Basic Research On Application Of Immobilized Microorganism Degradation Of Formaldehyde

Recently, the indoor formaldehyde pollution problems aroused people’s attention. Formaldehyde is a colorless irritating toxic gas, which may induce a variety of diseases and be seriously harm to human health. Therefore, there is essential for finding an economical, environmentally friendly, simple way to treat indoor formaldehyde pollution. Currently, some measures may be used to reduce indoor formaldehyde pollution, such as strengthening ventilation, physical adsorption, plant decomposition, chemical method and so on, which have their own advantages and limitations. Biological method is relatively convenient and environmentally friendly for removing formaldehyde, but this method is affected by microbial activity and the environment of microbial survival. Acclimating microorganism of efficiency degradation of formaldehyde and providing appropriate environment is the key of this method to apply to the degradation of indoor formaldehyde. The goal of this experiment is the degradation of indoor formaldehyde, on the basis of our previous research, by adding six kinds of sulfur-containing compounds this thesis choose the microorganisms of efficient formaldehyde-degradation(functional microbes) to immobilize with the sodium alginate embedding, and use immobilized microorganism as a biological packed tower packing to treat low concentration indoor formaldehyde(1~10 mg/m3). The following conclusions:(1) Studying the preparation of sodium alginate immobilized gel ball and considering the gel balls on mechanical strength and mass transfer performance shows the best immobilization conditions: sodium alginate concentration 3%, CaCl2 concentration 6%, crosslinking 24 hours, respectively. The concentration of sodium alginate is the main factor affecting the performance of gel balls. Sodium alginate gel balls based on orthogonal experiment results prepared uniform shape, the mechanical strength(49.667) and mass transfer performance(0.088) are better than the single factor experiments(mechanical strength: 47.333, mass transfer performance: 0.084) results. Gel ball surface and cross-section were observed by SEM, found that the surface and cross-section are irregular pore structure, adapted to be fixed microorganisms.(2) Addition of sulfur compounds in acclimated microorganism degradation of formaldehyde by experiment, after eight days of acclimation degradation cycle, a clear role in promoting growth by addition of Na2S2O8 in experiment; adding Na2SO3 solution has the best effect on microbial degradation of formaldehyde, the removal the highest rate of formaldehyde up to 100%; adding Na2SO3 and Na2S2O8(0.10 mol/L, volume ratio 1:1) mixture cannot promote microbial growth and improve the removal rate of formaldehyde at the same time; as can be seen from the SEM of the microorganism, Na2SO3 is the best sulfur compound additive. Na2SO3 in 0.05 mol/L, 0.10 mol/L, and 0.15 mol/L concentration range to promote the growth of microbes and formaldehyde removal effect had no obvious difference. Therefore, 0.05 mol/L Na2SO3 as the most suitable sulfur compound additive acclimated microorganism degradation of formaldehyde.(3) Immobilization and properties of the microorganisms of efficient formaldehyde-degradation(functional microbes) showed that when the amount of functional microbes increases, the immobilized microbial degradation of formaldehyde were also increased, however, the amount of functional microbes more than 80 g, immobilized gel balls microbial leakage phenomenon is obvious. Considering immobilized microorganisms’ formaldehyde degradation rate and the microbial leakage, the amount of immobilized functional microbes’ best value is 80 g. The immobilized functional microbes’ ability to remove formaldehyde, pH tolerance range and activity were higher than the free microorganism; adding activated carbon, silica gel, nano titanium dioxide to improve the immobilized functional microbes and finding formaldehyde removal: adding activated carbon group > adding silica gel group > adding nano titanium dioxide group, adding activated carbon can improve the degradation ability of immobilized functional microbes.(4) An experimental investigation on biological packed tower for degradation of indoor formaldehyde by immobilized microorganism for packing shows, reference index for formaldehyde removal, using single factor experiment respectively investigates the degradation ability for 1~10 mg/m3 of indoor formaldehyde by regulated the spray flow rate, gas flow rate and concentration of formaldehyde import in the biological packed tower of immobilized microorganism. The optimum reactive condition was determined by means of orthogonal experiment:for packing spray flow rate of 0.6 L/h, gas flow rate of 0.4 m3/h, gas phase concentration of formaldehyde import 9 mg/m3, under the condition of the biochemical removal rate can reach 8.243 m3/(L·h),and be higher than that of single factor test results 8.038 m3/(L·h).(5) Essential study on mechanism of degrading formaldehyde by the immobilized microorganism results suggest that the approach for microbial metabolism of formaldehyde was by the assimilation and dissimilation. When adding Na2SO3 in domestication system chemical reaction between the Na2SO3 and formaldehyde was occurred and got CH2(OH)SO3Na, CH2(OH)SO3Na can be used as carbon source and sulfur nutrient elements and promote the growth of microorganismsThe research conclusion of this paper will provide experimental basis and feasibility foundation for immobilized microbial degradation of indoor formaldehyde.