Study On Pollutants Degradation By Combined Processes Of Photocatalytic Oxidation Technique

Because of its notable advantages, photocatalytic oxidation is considered as one of the most potential water treatment techniques. At present, the bottlenecks which restrict the application of photocatalytic technique have not been solved. Therefore, it is practical to develop the combined process of photocatalysis and other technique according to the feature of target pollutant. In combined process, the advantages of both single processes could be utilized, and the more efficient or economical removal could be achieved. In this study, a combined independent photocatalytic and electrochemical process (CPE) was investigated for phenol degradation, a coupled electrochemical and photocatalytic process (CEP) for Acid Orange II (AOII) mineralization and a coupled biology slow filtration and photocatalytic process (CFP) for nitrate removal form solution. The main results were as follows:(1) The CPE process exploited both single processes to produce a synergistic enhancement effect, and this effect was enhanced by adding NaCl into solution. The higher productivity of oxidizing substances resulting from the interaction between photocatalysis and electrolysis is probably the main reason for this synergy. In CPE process, the required time for mineralization was shorter and the energy efficiency was higher than that in both single processes. In this process,100% of phenol and 75% of total organic carbon were removed within 6 hours in the presence of 0.3 g/L NaCl electrolyte at a current density of 30 mA/cm2 and initial pH 6.10;(2) During the degradation of AOII with the CEP process, the electrochemical pretreatment made the solution faded rapidly and the dye molecular decomposed. Thus, the removal rate of TOC with the posterior photocatalysis increased significantly. Moreover, the accumulation of intermediates which appeared during the anterior electrolysis was eliminated efficiently by the posterior photocatalysis. After one hour of electrolysis followed with six hours of photocatalysis,81% of TOC was removed from the solution. The time consumed for mineralization with CEP process was much shorter than that with photocatalysis. The power consumption for 50% of TOC removal by CEP process was just 71% of that for the same TOC removal by electrolysis;(3) In the CFP process, the nitrate in the polluted groundwater was removed efficiently by the anterior biological slow filtration, and the residual organics, ammonia and total ba(?)terial count was reduced partially in the subsequent photocatalytic treatment. Under the running conditions of influent NO3--N=27.8-43.7mg/L, dosage of glucose as C/N=2:1 and filtering velocity=0.35 m/h, the effluent NO3--N was always below normative limit of drinking water in china, and the CODMn and tatal bacterial count also met the drinking water requirement after photocatalytic treatment.