Peter J. Harbour

Chrysiogenes arsenatis gen. nov., sp. nov., a new arsenate-respiring bacterium isolated from gold mine wastewater.

A new strictly anaerobic bacterium (strain BAL-1T) has been isolated from a reed bed at Ballarat Goldfields in Australia. The organism grew by reducing arsenate [As(V)] to arsenite [As(III)], using acetate as the electron donor and carbon source; acetate alone did not support growth. When BAL-1T was grown with arsenate as the terminal electron acceptor, acetate could be replaced by pyruvate, L- and D-lactate, succinate, malate, and fumarate but not by H2, formate, citrate, glutamate, other amino acids, sugars, or benzoate. When acetate was the electron donor, arsenate could be replaced by nitrate or nitrite but not by sulfate, thiosulfate, or iron oxide. Nitrate was reduced to ammonia via nitrite. The doubling time for growth on acetate (5 mM) plus arsenate (5 mM) or nitrate (5 mM) was 4 h. The G+C content of the DNA is 49 mol%. The 16S rRNA sequence data for the organism support the hypothesis that this organism is phylogenetically unique and at present is the first representative of a new deeply branching lineage of the Bacteria. This organism is described as Chrysiogenes arsenatis gen. nov., sp. nov.

The use of soluble organic polymers in waste treatment

Organic polymeric flocculants have been used in water purification for several decades as coagulant aids or floc builders, after the addition of inorganic coagulants like alum, iron salts or lime. The increased use of cationic polyelectrolytes as primary coagulants instead of inorganic salts, which has occurred in recent times, arises from their significant inherent advantages. The main ones are faster processing, a lower content of insoluble solids to handle, whether by sedimentation, filtration, flotation or in biological conversion, and a much smaller sludge volume. Polymers have often been used in chemically assisted sedimentation of sewage solids to enhance the removal of suspended matter. The concept is applicable as well to the primary coagulation of industrial wastewaters where the separation may be based on flotation, as in examples from the leather, steel, wool scouring, cosmetic, detergent, plastics, dyehouse, paper, food processing and brewing industries. A cationic polymer of particular charge density is optimal, and hydrophobically modified polymers have relevance in the case of oil and grease removal. The burden of solids which must be floated is much reduced relative to systems utilising inorganic coagulants, and the dosage of chemicals overall is lower. In some cases the addition of some inorganic coagulant is unavoidable, as in the case of highly coloured effluents; in others, an anionic surfactant is needed to facilitate flotation.

Effect of polyelectrolyte charge density and molecular weight on the flotation of oil in water emulsions

Abstract The effect of polyelectrolyte charge density and molecular weight on the flotation of oil emulsified in aqueous electrolyte was investigated. Flotation performance improved with increasing polyelectrolyte charge density, while polyelectrolyte intrinsic viscosity (molecular weight) had no effect on flotation over the range 6–12 dl g −1 . Turbidity removal improved as floc size increased, indicating that polyelectrolyte enhanced flotation by increasing the floc size. The trends in the flotation and flocculation behaviour of the emulsion with changing polyelectrolyte intrinsic viscosity (molecular weight) were consistent with electrostatic patch flocculation. Raising the charge density of the oil increased the amount of polyelectrolyte required for optimal flotation and led to improved performance, while raising the background KNO 3 concentration from 10 −3 to 10 −1 M decreased flotation performance. The effect of electrolyte concentration was greatest at low oil charge density (pH 5) and low polyelectrolyte charge density. It is proposed that the reduction in flotation performance with rising electrolyte concentration was due to increased electrostatic shielding leading to smaller floc sizes, as electrostatic attraction between charged patches on the oil was thought to be the flocculation mechanism. The flotation process was more robust towards changes in polyelectrolyte dose when polyelectrolytes of lower charge density were used.