| Membrane manufacturing is a sort of organic synthesis industry. The effluent from the membrane-making plants is a kind of toxic and difficultly degradable wasterwater with high concentration organic, for it mainly contains Dimethylformamide(DMF) and Dimethylacetamide(DMAC) which is of strong polarity, chemical stability and biological toxicity. Presently, the treatment methods include biochemical method, supercritical water oxidation, photocatalytic oxidation, physico-chemical method, chemical method, and so on. However, biochemical method results to activated sludge to disintegration and loss due to the inhibition by biological toxicity of DMF; supercritical water oxidation is expensive on cost and operation expend; photocatalytic oxidation is not suitable in reactor design and immobilization of catalysts; and physico-chemical method is usually applied to single-pollutant wastewater as well as chemical method. Therefore, the methods above are not suitable enough for the membrane-making wastewater more or less, yet the pollution is serious currently, it is indispensable to find an efficient method.There is a company in Zhejiang Province which produces hollow fiber membrane mostly, and the effluent from the processes contains dimethylformamide and dimethylacetamide. Membrane process following Anoxic and aerobic was taken in the wastewater treatment station in the company, but the chemical oxygen demand (COD) of effluent can't meet the standard of the wastewater discharge. Thereby, a new method, iron-carbon micro-electrolysis+ catalytic electro-oxidation reactor +biological contact oxidation process was utilized in the work. It was found that the craft is feasible. The effluent COD concentration was below the demand in national emissions standards (GB8978-1996) as the raw COD was 10000-20000mg·L-1.The results from pilot tests are as follows:Firstly, some toxicity of the raw water and most organic are get rid of when iron-carbon micro-electrolysis and catalytic electro-oxidation was taken as the pretreatment. Meanwhile, the bio-degradability of the water rises from below 0.3 to above 0.55. And then after disposing continuously by anaerobic and aerobic contact oxidation of the effluent, the quality is stable, and also meet the first grade national standard of the wastewater discharge.Secondly, three parameters, pH, reation time and aeration, were investigated in the iron-carbon micro-electrolysis tests. When pH value is 2-3, single-stage residence time is 120min with aeration, the COD removal rate could improve 5%-13%.Thirdly, there are twice transitions of COD removal as the two-stagesiron-carbon micro electrolysis connects, which indicates that the inlet pH and retention time are the main factors influence the final efficiency. Fourthly, the repolarization catalytic electro-oxidation tests shows that the best result appears in the influent pH 6, hydraulic retention time for 90-120min, cell voltage for 10V and distance of plates 5cm, then COD removal efficiency can be achieved 60%. Consequently, catalytic electro-oxidation could be used as a pretreatment process to deal with strongly polar organic industrial wastewater.Meanwhile, it is found there are three steps in the catalytic electro-oxidation process. The first is the electro-chemical controlling, the kinetic formula is as follows.The second step is spread controlling, the kinetic formula is as follows.The last step is mixing controlling. The dividing point isWhen X > X0, he reaction is controlled by spreading step, and agrees with the spreading kinetic mode; when X 0, the reaction is controlled by electro-chemical step, and agrees with the electro-chemical kinetic mode.In the catalytic electro-oxidation reactor, the filling between the negative and positive plates forms a layer of dense cement sensor electrode spontaneously. The side facing the anode is negative, and the other side is positive,which is a bipolar catalytic electro-oxidation reactor. Sensor polar is shaped under the condition that voltage between the positive and negative plates is distribute averagely, the filling is not mixed for long time and the iron salt exists. The organic matters removal rate can be improved by adding thin iron sheet as sensor polar artificially. Particularly, under the condition for the best result, the removal rate is more higher than non-iron sheet with the increasing of voltage.Finally, the 30d test results show that when the raw COD of water is 10000-20000mg·L-1, NH3-N 0.2-5.2mg·L-1, BOD5 2000-4600mg·L-1 and TOC 4100-11986mg·L-1, the effluent COD reaches 11-96mg·L-1, BOD5<16mg·L-1,NH3-N <5.0mg·L-1 and TOC < 20mg·L-1. Effluent of sewage can meet the national emission standard, which indicates that the combination processes have a strong resistant on the inlet organic load, and treatment effect is good. Consequently, the iron-carbon micro-electrolysis+ catalytic electro-oxidation reactor +biological contact oxidation process as a new method , provides an efficient way to deal with the strongly polar and toxic industrial wastewater.
|
PDF Full Text Request