Study On Treatment Of Municipal Sewage By A/O Biological Contact Oxidation Process

The traditional bio-contact oxidation technique has the advantages of high organicremoval ratio, high adaptability, easy operation and control. But its application islimited by its rigid sink structure, tendency of membrane to harden, low capability innitrogen and phosphorus removal. In this research we developed A/O bio-contactoxidation reactor based on the classic Anoxic/Aerobic nitrogen and phosphorusremoval, by using innovative suspended packing bioreactor incorporating traditionalactivated sludge and bio-film method. This more manageable improvement increasedthe efficiency, nitrogen/phosphorus removal, reduced the energy consumption andinvestment.The designed capacity of A/O bio-contact oxidation reactor is4m³/d. This researchanalyzed the inflow of Dadukou wastewater treatment plant, focusing on the removalefficiency of every measure under various hydraulic loadings, reflux ratios, gas-waterratios and temperatures, exploring optimized parameter in operation, analyzingmicrobial activity in suspended packing of both anoxic and aerobic tank in order tofurther study the feature and function of this reactor and promote the development andapplication of this technology.This reactor started up with granular sludge inoculation. Successfully started-up in15days, the reactor had the removal ratio more than85%in COD and90%inammonium separately. At this time the anoxic zone （A zone） was attached with ashblack biofilm, massive anaerobion, amphimicrobe and some metazoans were observedunder microscope, with packing MLSS of2300mg/L, and suspended MLSS of400mg/L; The aerobic zone （O zone） was attached with a1mm sepia biofilm, abundantmetazoans such as vorticella and rotifer were observed under microscope, with packingMLSS of2600mg/L, and suspended MLSS of600mg/L. Under electron microscopeboth A and O zone had good sludge inoculation which was matched with microscoperesults.After the univariate analysis of hydraulic loading, gas-water ratio, reflux ratio andtemperature which can affect the wastewater treatment efficiency, the result showed thatwith hydraulic loading of4m³/（m³·d）, temperature of20℃to30℃, gas/water ratio of7:1, reflux ratio of100%, the reactor had a more optimized operating condition. Underthis condition, the average removal ratio of COD, NH₄⁺-N, TN, TP and SS are85.9%, 95.2%,53.7%,77.4%,80.0%separately. The outflow quality was steady and reachedlevel I B standard of Discharge Standard of Pollutants for Municipal WastewaterTreatment Plant （GB18918-2002）. During the operation, the system encountered theindustrial wastewater and operated normally after a week. This indicates that thissystem has good impact resistance and recovery capability.Microbiological characteristic analysis revealed that the majority ofmicroorganisms in A zone and O zone were existed as biofilms. Biofilm was moremicrobial activated than suspended microorganisms, and O zone was more microbialactivated than A zone. In A zone, the COD degradation rate was141.6(mg·g^-1)/h and58.8(mg·g^-1)/h in biofilm and suspended microorganism separately, NO3--N decay ratewas29.6(mg·g^-1)/h and11.4(mg·g^-1)/h separately. In O zone, the specific oxygenuptake rate （SOUR） in biofilm and suspended suspended microorganism was27.22mgO₂/VSS·h and16.05mgO₂/VSS·h separately. From DGGE analysis, in differentareas of anoxic tank and different time periods of biofilm, there were significantchanges in bacterial species and dominant bacterial community in comparison withinoculated sludge. Biofilm and bottom sludge in anoxic tank had larger contribution tothe denitrification and anaerobic phosphorus release; and the aerobic tank showedhigher organics degradation and nitrification ability under the function of biofilm,suspended sludge and bottom sludge.