The Immobilization Of Flocculating Bacterium And Mixed Fermentation

Microbial flocculants are the product sresulted from the synthesis and secretion of extracellular biopolymeric flocculants(EBFs)by microorganisms. With the properties of high flocculating efficiency,without toxicity and second-pollution,self-degradability and high-produced rate,the research on development and application of bioflocculant has been a focus of the area of biological preparation in recent years.And moreover,the immobilization of microorganisms has been widely used in the applications as a new kind of technology in the wastewater treatment because of the characteristics of high removal efficiency,stability of operation,and less yield of sludge.In order to make microbial flocculants have more efficiency in practice,the immobilization of flocculating bacterium and the flocculant produced by effective microorganisms(EM)were discussed in the paper.First of all,three kinds of flocculating microbes with good flocculating ability,namely X-1,X-2 and X-3,were obtained by repetitious enrichment and reselection from three kinds of activated sludge.At the optimum flocculation condition(8.0 for initial pH,4ml/100ml for the dosage of CaCl₂, 5ml/100ml for the dosage of strain,15min for the sedimentation time),X-1 had the best flocculating ability,the efficiency of which could reach 83.45%.X-1 was separately imbedded in the imbedding beads including Sodium Alginate(SA),PVA and SA and polyacrylamide(PAM)composite gel to research the prime immobilizing conditions and the optimal flocculating conditions,using the free bacterium as comparison.Aiming to find out the optimal immobilization condition,L9(3⁴) orthogonal experiments were carried out for each imbedding material to research the influence of the concentration of imbedding material,the volume rate between microbe and imbedding material,the crossing time and the concentration of additives.To enhance the flocculating rate,free bacteria was absorbed by kieselgur or activated carbon before imbedded in the immobilized beads.Then the imbedded beads were treated by chemical method to improve their mechanical characteristics.For the purpose of obtaining the highest flocculating rate of immobilized bacteria,some experiments were carried out to find the optimal flocculating condition.Then,the structure of imbedding bead and distribution of immobilized microbial were observed and analyzed by electron microscope.The highest flocculation was obtained when X-1 was imbedded in SA and polyacrylamide(PAM)composite gel beads.An optimal immobilization condition was achieved when the imbedded beads were composed of 2%SA and 3%PAM,the strains and imbedded material mixed as the volume ratio of 1:1,4%CaCl₂ as additives,pH 6 of additives,the reaction time of 24h,25℃in the temperature of additives.And the highest of the flocculating rate was gotten when 10ml flocculating bacteria were absorbed by 0.4g activated carbon with the efficiency(up to 94.23%),which was enhanced 10.7%, 2.46%and 6.44%compared to free bacteria,immobilized bacteria in SA beads and PVA beads respectively.The optimum flocculation condition were 9.0 for initial pH,4ml/100ml for the dosage of CaCl₂,1ml/100ml for the dosage of strain,15min for the sedimentation time.The complex microbial flocculant was developed by inexpensive substrate through fermentation.When the flocculating efficiency was determined by mixed fermentation of the three chosen flocculating strains (X-1,X-2 and X-3)in different combinatorial ways,the best efficiency(up to 87.56%)was found out when X-1 and X-2 were combined.The mixed fermentation produce of X-1 and X-2 had more efficiency than the one of single strain.