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Conclusions and Recommendations 113 ___________________________________________________________________________ 6 CONCLUSIONS AND RECOMMENDATIONS The massive use of chloride salts (NaCl and CaCl ) for roadway deicing, 20’000 tonnes 2in Vaud canton in 1998, is the cause of serious corrosion and major environmental problems. Evidence of long-term negative impacts has been documented in the literature (Labadia and Battle, 1996). These problems include deterioration of concrete bridge decks through chloride ion corrosion of reinforcing steel, corrosion of underground electrical cables, corrosion of structural members in bridge structures and other highway appurtenances; corrosion of vehicle chassis, pollution of aquatic habitats and drinking water sources by sodium and chloride ions in runoff, and harm to roadside vegetation due to an increase of the salinity of receiving waters as the sodium dissolves and to an increase of the acidity of soil and water as the chloride accumulates (Granato et al., 1995). In addition to the accelerated corrosion of automobiles, damage to concrete and asphalt, ruining of bridges, the use of sodium chloride for deicing the roads has many other drawbacks, such as adverse effects on underground cables. There are also many subtle costs of deicing with corrosive salts, for example, gasoline wasted because of slow traffic during repairs to ...

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• Publié par: Mothug
• Nombre de lectures: 26
• Langue: English

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Conclusions and Recommendations 113 ___________________________________________________________________________

6 CONCLUSIONSAND RECOMMENDATIONS

The massive use of chloride salts (NaCl and CaCl 2 ) for roadway deicing, 20’000 tonnes in Vaud canton in 1998, is the cause of serious corrosion and major environmental problems. Evidence of longterm negative impacts has been documented in the literature (Labadia and Battle, 1996). These problems include deterioration of concrete bridge decks through chloride ion corrosion of reinforcing steel, corrosion of underground electrical cables, corrosion of structural members in bridge structures and other highway appurtenances; corrosion of vehicle chassis, pollution of aquatic habitats and drinking water sources by sodium and chloride ions in runoff, and harm to roadside vegetation due to an increase of the salinity of receiving waters as the sodium dissolves and to an increase of the acidity of soil and water as the chloride accumulates (Granato et al., 1995). In addition to the accelerated corrosion of automobiles, damage to concrete and asphalt, ruining of bridges, the use of sodium chloride for deicing the roads has many other drawbacks, such as adverse effects on underground cables. There are also many subtle costs of deicing with corrosive salts, for example, gasoline wasted because of slow traffic during repairs to bridges and roads, cost of transporting materials for repair, and labor and materials for replacement. For example, it is estimated that the damage done by salt is probably 1240 times the cost of salt (for salt at roughly $30 per ton) (McCrum, 1989). The lower estimate primarily considers the corrosion damage while the higher one also takes into consideration environmental effects. Consequently, reevaluation of the conventional deicing salt has driven many scientists to seek alternative deicers. To overcome the disadvantages associated with the damaging properties of conventional deicing salts, new types of deicers have been developed that are effective, environmentally acceptable, and economically feasible. For example, calcium magnesium acetate (CMA) was introduced and identified as an environmentally favorable alternative deicer, which may lack the disadvantages shown by the conventional inorganic deicers (Winters et al., 1984; Horner, 1988; Buteau et al., 1992). CMA, a mixture of calcium acetate and magnesium acetate, is used as an environmentally benign roadway deicer. However, the present commercial CMA deicer made from glacial acetic acid and dolimitic lime or limestone is expensive ($1100 per ton) compared with salt and other deicers. Also, a liquid acetate deicer, 50% potassium acetate (KA), is replacing glycols and urea in airport runway deicing. These acetate deicers can be made from cheap feedstocks, such as whey or milk permeates, more economically than the present commercial methods. Milk permeate is an important byproduct of the Swiss cheese industry, which generated

an annual production estimated at 150 millions kg in 1998. Ultrafiltration (UF) of milk is frequently used for concentrating milk in several cheese producing plants (e.g., feta cheese) as well as in manufacturing special milk products. This permeate is approximately composed of 94% water and 6% solids, the latter containing mainly lactose. The milk permeate is practically free of Ncompounds and thus unsuitable for animal feeding (Käppeli et al., 1981). Consequently, it is a subject of environmental concern due to its high biological oxygen demand (BOD) of approximately 50 g/L, 90 % attributed to lactose component (Kisaalita et al., 1989a). Thus, the question of milk permeate disposal/utilization is effectively a question of lactose disposal/utilization: utilizing lactose economically is crucial to the treatment of this

Conclusions and Recommendations 114 ___________________________________________________________________________

high BOD wastewater, especially for small factories at scattered locations (Yu and Pinder, 1993). Traditional methods of whey and permeates utilization include direct animal feeding by nearby farmers (Muller, 1979), direct soil application (Watson et al., 1977), and sewage disposal (Osborn, 1979). Today, because of growing concern about environmental pollution, sewage disposal is undesirable due to the high BOD. Most recent investigations have focused on conversion to forms that are suitable for human consumption (Zadow, 1983; Teixeira et al., 1984; Gekas and LopezLeira, 1985) or for industrial alcohol production (Everson, 1979; Jones et al., 1993) and methane fermentation (Boening and Larsen, 1982; DeHaast et al., 1985; Kisaalita et al., 1989b; Yang and Guo, 1991). However, the production of acetic acid from milk permeate can also represent an attractive method for conversion of community waste to a community resource, with the doubled benefit of reducing waste disposal problems and environmental pollution from salts. The goal of this project was to develop lowcost acetate deicers from cheap feestocks,

such as industrial wastes (milk permeate). The aim of this research was to investigate the feasibility of an anaerobic thermophilic fermentation process using milk permeate as feedstock for acetic acid production. Since this subject of acetic acid production from thermophilic fermentation has never been studied, no literature review was available. Therefore, the first aim was to screen many different anaerobic thermophilic strains to select the bestavailable species for acetic acid production from lactose in pure or mixed culture. It has been found that under uncontrolled pH, two strains,Moorella thermoautotrophica

DSM 7417 andMoorella thermoaceticaDSM 2955 were able to convert lactate to acetate at thermophilic temperatures with a yield of~0.93 g/g. Among the strains screened for their abilities to produce acetate and lactate from lactose,Clostridium thermolacticumDSM 2910 was found to produce large amounts of lactate and acetate. However, it also produced significant amounts of ethanol, CO 2  andH 2 . The lactate yield was affected by cell growth. During the exponential phase, acetate, ethanol, CO 2 H and 2  werethe main products of fermentation with an equimolar acetate/ethanol ratio, whereas during the stationary phase, only lactic acid was produced with a yield of 4 mol per mol lactose, thus reaching the maximal theoretical value. When this bacterium was cocultured withM. thermoautotrophica, lactose was first converted mainly to lactic acid, then to acetic acid, with a zero residual lactic acid concentration and an overall yield of acetate around 80%. Under such conditions, only 13% of the fermented lactose was converted to ethanol byC. thermolacticum. Under controlled pH, acetic acid was produced from milk permeate using the coculture

ofClostridium thermolacticum andMoorella thermoautotrophica whenprovided with appropriate levels of growth nutrients and an optimal pH of 6.40 at 58°C. Lactose was converted to mainly lactate and hydrogen, and then to acetic acid using this mixed culture fermentation. The overall acetic acid yield from lactose was about 68 %. In batch fermentation of milk permeate containing 18 g/L of lactose at pH 6.40, the acetic acid concentration reached 13 g/L with a productivity of 0.13 g/(L.h). In order to increase this acetate productivity and to maintain a limited cell growth required to avoid ethanol production, an immobilized cell fermentation was used. Then, milk permeate was used as feedstocks to produce acetate using the coculture

immobilized in a fibrousbed bioreactor with a minimal nutrient supplementation. About 0.96 g of acetic acid was produced from each gram of lactose consumed in the coculture fermentation. A final acetate concentration of 27 g/L was reached in fedbatch fermentation. This mode of operation adapted the culture to tolerate higher acetate concentration, induced

Conclusions and Recommendations 115 ___________________________________________________________________________

and enriched acetatetolerant strains in the bioreactor. The productivity was only about 0.18 g/(L.h) based on the fibrousbed bioreactor volume, with a cell density of 20 g/L. The maximum acetate concentration that the heterolactic bacterium,C. thermolacticum, could tolerate was 26 g/L (against 15 g/L for the original culture), whereas the acetic bacterium,M. thermoautotrophica, could tolerate higher acetate concentration (35 g/L) without any adaptation. However, the productivity and maximal acetate concentration can be improved by increasing the cell density with continuous repeats of fedbatches until complete colonization of the fibrous matrix and adaptation to higher acetate level. Morever, the lactic fermentation was inhibited before the acetic fermentation by the acetate concentration accumulated in the coculture medium, problem which can be overcome by using a continuous acetic acid extraction. The lactate formation and consumption was well balanced, since its residual concentration in the medium broth was close to zero. This is an advantage for using continuous acetate extraction to reduce product inhibition problems found in fermentation. A costeffective method to recover and separate acetic acid from the fermentation broth, required for economical production of acetate deicers, have been studied by Yang et al. (1999). It was concluded that acetic acid can be effectively extracted and separated from the medium broth using a low content of a secondary amine in a longchain alcohol. This extraction system also can be used in extractive fermentation to reduce product inhibition problem found in fermentations. In comparison with the mesophilic process at pH 7.60 with the coculture of Lactobacillus lactisandClostridium formicoaceticum, where an acetate yield from lactose of 90%, a final acetate concentration of 75 g/L, and a productivity of 1 to 2 g/(L×h) were obtained (depending on the acetate concentration and the nutrient supplementation) the thermophilic process found in this study has some advantages: 1)C. thermolacticum andM. thermoautotrophica aresporulating bacteria, allowing the fermentation to be easily stopped and restarted since the spores are preservable during several months and resistant to oxygen; 2) it is easier to maintain anaerobiosis in thermophilic conditions; 3) the optimal pH of fermentation is lower (6.40), allowing a better acetic acid extraction; 4) no lactic acid is present in the medium, thus there is no need to separate acetic acid from lactic acid during the extraction, and an inhibition by this compound is avoid for both species; 5) no nutrient supplementation is required; 6) contamination of CMA with spores from thermophiles would create a less potential problem for the environment because soil and sediments would barely reach a high temperature required for the germination and growth of thermophilic spores; 7) almost the total cell population was immobilized in the fibrous matrix, preventing the bioreactor and the allow fiber (extraction) from clogging, and allowing cells to be rapidly adapted to higher acetate tolerance. Also, the reactor was stable for longterm operation in fedbatch mode. These preliminary fermentation results indicate that commercial production of acetate from milk permeate should be feasible (since large amounts of milk permeate are available) if further experiments with this fibrousbed bioreactor are performed in order to increase the productivity to 1g/(L.h) by increasing the cell density and using a continuously acetic acid extractive fermentation to avoid an inhibition. It should be possible to obtain a cell density of 100 g/L without clogging the fibrousbed bioreactor, and a final acetate concentration of 40 g/L with a cell adaptation, values required for a commercial production of acetate.

Conclusions and Recommendations 116 ___________________________________________________________________________ 6.1 References

Boening PH and VI Larsen(1982) Anaerobic fluidized bed whey treatment.Biotechnol. Bioeng.24 : 25392556 Buteau GH, Cushman JR, Griffis LC, Rogers BC, Duke JT and PN Cooper(1992) The effects of exposure Chevron IceBGon deicer in laboratory animals and human volunteers.Resour. Conserv. Recycl.7 : 133138 DeHaast J, Britz TJ, Novello and EW Verwey(1985) Anaerobic digestion of deproteinated cheese whey.J. Dairy Res.52 : 457467 Everson TC(1979) Fifth proceedings of whey products conference.Agriculture Research Service, U.S. Department of Agriculture, p. 9 Gekas V and M LopezLeira(1985) Hydrolysis of lactose: a literature review.Proc. Biochem.20 : 212 Granato GE, Church PE and VJ Stone(1995) Mobilization of major and trace constituents of highway runoff in groundwater potentially caused by deicing chemical migration. Transportation Res. Record1483 : 92104 Horner RR (1988)Environmental monitoring and evaluation of calcium magnesium acetate (CMA). National Cooperative Highway Research Program Report 305, p. 160 Jones TD, Havard JM and AJ Daugulis(1993) Ethanol production from lactose by extractive fermentation.Biotechnol. Lett.15 (8) : 871876 Käppeli O, Halter N and Z Puhan(1981) Upgrading of milk ultrafiltration permeate by yeast fermentation. In : Advances in Biotechnology, vol 2, Fuels, chemicals, foods and waste treatment, MooYoung M (eds.), Pergamon Press, New York Kisaalita WS, Lo KV and KL Pinder(1989a) Kinetics of wheylactose acidogenesis. Biotechnol. Bioeng.33 : 623630 Kisaalita WS, Lo KV and KL Pinder(1989b) Influence of dilution rate on the acidogenic phase products distribution during twophase lactose anaerobiosis.Biotechnol. Bioeng. 34 : 12351250 Labadia CF and JM Battle(1996) Road salt accumulation in highway snow banks and transport through the unsaturated zone of the Oak Ridge Moraine, Southern Ontario. Hydrol. Proc.10 : 15751589 McCrum RL(1989) Calcium magnesium acetate and sodium chloride as highway deicing salts.Environment Treatment and Control,pp. 2428 Muller PG (1979)Economic evaluation of feeding whey to livestock,part 2, Agriculture Canada, Ottawa Osborn G(1979) Utilizing British Columbia whey as an animal feed. Fraser Valley Milk Producers Cooperative Association, Vancouver

Conclusions and Recommendations 117 ___________________________________________________________________________ Teixeira AA, Johnson DE and RR Zll(1984) Food Engineering, August 1984, p. 1 Watson SW, Peterson AE and RD Powel(1977) Benefits of spreading whey on agricultural land.Wat. Pollut. Contr. Fed.49 : 2434 Winters GR, Gidley J and H Hunt(1984) Environmental evaluation of calcium magnesium acetate (CMA). FHWA/CA/TL84/03, California Department of Transportation, CA Yang ST and M Guo(1991) A kinetic model for methanogenesis from whey permeate in a packed bed immobilized cell bioreactor.Biotechnol. Bioeng.37: 375382 Yang ST, Huang YL, Jin Z, Huang Y, Zhu H and W Qin(1999) Calcium magnesium Acetate at lowerproduction cost: production of CMA deicer from cheese whey, U.S Department of transportation, Federal Highway Administration. Report No FHWA RD98174 Yu J and KL Pinder(1993) Intrinsic fermentation kinetics of lactose in acidogenic biofilms. Biotechnol. Bioeng.41: 479488 Zadow JG(1983) Whey utilization.CSIROFood Res. Quart.43: 121