| The textile industry as a pillar industry of national economy not only demands a great deal of water but also generates large amount of organic wastewater.Dyeing and finishing wastewater characterized by complicated composition,a great number of nondegradable substances,is generally difficult to be effectively disposed using conventional methods, and such wastewater recovery rate is quite low.Therefore,it is very important to develop a technology of recovery and recycling of water coming from textile wastewater in order to reduce the pressure of water scarcity and impact on environment from discharged textile wastewater.Knitting dyeing and finishing wastewater was studied in this paper by two-stage biological aerated filter(BAF) and pre-coating dynamic membrane technology for advanced treatment,respectively.The influential factors such as operational conditions, reaction kinetics and purification mechanism were systematically explored,and the experimental results obtained are as follows:1.The effect of operational parameters of BAF on removal efficiency of organic matter, including gas water ratio,hydraulic load,hydraulic retention time,temperature,inlet concentration,pH value was studied in detail.The results showed that:air/water=2, hydraulic load=0.39 m3/(m2·h),HRT=1 h,temperatures=25℃～30℃,pH value= 7.0～8.5,the removal efficiency of NH4+-N,CODcr,SS,turbidity,color were above 89%, 55%,87%,83%and 75%,respectively.The effluent concentration under the above operational conditions are below 1.5 mg/L,50 mg/L,10 mg/L,5 NTU and 20 times, respectively,which can meet quality standards of municipal reuse water,and such parameters can be referenced for industrial scale application for textile wastewater advanced treatment and reclamation.2.The purification mechanism and reaction kinetics of BAF were analyzed.According the removal of organic pollutants along the way in BAF,a experiential model has been set up to correlate the effluent concentration of treated wastewater with height of reactor,as S=S0exp{-3.8562HS0-0.1697(Q/A)-0.1804},which were verified by a series of experiments.3.Based on the flux of secondary effluent treatment and membrane pollution,the pre-coating experiments showed that the more stable dynamic membrane was formed under the conditions of kaolin with 6000 mesh used as film materials,the crossflow velocity=0.5m/s,transmembrane pressure=0.2MPa,kaolin concentration=0.3g/L, time=15 min.Under the above conditions of pre-coated membrane,the operating pressure =0.1 MPa,cross-flow velocity=1m/s,removal efficiency of CODcr and turbidity of secondary effluent treatment using dynamic membrane were 50%and nearly 100%, respectively,however,without the effect on color removal rate.By comparison of secondary effluent treatment between direct filtration and dynamic membrane filtration,it was found that pre-coating membrane played a significant role in reduction of flux,which also chieved better CODcr removal than that of direct filtration,which can be explained that the film formed on base membrane acted as a additional filter to enhance the filtering for wastewater treatment.4.According to SEM and ICP element analysis of acid leachate from ceramics supporter, it was found that Ca,Mg were detected as the main composition of inorganic pollutants of the internal membrane,Fe and P were in the second abundance.While comparing the TOC contained in basic leachate,it indicated the pollution within supporter with dynamic membrane was not as serious as that without the micro-filtration inorganic membrane, which mean that dynamic membrane played better performance of anti-pollution inside ceramics dynamic membrane.5.Comparing the effect of different order of chemical washing method on membrane fouling it was indicated that alkaline washing(0.2/mg·L-1NaOH) 1 h-acidic washing (0.1/mg·L-1HCl) 1 h better than that of acidic washing(0.1/mg·L-1HC1) 1 h-caustic washing(0.2/mg·L-1NaOH) 1h.After repeated chemical washing experiments,the results showed that flux of pre-coating membrane restored with the capacity of 90%by chemical cleaning,however,it only restored into 60%of the original capacity for the filtration,which means pre-coating membrane can effectively prevent the non-reversible contamination inside membrane.It was indicated that recovery rate of MF for pre-coating membrane via tap water washing significantly higher than that of inorganic micro-membrane,namely,it was generally restored to the original capacity of 45～55%.It can be explained that the pre-coating film can increase the utilization efficiency of membrane,and that the chemical washing step was basically omitted in engineering application.Finally,the actual wastewater from Haida knitting& weaving company in Ningbo city was targeted in this study.The plan of technical process was proposed as:separate the clean flow from contaminated flow and supply the water in corresponding to the quality requirement of the manufacturing.In this case,the combined technology of BAF and membrane was applied into wastewater advanced treatment with a pilot scale of 300t/d, and the treated water was recycled and reused.The conclusions of the test were shown as follows:(1)The results showed that the average concentration of CODer,color and turbidity in the effluent were less than 50 mg/L,10 times,1NTU,respectively when influent-quality index fluctuated.Each quota of the treated water has the superiority over the gray water standards(GB/T 18920-2002).The average CODer,color,turbidity removal efficiencies were 91%,95%and 96%,respectively.The treated effluent quality satisfied the requirement of water quality for printing and dyeing process.(2)At present,there is no standard of water quality for reuse and reclamation of dyeing and finishing wastewater applied into production process in China.Therefore,the essential parameters of water quality affecting dyeing and finishing process should be selected in according to the native situations such as pH and salinity.The experimental results of dyeing and finishing process using reclaimed water showed that reused water,pH value of 6.5～8.5 and salinity within 0.924g/L,can satisfy the product quality requirement.(3)The reclaimed water obtained from combined technology of BAF and membrane treatment suits for the process of scouring,bleaching,dyeing,washing and etc.in dyeing and finishing process,what's more,the reclaimed water also can be applied into scouring and washing process.While for some products with higher requirement,tap water is only necessary for the final step of washing and dyeing to guarantee the product quality.The conclusions of this study have further not only improved the fundamental theory for integrated technology of reclaimed and recycled water from knitting dyeing and finishing wastewater,but also provide the technical support to upgrade the recovery rate for manufacturing water in such industry as well as the parameters for operation and design in industrial scale application.
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