Study On The Treatment Of Papermill Effluent Using Nano-TiO₂ Photocatalysis In Combination With Irradiation Technique

Photocatalysis technique applied to environmental contaminants treatment has attracted wide attention for recent sereval decades. But main research work has been put on photocatalytic degradation of trace organics in water with TiO₂ catalyst and few of the investigation on industry wastewater.Papermill effluent has a character of large amount,high concentration,fuscous and little reusable as well as containing a lot of contaminants, so this wastewater treatment is difficult. The treatment of papermill effluent includes, physicochemical method,activated sludge method and so on. However, the final effluent COD concentration is mostly above 100mg/L, which cannot meet the national wastewater discharge standards.In this work, nano-TiO₂ loaded on mineral material is selected as a photocatalyst. Several preparation methods of photocatalyst and influencing conditions of photocatalysis have been reseached for better photocatalytic degradation of papermill effluent. The results and data obtained have an important value for engineering practice.Irradiation technique applied to environmental protection is a kind of advanced oxidation process which has developed for several decades and is listed as one of the 21st century atomic energy utilization methonds by the International Atomic Energy Agency. However, high dosage will be devoted by irradiation treatment for wastewater only, which is so expensive as to be applied hard to industrial wastewater. In this paper, by combining photocatalysis with irradiation, we found that the dosage needed was lower and COD removal was higher. And by combining conventional biological method with irradiation, we also found that the cost for papermill effluent treatment was much cheaper.Our work has indicated that:(1) The preparation conditions of TiO₂/limonite composite material were TiO₂/limonite ratio of 40 m mol/g at a reaction temperature of 60℃and calcined at 500℃for 2h. The order of importance of these influent factors was: calcine temperature＞ reaction temperature＞calcine time＞TiO₂/limonite ratio;(2) It was hard to treat wasterwater with high concentration and fuscous by nano-TiO₂ photocatalysis, but irradiation combined with pure oxygen aeration significantly enhanced the treatment efficiency of the paper-mill effluents, with COD removal of 68.85%, 50.0% and 42.86% for anaerobic influent, anaerobic effluent and aerobic effluent, respectively, at the dosage of 1 kGy absorbed energy and 1 g/L nano-TiO₂ (P25). This process could effectively reduce the biological toxicity of the paper-mill effluents.(3) This paper was based on the national natural science foundation of China (NSFC 50678089) of Institutes of Nuclear and New Energy Technology, Tsinghua University. By combining irradiation technique with conventional biological method, we found that the addition of coagulationt could be reduced because of irradiation, which would give an example for photocatalysis applied to treat industrial wastewater.