Influence of immobilization procedure and salt environment on functional stability of chloroplast membranes: experimental data and numerical analysis

The interactions between chloroplast membranes and their microenvironment within artificial matrices (albumin-glutaraldehyde matrix, polyurethane foam) where investigated. Particularly, the influence of a high-ionic-strength medium (0.75 M potassium citrate) on the stability of the photosynthetic ferricyanide reduction by immobilized thylakoids has been studied. A method of data analysis based on a nonlinear identification method combined with the numerical integration of the equation of the transient state of the continuous stirred tank reactor (CSTR) is proposed to estimate the actual degradation of the photosynthetic electron transfer. A statistical analysis achieved on the parameter values has allowed a quantitative assessment of the global behavior of immobilized chloroplast membranes. From the mathernatical analysis of the experimental data, we demonstrate that citrate used in the reaction media prevents the photoinactivation of the electron transfer chain whatever the nature of the matrix or the type of the reactor. The use of an albumin-glutaraldehyde matrix or an open reactor during experiments also has allowed a better stabilization of the photosystems under operational conditions.     

Improved performance of intensive semicontinuous cultures of Scenedesmus by biomass recirculation

The microscopic green alga, Scenedesmus obliquus, was used in a semicontinuous culture system for the tertiary treatment of urban wastewater, with the simultaneous production of usable biomass. Partial biomass recycling was used to increase the productivity of the system by overcoming the limits imposed by the low maximal growth rate of the alga. The biomass to be recycled was collected by simple gravity settling of the removed culture.The culture system was operated at different dilution rates and its productivity measured at each rate. An evaluation of the crude nutrient composition of the algae produced at each dilution rate was also carried out.The system was found to operate stably at dilution rates of up to 0.8 day(-1) which represents a 20% net increase over the maximum dilution rate allowed under the same conditions in a system without recirculation. The composition of the biomass produced varied little over a range of dilution rates, which may be of relevance to its projected end-use.The study indicated that such a system can exploit available light to the full and should be of particular value for the treatment of low-strength wastes such as we employed.     

The production of cellulase in a spouted bed fermentor using cells immobilized in biomass support particles

Continuous cellulase production by Trichoderma viride QM 9123, immobilized in 6 mm diameter, spherical, stainless steel biomass support particles, has been achieved using a medium containing glucose as the main carbon source. Experiments were carried out in a 10-L spouted bed fermentor. In this type of reactor-recycled broth is used to create a jet at the base of a bed of particles, causing the particles to spout and circulate. During the circulation, particles pass through a region of high shear near the jet inlet. This effectively prevents a buildup of excess biomass and thus enables steady-state conditions to be achieved during continuous operation. Continuous production of cellulase was achieved at significantly higher yield and productivity than in conventional systems. At a dilution rate of 0.15 h(-1) (nominal washout rate for freely suspended cells is 0.012 h(-1)), the yield of cellulase on glucose was 31% higher than that measured during batch operation, while the volumetric productivity (31.5 FPA U/L. h) was 53% greater than in the batch system. The specific cellulase productivity of the immobilized cells was more than 3 times that of freely suspended cells, showing that diffusional limitations can be beneficial. This offers significant opportunity for the further development of biomass support particles and associated bioreactors.     

Effects of solute hydrophobicity and phospholipid composition on permeability of composite membranes containing phospholipids

Permeabilities of several solutes through the composite membranes containing phospholipids have been measured. They were inversely proportional to the content of the phospholipids in the membrane. Both the permeability of solutes and the degree of permeability change around the phase transition temperature of the phospholipids for the hydrophobic solutes such as n-butanol and salicylamide were larger than those for the hydrophilic solutes such as amino acids and pyridoxine. These results suggest thatthe permeation path of hydrophobic solutes is different from that of hydrophilic ones. The addition of phosphatidyl ethanolamine, phosphatidyl serine, or phosphatidic acid to the composite membrane influenced the solute permeability due to the introduced negative charge and/or the change in the molecular packing of phospholipid.     

Methane recovery from water hyacinth through anaerobic activated sludge process

The concepts of phase separation, anaerobic activated sludge process, and alkali pretreatment have been incorporated in this investigation with the objective of developing rational and cost-effective designs of diphasic anaerobic activated sludge systems, with and without alkali treatment, for methane recovery from water hyacinth (WH). Evaluation of process kinetics and optimization analyses of laboratory data reveal that a diphasic system with alkali treatment could be designed with an alkali pretreatment step (3.6% Na(2)CO(3) + 2.5% Ca(OH)(2) (w/w) of WH, 24 h duration) followed by an open acid phase (2.1 days HRT) and closed methane reactor with sludge recycle (5.7 days HRT, 7.7 days MCRT) for gas yield of 50 L/kg WH/d at 35-37 degrees C. Likewise, a diphasic system without alkali treatment could be designed with an open acid phase (2 days HRT) followed by closed methane reactor with sludge recycle (3.2 days HRT, 6 days MCRT) for gas yield of 32.5 L/kg WH/d at 35-37 degrees C. Detailed economic analyses bring forth greater cost-efficacy of the diphasic system without alkali treatment and reveal that the advantage accrued in terms of higher gas yield is overshadowed by the cost of chemicals in the diphasic system with alkali treatment.