Influence Of Cellulase On The Release Of Heavy Metals From Rice Straw And Development Of Process For Ethanol Fermentation And Heavy Metal Recovery

With the rapid development of industry,nonrenewable energy has been consumed,environmental pollution is also increasing.Energy shortages and environmental pollution have become the two major problems in today's society.In environmental pollution,about 80% is heavy metal pollution.Heavy metals that are absorbed by crops get into environment and human and cause serious harm.Therefore,how to remediate contaminated soil and heavy metal-contaminated plant has important research value.At present,the remediation of heavy metal contaminated soil has achieved some results,but the heavy metal pollution plant repair and use of research is also relatively rare.The first part of this study explores the effect of cellulase on the release of heavy metals during saccharification for contaminated rice straw.The second part explores the effects of heavy metals on ethanol fermentation and the development of process for ethanol fermentation and heavy metal recovery.In this study,rice straw is from heavy metal pollution area in Hunan province.The contents of metal ions in rice straw and the enrichment of heavy metals in different components were investigated by inductively coupled plasma emission spectrometry(ICP).The results showed that the heavy metals of Cr,Cd,Mn,Cu in rice straw exceeded.Mn,Cu and Cr ions were mainly enriched in cellulose and hemicellulose,and Cd was mainly enriched in cellulose and lignin.The results provide a theoretical reference for the release of heavy metals during the saccharification.To explore the feasibility of the release of heavy metals during the saccharification process,we used the Acremonium cellulase,Trichoderma viride cellulase and Trichoderma reesei cellulase to hydrolyze rice straw.First,the release of heavy metals from cellulase was studied during saccharification.The results showed that the release rate of heavy metal Mn was up to 55%,the release rate of heavy metal Cd,Cu,Cr were 68%,38% and 29%,respectively.Taken into account the effect of sugar production,polyphenol and heavy metal release rate,Acremonium cellulase was the most suitable for saccharification and heavy metal release.Then we discussed the relationships between the hydrolysis of cellulose,hemicellulose,the release of polyphenols and the release of heavy metal ions.It was found that the release rate of heavy metals Mn and Cr was related to the yield of glucose and xylose,while polyphenol production was related to Cu and Cr,suggesting the feasibility of the release of heavy metals in the saccharification process.On the basis of the above study(the high cellulase activity and low xylanase activity of Acremonium cellulase,and the correlation between xylose and heavy metal release),we enhanced the release of heavy metals using mixed enzymes and weak acid pretreatment.It was found that the xylose production of the mixed enzyme was 1.7 times higher than that of the individual Acremonium cellulase.Saccharification plus weak acid pretreatment provided 1.3 times and 2.5 times higher glucose and xylose than that of Acremonium cellulase alone.The release rates of heavy metals Cr,Mn and Cu were increased by 1.9,1.6 and 1.8 times than the individual Acremonium cellulase,suggesting the feasibility of heavy metal release during saccharification once more.Finally,the effects of heavy metals on ethanol fermentation were studied.It was found that Cd inhibited the yield of ethanol,and the yield was only 19%.The process for ethanol fermentation and heavy metal recovery were developed by using the polymer effect and thermos-sensitive phase transition characteristics of thermos-sensitive polymer.In the fermentation broth,the temperature-sensitive polymer PG1-co-PHEDTA containing HEDTA repeating unit,HEDTA chelating heavy metal Cd,restricted the Cd went into the yeast cells,thus effectively alleviate the inhibition of Cd on ethanol fermentation.Ethanol yield of 53%,which was equivalent to the ethanol yield in the control fermentation.In the fermentation process,the recovery of heavy metals reached more than 90%.Finally,using the polymer phase change characteristic,the recovery of heavy metals and polymers recycling were achieved.