Synergistic Degradation Of Nitrite By CdS/Bi₂S₃/Bi₂MoO₆ Photocatalytic Membrane Coupled Bacillus

With the modernization of industry,agriculture and animal husbandry in our country,nitrite has become a kind of widely existing nitrogen-containing pollutant in wastewater.Therefore,the efficient treatment of nitrite in wastewater has become an urgent problem.In recent years,photocatalytic technology has attracted much attention because of its ability to utilize sunlight.Microorganisms have the ability to degrade pollutants continuously and cheaply.Hence,a novel wastewater treatment technology combining the advantages of microorganism and photocatalysis is proposed,namely photocatalysis-biological system.Due to the potential application prospect of photocatalysis and biological system in wastewater advanced denitrification treatment,the photocatalysis-biological coupling membrane system was proposed in this paper,and nitrite was taken as the main target pollutant for exploration.The main research contents are as follows:The Aurivillius semiconductor Bi₂MoO₆ was used as the photocatalyst.Then,in order to solve the problems of high recombination rate of photogenerated electrons and holes and weak absorption ability of visible light in a single photocatalyst,Bi₂MoO₆ with flower-like microsphere structure was prepared,and Bi₂S₃ and Cd S were deposited on the surface of microspheres by in-situ deposition method to form a photocatalyst Cd S/Bi₂S₃/Bi₂MoO₆.The mechanism of“conductive ladder”formed by composite photocatalysts can enhance the mobility of photogenerated carriers and inhibit the recombination of photogenerated electron-hole pairs.In addition,the introduction of photocatalyst Cd S,which is responsive to visible light,can broaden the absorption range of photocatalytic materials to visible light,increase the specific surface area of photocatalyst and enhance the effective active electron density on the surface of semiconductor materials,and finally improve the photocatalytic performance of composite semiconductors.The experimental results showed that the synthesized ternary photocatalytic material Cd S/Bi₂S₃/Bi₂MoO₆ has good photocatalytic performance,and the degradation efficiency of nitrite can reach100%under visible light irradiation for 180 min.In order to solve the shortcomings of the photocatalyst being powders,photocatalyst agglomeration and low recovery rate in the treatment of pollutants in water,based on the preparation of photocatalyst Cd S/Bi₂S₃/Bi₂MoO₆,the photocatalyst was successfully supported into the organic hybrid base membrane polyvinylidene fluoride(PVDF)through liquid-liquid conversion method.The PVDF/Cd S/Bi₂S₃/Bi₂MoO₆ composite material was obtained for the degradation of nitrite in water.A high-efficiency denitrifying strain was successfully isolated and purified from soil samples,which was identified as Bacillus cereus(BC16)by morphology observation and 16S r DNA gene sequence analysis.The upper layer of the coupling system was supported by PVDF/Cd S/Bi₂S₃/Bi₂MoO₆,and the lower layer was embedded with polyvinyl alcohol(PVA)to prepare the photocatalytic-biological coupling membrane.The results showed that,compared with the pure photocatalytic and biological degradation systems,the coupling membrane system showed better performance for the degradation of nitrite,and reached 100%within 1 h.The results of cyclic experiments showed that the removal performance of the photo-biological coupling system can remain relatively stable within a certain period.In addition,toxic by-products such as nitrate and ammonia nitrogen will hardly accumulate in the system after the end of the degradation experiment,which is environmentally friendly.Finally,the possible mechanism of photocatalysis and biological synergistic degradation of nitrite was proposed by studying the effects of pH value,electron and hole scavcleaners on the degradation performance of nitrite and measuring the product transformation in the process of nitrite degradation.The results of free radical trapping experiment showed that:·O₂^-and h⁺are the main active substances in the nitrite photocatalytic degradation system.As for the coupling membrane,photocatalyst can slightly up-regulate the functional genes involved in nitrite degradation and promote the absorption of nitrite by microorganisms.At the same time,the nitrate product of photocatalytic degradation was supplied to the strain as nutrients needed for growth,so as to completely degrade nitrite and improve the degradation efficiency of the system.Therefore,this study provides an efficient strategy for the sustainable restoration of nitrite contaminated water.