Biotechnological aspects of sulfate reduction with methane as electron donor

Biological sulfate reduction can be used for the removal and recovery of oxidized sulfur compounds and metals from waste streams. However, the costs of conventional electron donors, like hydrogen and ethanol, limit the application possibilities. Methane from natural gas or biogas would be a more attractive electron donor. Sulfate reduction with methane as electron donor prevails in marine sediments. Recently, several authors succeeded in cultivating the responsible microorganisms in vitro. In addition, the process has been studied in bioreactors. These studies have opened up the possibility to use methane as electron donor for sulfate reduction in wastewater and gas treatment. However, the obtained growth rates of the responsible microorganisms are extremely low, which would be a major limitation for applications. Therefore, further research should focus on novel cultivation techniques.     

Cell wall polysaccharides in black currants and bilberries—characterisation in berries, juice, and press cake

Cell wall polysaccharides from black currants and bilberries were characterised in three approaches. First, compositions of skin, pulp, and seeds show the distribution of polysaccharides over these tissues. A sequential extraction of cell wall material with different aqueous extractants informs about the extractability of the different polysaccharides, viz. pectins, hemicellulose, and cellulose. Finally, by isolation of cell wall polysaccharides from juice and press cakes obtained by the conventional juice manufacturing. The polysaccharide distribution was followed during juice processing. The main difference between bilberries and black currants is the dominant sugar residue in seeds: mannose for black currants and xylose for bilberries. Most of the hemicellulolytic sugars and cellulose can be found back in the press cake. The sugar composition of the press cake is similar to the composition of the residue after sequential extraction. Black currants contain more pectic sugars than bilberries. Consequently, a commercial enzyme used during processing releases more pectic material into the juice.     

Sulphur and sulphate reduction with acetate and propionate in an aerobic process for sulphide removal

Summary Sulphide production rates of sulphur-and sulphate-reducing bacteria up to 50 mg per biomass support particle per day were observed in an aerated sulphide-removal reactor with polyurethane (PUR) foam as carrier material. The optimal pH and temperature for the sulphide-producing bacteria were 8.0 and 30°C respectively. Raschig rings and four types of cube-shaped PUR particles were tested as carrier materials. When using PUR particles, the sulphide production rate was always between 3% and 4% of the sulphide removal rate, dependent on the dimensions and pore size of the polyurethane support particles. With the Raschig rings this ratio was only 2% and for reactors in which no carrier materials were present it was even lower (0.6%). Media containing different mixtures of acetate, propionate, sulphur and sulphate inoculated under anoxic conditions with sludge from the aerated reactor showed the presence of acetate-degrading sulphur-reducing, but not of acetate-degrading sulphate-reducing, bacteria. With propionate as sole electron donor no degradation occurred in the presence of sulphur within 2 weeks, whereas sulphate-dependent propionate oxidation started after 5–6 days incubation. Bacteria were isolated and resembled Desulfuromonas acetoxidans and Desulfobulbus propionicus morphologically and physiologically.