| Petrochemical wastewater has large production,wide pollution,complex composition and strong toxicity,and is difficult to treat.An environmentally friendly,convenient and economical treatment technology is urgently needed.Micro-nano bubbles have the characteristics of long residence time,high mass transfer efficiency and strong oxidizing ability,and have great potential in realizing advanced wastewater treatment.This paper takes micro-nano bubbles as the key technology,combined with flocculation flotation and advanced ozone oxidation,to deal with the typical petrochemical wastewater such as oil and phenol produced in the petrochemical industry.The main research work is as follows:Firstly,comprehensive characterization and related characteristic analysis of micro-nano bubbles were carried out.The micro-nano bubbles were generated by the gas-dissolving method,and it was found that with the increase of time,the number of micro-bubbles increased significantly,and the gas-liquid mixing effect became better.The particle size and distribution of micro-bubble and nano-bubble were measured by laser particle size analyzer,and it was found that the particle size of micro-bubble was mainly distributed around 25 μm,and the particle size of nano-bubble was mainly distributed around 1 μm.The suspension residence time of micro-nano bubbles in water was investigated,and the results showed that when prepared for 30 min,the micro-bubbles could be suspended for 64.7 s,while the nano-bubbles could exist stably for several days without interference.The redox potential test results show that the redox potential of the aqueous solution containing micro-nano bubbles is significantly increased,and the combination of micro-nano bubbles and ozone will increase the oxidative capacity of the solution again.Secondly,for the oily petrochemical wastewater,the main influencing factors(time,load gas,bubble size,temperature,pH and initial oil concentration)on the oil removal rate were explored.The simulated oily wastewater belongs to the emulsified oil that is difficult to remove.The optimal inorganic flocculant is PAC,the concentration of which is 80 mg/L,and the compound ratio of PAC and PAM is 15:1.The optimal treatment parameters under the experimental conditions in this paper are as follows:the total flotation time was 20 min,the flocculation flotation time was 1 min,the standing time was 10 min,the initial temperature was 25℃,and pH=7.After the initial flocculation and flotation,only the micro-nano bubble flotation was used for further advanced treatment,and the oil removal rate increased by 7.43 percentage points to 93.18%.Combined with the flocculants before and after treatment,infrared spectrum analysis was carried out,and the oily wastewater was subjected to oil droplet size measurement and microscope observation.The oil removal mechanism is that the flocculant destroys the stability of emulsified oil droplets through electrical neutralization,and then further bridges and traps to form flocs.The flocs provide entanglement sites for the micro-nano bubbles to form a firm floc-oil drop-microbubble aggregate,which eventually floats to the surface quickly under the action of buoyancy for the purpose of removal.Then,for the phenol-containing petrochemical wastewater,the main influencing factors(ozone concentration,initial phenol concentration,pH,temperature and bubble size)of the micro-nano bubble couped with ozone advanced oxidation on the degradation rate of phenol were explored,and kinetic calculations were carried out.The mechanism of phenol removal was also analyzed.The degradation rate of phenol increased with the increase of ozone concentration.Considering the economy,the ozone concentration of 40 mg/L was selected in this study,the treatment temperature was 35℃,and the alkaline environment was the most favorable for the removal of phenol.According to the above factors,the regression equations were calculated respectively,and the pseudo-first-order kinetic equation of micro-nano bubble synergistic ozone oxidation of phenol-containing wastewater was obtained,which was consistent with the actual results and could be used to predict the degradation process of phenol.By detecting the intermediate products of phenol degradation,deducing the degradation path,it is proposed that the mechanism of removing phenol is that a large amount of ·OH is generated when the micro-nano bubble promotes ozone and self-breakage,and OH and ozone are cooxidatively degraded to achieve deep purification of phenolic substances in water.Finally,the real petrochemical wastewater was treated with micro-nano bubble combined with flocculation flotation and ozone oxidation,and it was found that the effect of removing oil first and then removing phenol was better.The research results have guiding significance and reference value for the advanced treatment of oily and phenolic petrochemical wastewater. |
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