Preparation,Characterization Of Lignin Nanoparticles And Its Application In Bacterial Flocculation

Water pollution is a serious problem in today’s society.Pathogens consisted in the wastewater,especially food processing wastewater,has become a threat to environmental protection and human safety.Flocculation is always considered to be a convenient method to aggregate,settle and finally remove bacteria.Flocculants mainly include inorganic coagulants,synthetic organic polymer flocculants and natural polymeric flocculants,among which natural organic flocculants have attracted extensive attention due to some merits,such as biodegradability and environmental friendliness.Agricultural wastes,for example,straw,contain about 25% of lignin.Lignin is a kind of macromolecule which composed of p-hydroxyphenyl(H),guaiacyl(G)and syringyl(S)phenylpropanoid units.Recently lignin have been used for some applications,such as rubber reinforcing agents,building materials and surfactants.However,there was no report on the studies of lignin as microbes flocculants so far.In this study,three kinds of lignin were extracted from wheat straw,corn stover and switchgrass.They were fabricated into nanoparticles which were named WS L-NPs,CS L-NPs and SG L-NPs.Physiochemical properties and flocculation capacity were evaluated.SG L-NPs whose yield were highest were assembled with gelatin to constitute complex.Physiochemical properties and flocculation capacity of the complex were also determined.The results are following:1.Characterization of L-NPs: The mean particles sizes of three kinds of L-NPs were similar(WS L-NPs:255.0 nm;CS L-NPs:220.2 nm;SG L-NPs:220.2 nm)which was in accordance with the results observed from SEM.Zeta potentials of three kinds of L-NPs were all negative with absolute value exceeding 30 mV.Furthermore,the UV-vis spectra have no significant changes in 15 days which proved the L-NPs have good stability.From spectra of UV-vis and FTIR,the structures of three kinds of L-NPs were found no significant differences exist.FTIR spectra indicated that the C-O linkage may be cleaved to some extent in ultrasonic-assisted process.2.S.aureus and E.coli suspensions were used as flocculation objects in this study.Flocculation capacity of three kinds of L-NPs was evaluated and the results showed flocculation was affected by pH obviously.The pH range was 2～3 which was too low to be applied.3.It was found that L-NPs-gelatin complex exhibited relatively better flocculation capacity than L-NPs.The study found that:(1)Flocculation efficiency was greatly affected by pH and dosage.When L-NPs was assembled with gelatin,the range of flocculation pH was broadened to 5.0.(2)At pH4.5,the effect of initial bacteria concentration was not obvious.However,the higher bacteria concentration affected the flocculation efficiency at pH5.0.(3)For both indicator strains,flocculation efficiency(> 95%)was achieved within 30 min at pH4.5,while the flocculation efficiency of 90% costed 60 min at pH 5.(4)Flocculation mechanisms at various pH were different.When the pH value was 4.5,multiple mechanisms dominated in flocculation.When the pH value was 5.0,the mechanism was considered to simple charge neutralization.The L-NPs-gelatin complex was promising to be applied for flocculating bacteria in wastewater treatment,enrichment and detection of microorganism,etc.