Study On Treatment Of Rural Dispersed Domestic Sewage By A/O-DMBR Process

With the rapid development of China’s rural economy,the discharge of domestic sewage in China’s rural areas has been in _Creasing,posing a huge threat to the surrounding ecological environment.It is necessary to find a suitable treatment way.In China,most rural areas are not suitable for centralized sewage treatment technology.Therefore,considering the economic conditions,location and management difficulties in rural and remote areas,the use of local conditions of decentralized wastewater treatment technology will be the future direction of sewage treatment in rural areas.Dynamic membrane bioreactor（DMBR）is a kind of membrane bioreactor（MBR）.It retains the advantages of traditional MBR,such as good effect,less land occupation,and low sludge output.At the same time,it makes membrane filtration components cheaper and has significant advantages such as low cost of ownership,low operating energy consumption,easy cleaning and maintenance,and long service life.Therefore,it has good development prospects in the field of rural decentralized domestic sewage treatment.This topic is aimed at the decentralized rural domestic sewage in Chongqing area,using stainless steel wire mesh as the membrane base material to make flat dynamic membrane modules,and constructing anoxic/aerobic-dynamic membrane bioreactor（A/O-DMBR）pilot test device research.The article mainly explores the start-up of the A/O-DMBR reactor and the influence of operating parameters such as reflux ratio,hydraulic retention time,dissolved oxygen and temperature on the process operation effect.On the basis of the optimization of the above parameters,the article also explores the effect of the external carbon source on the treatment effect of nitrogen and phosphorus removal.Finally,the changes of membrane fouling and the way of membrane cleaning are discussed.The experiment shows:（1）After 18 days,the test device was successfully started up using the inoculation culture method,and the removal rate of COD_Cr and NH-N of the device reached more than 90%.At that time,the MLSS in the aerobic tank of the reactor was above 5,000mg/L,and the sludge floc structure was dense.Then,through mi _Croscopic examination,it can be found that protozoa such as bellworms and larvae are present in large numbers,and metazoans such as rotifers were found.The mi _Crobial population was rich and the biological community structure was complete.（2）It is determined by experiments that the better operating conditions of the A/O-DMBR process are:reflux ratio at 150%,HRT at 8 h,aerobic tank DO value at2.5-3.5mg/L,and temperature at 23-25°C.Under the condition that the average concentrations of influent COD_Cr,NH-N,TN and TP are 427.86mg/L,56.16mg/L,63.56mg/L and 5.46mg/L respectively,the A/O-DMBR combined process adopts the above the better operating conditions.The average removal rate of COD_Cr,NH-N,TN and TP by the device can reach 93.24%,97.40%,69.16%and 23.24%.The average concentrations of COD_Cr,NH-N TN and TP in the effluent were 28.00mg/L,1.46mg/L,19.61mg/L and 4.17mg/L,respectively.Both COD_Cr and NH-N meet the first-level A standard for urban sewage discharge,while TN and TP meet the first-level B standard and third-level standards respectively.（3）When the dynamic membrane module is used for effluent,the initial turbidity is higher.After the dynamic membrane is formed,the turbidity of the effluent is maintained at about 1 NTU,and the SS is almost 0,which shows the good solid-liquid separation ability of the dynamic membrane module.（4）When the C/N in the feed water is insufficient,the addition of an external carbon source（CH₃COONa）can effectively improve the ability of the A/O-DMBR combined process to remove TN and TP.When the dosage was 200mg/L,the removal rates of TN and TP reached 79.29%and 39.53%,respectively.TN can reach the first-level A standard for urban sewage discharge,but TP still needs additional treatment.（5）Without on-line physical cleaning,after the dynamic membrane module runs stably for about 10 days,the TMP rapidly rises to above 50KPa,and it needs to be cleaned and replaced at this time.The use of air backwashing as a cleaning method can effectively extend the stable running time of the dynamic membrane module.If the dynamic membrane module has been seriously polluted,it is cleaned by manual cleaning with brush and ultrasonic cleaning after taking it out.In this way,the flux of the dynamic membrane module can be restored to almost 100%,showing a good cleaning effect.