The Efficient Biomineralization And Adsorption Of Cadmium (Cd²⁺) Using Secretory Organo-biominerals(SOBs) Produced By Screened Alcaligenes Faecalis K2

Cadmium pollution as the most toxic and non-biodegradable has caused many public hazards.In this paper,a strain of Alcaligenes faecalis K2 was screened from the shallow sediments of ponds,using methods such as cell sub-hierarchical cadmium distribution analysis,microscopic morphology and structure characterization,proteomics,and biofilm reactors.The effect of K2 on the removal of Cd²⁺in the solution and the mechanism of cadmium removal were studied.The work completed and the results obtained in this paper are as follows:(1)Successfully screened and identified a strain of Alcaligenes faecalis K2.Under the stimulation of Cd²⁺,the body length of K2 becomes shorter,which is beneficial to increase the specific surface area and speed up the material exchange.K2 mineralizes and discharges intracellular cadmium by secreting a large amount of organic biominerals(SOBs),and SOBs can be used as a high-efficiency adsorbent for Cd²⁺after drying.(2)The maximum adaptable concentration of K2 to Cd²⁺is 125 mg/L.When the initial concentration of Cd²⁺was 75 mg/L,K2 showed the highest Cd²⁺removal rate of 85.5%,and50.6%of the Cd²⁺removed from the solution was fixed in SOBs.The blocking effect of K2cell wall on Cd²⁺is relatively weak,and the cadmium is mainly excreted in the form of SOBs to protect cell life activities.(3)The SOBs produced by K2 can be collected with a 400-mesh filter,the microscopic morphology of SOBs can be observed by SEM,and the structure and composition of SOBs can be analyzed by FITR,XPS and HRTEM.It is found that SOBs are mainly composed of organic particles wrapped with nano-cadmium salts and contain a large amount of nitrogen-containing compounds.The organic particles gradually fragmented with the increase of Cd²⁺concentration,and the cadmium salt components contained therein are relatively stable Cd S,Cd(OH)₂ and Cd CO₃.(4)The differentially expressed protein of K2 under Cd²⁺pressure was analyzed by label-free proteomics.After cadmium stress for 144 h,K2 up regulated the expression of proteins in the tricarboxylic acid cycle system to meet higher energy consumption.This energy is used to perform cell oxidation,detoxification and thermal repair;to meet the needs of a large number of SOBs exocytosis;and to enable K2 to perform more violent chemotaxis.Corresponding to these three,hydrogen peroxide reductase,cell wall constituent protein,and flagellin are also overexpressed.(5)After SOBs are dried at 60?as an adsorbent,the adsorption capacity of Cd in the solution reaches 77.1 mg/g.Load K2 in the MBBR reactor.In the 45-day two-stage experiment,the efficiency of biofilm removal of cadmium steadily increased,and the removal rate of 75 mg/L Cd²⁺reached 90%.In this paper,the cadmium removal effect of K2 is systematically studied to its mechanism.As a high-efficiency cadmium removal bacterium,K2 continuously removes Cd²⁺in the solution in a mineralized way,and produces SOBs that can be used as a Cd²⁺adsorbent material in the process.Compared with the traditional research of using only bacteria or bacterial secretions,this paper provides a more three-dimensional treatment method,which realizes the continuous work of microorganisms,reduces the production of sludge,and uses raw materials more efficiently to remove microorganisms.Cadmium expands new ideas and is a promising technology for microbial removal of cadmium.