Development Of Dissolved Oxygen And Ammonium Micro-electrodes And Research Of Application In Biofilm

At present the study of biofilm focus more on the choice of carrier,thecharacteristics of reactor mass transfer,and optimal control and other macro-areas inChina.Due to lack of effective tools,it is difficult to achieve system study ofmicro-biofilm field,and it is hard to analyze the reaction mechanism ofmicro-environment in biofilm.Micro-electrode technology can quantify material changesof micro-environment in biofilm,which is of great significance to the establishment of micro theories and guiding practice.In this paper ammonium and dissolved oxygen micro-electrodes have beenproduced,and linear range,response time,stability,life and other properties ofmicro-electrodes were menstruated.Based on the micro-electrode with good performance,through menstruating the concentration changes of various substances ofmicro-environment in the biofilm in biological filter and the fluidized bed reactor,the feasibility of micro-electrodes for biofilm microscopic studies was certified,and theresponse characteristics of various substances of internal biofilm were studied.The mainresults are as follows:(1) The detection limit of dissolved oxygen microelectrode is 7.2×10^-4mol/L,linearregression is better,regression coefficient reaches 0.9999,regression curve comesinto a straight line basically.The slope of standard curve is 0.0788,and life is morethan a month generally.(2) The linear response range of ammonium microelectrode is 10^-1～10^-5- mol/L,theslope of standard curve is -59.2 mV/log [NH₄⁺],close to the theoretical value -59mV/log [NH₄⁺],linear regression coefficient reaches 0.9991.Electrode responsetime is t₉₀≤5s.Life has a slight difference due to the differences of production,and is about three days generally.(3) The nitrification of biofilm in the biological filter reactor was determined bymicro-electrodes.The results show that:When NH₄⁺ concentration increases from 15mg/L to 30 mg/L,the removal rate of NH₃-N decreases slightly,while the removalrate increases to 75.1% after half a month training.The results of fivemicro-electrodes basically consistent with the macroeconomic results .When NH₄⁺concentration is 30 mg/L,nitrate and nitrite can not be detected in effluent by spectrophotography.Analyzing the decrease of NH₄⁺ concentration in solution usingmicroelectrode from micro-view,there are two reasons:on the one hand because ofadsorption of the biofilm,ammonium transfers into the biofilm;on the other hand microbial organisms in the liquid phase change organic materials into ammonia through the role of Ammonium.(4) The nitrification of biological fluid bed reactor was determined by micro-electrodes.The results show that:At C/N=20 and C/N=5,dissolved oxygen is not be exhaustedin the biofilm,and nitrification occurs in both cases.Compare to C/N=20,theremoval rate of NH₃-N increases 5.1% at C/N=5,which indicates that maintainingCOD unchanged,a certain increase of NH₃-N concentration can help to improve theremoval rate of NH₃-N.At C/N=2,the dissolved oxygen is completely exhaustedwhen it comes to internal biofilm,but no nitrification and denitrification occur.Compared with the previous two conditions the removal rate of NH₃-N significantlydecreases,only 68.5%.This is because maintaining COD unchanged,the increasingammonium concentration leds to depletion of dissolved oxygen,and dissolvedoxygen constraints nitrification.(5) Micro-electrodes verify nitrification from the micro-perspective in biofilm and quantify the concentration change of DO,NO₃^-,NO₂^- and NH₄⁺ in biofilm.The resultsshowed that micro-electrode as a micro-tool in biofilm is feasible.