A Novel Impinging Stream Bioreactor And The Application In Wastewater Treatment

Efficient and energy saving wastewater device has been the pursuing goal inwastewater treatment field. New types of bioreactor can be used extensively inwastewater treatment and their development has been the relatively popular researchsubject in recent years. However, the further application of these bioreactors isseriously hindered by such problems as low efficiency of traditional aerationfacilities and low mass transfer rate of substrates. Therefore, how to improveaeration efficiency and mass transfer rate of substrates need to be solved indeveloping new bioreactors. As one of the most efficient technology in promotinginterphase transfer in chemical engineering field, impinging stream has greatadvantages in improving aeration efficiency and mass transfer rate of substrates.Consequently, a novel bioreactor was developed by combination the strong points oftechnologies such as biofilm, circulating flow and impinging stream withemphasizing the following aspects: fast and sufficient absorbing of oxygen duringaeration, improving of mass transfer rate of substrates, suitable for the fast aerobicbiological treatment of wastewater, simple flow structure, efficient and energysaving. The bioreactor is named Inner Circulation Impinging Stream BiofilmReactor （ICISBR） and its main structure comprises the upper fluidized bed （FB）section and the lower inner circulation impinging stream absorber （ICISA） section.Basic performance of ICISBR was studied systematically by studying the residencetime distribution （RTD）, synthetic domestic wastewater treatment and high ammoniawastewater treatment by ICISBR; corresponding results were obtained as follows.In the study of RTD of ICISBR, RTD was determined by impulse inputting thetracer （KCl solution）, and then inspection the variations of tracer concentrations ofoutlet solution with residence time at conditions of different rate of inflow Vi andconstant aeration rate Va0.1m³/h. According to the analysis of nondimensional RTDfunction, nondimensional RTD density function and nondimensional RTD varianceof the test results, liquid flow pattern falls in between plug flow and perfect mixingflow and there exists sizable stagnant area in ICISBR. Vi of13.47L/h is the criticalvalue for the transitions of liquid flow pattern, under this flow rate, flow patternchanged with the change of flow rate and the backmixing extent is proportional tothe liquid flow rate. Above this critical flow rate, flow pattern and the backmixing extent stop changing despite of the increase of the liquid flow rate.In the study of synthetic domestic wastewater treatment by ICISBR, two typesof corncob fillers and suspended polypropylene filler were used as biofilm carriersin FB section of the reactor in order to study the effects of biocarriers on thesubstrate removal performance of ICISBR. Removal of COD and NH₄⁺-N andvariations of solution DO were used as the performance index, performance ofICISBR in wastewater treatment was studied in three stages, namely biofilmformation stage, batch operation stage and continuously operation stage.In the biofilm formation stage, effect of biocarriers on the time of biofilmformation was studied. biofilm was cultivated in batch mode with22h’s reactiontime every cycle after inoculation. It takes merely15reaction cycles for corncobbiocarriers and25reaction cycles for polypropylene biocarriers to complete thebiofilm formation in ICISBR. Substrate removal capacity of ICISBR slightlyincreased with the increase of specific area of biocarriers after biofilm formation.Variations of substrate concentration according to reaction time were studiedwhen ICISBR operated in batch mode. It was found that more than70%of COD and60%of NH₄⁺-N were removed during0-1.5h of reaction time and solution DO wasthe lowest at outlet of ICISBR.When ICISBR run continuously, effects of inflow substrate concentration, HRTand aeration rate on the removal of COD and NH₄⁺-N were studied. Resultsindicated that increasing the inflow substrate concentration or decreasing the HRT,the removal capacity of organic loads and NH₄⁺-N loads all increased althougheffluent COD and NH₄⁺-N increased either. By comparison, decreasing HRT wasmore efficient than increasing substrate concentration in the improvement of theremoval capacity of organic loads and NH₄⁺-N loads. The highest substrate removalof ICISBR can be achieved at modest aeration rate of0.3m³/h. A high or lowaeration rate would reduce the removal capacity of organic loads and NH₄⁺-N loads.By comparing the removal capacity of organic loads and NH₄⁺-N loads at ICISApart and FB part of ICISBR at different operation condition, it was found thatremoval of organic loads and NH₄⁺-N loads were insignificant in FB part,consequently, influence of biocarriers on the domestic wastewater treatment ofICISBR were insignificant.In the study of high ammonia wastewater treatment by ICISBR, first, comparedwith comparative experiment with propylene as biocarriers and glucose as liquid carbon source, denitrification ability of corncob was studied by treating nitratewastewater with corncob as biocarriers and solid carbon source. Effects of solutionCOD/N ratio and reaction time on denitrification were discussed. Results of theexperiment indicated that carbon source released from corncob can be easier used bydenitrification bacteria than liquid carbon source, as denitrification bacteria grows inthe inner layer of biofilm. Because the release rate of carbon source was slow,efficiency of denitrification decreased obviously by decreasing reaction time lowerthan8h in treating nitrate wastewater with corncob used as biocarriers and carbonsource.Second, corncob was used as biocarriers and carbon source in treating highammonia wastewater by filling the ICISA part and the FB part of ICISBR withcorncob filler. Taking the removal of COD, NH₄⁺-N, total nitrogen （TN） anddenitrification ratio as performance index of ICISBR, effects of solution C/N ratioand DO on the performance of treating high ammonia wastewater were discussed.Experimental results showed that high ammonia wastewater treatment performanceof ICISBR was significantly influenced by solution C/N ratio and DO, the bestcomprehensive performance in treating high ammonia wastewater obtained atconditions of solution C/N ratio of1.5and DO of2mg/L with the highest TNremoval percent. Removal of COD, NH₄⁺-N and TN reached92.7%,41.2%and23.8%, respectively, and denitrification ratio57.7%although the inflow NH₄⁺-Nconcentration reached up to200mg/L.In conclusion, ICISBR is a novel, energy saving and efficient wastewaterbiological treatment device and possess of good application prospect in wastewatertreatment. Results from basic performance study provide the essential data and thetheory reference for further development and structure optimization of ICISBR.