Study On The Change Of Oxygen Transfer Capacity And α Value In Moving Bed Biofilm Reactor

Under the policy of"carbon peak"and"carbon neutral",energy consumption in sewage treatment has been widely concerned.MBBR（Moving-Bed Biofilm Reactor）is widely used in the treatment of municipal sewage and industrial wastewater due to its high treatment efficiency and low sludge yield.The main energy consumption unit of MBBR process is the aeration system.Its oxygen transfer capacity has a great influence on the energy consumption in the process of sewage treatment.Up to now,the research on oxygen transfer capacity of MBBR aeration system is still not comprehensive.Therefore,in order to study the change law of oxygen transfer capacity in MBBR reactor,this paper carried out research work from the aeration conditions（carrier filling rate,perforated pipe gas flow rate,aerator layout,etc.）,water quality（surfactant,total dissolved solids,etc.）,environmental factors（water temperature）and other aspects.The influence of the above conditions and factors on the oxygen transfer capacity in MBBR reactor was objectively evaluated with the standard total oxygen transfer coefficient(K_La₂₀)and specific standard oxygen transfer efficiency（SSOTE）as evaluation indexes.In addition,the temperature correction coefficient of the oxygen transfer capacity of MBBR reactor was optimized,and the key factors affecting the oxygen transfer capacity of MBBR reactor were identified.Based on the experimental results,the variation of oxygen transfer capacity andαvalue in aerobic reactor of MBBR system under actual wastewater treatment was analyzed.The main conclusions of this paper are as follows:（1）The change of oxygen transfer capacity under different carrier filling rates shows that K_La₂₀ value increases gradually under different aeration intensities when the carrier filling rate increases from 0 to 65%.At low aeration strength(4 m³·h^-1·m^-2),SSOTE increased from 2.00%/m to 2.87%/m when the carrier filling rate was less than 45%,and decreased from 2.87%/m to 2.54%/m when the carrier filling rate was more than 45%.At high aeration strength(12 and 20 m³·h^-1·m^-2),SSOTE increased with the increase of carrier filling rate.（2）The experimental results show that:The aeration intensity is controlled unchanged,and different gas orifice flow rates are obtained by setting different hole densities of perforated pipes.With the increase of gas orifice flow rates from 10 m/s to 30 m/s,K_La₂₀ and SSOTE decrease gradually under the condition of different carrier filling rates when single side perforated pipes are used for aeration.When uniform perforated tube aeration is used,K_La₂₀ decreases from 8.17 h^-1to 6.71 h^-1 and SSOTE decreases from 2.31%/m to 1.89%/m with the increase of gas orifice velocity and carrier filling rate at 0.When the carrier filling rate is 35%and 65%,K_La₂₀ and SSOTE increase gradually when the gas orifice velocity increases from10m/s to 20m/s to 20 m/s,and K_La₂₀ and SSOTE decrease gradually when the gas orifice velocity increases from 20 m/s to 30 m/s.（3）The variation rule of oxygen transfer capacity under different types and arrangements of aerators shows that:K_La₂₀ and SSOTE of microporous aeration are larger than those of perforated aeration,but the carrier movement speed is reduced by31.2%compared with perforated aeration.At the same time,K_La₂₀ and SSOTE values of single-side microporous aeration are larger than those of uniform microporous aeration under different carrier filling rates.At low gas orifice velocity（10 m/s）,K_La₂₀and SSOTE values of single-side perforated tube aeration are greater than those of uniform perforated tube aeration.However,K_La₂₀ and SSOTE values are smaller when aerated with single-side perforated pipe at high gas orifice velocity（30m/s）.Although the oxygen transfer capacity of microporous aeration is high,the carrier movement speed is low,which is not conducive to the full contact between microorganisms and sewage in the actual sewage treatment process.Therefore,the MBBR aeration system should choose one-sided perforated tube aeration,and the flow rate of the designed gas orifice should not be too high.（4）The experimental results of the influence of typical water quality factors on oxygen transfer capacity show that:When the SDS concentration increased from 0 to10 mg/L,K_La₂₀ decreased by 43.7%and 37.4%,SSOTE decreased by 44.5%and33.9%,respectively,when the carrier filling rate was 0 and 45%,respectively.The presence of carrier weakened the negative effect of SDS on oxygen transfer ability.When SDS concentration increased from 12mg/L to 20 mg/L,the oxygen transfer ability increased slightly.When TDS value increases from 2000 mg/L to12000 mg/L,K_La₂₀ increases by 22.2%and SSOTE increases by 24.9%.When THE TDS value is greater than 12000 mg/L,K_La₂₀ and SSOTE tend to remain unchanged when the TDS value increases.With the increase of p H from 4 to 10,K_La₂₀ and SSOTE increase by 19.9%and 24.0%,respectively.When p H was high,the change of p H has little effect on oxygen transfer ability.（5）Oxygen transfer ability under the conditions of different temperature change with temperature correction coefficient optimization value research shows that:when the temperature increased by 8.43℃to 31.54℃,as the carrier of filling ratio and aeration intensity increases,the total mass transfer coefficient of oxygen showed a trend of increase,and the carrier fill rates or aeration intensity is high,temperature changes have less effect on the oxygen transfer ability;In MBBR,the optimal value of temperature correction coefficientθranges from 1.030 to 1.044.（6）Multiple linear regression analysis results show that within the range of experimental conditions,the most critical factor affecting K_La₂₀ is aeration intensity,and the most critical factor affecting SSOTE is gas orifice velocity of perforated pipe.（7）The test results of oxygen transfer capacity under actual sewage condition show that the oxygen transfer capacity increases gradually with the progress of sewage treatment process or the increase of aeration intensity.When the aeration intensity is constant,theαvalue increases by 0.28 on average with the process of sewage treatment.When the aeration intensity increases in the range of 8–28m³/（h/m²）,theαvalue increases by 0.29 on average.