Experimental Study On Treatment Of Domestic Sewage With Low Carbon Nitrogen Ratio By Inverted A~2O-MBR Process

With the decrease of water resources and the improvement of living environment urbanization,the standard of sewage treatment is becoming more and more strict.At present,most of the sewage treatment plants in China are facing the situation of upgrading.For the northwest of China,water resources are extremely scarce,and the secondary utilization of water resources highlights the particularly strong demand here.Among the many process options for upgrading,the inverted A²/O-MBR combination process has the advantages of low energy consumption for non nitrated liquid reflux,high efficiency of nitrogen and phosphorus removal,high efficiency of solid-liquid separation,stable effluent and flexible control in MBR membrane bioreactor,which is the best choice under the current situation.In this experiment,inverted A²/O-MBR process was used to treat domestic sewage with low carbon nitrogen ratio.The start-up of the combined process,the influence of subsection water inlet on the effluent effect of the combined process,the influence of process parameters change on the effluent effect after stable operation,and the effluent,pollution and cleaning of MBR membrane module were studied.The results show that:?1?In the start-up stage of the experiment,due to the increasing sludge concentration in the reactor,the sludge load of the reactor is continuously reduced to 0.19kg COD/?kgMLSS·d?.In the later stage of the experiment,the system has been in a low load operation state,with sufficient organic matter removal capacity;in this stage,the operation strategy of no sludge discharge makes the MLVSS/MLSS value in the biochemical tank of the reactor drop from 0.94to 0.68,and the sludge load is continuously reduced to 0.19kgCOD/?kgMLSS·d?With the increase of operation time,the removal rate of ammonia nitrogen and TN in effluent also increased gradually,which were 86.97%and 69.13%respectively,and the removal rate of TP decreased from 71.32%to 36.21%.?2?The average removal rates of COD,NH₄⁺-N and TN were 82.67%,96.17%and 45.20%respectively,and the removal effect of phosphate(PO₄^3—P)was not good.The removal efficiency of organic pollutants in sewage was significantly improved after adopting the two-point feeding mode under the condition of segmented feeding.The removal efficiency of COD and NH₄⁺-N basically did not change under the three different proportion of segmented feeding:2:1,1:1 and 1:2.The removal efficiency of TN increased with the increase of water inflow in anoxic section,reaching 80.69%.The removal efficiency of PO₄^3—P increased with the increase of water inflow in anaerobic section The average removal rates were 13.91%,33.25%and 58.53%respectively.Considering the removal effect of various pollutants,it is concluded that the best way of water inflow is two points,and the best proportion of subsection water inflow is 1:2.The water quality index concentration of the experimental effluent is lower than the limit value specified in water quality for municipal wastewater reuse?GBT 18920-2002?^[1].However,in order to make the effluent quality meet the requirements of landscape environment water?GBT18921-2002?or industrial water?GBT 19923-2005?,it is necessary to explore the method of optimizing phosphorus removal process^[2,3].?3?By changing the length of sludge age?SRT?,the effluent effect of inverted A²/O-MBR combined process was explored.As far as the removal effect of COD is concerned,the change of SRT has no significant effect,which can meet the discharge standard of primary A.as far as ammonia nitrogen?NH₄⁺-N?and total nitrogen?TN?are concerned,the extension of SRT will improve the removal effect of both,but too long SRT will be counterproductive.As far as this experiment is concerned In addition,the ammonia nitrogen can meet the first level a discharge standard.Due to the low carbon nitrogen ratio,the denitrification in the anoxic section is not complete and the total nitrogen in the effluent is on the high side.In terms of total phosphorus?TP?,the effluent concentration is not ideal and generally meets the first level B national discharge standard.Therefore,the best SRT of the inverted A²/O-MBR combined process in this experimental stage is determined to be 20d by comprehensive consideration.?4?Reasonable aeration intensity is the prerequisite for the normal and efficient operation of the combined process of inverted A²/O-MBR.When the aeration amount in the MBR membrane tank is too high or too low,it will cause serious membrane module pollution.In this experiment,the reasonable aeration intensity of the MBR membrane tank is 0.09Nm³/h.Considering the time cost and membrane module cost,the best extraction stop ratio of the effluent determined in this experiment is 8min:2min,Under this pumping stop ratio,the growth rate of effluent and pollution degree of membrane module reaches the best balance point of this experiment.The relationship between sludge concentration and membrane module pollution in MBR membrane tank is explored through experiments.It is shown that with the increasing sludge concentration in MBR membrane tank,the time for MBR membrane module to reach the upper limit of pollution degree will be gradually shortened;the time for MBR membrane module to reach the upper limit of pollution degree will be gradually shortened After cleaning,the time to maintain normal operation often decreases with the increase of sludge concentration,so the pollution of MBR membrane module under high sludge concentration is irreversible;the pollution recovery of membrane module will increase with the extension of backwash time,but when the backwash time reaches 6min or later,the pollution recovery of membrane module is no longer obvious,so the simple backwash Washing can not completely remove the pollution of membrane components,but can only play a role of temporary relief to ensure the normal water of membrane components;by using 0.2%NaClO solution for off-line cleaning,the pollution of MBR membrane components can be alleviated to a large extent,and the recovery degree of the first four cleaning can reach 98.7%±0.1%.Later cleaning effect will be greatly reduced.