| Since the promulgation of the "Ten Water Regulations",China has intensified its efforts in water environment management.Since 2018,Zhejiang Province governments has successively issued provincial-level mandatory standards.Among them,the improvement of the quality of industrial wastewater is an urgent goal,but great difficulties have been encountered in the process,which is manifested from class A to class Ⅳ surface water.Ozone is widely used in the treatment of industrial wastewater due to its highly reactive oxidation process.However,due to the low concentration of dissolved ozone,the treatment efficiency on wastewater is limited.As a means of mass transfer,fine bubbles greatly enhance the dissolution efficiency of ozone,but its influence mechanism on industrial wastewater treatment and suitable process conditions are still unclear.For the mass transfer process,the ozone liquid concentration of microbubbles under the same conditions is significantly higher than large bubble(12.69 mg/L and 5.02 mg/L at p H=7),and the volume mass transfer coefficient KLa of microbubbles is 1.47 times that of large bubbles.It indicating that microbubbles significantly enhance the mass transfer rate.Secondly,based on the chemical kinetics method and ·OH reaction rate,the ozone exposure value ∫[·OH]dt has a good linear relationship with the ORP value,so ORP is introduced in this paper instead of ∫[·OH]dt to evaluate the efficiency of ozone reaction in practical engineering applications,and this conclusion was verified in a laboratory scale experiment of dyeing wastewater.The results of the systematic process for three typical industrial wastewaters(electroplating,leather and dyeing wastewater)show that the optimal treatment process is the hydrogen peroxide catalyzed,direct ozonation and direct ozonation-catalyzed ozone microbubble process respectively.The results show that three waste waters can reach the target removal after specific ozone dosage.Among them,the COD of electroplating water effluent is basically stable at18.5～21.8 mg/L,the removal rate of COD is 54% ～ 58.3%,O/C is 1.38～1.62,and the average O/C ratio is 1.51.The water quality reaches the standard Ⅳ of surface water steadily,and the treatment cost is about 0.86 yuan/(t water).The COD of the leather wastewater effluent is 28.1～36.7mg/L,the water quality reaches the standard Ⅴ,the average O/C ratio is 2.86,the total removal rate is 18.5%～34.2%,and the treatment cost is about 0.42 yuan/(t water).Dyeing wastewater effluent is17.8～25mg/L,COD removal is 30.6～34.6mg/L,total removal rate is 56.9%～66%,average O/C ratio is 1.51,which reaches surface water quality of Class IV,and treatment cost is about 0.35 yuan/(t water).After the biological acute toxicity test on the tail water of leather water,it has been reduced from poisoning(IR=34%)to slightly toxic(IR=18%),indicating that ozone may modification of macromolecular pollutants to small molecules reduces toxicity.According to the wavelength and the molecular properties are divided into four fluorescent regions: protein,tryptophan,fulvic acid,and humic acid(B,T,A,C).Among the three waters,the C substance was the weakest,and the T substance was detected in large quantities in leather water and dyeing wastewater.It is worth noting that A substance in leather water is the strongest.Since fulvic acid organics contain a large amount of phenolic structure,they are powerful antioxidants.This may be due to the low ozonation efficiency of leather water.According to the analysis of the organic matter in the three water qualities by the ozonation process,it has a very significant effect.Among them,the direct ozonation-catalyzed ozone treatment has the best removal effect in dyeing water,and the removal rates of B,T,A,and C zones are 95.5%,99.6%,70.7%,and 86.2%,respectively.The results of gel chromatography showed that catalytic ozone mainly degraded electroplating high-molecular polymers with above 1200 Da,and the total TOC removal rate was 12.1%.Direct ozonation has a removal rate of81.6%,63.7%,88.1%,and 89.6% for the four zones of organic matter in leather wastewater,respectively.It has a significant removal effect on TOC below 5500 Da,and those in the range of 5500～8100Da is not obvious,and the total TOC removal rate is 21.9%.In the UV254 content change,organic matter with a molecular weight of less than 1900 Da in the effluent is completely removed.In summary,when microbubbles are used as a means of mass transfer,ozone microbubbles and its catalytic process have significant effects on three wastewater.·OH,ozone,and hydrogen peroxide oxidants cooperate with each other.Under this complex system,use of ORP value for real-time monitoring can ensure the good economy and the high efficiency of the treatment results.The type of organic matter,concentration change,and degree of easy oxidation are closely related to water quality characteristics and industrial types.When there is a large amount of fulvic acid organics in the solution,it may have an impact on the efficiency of ozone oxidation.Overall,the application and popularization of this technology is of great significance to the development of water purification technology in China. |
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