Isolation And Characterization Of Bleaching Wastewater-resistant Bacteria And Cheap Method For Preparation Of The Bioflocculant

Adsorbable organic halides(AOX) are generated in the pulp and paper industry during the bleaching process.These compounds are formed as a result of reaction between residual lignin from wood fibres and chlorine/chlorine compounds used for bleaching.Many of them are proven carcinogens and mutagens.National wastewater discharge standard has described BOD,,CODcr,SS and so on,but it hasn't mention AOX which is truly the main toxicities. Hence,it is necessary to remove or degrade these compounds from bleaching wastewater.Microbial flocculant(MBF) is safe,effective,biodegradable and without secondary pollution. Because of these concerns,the use of microbial flocculant is expected to increase in various fields.However,the expensive cost hinders the application of microbial flocculant.To find a low-cost medium and explore a cheap method for the preparation of microbial flocculant are essential.To remove toxicities in the bleaching wastewater is the main aim in this study.A bleaching wastewater-resistant and bioflocculant-producing bacterium was isolated from activated sludge, it was named BF-11 and was identified as Klebsiella sp.At the same time,we also had isolated three other bioflocculant-producing bacteria.BF-11 was not only able to produce highly effective bioflocculant,but also had its own special characteristics:growing fast,bleaching wastewater-resistant,most of the bioflocculant was closely bound to the cell wall and only the minority was secreted to the supernatant,the supernatant of the bioflocculant-producing fermentative liquid had already performed better than the other three strains,cell bioflocculant flocculated kaolin suspensions into bigger flocs than the others and the flocs settled faster.All these characteristics indicated that Klebsiella sp.BF-11 might have a very good prospect in removing toxicities in the bleaching wastewater.In order to further prove BF-11's resistance to bleaching wastewater,we compared the biomass,glucose consumption and the production of bioflocculant of BF-11 cultivated in glucose medium containing 50%bleaching wastewater and 100%deionized water.The experiment showed that BF-11 performed better in the glucose medium containing 50%bleaching wastewater,the strain is bleaching wastewater-resistant.We also compared the characteristics of BF-11 and another bleaching wastewater non-resistant strain:HW-7.It contains optimization of the flocculating system,physical and chemical properties of the two purified extracellular bioflocculant and flocculation mechanism. It showed that both BFF-11 and HWF-7 acted under basic conditions.The flocculation activity of them depended strongly on bivalent or tervalent cations and no flocculation occurred when the flocculants were present alone.The BFF-11 was comprised of extracellular bioflocculant and cell bioflocculant.The composition of BF-11 extracellular bioflocculant was mainly polysaccharides,of which galactose,glucose,rhamnose and glucuronic acid(33%) were the principal constituents.The BF-11 extracellular bioflocculant was thermo-stable.BF-11 cell bioflocculant was glucoprotein with 13.9%protein,when this glucoprotein bioflocculant was heated,its flocculating activity decreased a little,the flocs formed became smaller and smaller.It indicated that the protein component may play an important role in the process of forming big flocs.HWF-7 was comprised of mainly extracellular bioflocculant,it was a kind of glucoprotein consisting of protein 10.3%,glucuronic acid 14.6%,galactose and rhamnose.Therefore,when it was heated, flocculating activity was decreased at some degree.From what have been discussed above,we may draw a conclusion that both BFF-11 and HWF-7 may share similar flocculating mechanism—Ca²⁺ assistant bridging.Finally we tested the binding linkage of BF-11 cell bioflocculant,practical results showed they were electrovalent bond,and it further proved the Ca²⁺ assistant bridging mechanism.Finally,we explored a cheap method for the preparation of BFF-11.BF-11 cells were able to act as bioflocculant,we can create a condition to decrease the viscosity of the fermented liquid and even made cells produce autoflocculation to get cell bioflocculant.The experiments showed that in 20ml fermentative liquid,when pH adjusted to 9,15 mlCaCl₂ solution(0.2 M) was added, after centrifugation we can get a better compacted precipitation of the cell bioflocculant.The prepared cell bioflocculant was dried to powder,then dissolved this powder to solution and tested the flocculating activity,the dried powder kept a good function.