of NO₃^--N,424.68mg/L ofnicotinamide,882.62mg/L of acrylonitrile,972.57mg/L of3-cyanopyridine and other threeunknown pollutants, named1#,3#and5#respectively in this study. The long term operationof continuous flow experiments showed that about92%of COD,88.73%of NO₃^--N could beremoved at the optimum conditions（30℃, HRT=91.3h, reflux ratio=90%, DO（mg/L） andMLVSS/MLSS（mg/L/mg/L） of A, O1and O²zone were＜0.5,2.5³.0and2.5³.0and3420/5462,6013/8233and7155/9035respectively）, corresponding to the effluent COD123mg/L. Removal efficiency of COD and NO₃^--N decreased with the increase in the loadingrate.Furthermore, the content of1#increased continuously as the removal of3-cyanopyridinein the anoxia phase and would reduce only if the biodegradation of3-cyanopyridine wascompleted. This indicated that1#was one of the catabolites of3-cyanopyridine. Besides, bothhypoxia and aerobic microorganisms could use nicotinamide, acrylonitrile,5#and3-cyanopyridine as the carbon source and hence degraded them. Moreover, the results ofexperiments manifested that3#was a very refractory pollutant with serious toxicity.Accordingly, it had a negative effect on the metabolism of microorganisms and especially inhibited the nitrification of nitrifying bacteria. This is the reason that the concentration ofNH₄⁺-N in effluent of A/O²system was higher than that in influent.