Preparation Of Bacterial Cellulose Nanocomposites And Its Application In The Efficient Treatment Of Food Industry Wastewater

Food industry is one of water-based industries.With the rapid development of food industry,water demand and waste water production increase.Food industry wastewater usually contains high concentrations of organic matter,heavy metals and a large number of suspended solids.Improper treatment of these wastewater will have a negative impact on the ecosystem.In membrane separation technology,nanofiltration and reverse osmosis can effectively remove heavy metal ions and organic pollutants from wastewater,but their operation process requires high pressure and relatively high energy consumption,while traditional ultrafiltration membranes are difficult to achieve the multi-component removal of macromolecules and small ionic pollutants in water.Therefore,developing multifunctional,efficient and sustainable wastewater treatment technology is of great significance.In this study,we propose a feasible method with bacterial cellulose（BC）bio-fabrication by Acetobacter xylinus as the substrate material and polydopamine（PDA）as the functional layer and molecular linker to immobilize carboxylated cellulose nanocrystals（C-CNCs）to prepare BC/PDA14h/CNCs membrane（BCM/PDA14h/CNCs）,and the structures and properties of the composites were characterized.At the same time,the static adsorption performance and dynamic filtration adsorption performance of BCM/PDA14h/CNCs on heavy metal ions and organic dyes were investigated,and the adsorption mechanism was analyzed.Its antifouling performance and purification effect on simulated juice processing wastewater were further tested.The main results and conclusions are as follows:（1）The BCM/PDA14h/CNCs composite nanofiber membrane was prepared by using the bioprepared BC hydrogel membrane as a matrix,and the high adhesion and good chemical reactivity of PDA material were loaded on the surface of BC nanofibers,and C-CNCs were fixed.The main conclusions were as follows:The pure water flux of BCM/PDA14h membrane reached the maximum,45.56 L m^-2 h^-1,when the polymerization time was 14 h in the dopamine solution with a concentration of 0.5 g L^-1.The initial thermal degradation temperature and tensile strength of BCM/PDA14h/CNCs are 317℃and 50.78 MPa,respectively,indicating that the membrane has good thermal stability and excellent mechanical properties.The static water contact angle of BCM/PDA14h/CNCs is 8.14°,indicating that the composite has excellent hydrophilicity.When transmembrane pressure（TMP）is 2 bar,the pure water flux and molecular weight of BCM/PDA14h/CNCs are about 41.35 L m^-2 h^-1 and 240 KDa,respectively.The above results prove that BCM/PDA14h/CNCs has potential application value in ultrafiltration separation technology.（2）BCM/PDA14h/CNCs were used to test the static adsorption performance,dynamic filtration removal performance,and regeneration performance of heavy metal ions and dyes.The results show that the optimum p H values of Pb²⁺and methylene blue（MB）adsorption by BCM/PDA14h/CNCs are 6.0 and 10.0,respectively.At optimal p H,the adsorption capacity of Pb²⁺and MB was 96.61 mg g^-1 and 75.12 mg g^-1,respectively.The adsorption data of Pb²⁺and MB by BCM/PDA14h/CNCs fit well with the Freundlich isotherm model and pseudo-second-order model,indicating that Pb²⁺and MB are adsorbed on the surface of BCM/PDA14h/CNCs in multimolecular layers,and the adsorption rate is determined by chemisorption.In the process of dynamic filtration,the removal rates of Pb²⁺and MB by BCM/PDA14h/CNCs remained above 90%within 1.5 h and 3 h,respectively.The removal rate of mixed heavy metal ions by BCM/PDA14h/CNCs is inversely proportional to the radius of hydration ions.The study on the selective separation of binary dye mixture shows that the separation efficiency of the membrane is mainly related to the electronegativity of the dye.BCM/PDA14h/CNCs show the preferential adsorption of cationic dye,and the separation efficiency can reach 98%.Finally,after 5 cycles,the Pb²⁺and MB removal rates of BCM/PDA14h/CNCs decreased by about 13%and 5%,respectively,and the flux stabilized at36 L m^-2 h^-1,which proved that the membrane showed good reusability in the filtration process and showed great potential in future long-term process applications.（3）The antifouling performance of BCM/PDA14h/CNCs and the purification effect of simulated juice processing wastewater were systematically evaluated.Compared with BCM and BCM/PDA14h,BCM/PDA14h/CNCs had a higher flux recovery rate（FRR）.After 5pollution cycles,the FRR of BCM/PDA14h/CNCs for bovine serum albumin（BSA）,humic acids（HA）,and sodium alginate（SA）were 88.9%,92.6%,and 75.7%,respectively.The removal rates of BSA,HA,and SA were 81.8%,86.2%,and 92.0%,respectively.The results show that the membrane has good antifouling performance and pollutant removal effect.Finally,the purification effect of BCM/PDA14h/CNCs on juice processing wastewater was studied.The removal rates of total organic carbon（TOC）,chemical oxygen demand（COD）,and suspended substance（SS）of simulated juice processing wastewater were maintained at53.85%～59.44%,63.72%～70.13%,and 94.36%～98.79%,respectively.The results showed that BCM/PDA14h/CNCs could effectively remove suspended matter and most organic matter such as carbohydrate in juice processing wastewater.In addition,BCM/PDA14h/CNCs can effectively remove Pb²⁺and chroma from juice processing wastewater.The results show that BCM/PDA14h/CNCs still has a good removal effect on pollutants in the complex wastewater environment,and has great application potential in actual wastewater treatment.In conclusion,the multifunctional characteristic,high removal efficiency,excellent reusability as well as natural degradability of the prepared BCM/PDA14h/CNCs membrane in the present study provide a sustainable approach for multi-function ultrafiltration membrane fabrication and promising application in industrial water purification.