Study On The Efficiency And Mechanism Of Enhanced Coagulation/Ultrafiltration In The Treatment Of High-Concentration Cadmium Pollution Water

At present,heavy metal pollution in water occurs from time to time,and traditional drinking water treatment processes are faced with severe challenges and threats,especially cadmium pollution,which is mainly caused by Cd（Ⅱ）in water.Conventional water treatment processes have limited capacity to treat cadmium pollution.In recent years,people’s demand for water supply safety is constantly improving,and ultrafiltration technology has been widely used in the advanced treatment of drinking water.On the premise of ensuring safe water use,it is of great significance to treat cadmium-polluted raw water by the coupling of conventional coagulation process and ultrafiltration process.In this paper,the efficiency of removing Cd（Ⅱ）by conventional coagulation,ultrafiltration and Polymer enhanced ultrafiltration（PEUF）for treating cadmium-contaminated water has been studied.Based on the characteristics of humic acid（HA）removal by conventional coagulation process and the high efficiency of cadmium retention by PEUF process,the combined process of Powder activated carbon（PAC）enhanced coagulation and PEUF was constructed to treat simulated cadmium contaminated water.The effects of the combined process on the treatment of cadmium and the effluent qua lity were studied.The relationship between the morphological characteristics of the flocculant and the removal efficiency of cadmium and the mechanism of the combined process in the removal of cadmium were explored.The ultrafiltration membrane pollution and the control of membrane pollution were also studied.In this study,conventional coagulation process and ultrafiltration process were firstly used to treat cadmium-contaminated water,and the removal efficiency of the two processes on cadmium-contaminated water was investigated.Research showed that in conventional coagulation process with polyaluminium chloride（PACl）as the coagulant when the dosage of 20 mg/L materials such as cadmium and HA removal rate was highest,with the aid of the HA with Cd（Ⅱ）the complexation reaction of ultrafiltration technology on cadmium had better removal.But the two processes to exceed bid 100 times of cadmium pollution water removal effect is poorer,ultrafiltration process better treatment effect with regard to the s ame conditions.The mass balance distribution of cadmium in the ultrafiltration process was studied.It was found that the mass content of cadmium trapped by ultrafiltration membrane accounted for about 80%of the total cadmium,which provided a reference for strengthening ultrafiltration process to treat Cd（Ⅱ）polluted water.The removal efficiency of cadmium contaminated water by PEUF process was studied.Based on the removal rate of cadmium,Polyacrylate sodium（PAAS）was optimized as the enhanced ultrafiltration polymer,and the retention rate of Cd（Ⅱ）could reach 100%under P/M≥5 conditions.The effect of inlet water quality on the removal of Cd（Ⅱ）was investigated.The results showed that the influent p H and Ca²⁺were the main factors affecting the retention of Cd（Ⅱ）,and high p H,low Na⁺,low Ca²⁺and low HA were beneficial to the removal of Cd（Ⅱ）.The performance of regeneration and reuse of PAAS was investigated.The regeneration rate of PAAS reached 99.8%at p H2.5.Adding a certain proportion of unused PAAS could make the cadmium polluted water reach the standard which exceeded 100 times.At the same time,the ultrafiltration membrane pollution of PEUF process was studied.Combined with the TMP growth curve,and the SEM image of the polluted membrane section,it can be seen that PAAS mainly causes the reversible fouling,but the existence of HA can aggravate the irreversible fouling,so the pretreatment measures should be added.Based on the high efficiency retention of Cd（Ⅱ）by PEUF and the characteristics of HA removal by coagulation process,the combined process of PAC adsorption enhanced coagulation and PEUF treatment of cadmium pollution was constructed.The cadmium adsorption efficiency of PAC and its configuration with coagulation process were determined.The combined process can remove 100%of the cadmium polluted water which is 10 times above the standard,and can make the cadmium polluted water which is 200 times above the standard reach the drinking standard under certain conditions.The effect of influent water quality conditions on the removal of Cd（Ⅱ）was studied.It was shown that influent p H and Ca²⁺were the main factors affecting the removal of Cd（Ⅱ）.The reason lies in the competition mechanism of excessive H⁺,Ca²⁺and Cd（Ⅱ）,while the relatively low content of Cd（Ⅱ）made the competition inferior.Low Na⁺and HA can promote the removal of Cd（Ⅱ）by the combined process.Combined process effluent quality is good,the effluent UV₂₅₄,TOC and residual Al,Ca,Mg concentrations are at a low level.The mechanism of synergistic removal of cadmium by enhanced coagulation and PEUF was studied.The study shows that HA,kaolin particles,PAC and PACl hydrolysate in the coagulation process can adsorb Cd（Ⅱ）,PAC is the core of flocculation in the formation process of flocculation,and PAC can micro-regulate the morphological characteristics of flocculation,making the substances combined with cadmium condense rapidly to generate flocs with more branches and loose inside.The removal efficiency of pollutants is improved.The residual Cd in the coagulation effluent was intercepted by ultrafiltration membrane under the complexation of PAAS,and the synergistic effect of coagulation and PEUF was strengthened to achieve the efficient removal of cadmium.In addition,the mechanism and control of membrane fouling were studied.The Hermia model was used to fit the membrane fouling parameters.The results show t hat the membrane fouling mechanism of the combined process is a mixed fouling mechanism mainly composed of standard blocking,intermediate blocking and filter cake blocking,among which the filter cake blocking caused by PAAS is the dominant fouling mechanism.The relationship between the removal efficiency of pollutants and the control of membrane fouling was studied.In this paper,the combined process of PAC enhanced coagulation and PEUF was constructed to treat high concentration of cadmium pollution water,and the removal efficiency and mechanism of Cd（Ⅱ）were studied,which provided technical guidance for the treatment of high concentration of cadmium pollution in water.