Transformation Of Agricultural Wastes To Produce Bioflocculant And Its Application

The treatment of industrial wastewater and the harvest of microalgal biomassesare the hot topics nowadays.The traditional physical and chemical methods are not recognized by the people because of the application of traditional treatments was high equipment costs,energy-inefficient and would lead to secondary pollution.The bioflocculation technology for the treatment of industrial wastewater and harvest of microalgal biomasses has become an important research direction in the field of environmental protection industry.Bioflocculants are extracellular polymeric substances including polysaccharides,proteins and nucleic acids secreted by microorganisms.Bioflocculants are advantageous over inorganic flocculants and chemically synthetic flocculants in numerous applications including low-cost harvest of microalgae and wastewater treatment,due to their nontoxic,harmless,and biodegradable properties.However,a major bottleneck for commercial application of these bioflocculants is the high production costdue to the use of expensive substrates and low yield.Hence the seeking for low-cost substratesto effectively reduce the production cost of microbial flocculant is still needed.As an agricultural country,China produces a large numberof agricultural wastes per year,these agricultural wastes contain large amounts of cellulose and hemicellulose,whichcan be converted into sugars to produce other high value-added products.Microbial transformation of agricultural waste into bioflocculants not only can effectively solve the problem of the accumulation of agricultural waste and resource utilization,but also can reduce the cost of bioflocculant production.Based on this,the purpose of this study is to excavate high-efficiency strains that can produce bioflocculants withuse the agricultural wastes as cheaply substitute carbon sources,and promote the application of bioflocculants in microalgal harvest,ash-flushing wastewater and Mineral processing wastewater.The main findings were as follows:1.Bioflocculant produced by Pseudomonas veronii L918 can convert the hydrolyzate of agricultural waste as carbon source for fermentation to produce bioflocculantwas,which caneffectively reduce the production cost of bioflocculant.The fermentation conditions of strain BWL918 were as follows: 300 m L/L peanut hull hydrolyzate,Yeast extract 3 g/L,Mg SO4.7H2 O 0.1 g/L,K2HPO40.3 g/L,p H 7.0,temperature 28?.The highest flocculation activity was 91.93% and the yield was 3.39 g/L.The bioflocculant MBF-L918 contains 77.14% polysaccharides and 4.84% proteins,and the molecular weight(MW)of MBF-L918 is 24.77 k Da.Furthermore,MBF-L918 showed good flocculating efficiency of 92.51% to ashflushingwastewater when 2.83 mg/L MBF-L918 was added,and thus achieved the recycling of ashflushingwastewater.2.As studies have shown that toxic by-products,including furan derivatives,organicacids,phenolic compoundsaregenerated during the dilute-acid hydrolysis process.These toxins not only severely inhibit fermentationefficiency,but also influence the safety of the bioflocculantproducts.So in this study we found the alkaliphilic strain Bacillus agaradhaerens C9 can secrete 1.69 IU/m L of alkali-tolerant xylanase and 0.06 IU/m L of cellulase,indicating that this particular strain can efficiently convertuntreated rice bran into bioflocculant(RBBF-C9),thereby circumventing rice bran pretreatment for downstreamfermentation.The optimal fermentation conditions that result in the highest bioflocculant yield(12.94 g/L)were asfollows: 20 g/L of untreated rice bran,3 g/L of yeast extract,and 20 g/L of Na2CO3 at 37? for 24 h.RBBF-C9 contained74.12% polysaccharides and 4.51% proteins,and was estimated to be 137 k Da.Furthermore,the bioflocculant RBBFC9 exhibited good flocculating efficiency(91.05%)of oil alga Chlorella minutissima UTEX2341 when 60 mg/L of RBBFC9 was added into the algal culture broth.