The Experimental Study Of Combined Technology With Two Stages Of A/O BAF And Ultrafiltration In Advanced Municipal Sewage Treatment

Lanzhou is a typical heavy industry city that mainly composed of petroleum chemicalindustry and is also a river city that use the Yellow River as the main water resources. Withthe development of western region in recent years, and the rapid development of industrialzone in Lanzhou city as the center to made plenty of industrial wastewater discharged into theYellow River，and to made the dilute self-purification ability declined for Lanzhou section ofYellow River, and it also impacted on the urban residential water and agricultural waterseriously. So we have to " open source and throttling ", protect the Yellow River and reducethe pollution of wastewater discharged into, to achieve sustainable development of theenvironment and industrial. Here，the " open source " means the development of new waterresources, that is urban sewage reuse, strengthen water recycle technology and promote thereuse water."Throttling" refers to: in recent years, with the country’s water programsthroughout the year, it provides local water consumption reduced year by year, which requirestransformation for high water consumption enterprise and raises water use efficiency to savewater.BAF is more popular wastewater treatment technology currently, it has some advantagesof small occupation space, less investment, high water quality for process, stable operationand simple technological process etc. Ultrafiltration technology in general as the sewagedepth process technology and applied in after sewage secondary biochemical treatment, whichcan remove micro-sized particles in water, and avoid the trial of flocculation and precipitationetc. Make two stages of A/O BAF and ultrafiltration technology organic union, use thehydrolysis of AF period in two stages of A/O BAF, strengthen the biodegradability of secondpond effluent, and turned the refractory organic compounds in water into biodegradableorganic matter, then use BAF section to remove the COD of second pond effluent and most ofNH3-N. wo stages of A/O BAF effluent treated by ultrafiltration membrane again to madeorganic matter was further removal, UV254and turbidity also get higher removal at the sametime, it can be as the high-quality reuse water and directly used in industrial and agriculturalcity owing to its high water quality and stability.In order to keep the combination process of two stages of A/O BAF and ultrafiltrationcan be advanced treat the urban sewage efficient and stable, so the whole experimental stageis divided into four parts: BAF preparation phase, that is the selecting of fillers anddetermination of hanging membrane method, the up and running of two stages of A/O BAF,ultrafiltration operation phase and the combination process operation stage.BAF preparation phase, that is with the second pond water of a sewage plant in Lanzhoucity as raw water, in-depth study the effect that different fillers and hanging membranemethod on BAF of urban sewage depth processing. The contrast experiment of select thefillers and different ways of hanging membrane with BAF process of raw water COD and ammonia nitrogen removal as the main index, the experimental results show that: ceramsitefillers hanging membrane stability and the removal rate on raw water’s COD and ammonianitrogen is superior to volcanic rocks and zeolite in the filler selection experiments, so chooseceramsite as the BAF process fillers; In the contrast experiment that with ceramsite as fillersand different hanging membrane method, BAF natural hanging membrane start time is shorterthan composite water hanging membrane, the effluent stability, the high removal rate of CODand ammonia nitrogen, so using natural hang membrane method to start on BAF of urbansewage depth processing.Two stages of A/O BAF start-up operation stage includes both up and running. Startsection: AF adopts two steps starting method, that is aerobic pre hanging membrane start andanaerobic start; BAF and AF in series to natural hanging membrane and made AF effluent asBAF inflow. The run part by changing the the hydraulic load of two stages of A/O and the gaswater ratio of BAF period to choose the best operating conditions. The experimental resultsshow that: in the cases that raw water CODCrfor33~68(mg/L), ammonia nitrogen for10~25(mg/L), two stages of A/O BAF in HRT for2.5-3h, BAF is successed hanging membraneafter54days under the condition of gas water ratio of7:1,the CODCrremoval rate is39.12%on average, ammonia nitrogen removal rate is over97%; In the best operating conditions forthe hydraulic load is0.367m3/（㎡*h）, BAF section under the condition of gas water ratio of7:1, two stages of A/O BAF on the CODCrremoval rate is49.1%on average, ammonianitrogen average over97%.Ultrafiltration operation stage is divided into two parts. The first part is the basicproperties experiment of the ultrafiltration membrane, through analyse the changes ofmembrane flux and transmembrane pressure difference to investigate basic performance ofultrafiltration membrane and continuous operation ability. Second part for the optimaloperation parameters of ultrafiltration technology, adopt orthogonal experiment to determinethe optimum operation parameters of ultrafiltration for: run for half an hour and back flush for10min, water cleaning method for pulse method.The combined technological process of two stages of A/O BAF and ultrafiltration inurban sewage depth processing experiments are divided into two parts. Part one by examiningCOD volume load and temperature effect on processing efficiency of the combination process,which shows the combination process of effluent stability, resistance to shock loads; Anotherpart by the combined process and the processing unit run separately on the depth of the urbansewage treatment of contrast test, investigate each processing unit whether can be organicallycombine to achieve the desired treatment effect, the experiment results show that: thecombined technological made the hydrolysis of AF, BAF nitrification and oxidationdecomposition and the ultrafiltration filter function effectively together. Process effluent waterquality: COD at13.54mg/L, ammonia nitrogen at0.42mg/L, UV254at0.095and turbidity at0.47NTU, the average removal rate on the second pond water at70%and97.7%, UV254at82.3%and97.7%. At the same time, two stages of A/O BAF as pre-processing of ultrafiltration process, which decreased of ultrafiltration membrane fouling effectively andreduces the cleaning frequency of ultrafiltration.The combined technological process of two stages of A/O BAF and ultrafiltration issimple, small occupation space, effluent stability, resistance to shock loads, the effluentcontents city reclaimed water use of landscape water, industrial water and miscellaneouswater and city water quality index, so the combination of process effluent can be directly usedin industrial and agricultural water back, the broad prospect of application.