The Treatment Effect Of BAC On Aldehyde And Ketone Pollutants In Ozonated Effluent Water

With the deterioration of domestic water source, ozone-biological activated carbonprocess becomes popular in recent years due to its significant advantages in efficienttreatment performance on organic matter and ammonia nitrogen in drinking water.However, it may also bring about some noteworthy problems such as producing ozoneoxidation by-products, reducing the biological stability of water and giving rise to totalbacterial amount in effluent, etc.The aims of this study were as follows:（1） to explore the influence of biologicalactivated carbon （BAC） on the removal of harmful aldehyde and ketone by-products inozone oxidation effluent as well as assailable organic carbon （AOC）, which is used tocharacterize biological stability of water,（2） to investigate the effect of operationparameters such as water temperature, empty bed contact time （EBCT） and ozonedosage on the removal efficiency of BAC.Activated carbon filter was flushed with ozone oxidation effluent to form biofilmin natural way. In order to study the biofilm situation of activated carbon filter untilbiofilm being matured （about100d in total）, three ways were used: measuringconventional index (potassium permanganate index、UV₂₅₄and NH₃^-N) of the influentand effluent water, observing biofilm by microscope and determining biomass duringthe biofilm formation. The results indicated that at the early stage of biofilm formation,potassium permanganate index and NH₃^-N removal rates fluctuated greatly, thevariation law of UV₂₅₄was not obvious, species and quantity of microorganism wererare and the structure was loose. At the later stage of biofilm formation, the removal ratetended to be stable and microbial biomass maintained at about80nmol per gramactivated carbon.After the biofilm matured, water temperature and EBCT were selected as variableparameters to study the quantitative removal of conventional pollutants (potassiumpermanganate index, UV₂₅₄, DOC, NH₃^-N, NO₂^--N, NO₃^--N) by BAC at five points oftemperature （5℃,10℃,15℃,20℃,25℃） and four points of residence time （5min,10min,20min,30min）, so as to determine the actual operation of the BAC filter. Theremoval changes of potassium permanganate index and DOC with temperature andEBCT were similar, and both had trend of increase, which were not as obvious asNH₃^-N and NO₃^--N variation law. NO₂^--N removal law was relatively special, namelyremoval rate increased firstly and then decreased. Finally, the molecular weightdistribution measurement,3D fluorescence spectrometry and UV spectral scanning wereconducted to qualitatively describe the organic matter category removed by ozone and BAC, which did preparation for subsequent analysis of the formation of aldehyde&ketone by-products and AOC.In order to investigate the production of ozone oxidation by-products before andafter ozone oxidation, the content of four common formaldehyde, acetaldehyde,propanal, acetone and AOC were compared. The result showed that formaldehyde yieldwas the largest, which was between5-24μg/L. AOC ineffluent water was50-101μg/L,of which the average growth was about140%. Meanwhile, the removal of fouraldehydes and ketones by BAC at different temperature and EBCT were also examined.It was found that formaldehyde removal was also the highest, and their removalefficiency were slightly affected by temperature and EBCT, but it rised little astemperature increased. Yet the minimum removal rate could reach more than50%.Raised ozone dosage could improve DOC and UV₂₅₄removal, but also induce thecontent of aldehydes, ketones and AOC in ozone oxidation effluent. The ozone dosagewas not completely the same when each aldehyde concentration reached the highest.However, too much ozone could reduce aldehydes, ketones and AOC yields, and raiseliquid ozone surplus, but there was no significant influence on the BAC removalefficiency.