| The pollution and shortage of water is a problem that is becoming more and more serious, and the recycling of municipal sewage for the city is especially important. Generally, the complex pollutant composition is still there in the municipal sewage after secondary biochemical treatment, so the further processing of wastewater is particularly necessary. The main composition in municipal secondary effluent is humic acid. In this paper, humic acid was used to simulate wastewater and nano-TiO2 as photocatalyst. The paper mainly explores the removal efficiency of the dissolved organic matter of wastewater and its influencing factors. By the comparison of water quality indices in the influent and effluent, including total organic carbon(TOC), ultraviolet absorbance(UV) and other indices. Membrane fouling in membrane filtration process were studied. The results are as follows:(1) The Static photocatalytic experiment results indicate that the dosage of nano-TiO2 affected the removal rate of dissolved organic matter. The dosage of nano-TiO2 was between 250 mg/L and 350 mg/L, and the removal efficiency of DOM increased with the addition of dosage. But the removal rate reduced when the dosage of photocatalyst increased to 400 mg/L. Aeration rate also affected the degradation rate of the photocatalytic reaction, aeration rate in the range of 0.5 L/min and 1.5 L/min, With the increasing of aeration rate in simulated wastewater, the removal efficiency increased firstly, and then decreased. The removal efficiency increased while the temperature of the photocatalytic reactor rose from 15℃ to 35℃. The rise of reaction temperature was beneficial to the adsorption of organics on the surface of photocatalyst, which can promote the degradation of organics.(2) The study on the treatment of simulation wastewater by photocatalytic-ultrafiltration combined process showed that the removal rate was related to the membrane flux and the reflux ratio. The membrane fouling would be controlled effectively when the membrane flux was 115 L/(m2·h) and the reflux ratio was 200%, and it was good for the stability and longevity of integrated process. Compared with 172 L/(m2·h), the residence time of wastewater in the photocatalytic reactor would be prolonged when the membrane water flux was 115 L/(m2·h), that is, the time of degradation increased and the degradation of organic would be more complete. The shearing force on membrane surface was greater when the reflux ratio was 200% comparing with 100%, in this condition the cake layer on membrane surface would maintain the appropriate thickness for a longer time, and the removal rate would increased.(3) The efficiency of catalytic gradually reduced in the reuse process, the removal of TOC from 66.7% to 44.6%, the removal of Color436 from 88.6% to 69.1%. When photocatalysts absorbed the intermediates produced during the process and its particles condensed, the surface area of photocatalysis shrank and the shrink was the main reason for the photocatalyst deactivation.Ultrasonic cleaning and UV irradiation are the two methods to regenerate photocatalyst.After ultrasonic cleaning regeneration and distilled water ultraviolet irradiation regeneration, the catalyzing efficiency of photocatalyst could be restored to 85.9% and 83.9% respectively, while after 30% H2O2 ultraviolet irradiation regeneration, the efficiency could reach 86.9%, the highest of the three.(4) The ultra membrane filtration shows that: photocatalyst had a little influence on the flux, however, membrane fouling caused by wastewater could not be ignored and the mixed system of photocatalyst and wastewater caused the flux to decline. After cleaning of membrane, the membrane specific flux is recovered to 98% of pure water specific flux. The cake layer would form on the surface of polluted membranes, and the roughness of polluted membrane surface was greater than that of new membrane.(5) The membrane fouling of combined process was studied, and the results showed that: the specific flux dropped as the dosage increased and membrane fouling would be more serious. The membrane fouling caused by mixed system would be mitigated after the photocatalytic degradation reaction. Compared with 120 min, the membrane fouling was relatively slight when the time of degradation reaction was 150 min. The membrane fouling could be controlled effectively when the reflux ratio was 200% and lower membrane water flux.(6) The results showed that the best treatment performance could be achieved when the dosage of nano-TiO2 was 250 mg/L, reaction time was 150 min, aeration rate was 1.0 L/min, the membrane water flux was 115 L/(m2·h) and the reflux ratio was 200%. Besides, the removal rates of UV254 and TOC in the final effluent were 96% and 84% respectively. |
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