| Textile printing and dyeing industry is one of the pillar industries of China’s national economy,which develops rapidly in Jiangsu and Zhejiang provinces.Textile printing and dyeing wastewater is of great quantity,high chrominance,complex components and difficult degradation.Most sewage treatment plants adopt the combination process of physicochemical and biochemical treatment.Whereas,the biochemical effluent is hardly to meet the strict discharge standard.Thus,it is urgent to add advanced treatment process.In this study,hydrodynamic cavitation combined with ozone(HC/O3)process was used to treat biochemical effluent of textile printing and dyeing wastewater.The effluent quality of continuous HC/O3 process reached the standard stably.Through the degradation of azo dye,the action mechanism of HC/O3 process was defined.The HC/O3 process was further comprehensively evaluated from the treatment effect,effluent safety and process operation cost.The removal of acid red 73(AR73)azo dye by HC/O3 process was efficient.The decolorization rate of AR73 is 100%,and the removal rates of NH3-N and UV254 are all over 70%,in 30 min.The optimum conditions for AR73 degradation by HC/O3 process are as follows:inlet pressure of 0.15 MPa(cavitation number<0.5,cavitation phenomenon occurs remarkably),O3 dosage of 45 mg/min,initial dye concentration of 10 mg/L,initial pH value of 7.5±0.3.The degradation of hydrophilic azo dyes by HC/O3 process was more efficient than hydrophobic azo dyes,the decolorization rate was 0.99 min-1,which is twice as high as that of single O3 process.In addition,nitrite significantly inhibited the effect of HC/O3 process.The mechanism of HC/O3 process includes hydrodynamic cavitaion,ozone oxidation,and reactive species oxidation.There are three reactive species:1O2,·OH and ·O2-in the HC/O3 process system,among which 1O2 plays a crucial role in the degradation of azo dyes.In the process of dye degradation,azo bond and sulfurcarbon bond are broken,sulfonic acid group falls off,and intermediate products such as aniline,p-phenylenediamine and 1-amino-2-naphthol are produced.Finally,with the oxidation of reactive species,benzene ring and naphthalene ring are further substituted and ring-opened,small molecular substances are generated,and pollutants are completely degraded.The CODcr and chrominance of textile printing and dyeing wastewater biochemical effluent can be effectively removed by HC/O3 process.The effluent quality of HC/O3 process meets the standard of "Special Discharge Limit of Water Pollution" of "Discharge Standards of Water Pollutants for Dyeing and Finishing of Textile Industry"(GB 4287-2012).The optimal operation conditions for the treatment of biochemical effluent from textile printing and dyeing wastewater by HC/O3 process were:hydrodynamic retention time of 120 s,reflux ratio of 75%,O3 dosage of 50 mg/min,inlet pressure of 0.15 MPa.The value of CODcr reduced from 87±19 mg/L to 57±2 mg/L,the chrominance reduced from 70±3 times to 5±2 times.Aniline was not detected,the biological toxicity of effluent was reduced,the safety was improved,and the operation cost of HC/O3 process was 0.37 CNY/t.The analysis of dissolved organic matters(DOM)showed that the unsaturated bonds of organic pollutants in textile printing and dyeing wastewater were destroyed by reactive species,and the refractory aromatic protein and microbial metabolites were effectively removed.HC/O3 process can provide theoretical and technical support for the advanced treatment of textile printing and dyeing wastewater. |
