Adsorption And Removal Of Dyes And Nitrites From Wastewater By Bacillus Amyloliquefaciens Biofilm

With the development of industry and agriculture,the discharge of wastewater has increased sharply.Dyes and nitrite are the most important pollutants of wastewater,and they will produce toxic and carcinogenic by-products when they enter the human body.Therfore,it’s important to develop efficient and simple treatment technologies of wastewater.Adsorption has become the focus of research in the environmental field due to its strengths of flexible application,low cost,simple design,easy operation and no harmful substances.Studies have found that biofilm has the ability to adsorb metals and organics,and our subject team found that the biofilm produced by B.amyloliquefaciens can effectively adsorb crystal violet.Therefore,this study aims to investigate the feasibility of biofilm as a bacterial adsorbent,and explore its optimal conditions for the adsorption of dyes and nitrites.The biofilm before and after adsorption are characterized by SEM,FTIR,XPS and zeta potential to analyze the groups that play a major role in adsorption for different contaminants.Finally,the adsorption mechanism was evaluated by kinetics,isotherms and thermodynamics,thereby providing a theoretical basis for the development of biofilms as a novel adsorbent.The main results of this paper are as follows:（1）Establishment of efficient film-producing conditions for Bacillus amyloliquefaciens DT bacteriaIn this study,the film-producing conditions of B.amyloliquefaciens DT were optimized,and the optimal conditions were determined to be pH 7.0,incubation temperature and resting temperature of 25℃,and 30 h incubation time.Under these conditions,200 mL of culture medium could produce up to 0.737 g biofilm.By chemical methods,SEM,TEM,and FTIR,it is known that biofilm is a fold substance containing bacteria,proteins,humic acids,polysaccharides and DNA,and the surface contains abundant groups such as-OH,C-H,C-C,C=C,C=O,C-O-C,C-N,etc.,which provide rich active sites for adsorption of pollutant molecules.（2）Differences between biofilm treatment of anionic and cationic dyesFor the two representative dyes with different charge properties（MG and MB）selected in this paper,the biofilm had good adsorption performance for them,and the processes were mainly physical adsorption and chemisorption,respectively.The adsorption processes were both spontaneous and endothermic.The maximum adsorption contents could reach 161.3188 mg/g（dosage:5 g/L;pH:4.0;temperature:40℃）and 183.44 mg/g（dosage:5 g/L;pH:5.0;temperature:40℃）,respectively.The main adsorption groups were protonated amine group（MG）and O=P-O-in phosphate ester or O=C-O-group in carboxylic acid ester（MB）.The differences in the adsorption mechanisms were mainly in kinetic and isotherm models.The fitting results of the Weber-Morris model demonstrated that intraparticle diffusion was the key rate-limiting step for MB adsorption,but did not limit the adsorption process of MG.The fitting results of the isotherm model showed that the adsorption capacities of biofilm for MG was proportional to the initial concentration,while the adsorption capacity for MB was proportional to the initial concentration at low concentrations but tended to saturate at high concentrations,indicating that chemisorption limits the rate of MB adsorption by biofilm.（3）Biofilm adsorption to remove nitrite from water bodiesThe adsorption of nitrite by biofilm was also a spontaneous and endothermic reaction,and the maximum adsorption content of 116.84 mg/g could be achieved at C₀=2000 mg/L,40℃ and pH 3.0.By FTIR,XPS,zeta potential and other techniques,combined with kinetic and isotherm analysis,it could be seen that the main forces for adsorption are intraparticle diffusion and electrostatic.The main adsorption group was the protonated amine group.