| The threaten of microcystins(MCs) to drinking water caused by cyanobacterial bloom,especially microcystis bloom is increasingly severe with increasing eutrophication phenomenonof water body. In order to ensure the security of drinking water, a technology for dealing withmicrocystis bloom fast and efficient is needed.In this study, a natural-aeration biofilter was designed on the basis of informed research oflaboratory, the feasibility of it to deal with microcystis bloom and the effect of removalefficiency by filter materials, hydraulic loading rate (HLR) and influenct condition were studied.Best operating condition for MCs removal was investigated to provide theoretical reference fordesign and optimization of relevant parameters and operation of device in practical application.The main results were as fellows:1. Essentially, the removal of pollutants by aeration biofilter was through the activitymetabolism of microorganism in the biofilm. So the HRT and microbial communitycomposition and biofilm developmen under different were studied by NaCl tracer method, SEMand MPN in the initial stage of filter bed operation to discuss the effect of HLR on the removeefficiency of biofilter, the results were as fellows: that pollutants were better removed on theHLR of1.5m/d, and the removal load of TN, NH4+-N, COD and Chl a were1.08、1.30、3.36and26.02g/(m2·d), respectively. With the increase of HLR, the proportion of heterotrophicbacteria increased from7.0%to98.4%, but the proportion of autotrophic bacteria decreasedfrom93.0%to1.6%. The biofilm and mycelium structure also increased with the increase ofHLR. HLR has negative correlation with HRT, the formula of two was HRT=21.04/L0.52.2. The natural-aeration biofilter had the ability to remove MC-LR by studying the removalefficience of three kind biofilters(ceramsite, vesuvianite and zeolite) under different HLR andMC-LR concentration of infuenct, and the removal efficiency was significant affected by filtermaterials, HLR and MC-LR concentration of infuenct (p<0.05). The remove load of ceramsite,vesuvianite and zeolite biofilters increasesd with increase of HLR and MC-LR concentration ofinfuenct, and the removal efficiency of vesuvianite biofiler was better than the other two. Thehighest remove load of MC-LR was17.26μg/(m2·d) when treated by vesuvianite biofiler at theHLR of7.50m/d and MC-LR concentration of4.0μg/L of influent. However, the remove rate of these three biofilters decreased with increase of HLR and MC-LR concentration of infuenct,and vesuvianite biofiler was also better than the other two. The highest remove rate was81.7%when MC-LR treated by vesuvianite biofilter at the HLR of3.75m/d and MC-LR concentrationof0.5μg/L of influent. Besides, the effluent all had direct (>1.0μg/L) or potential (>0.3μg/L)harm when the concentration of MC-LR in the influent was above0.5μg/L. The remove load ofMC-LR had a linear relationship with height of filter materials in the biofilter, which couldprovide references for improvement of biofilter. The resuls above showed MC-LR was betterremoved by vesuvianite biofilter and HLR should be decided by the required removal load orremoval rate.3. The purification effect of MC-LR, Chl a, SS, TCOD and SCOD in the microcystisbloom by biofilter was studied to verify the feasbility of biofilter as the treatment technologyfor microcystis bloom. The results were as fellows: In general, filter msterisld and HLR hadsignigicant effects on the remove of MC-LR, Chl a, SS and COD (p<0.05), these pollutantswere better removed by vesuvianite than the other two and the remove efficiency was higher atthe HLR of3.75m/d than7.50m/d. The microcystis bloom water was best purificated byvesuvianite biofilter at the HLR of3.75m3·m-2·d-1and the remove efficiency of MC-LR, Chl a,SS, TCOD and SCOD were69.1%，72.3%，64.2%，33.8%and23.2%, respectively. So MC-LR,Chl a, SS and COD in microcystis bloom water were well removed in the study which indicatednatural-aeration biofilter could be applide into the purification of microcystis bloom waterbody.In addition, the remove of MC-LR had positive correlation with Chl a, SS and COD, negativecorrelation with DO and no correlation with TCOD and SCOD. This indicated theconcentration of MC-LR in the waterbody was correlated with algae and the removal ofMC-LR was not limited by COD because of the high reaeration ability of natural-aerationbiofilter.4. The adsorption of MC-LR by ceramsite, vesuvianite and zeolite which hadbioflim-formed, sterile and not-used three conditions was studied and fitted byLangmuir-Freundlich isotherm model to discuss the removal mechanism of MC-LR in thebiofilter. The results were as fellows: in the experiment of adsorption kinetics, the MC-LRconcentration of MC-LR had no significant difference in the bottles added with the sterile filtermaterials between time of Equilibrium absorption and24h, and decreased0.15,0.11and0.03 mg/L in the bottles added with bioflim-formed ceramsite, vesuvianite and zeolite, respectively.The results indicated MC-LR was mainly removed by the adsorption of filter materials at theinitial stage of filter bed operation and synergistic effect of adsorption of filter materials andbiodegradation of microorganism after biofilm formation, besides, the materials of saturationadsorption could continue to adsorp MC-LR due to the biodegradation.In the experiment ofadsorption isotherm, the saturated extent of adsorption of ceramsite, vesuvianite and zeolitewith bioflim formation were11.91，8.98and5.21mg/g, respectively, which were higher thanthem of sterilization or not used. With the increase of MC-LR concentration, the isothermbecame flat and the extent of adsorption increased. The order of adsorbance per unit quality wasceramsite> vesuvianite> zeolite, but the order of adsorbance per unit volume was vesuvianite(8.35mg/cm3)> zeolite(6.67mg/cm3)> ceramsite (4.65mg/cm3), which showed vesuvianite were most suitable as the removal material of MC-LR. |
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