Pramod K. Bajpai

High ethanol productivities using small Ca-alginate beads of immobilized cells of Zymomonas mobilis

SummaryZymomonas mobilis cells were immobilized into small 1 mm diameter beads of Ca-alginate in order to minimize mass transfer limitations and maximize immobilized cell activity. A combination of small bead size with a high cell concentration of 58 g dry wt. cell per lit. bead volume resulted in high ethanol productivities using a newly designed packed bed bioreactor system. Steady-state dilution rates ranging from 0.4 h-1 to 3.9 h-1 were run resulting in a maximum productivity of 102 g ethanol/l/h for an inlet substrate concentration of 100 g glu/l and 87% conversion. The bioreactor was run continuously at a fixed dilution rate for 384 h and short intermittent treatment of the beads with CaCl2 temporarily increased ethanol productivity to a maximum of 116 g ethanol/l/h.

Biotechnology for environmental protection in the pulp and paper industry

Wood Pretreatment to Remove Toxic Extractives.- Biopulping: a Less Polluting Alternative to CTMP.- Pulp Bleaching with Xylanases.- Pulp Bleaching with White Rot Fungi and Their Enzymes.- Enzymatic Deinking.- Treatment of Wastewaters with Anaerobic Technology.- Decolorization and Detoxification of Bleached Kraft Effluents.- Purification of Process Water In Closed-Cycle Mills.- Management of Wastewater Treatment Sludges.- Biofiltration of Exhaust Gases.

Rapid production of ethanol in high concentration by immobilized cells of Saccharomyces cerevisiae through soya flour supplementation

SummaryEthanol concentration and fermentation productivities were substantially increased when soya extract was added to the fermentation medium using immobilized cells of a locally isolated strain of S. cerevisiae. Very high concentrations, 152 and 162 g/l of ethanol, were obtained from a medium containing 300 and 350 g/l sugars respectively by supplementing the medium with soya extract. The fermentation time was also reduced by more than 50%.

Kinetics of ethanol production by immobilized cells of Zymomonas mobilis at varying d-glucose concentrations

Abstract Ethanol fermentation by cells of Zymomonas mobilis immobilized in calcium alginate gel has been studied using 5 to 30 wt% initial d -glucose in the medium. Up to 27% d -glucose was completely fermented and the maximum ethanol concentration of 12.6% (w/v) was obtained using an immobilized cell concentration of 58 g dry wt l−1 of bead volume. The ethanol yield coefficient was almost unaffected by initial d -glucose concentration and its value was >95% of theoretical. The rates of ethanol production and d -glucose utilization first increased, with an increase in initial d -glucose concentration up to 13.6%, and then started to decrease upon a further increase in initial d -glucose concentration. Cell leakage from the calcium alginate beads was very low.

Effect of calcium chloride on the growth and ethanol production by free cells of Zymomonas mobilis

SummaryThe effect of calcium chloride concentration on the growth rate and ethanol production using free cells of Zymomonas mobilis was studied. There was no appreciable change in rates of cell mass production and ethanol formation in the medium containing upto 2g/L CaCl2. On further increase in CaCl2 concentration, the rates started decreasing. However, the ethanol yield decreased and biomass yield increased with increase in CaCl2 concentration.

Effects of ethanol concentration on immobilized Zymomonas mobilis for continuous production of ethanol

Abstract The effects of ethanol concentration on the ethanol productivity and activity of immobilized Zymomonas mobilis cells during continuous fermentation of glucose has been studied at various ethanol concentrations. On changing the inlet ethanol concentration, Po, from 0.0 kg/m3 to any other level, 8 h were required to fully experience the effects of a change in Po, whereas 8 h to 2 days, depending on Po, were required to reach the steady state on switching back to the ethanol free medium. The volumetric ethanol productivity decreased from 92.5 to 0.0 kg/m3·h as the ethanol concentration in the bioreactor was changed from 46.3 to 126 kg/m3. The activity of the immobilized cells recovered up to 63% in 2 days even after exposing the cells to 126 kg/m3 of ethanol.

Decolorization and Detoxification of Bleached Kraft Effluents

The pulp and paper industry ranks third in terms of water consumption and fifth among the major industries in its contribution to water pollution problems in the USA. Pulping, bleaching, and paper-making operations are the three major wastewater sources of the industry.

Biopulping: a Less Polluting Alternative to CTMP

At present, pulp is produced from wood either by chemical delignification, mechanical separation of the fibers, or combinations of chemical and mechanical methods. Mechanical pulping methods are being used increasingly because they give much higher yields (>90%) than do chemical methods (40-50%) and require less capital investment. The main disadvantages of mechanical pulping are the high energy requirement, the low strength and the low brightness stability of mechanical pulps (Table 3.1). Addition of chemical pulp is often required to produce papers with adequate strength.

Pulp Bleaching with Xylanases

The kraft process accounts for 85% of the total pulp production in the United States. Bleached kraft pulp is a relatively high-value component of the total production of kraft paper. Kraft pulping removes most of the lignin and dissolves and degrades hemicelluloses without severely damaging cellulose. The kraft process results in excellent pulp from a wide variety of wood species. Unfortunately, kraft pulping also generates large quantities of chromophores. Chromophores are composed of residual lignin and carbohydrate degradation products. They are hard to extract because they are physically entrapped in and covalently bound to the carbohydrate moieties in the pulp matrix. Manufacturers use elemental chlorine and chlorine dioxide to bleach the chromophores and then they extract them, along with the residual lignin to make white pulp. Because of consumer resistance and environmental regulation of chlorine in bleaching, pulp makers are turning to oxygen, ozone, and peroxide bleaching, even though these may be more expensive and less effective than chlorine. One new technology has evolved to decrease the use of chlorine for bleaching, and that is the treatment of the pulp with xylanase enzyme. The use of xylanase enzymes to enhance the bleaching of the pulp was first reported in 1986.1 The Finnish forest companies were the first in the world to start millscale trials in 1988.

Treatment of Wastewaters with Anaerobic Technology

The forest industry utilizes wood and other lignocellulosic feedstocks as raw materials for the production of paper. The major constituents of wood are cellulose, hemicellulose, lignin, and extractives. Softwoods, hardwoods, and straw have different proportions of chemical components (Table 7.1). The processing of wood in paper mills involves various operations including debarking, pulping, and bleaching that result in the discharge of highly polluted wastewaters. The quantity and types of pollutants in these effluents vary with the type of lignocellulosic feedstock used as raw material, the process conditions applied (pH, temperature, pressure, chemical and mechanical treatments), and the specific water consumption.1 Chemical additions and, to a lesser extent, high pressures and temperatures result in an increased release of organic matter into the process water and extensive lignin solubilization. Therefore, the pollution loads and the color due to dissolved lignin compounds is very high for chemical as compared to mechanical pulping effluents.2,3 The COD loads associated with mechanical pulping processes range from 20–50 kg COD/ton of pulp whereas those corresponding to soda pulping processes may be as high as 500–900 kg COD/ton of pulp.1,4 Nevertheless, the black liquors originating from kraft and soda processes are usually burnt to recover the pulping chemicals and the calorific power from the organic components, diminishing to a great extent, the environmental impact associated with these pulping processes. Conventional recovery processes are not economically viable in small paper mills and in those using nonwoody raw materials with a high silica content.4,5 Black liquors represent a very important pollution source in several countries where small-scale mills are common.4-6