Search

A species of Serratia bacteria has been used to manufacture hydroxyapatite in the form of coatings on solid supports, powder and scaffolds. The biomineralization mechanism involves an acid phosphatase enzyme located in the bacterial cell wall that cleaves organic phosphate groups liberating inorganic phosphates that then combine with calcium ions to form calcium-deficient hydroxyapatite. The same mechanism can be used to form other insoluble metal phosphates, reducing the concentration of free ions in solution and thus providing a means of water bioremediation. Encapsulation of the enzyme within liposomes was shown to be an effective means of removal of cadmium and uranium from solution and to recover silver phosphate and a form of palladium phosphate. Here, we also describe an alternative method of recovery of palladium ions via their reduction to metal (Pd(0)) using hydrogenase enzymes entrapped within membrane vesicles. This preliminary study gave catalytically active “bio-Pd(0)” with a catalytic efficacy of ~ 30% of that of equivalent “bio-Pd” on whole cells of Desulfovibrio spp. and Bacillus sphaericus , and of a commercial 5% Pd on a carbon catalyst and shows that, in principle, a liposome-based system could be used to make an organic/inorganic hybrid catalyst for use where whole bacteria may be undesirable.

An Integrated Biohydrogen Refinery (IBHR) and experimental net energy analysis are reported. The IBHR converts biomass to electricity using hydrothermal hydrolysis, extractive biohydrogen fermentation and photobiological hydrogen fermentation for electricity generation in a fuel cell. An extractive fermentation, developed previously, is applied to waste-derived substrates following hydrothermal pre-treatment, achieving 83-99% biowaste destruction. The selective separation of organic acids from waste-fed fermentations provided suitable substrate for photofermentative hydrogen production, which enhanced the gross energy generation up to 11-fold. Therefore, electrodialysis provides the key link in an IBHR for ‘waste to energy’. The IBHR compares favourably to ‘renewables’ (photovoltaics, on-shore wind, crop-derived biofuels) and also emerging biotechnological options (microbial electrolysis) and anaerobic digestion.

The imminent use of hydrogen as an energy vector establishes the need for sustainable production technologies based on renewable resources. Starch is an abundant renewable resource suitable for bio-hydrogen generation. It was hypothesised that starch hydrolysates from a large (250 mL) hydrothermal reactor could support bioH 2 fermentation without inhibition by toxic byproducts. Starch was hydrolysed at high concentrations (40–200 g L −1 ) in hot compressed water (HCW) with CO 2 at 30 bar in a 250 mL reactor, the largest so far for polysaccharide hydrolysis, at 180–235 °C, 15 min. Hydrolysates were detoxified with activated carbon (AC) and tested in biohydrogen fermentations. The maximum yield of glucose was 548 g kg starch −1 carbon at 200 °C. 5-hydroxymethyl furfural, the main fermentation inhibitor, was removed by AC to support 70% more hydrogen production than the untreated hydrolysates. The potential utilization of starch hydrolysates from HCW treatment for upscaled fermentations is promising.

H2 can potentially be produced in a two-stage biological process: the fermentation of glucose by Escherichia coli HD701 and the photofermentation of the residual medium by Rhodobacter sphaeroides O.U. 001. In a typical batch fermentation, E. coli consumed glucose and produced H2, organic end-products and biomass. Organic end-products and residual glucose were removed during subsequent photofermentation by R. sphaeroides, with associated growth and neutralization of pH. However, photoproduction of H2 did not occur during photofermentation of the residual liquor per se due to the presence of fixed nitrogen compounds. Nevertheless, this two-stage approach could be applied to dispose of sugar-containing industrial wastes, H2 being used for on-site power generation.

Hydrogen production by Escherichia coli is mediated by the formate hydrogenlyase (FHL) complex. E. coli strain HD701 cannot synthesize the FHL complex repressor, Hyc A. Consequently, it has an up-regulated FHL system and can, therefore, evolve hydrogen at a greater rate than its parental wild type, E. coli MC4100. Resting cells of E. coli strain HD701 and MC4100 were set up in batch mode in phosphate buffered saline (PBS) to decouple growth from hydrogen production at the expense of sugar solutions of varying composition. Strain HD701 evolved several times more hydrogen than MC4100 at glucose concentrations ranging from 3 to 200 mM. The difference in the amount of H 2 evolved by both strains decreased as the concentration of glucose increased. The highest rate of H 2 evolution by strain HD701 was 31 ml h −1 OD unit −1 l −1 at a glucose concentration of 100 mM. With strain MC4100, the highest rate was 16 ml h −1 OD unit −1 l −1 under these conditions. Experiments using industrial wastes with a high sugar content yielded similar results. In each case, strain HD701 evolved hydrogen at a faster rate than the wild type, showing a possible potential for commercial hydrogen production.

Publisher Summary This chapter discusses biochemical basis of microbe–radionuclide interactions. Microbial metabolism can significantly alter the mobility of radionuclides in the environment and is increasingly being proposed as the basis of novel remediation programmes. Enzymatically catalyzed redox transformations are discussed with respect to radionuclides, including U, Np, Pt, and Tc. Metabolism dependent uptake of radionuclides—such as Cs—are discussed in the chapter. The biochemical basis of indirect biomineralization processes driven by microbial products—including sulfide, phosphate and iron minerals—is reviewed. The broad range of techniques available to help characterize such transformations is also explained. The microbial reduction of technetium is used as a case study to illustrate the integrated use of (1) advanced spectroscopic techniques to characterize end products of radionuclide transformations, (2) physiological studies to characterize biochemical pathways of importance, and (3) the construction of defined mutants by using molecular biology to confirm the involvement of key enzymes in radionuclide transformations.

Publisher Summary This chapter describes the 3D MRI technique used to acquire images. MRI technique discussed in this article has great potential for studies not only of biofilms immobilized onto supports, but also of the overall functioning of bioreactors. MRI can also be used to monitor systems over a period of time. This technique is sensitive to motion and to temperature and it can be used to measure quantitatively in three dimensions dynamic changes, such as flow, diffusion, and mass- and heat-transfer. Besides the obvious importance of such experimental data in their own right, such data have unique potential for validation of the computer software used to model bioreactor processes. The chapter also provides an overview of the underlying principles of MRI and of some of the limitations of the technique with respect to imaging of biofilms. Other applications of MRI that are relevant to the study of bioreactors are described.

The MERESAFIN (MEtal REmoval by SAnd Filter INoculation) process presented here was designed to combine the optimum conditions for more than one of the well-known processes of biological metal immobilisation like biosorption and bioprecipitation. The approach makes use of a continuously operated moving-bed AstraSand filter which has been inoculated with a mixed population of metal biosorbing and bioprecipitating bacteria. A pilot plant operating at 1 m 3 /h has been erected at a metal plating company in Vienna to treat waste water from an electroless nickel plating line. In addition to several mg/L of nickel the rinsing water also contains some organic acids and inorganic phosphates, which make conventional treatment difficult. The main laboratory experiments as well as preliminary results from the pilot installation are presented.