Preparation Of Modified Fly Ash By Pdac To Depuration Of Printing And Dyeing Wastewater

Printing and dyeing wastewater is a source of water pollution which is more difficult to deal with in water pollution control, containing complex composition, large color, high concentration of organic matter and difficult to biochemical degradation. The direct use of biological treatment in dyeing wastewater get less effect, it must be pretreated to reduce the concentration of color and organic matter, reducing the biochemical treatment load.In the paper, PDAC-fly ash with high adsorption property was prepared by a method of solution adsorption with poly-diallyldimethylammonium chloride (PDAC) and coal fly ash that is a kind of industrial waste originally. The PDAC-fly ash was used as adsorbent to treatment simulated dye wastewater and the actual printing and dyeing wastewater. Meanwhile, adsorption effect and adsorption behavior of wastewater color, chemical oxygen demand(COD), NH3-N and SS on PDAC-fly ash were investigated successively.Comparative studies have shown that:(1) The decolorization rate and COD removal rate of dyeing wastewater reached 40.02% and 37.6% under the conditons:pH value in strong acid or alkali, coal fly ash dosage of 4g·100mL-1, reaction time 90min. (2) The removal rate of wastewater color and COD of PDAC-fly ash was 2.4 times,2 times as raw fly ash respectively. Compared with the conventional modification of acid, alkaline and fire, PDAC-fly ash had a better removal effect in color and COD of dyeing wastewater.Optimum preparation conditions obtained by experiments screening were follows: added dose of coal fly ash 50g, water bath temperature 40℃, PDAC concentration 50g·L-1, reaction time 2h, pH value around 3.4. The mechanism of PDAC modified fly ash was:the surface activation of fly ash was stimulated by modification, increaseing surface area, changing the surface from negatively charged into positively charged.Four kinds of simulated dye wastewater were prepared as a certain concentration by reactive red, reactive yellow, vat red and dispersed purpurin. Meanwhile, evaluated decolorization effect of PDAC-fly ash. The results show that:The adsorption of color on PDAC-fly ash was a rapid process, the decolorization rate reached more than 80% within 15min; The decolorization effect increased as a function of PDAC-fly ash dosage, reached a maximum at a dosage of 0.5～1g·100mL-1, then the increasing trend weakened; The pH value had a little influence on decolorization effect, decolorization rate fluctuations in a smaller range; PDAC-fly ash was added to the concentration between 20～120mg·L-1 of simulated dye wastewater, the decolorization rate increased with increasing concentration; In the best dosage, the order of decolorization effect was vat dye>dispersed dye> reactive dye.PDAC-fly ash was used for the actual printing and dyeing wastewater treatment, no pH value regulation to wastewater, the most suitable operation parameters were as follows: adsorption reaction time 60min, added dose of PDAC-fly ash 2g·100mL-1, the reaction temperature was 25℃or so, and 10min of settlement time, the decolorization rate was 92%, the removal rate of COD, NH3-N, SS was 66%,84%,86%, and color has been reduced significantly, the effluent concentration of printing and dyeing wastewater were COD 174.23mg·L-1, NH3-N 2.82mg·L-1,SS67mg·L-1.Results from adsorption isotherms experiments indicated:(1) COD adsorption capacity on fly ash was far less than that on PDAC-fly ash, both the equilibrium adsorption capacity increased as a function of COD initial concentration, then trended to saturation gradually. (2) The adsorption process of COD on PDAC-fly ash would belong to one kind of exothermic reactions, a larger adsorption capacity at low temperature was conducive to adsorption reaction. (3) Both Langmuir and Freundlich models were well describ the adsorption isotherms of COD on PDAC-fly ash, and indicated that the adsorption was a physisorption-based, which also covers the chemical adsorption, belonging to multi-layer adsorption; The fitting correlation coefficient of Freundlich model was better than that of Langmuir model, and more suit to describe the adsorption process.PDAC-fly ash combined the flocculation and adsorption advantages of PDAC and fly ash, had a good pretreatment effect in printing and dyeing wastewater. Research results put forward a new direction for the reuse of coal fly ash, and showed the method of waste control by waste,that achieved the dual benefits of environmental and economical.