Recently, a paper company in Tianjin due to illegal discharge of industrial waste water, and cause serious pollution to the surrounding environment, was fined of 500,000 RMB. It is reported that this paper-making company is mainly engaged in papermaking from waste paper, and has been handled the environmental protection acceptance procedures; according to the requirements, its generated wastewater should be recycled after treated with the treatment facility, but can not efflux. However, the data on-site inspection showed that the total suspended solids discharge ports exceeded by 18 times, chemical oxygen demand COD exceeded by 24.5 times; the suspended solids of sewage pit outside the plant exceeded by 163 times, chemical oxygen demand exceeded by 123 times, now you can see how serious the pollution is.

 

Papermaking industry occupies an important position in the national economy, which produces a large number of waste water, which is difficult to deal with, and causing serious pollution. Currently, the methods to treat the black liquor at home and abroad are: alkali recovery, coagulation, acid precipitation, biochemical and liquid membrane separation method, and so on. One of the most successful is the alkali recovery method, but because of the large investment, high cost, low alkali recovery and other disadvantages, it is difficult to promote.

 

Tungsten trioxide (WO₃) having catalytic properties, not only can be used as the main catalyst to bring out effective utility; but also can be used as the additives to assist an catalyst for improving its activity. WO₃ as a semiconductor photocatalyst, with its band gap of 2.4eV ~ 2.8eV, it can response to visible light, when irradiated under the sufficient light energy, electrons will carry out a transition to form a redox system by producing photo-generated electrons and holes, thus to play catalytic oxidation. Studies have shown that composite WO₃/α-Fe₂O₃/W photocatalyst has good results in the depth treatment of papermaking wastewater. Under the optimum conditions, the COD and color removal rate of papermaking wastewater can even reach to 68.3% and 71.2%, respectively, the waste level of water handled deeply with WO₃photocatalyst reached the national emission standards. Although, currently the most widely used photocatalyst is based on titanium dioxide, however, with the depth researching of photocatalyst, tungsten trioxide because of its superior performance and non-toxicity, is expected to become the main force of the photocatalyst.