Experimental Study On The Treatment Of Decentralized Domestic Sewage By Air-Stripping Bioreactor

In recent years,with the strengthening of water environment management and the promotion of beautiful countryside construction and rural revitalization strategy,the treatment of decentralized sewage such as rural sewage has been paid more and more attention.Although the traditional wastewater treatment process has a good effect,it has many processes and complicated processes,and a series of characteristics are not suitable for the treatment of distributed wastewater.Therefore,this study takes distributed sewage as the treatment object,and designs and develops an integrated treatment equipment.Due to the conflict of working principles of different strains,most of the traditional biological nitrogen removal processes are completed in two or more independent reactors,or in the same reactor that causes alternating anaerobic deficiency in time,and the process has the characteristics of high construction investment and operating costs,and large footprint.The distributed sewage treatment often has problems such as unstable operation at low temperature in winter and fluctuation of carbon nitrogen ratio of influent.Therefore,on the basis of summarizing the traditional sewage denitrification theory and technology,this paper constructs a mixed liquid circulation flow state in the reactor,and from the perspective of strengthening the performance of activated sludge bacteria micelles and improving the mass transfer efficiency,An Airlift loop bioreactor（Airlift loop bioreactor）was designed to remove pollutants from different dissolved oxygen environments simultaneously in the same space.At the same time,the current new nitrogen removal theory is applied to think from the perspective of changing the structure of the reactor,forming a role similar to vertical push flow to gradually reduce aeration,and constructing spatio-temporal intermittent aeration.The bacteria micelle continuously circulates in anaerobic environment along with the flow of the reactor,and stresses AOB and NOB with this unsteady environmental pressure,so as to explore the feasibility of short-range nitrification.At the same time,based on the distribution of matrix concentration,the utilization of denitrifying carbon sources and ways were explored,so that the denitrification mode was changed from full nitrification and denitrification to synchronous short-range nitrification and denitrification.Firstly,the feasibility of the gas stripping reactor for wastewater experiment was studied by using the clean water experiment to measure the overflow flow and other parameters.The research shows that the higher the aeration rate,the faster the oxygen saturation rate in the reactor,the smaller the protrusion height,the larger the overflow flow,and the faster the oxygen saturation rate.However,the DO in the reactor shows a trend of greater inner zone than outer zone,and the DO decreases gradually along the flow.The average DO values of the inner and outer zones from top to bottom were 3.58 mg/L,3.24mg/L,3.03 mg/L and2.72mg/L,respectively,which proved that different levels of DO environment would be formed in the reactor under sequential batch operation,and it was presumed that the difference of DO would be greater due to the presence of oxygen-depleting bacteria in the sewage experiment.In addition,the relationship between aeration volume,protrusion height and overflow flow rate was investigated under different inner diameter.The results showed that the ratio of hydraulic retention time in the inner and outer zone（good and anaerobic）under different inner diameter was the same as the ratio of volume in the inner and outer zone,that is,the hydraulic retention time in the inner and outer zone was 1:2 under 300 mm inner diameter.The internal and external hydraulic retention time is 1:1 under the inner diameter of350 mm;The hydraulic retention time in the inner and outer areas under the inner diameter of400 mm is 2:1.Secondly,according to the characteristics of distributed sewage quality and quantity fluctuation,combined with the flow field characteristics and synchronous nitrogen removal mechanism of the gas-stripping bioreactor,the synchronous pollutant removal performance and mechanism of the reactor under the conditions of C/N>8.0,C/N=4.0-8.0,and C/N<4.0were studied respectively,and the denitrification carbon source utilization rate under different working conditions was investigated.Determine the use of carbon and nitrogen.The results show that the effluent COD,NH₄⁺-N and TN of the reactor are maintained at 40 mg/L,0 mg/L and 10～15 mg/L at each carbon/nitrogen ratio.The simultaneous nitrification and denitrification rates were 68.83%,72.09%and 81.37%,respectively.The utilization rates of denitrification carbon sources were 11.61%,21.21%and 63.89%,respectively.When C/N<4.0,due to the change of water intake mode to intermittent 2h water intake,a suitable DO environment was created for denitrification bacteria,so the denitrification carbon source utilization rate was higher.At the same time,based on the preliminary reactor design prediction,emphasis was placed on the realization and stable maintenance of short-range nitrification.The research results showed that the reactor could achieve the accumulation of nitrous nitrogen,and maintain a relatively stable short-range nitrification process under the condition that the reactor sludge concentration and operation mode were stable.Meanwhile,it was speculated that the denitrification pathway of the reactor would gradually change to short-range nitrification and denitrification.In this reactor,the oxidation of nitrous nitrogen by NOB has a certain"lag"compared with the oxidation of ammonia nitrogen by AOB.At the same time,in the process of the gradual reduction of sludge concentration and carbon to nitrogen ratio in the later stage of the reactor,nitrous nitrogen gradually accumulates and nitrous nitrogen gradually vanishes in the reactor,thus achieving short-range nitrification.However,its accumulation theory and other influencing factors need to be further explored.Finally,based on the previous experimental results and data,the matrix degradation kinetics equation was deformed based on the Monod equation,and various microbial kinetic parameters during the reactor operation were fitted.The results showed that:The maximum ammonia oxidation rate(v_max)under different carbon to nitrogen ratios were 0.054d^-1,0.097d^-1and 0.103 d^-1,and the semi-saturation and constant of ammonia nitrogen were 4.165 mg/L,3.195 mg/L and 3.096 mg/L,respectively.In other words,the ammonia oxidation rate gradually increased when the influent-water ammonia nitrogen gradually increased.When C（NH₄⁺-N）was greater than 30.0 mg/L,the ammonia oxidation rate reached the maximum and did not change with the change of substrate concentration.The nitrite oxidizing bacteria were strongly inhibited after 20 days of reactor operation.The maximum nitrite oxidation rates were 0.017d^-1,0.000d^-1,0.000d^-1,and the semi-saturation constant of nitrite was 0.928mg/L,0 mg/L,0 mg/L.The maximum denitrification rates of denitrifying bacteria were 0.024 d^-1,0.116 d^-1 and 0.122 d^-1,respectively.Half-saturation and constant were 1.679 mg/L,6.694mg/L and 18.083 mg/L,respectively.After the regression model was established,the model data showed that most of the carbon sources were used in the direction of short-range denitrification with nitrite nitrogen as electron acceptor in the process of carbon-nitrogen ratio reduction.When C/N>8.0,about46.5%of nitrite nitrogen was reduced by short-range denitrification.When C/N=4.0～8.0,60.2%nitrite nitrogen was removed by short-range denitrification.When C/N<4.0,81.03%of nitrous nitrogen was reduced by short-range denitrification.At the same time,the utilization path of carbon source is also inclined to denitrification.When C/N>8.0,the COD used by heterotrophic denitrification is about 15.84%,the COD used by C/N=4.0～8.0 is about 19.36%,and the COD used by C/N<4.0 is about 72.19%.