Influence Of Environmental Factors And Mechanism Research On PVA Degradation By The Mixed Strains

Polyvinyl alcohol （PVA） is widely used in textile, paper industry, chemicalindustry, and other fields because of its good film strength, adhesion, wear resistance,chemical stability, and many other advantages. There are a large number of PVAwastewater generated every year. Due to the bad biochemical property and longbiodegradable cycle, PVA has caused serious environment pollution. In China, Morethan30000tons PVA are used in printing and dyeing process of the textile industryevery year. It is a great damage to our environment. And during the methods of PVAwastewater treatment, biological method gets the widespread concern of us for itseffective treatment, free of secondary pollution and many other advantages. Therefore,the study of PVA biodegradable is very important for reducing the environmentpollution and improving the ecological environment.In this subject, we used a kind of mixed strains which could completelydegradate PVA and the7kinds of single bacterium which were separated from themixed strains. All of the strains were screened from the sample （black massive, the“black”） which was carried from the bottom of the thick liquid yarn machine sink inXi’an No.3Cotton Textile Factory. The influence of some environmental factors forcell growth and PVA degradable efficiency was studied in the flask culture. Theresults showed that the growth of the mixed strains was better and the PVAdegradation rate was higher when24⁴8h inoculum age, or4%⁶%mixed bacteriainoculation, or100mL liquid volume. The optimum condition for PVA degradatationby the mixed strains was T=25℃³0℃, pH=7.0. The degradation ability could notbe influenced by osmolality when NaCl concentration was1g/L or less. And the lighthad no influence on the PVA degradation rate basically.The enzymatic properties and enzymatic reaction dynamics of thePVA-degrading enzyme were studied. The results showed that the PVA-degradingenzyme that produced by the mixed strains mainly was exocellular enzymes. During the unfinished degradation, the enzymatic activity would get lower when the PVAdegradation efficiency was enhancing. After the degradation was completely finished,the enzymatic activity would not change. Along with the increase of the PVAconcentration, the enzymatic activity increased gradually. The Michaelis constant ofthe PVA-degrading enzyme was Km=2.06×10^-3mol/L, the biggest reaction rate wasvmax=19.5unit/min.The mechanism of PVA degradation by the mixed strains was studied. Theresults showed that PVA with the initial average molecular weight of51260Da couldbe degraded thoroughly by the mixed strains. And some carboxylic acid and methylketone substance could be produced in the PVA degradation process. PVA could notbe thoroughly degraded by the7kinds of single bacterium which were separated fromthe mixed strains. The degradation of PVA by the mixed strains was a mutualcoordination process. At first, some bacterias which could use the highpolymerization degree of PVA to grow dominantly, and the macromolecules PVAwould be degraded into the smaller molecular polymer by these strains. Along withthe declining of PVA average degree of polymerization, the smaller molecularpolymer would be further degraded by the other bacterias in the mixed strains.To investigate the treating effect, the mixed strains was used to treat the simulatewastewater. The results showed that there is no influence for the degradation of PVAby the mixed strains after adding dyes into the fermentation. The degradationefficiency was about99%, and COD removal rate was about90%. But the dyesremoval rate was very low and less than20%. After adding starch into thefermentation, the PVA degradation efficiency dropped to92.83%and the CODremoval rate was less than80%.The cotton fabric desizing experiment results showed that the hot alkali desizingwas better than the hot water desizing, and the enzyme desizing was the best. Thedesizing rate was95.08%. Enzyme desizing could degrade PVA on the cotton fabricsbasically COD of the desized wastewater could be reduce and biodegradable propertycould be increased. Enzyme desizing could even reduce the heat consumption, waterconsumption and the cotton fabric damage.