Study On The Application Of Activated Carbon To Accelerate The Anaerobic Degradation Of Dyes

Removal of dyes is a major concern when treating textile-processing wastewaterbecause of its biological refractory, high chromaticity and high toxicity; Azo dyesrepresent the largest class of dyes, and they generally resist biodegradation due totheir xenobiotic nature. One effective strategy for the biological treatment of azo dyesis the anaerobic/aerobic sequential treatment, and the anaerobic decolorization of azodyes is usually the rate-limiting step. Therefore, it is signicant to explore the study onaccelerating the transformation of reactive azo dyes. The existing studies suggest thatcarbon surface containing benzoquinonyl can accelerate the anaerobic degradation ofazo dyes, but its role in promoting far below the liquid Quinones. The paper is basedon the research on active carbon were selectively modified to increase the content ofactivated carbon surface so as to increase the promotion of quinone by physical andchemical methods, and mechanism of active carbon to accelerate anaerobicdegradation rate of azo dye.The surface chemistry of a commercial AC (AC0) was selectively modified,without changing significantly its textural properties, by chemical oxidation withHNO3(ACHNO3) and O2(ACO2), and thermal treatments under N2(ACN2) flow.Nomajor changes were observed in the textural properties of AC for the liquid phaseoxidations and thermal treatments, as expected. Thermal treatments at hightemperature produce materials with low amount of oxygen containing groups andhigh basicity. The oxidation treatment (ACO2and ACHNO3) were the most effective tointroduce phenols and carbonyl/quinone groups, being almost the double whencompared with the AC0. On the other hand, sample prepared by O2oxidation presentsan increase of the micropore volume and average micropore width. Activated carbon(AC) is well known for its adsorbent of pollutants, here we describe the role of AC asredox mediator in accelerating the reductive transformation of pollutants as well as aterminal electron acceptor in the biological oxidation of an organic substrate. Thebiological decolorization of azo dyes(AO7、MY10and DB71) were conducted in aseries of batch experiments, which under the optimum pH, temperature were7and30℃. This study explores the use of AC as an immobilized redox mediator, usingacetate as the electron donor. The application of AC0in bioreactors improve the decolorizaiton rate to10%~50%, and the application of ACN2in bioreactors canimprove the decolorizaiton rate to35%than AC0.On the other hand,the applicationof ACHNO3and ACO2in bioreactors can improve the decolorizaiton rate to15~20%than AC0. That means, also other mechanisms may influence catalytic decolourisation,particularly in the absence of significant densities of surface oxygen-containinggroups.The decolorizaiton rates of azo dyes do not great increased with increasing theamount od AC. As a result of the study on accelerating the transformation of reactiveazo dyes, we investigated the batch expemments with reaction of sulfide, azo dyereduction results from a combination of biotic and abiotic processes during theanaerobic treatment of dye. The reaction stoichiometry of direct chemicalazo dyereduction by sulfide was investigated.The stoichiometry of the reaction was2.14molof sulfide per mol of dye reduced.The effect of modified AC on anaerobic chemical dye reduction was assayedwith sulphide at different pH values. The results shows that catalytic effect ofactivated carbon has a great relationship with pHPZC. In general, rates increased withincreasing the pH of point zero charge (pHpzc); Batch experiments were conducted toindicate AC can act as the terminal electron acceptor for the biological oxidation ofacetate, The ability of transporting electrons of AC following the trendACN2>ACHNO3>ACO2>AC0. Considering all the activated carbon samples withdifferent surface chemistries, their performance in dye decolourisation is probablyrelated to two different reaction mechanisms occurring in the presence/absence ofsurface oxygen groups: one involves the delocalized π-electrons and the other thesurface quinonic functionalities.