Screening Of Polyacrylamide Degrading Fungi And Study On Their Degrading Properties

Polyacrylamide is an important water-soluble polymer,which has been widely used in industry,agriculture,medical treatment and daily life.Polyacrylamide will degrade physically,chemically,and biologically in nature to generate various low polymers and acrylamide monomers.Acrylamide has neurotoxicity,reproductive toxicity,genetic toxicity and carcinogenicity,and poses a serious threat to the environment,organisms and human body.Research on the degradation of polyacrylamide is imminent.The biodegradation of polyacrylamide has the advantages of low cost and green.The current research on the biodegradation of polyacrylamide is focused on bacteria,and there are few studies on degradation by fungi.Therefore,the purpose of this experiment is to screen out polyacrylamide-degrading fungi and explore its degradation performance.This dissertation focuses on the study of fungi,and the main work is as follows:Screen 3strains of polyacrylamide high-efficiency degrading fungi,and explore the growth characteristics of single bacteria and compound bacteria and their degradation characteristics of polyacrylamide.At the same time,the degradation mechanism of the degrading bacteria and the biochemical treatment effect of the compound bacteria on the produced water of an oil production plant in Yanchang Oilfield are preliminary explored.The main findings are as follows:In this experiment,the soil samples around the oil selection station of Yanchang Oilfield were selected for the experiment.With 10^-2as the soil dilution,the strains were screened and cultured by the plate stress enrichment culture method,and finally three strains with high-efficiency degradation effect on polyacrylamide were determined.Fungi,denoted as HPAMF1,HPAMF2,HPAMF9,respectively.Then the three strains were morphologically identified.It was found that HPAMF1 hyphae grew rapidly,and the surface of the colony gradually changed from white to yellow-green to dark green;the HPAMF2 colony was grapefruit red with abundant velvety aerial hyphae,and the hyphae were White;HPAMF9 colony is light yellow,and the surface is nearly smooth.And under the scanning electron microscope,the strain HPAMF1 is oblate with depressions;the strain HPAMF2 is rod-shaped;and the strain HPAMF9 is ellipsoidal with fine wrinkles on the surface.Finally,by rDNA-ITS determination,the analysis strain HPAMF1 is Trichoderma aspen,HPAMF2 is Fusarium,and HPAMF9 is Merimbla.The growth characteristics of polyacrylamide-degrading fungi were explored and the degradation conditions were optimized.HPAMF2 can only use polyacrylamide as the sole nitrogen source for growth;HPAMF1 and HPAMF9 can use polyacrylamide as the sole nitrogen source,sole carbon source,and sole carbon and nitrogen source for growth.And the degradation ability of the three strains reached the strongest when using polyacrylamide as the sole nitrogen source for growth,so follow-up experiments will use polyacrylamide as the sole nitrogen source to study the growth and degradation characteristics of HPAMF1,HPAMF2,HPAMF9.After the plate confrontation experiment,the three strains of composite strains HPAMF1&HPAMF2,HPAMF1&HPAMF9,HPAMF2&HPAMF9,HPAMF1&HPAMF2&HPAMF9 all have no inhibitory effect.And the growth curves of single bacteria and compound bacteria are all S-type,which conforms to the growth law of microorganisms.By comparison,the degradation rate of composite bacteria is higher than that of single bacteria,and the degradation rate of HPAMF1&HPAMF2&HPAMF9 is higher than other combinations,so the composite bacteria HPAMF1&HPAMF2&HPAMF9 are selected as the follow-up experimental research object.The degradation conditions of the composite bacteria were optimized,and it was found that the degradation of polyacrylamide did not change significantly after the addition of carbon sources.Inorganic nitrogen sources had a certain promotion effect on degradation,while organic nitrogen sources had obvious competition effects.When the initial concentration of polyacrylamide is greater than 500mg·L^-1,the growth of the bacteria and the degradation rate of polyacrylamide show a decreasing trend,so 500mg·L^-1is selected as the optimal initial concentration of polyacrylamide for the composite bacteria.The growth rate of the compound bacteria and the degradation rate of polyacrylamide increase in the range of p H 3?8,and reach the maximum when the p H is 8,the growth amount of the bacteria reaches 170mg·L^-1,polyacrylamide The degradation rate is 48.36%;when the p H is greater than 8,the growth rate and degradation rate both show a downward trend.The degradation rate of polyacrylamide by the composite bacteria increases with the increase of the inoculation amount within the range of 0.5%to 4%.When the inoculation amount is4%,the degradation rate reaches the maximum,which is 45.96%.The growth rate was 131.3mg·L^-1,so 4%was selected as the best inoculation amount.The culture conditions further optimized by Box-Behnken experimental design and response surface analysis were the initial concentration of 523.2 mg·L^-1,p H 7.8,and inoculation amount of 4.2%.Under these conditions,the maximum degradation rate was 54.66%.According to the optimized conditions,after repeated verification experiments,the degradation rate is 54.48%,which is close to the predicted value of the regression model.After measuring the molecular weight of polyacrylamide by viscosity method,it was found that the action of microorganisms caused the long chain of polyacrylamide to break.Before and after the degradation of the composite bacteria,its molecular weight dropped from 4.71×10⁸to 9.09×10⁷;scanning electron microscopy revealed the surface structure of polyacrylamide before degradation.It is dense and forms many cavities of different sizes after degradation,indicating that the activity of complex bacteria leads to the appearance of cavities.Compared with the infrared spectrum before degradation,the peaks caused by CN stretching vibration and NH bending vibration in the spectrum after degradation by the composite bacteria disappeared,and the peak at 3200?3500cm^-1widened,which indicates that the polyacrylamide The amide group has been degraded into a carboxyl group.Compared with the high-performance gas chromatogram before degradation,the sample solution after degradation has an acetic acid peak,which further proves that polyacrylamide is degraded to produce acetic acid.And there is no peak corresponding to acrylamide in the high performance liquid chromatography after biodegradation,indicating that no acrylamide monomer is formed in the degraded polyacrylamide sample.The composite bacteria were used for the treatment of produced water from an oil production plant in Yanchang Oilfield,and were cultured under optimized conditions in the laboratory,respectively at 0,2,5,10,15,20,25,30d sampling and determination,the result is that the degradation rate of polyacrylamide in the produced water is 28.7%;COD is reduced from 928.20mg·L^-1to 545.37mg·L^-1;total phosphorus Reduced from 2.5mg·L^-1to 1.21mg·L^-1;total nitrogen decreased from38.7mg·L^-1to 17.2mg·L^-1.