Study On Biological Acidification Precipitation Treatment And Resource Utilization Of Black Liquor By Brown-rot Basidiomycete

Black liquor is a byproduct of the alkaline pulping process during the production ofpaper pulp.Pollution caused by black liquor is too serious to address because of its highalkaline,high COD loading and high lignin content.Traditional physical and chemicaltreatments of black liquor are gradually being replaced by biological treatment because ofits low-cost and environment-friendliness.Acidification precipitation of lignin from blackliquor can effectively address black liquor pollution by some microorganisms.However,treatment effects are limited,and mechanism of biological acidification precipitation is notclear.This article focused on the biological mechanism of black liquor treatment bybrown-rot fungi,wastewater treatment process and exploitation of lignin,which canprovide theoretical basis and technological support for biological treatment of black liquor.A comparative study about acidifying characteristics of black liquor by inorganic acidand organic acid was firstly investigated.The results showed that organic acid couldcompletely replace inorganic acid to acidify black liquor.When the pH of black liquor wasadjusted to 4.0 by oxalic acid,more than 75.0% lignin could be precipitated and separatedfrom the black liquor.In addition,the effluent COD and color might drop over 42.0% and92.0%,respectively.The key of acid precipitation of lignin,reduction of COD and colorwas lowering pH of black liquor.A strain IMER2 with an ability to adjust pH was identified as brown-rot basidiomyceteFomitopsis sp.IMER2 by morphological and molecular biology.The strain IMER2 couldexcrete and accumulate a large number of oxalic acid by qualitative and quantitative HPLCanalysis.In the process of straw biodegradation by the fungus,straw fiber was rigidlybroken,and some available carbon sources and hemicelluloses were rapidly consumed toproduce oxalic acid.So,the acid-producing brown rot fungus IMER2 could be used fortreatment of black liquor.After black liquor pH was 4.0 below,more than 93.0% lignincould be precipitated and separated,and COD and color reduction reached 82.7% and88.9%,respectively.Noticeably,biological treatment of black liquor by brown rot fungiwas better than conventional acidification treatment. Further analysis of biological treatment mechanism,the results indicated biologicaltreatment processes of black liquor was acidification precipitation of lignin as a main,biological adsorption and degradation of lignin as a supplement.Brown-rot fungi in blackliquor could produce a lot of oxalic acid to rapidly reduce black liquor pH,which resultedin lignin precipitation.Simultaneously,some lignins were adsorbed and degraded bybrown-rot fungi to form an amount of aromatic acids,which can assist in reducing blackliquor pH and enhance biological treatment of black liquor.In addition,the biodegradationof lignin was a primarily modified process with demethoxy,phenolic hydroxylation,dehydroxylation,side-chain oxidation.Some aromatic ring of lignin was retained,andactivities of function in lignin were improved by the fungus.According to previous studies,these lignins could be useful for a variety of industrial applications.To establish a practical treatment process of black liquor,influence of sodium salts andlignin on growth and acid-producing capacity of the fungus IMER2 were studied.Theresults suggested that metabolic products of the fungus such as C₂O₄^2- and precipitatedlignin could inhibit the fungal growth and acid-production.Therefore,a repeated batchtreatment of black liquor was suitably established.The optimal conditions for the repeatedbatch treatment of black liquor were initial black liquor pH 7.0,COD 42.0 g/L,inoculums24.0 g/L.Moreover,the repeated batch process was successfully carried out 12 times over36 days in an air bubble column bioreactor.The average reduction of COD and color wasapproximately 40% and 70%,respectively.At last,utilization of lignin precipitation by acidification was studied.The lignin canbe prepared a kind of high-performance activated carbon.Phosphoric acid concentration(65%),ration of activation reagent to material (4.84:1),activation temperature (400℃),activation time (124 min) were optimized using response surface method.The adsorption ofmethylene blue and the yield of activated carbon could reach 182±4.00 mg/g and 56.15±3.81%,respectively.The adsorption performance of methylene blue has achieved the firstdegree quality of wooden activated carbon for water purification in China.