Abstract: The invention provides a process for removing and immobilizing arsenic from an arsenic-containing waste. It comprises oxidizing the arsenic to pentavalent arsenic in an aqueous medium, contacting the pentavalent arsenic with trivalent iron to form an insoluble iron-arsenic compound and separating precipitated iron-arsenic compound from the aqueous medium. The oxidation of arsenic is effected using oxidizing bacteria at a pH between 0.5 and 4 and at a temperature between 20 and 90° C. in the presence of a mineral catalyst such as pyrite.

Abstract: A method of removing hydrogen sulphide from a gas stream wherein the hydrogen sulphide is scrubbed from the gas phase by an aqueous solution, the hydrogen sulphide in the aqueous solution is biologically oxidized in a bioreactor to produce elemental sulphur, and the elemental sulphur is separated from the aqueous solution, characterized in that the gas stream to be treated is cooled to such a degree that at least sufficient water vapour condenses from the gas stream to compensate for the discharge stream for the purpose of removing salts. This means that no water need be supplied to the bioreactor. This method is suitable, in particular, for gas streams which contain hydrogen sulphide, the hydrogen sulphide having been obtained by catalytic conversion of sulphur compounds.

Abstract: A process for the treatment of waste water containing heavy metals in which sulphur components and/or metals are biologically reduced to precipitate the metals as water-insoluble metal species, which are separated from the waste water. The biological reduction and the precipitation of the metal species are carried out in a moving sand bed, in which sand particles partly immobilize the bacteria and retain the precipitated metal species, treated waste water is separated from the precipitated metal species and the precipitated metal species are subsequently separated from the sand particles. Metals like selenium and uranium can be precipitated without sulphur components, whereas metals like antimony, cadmium, copper, zinc and the like are precipitated as sulphides.

Abstract: A device for purifying flue gas containing nitrogen oxides, in which the flue gas is scrubbed with a circulating scrubbing liquid which contains a transition metal chelate such as Fe(II) EDTA and the complex formed from nitrogen oxide and transition metal chelate and/or spent transition metal chelate is regenerated biologically in the presence of an electron donor, nitrogen oxide being reduced to molecular nitrogen. The biological reactor can be combined with the gas scrubber. The electron donor is, for example, hydrogen or methanol, but may also be sulphite which originates from sulphur dioxide in the flue gas.

Abstract: A process for the removal of sulphides, including hydrogen sulphide, carbonyl sulphide and carbon disulphide, from a gas stream by scrubbing the gas with an aqueous washing liquid and treating the washing liquid with sulphide-oxidizing bacteria in the presence of an electron acceptor and reusing the treated liquid as a washing liquid, wherein the scrubbing and the bacterial treatment are carried out in the same reactor and nitrate is used as the electron acceptor. The process is especially useful of desulphurising gas at high pressure, such as natural gas.

Abstract: A new sulfur-reducing bacterium denoted as KT7 is described. It is a low-GC Gram-positive bacterium related to the genus Desulfotomaculum, capable of reducing sulfite and sulfate to sulfide, having an optimum growth at a temperature between 48 and 70° C. at a pH of between 5 and 9 and at a conductivity of the liquid medium between 0 and 40 mS/cm. It can be used in a process for removing sulfur compounds from water, wherein the sulfur-containing water is subjected to anaerobic treatment with the new sulfur-reducing bacteria, with the addition of an electron donor. The sulfur-containing water can be spent scrubbing liquid from a flue gas desulfurization step.

Abstract: A process for scrubbing a gas containing hydrogen sulphide and/or carbonyl sulphide, in which the spent scrubbing liquid is treated with autotrophic sulphide-oxidizing bacteria capable of oxidizing at high pH, and elemental sulphur is obtained, the elemental sulphur is separated and the treated scrubbing liquid is recycled to the gas scrubbing step. Before recycling, the scrubbing liquid may further be treated with heterotrophic thiosulphate-oxidizing bacteria which produce polythionate which is useful for further enhancing the sulphide-scrubbing capacity of the scrubbing liquid.

Abstract: A process for the biological treatment of a spent caustic solution containing sulphides is disclosed, wherein the solution is introduced into an aerobic reactor containing sulphide-oxidising bacteria, and the sulphides are partly converted to elemental sulphur and partly to sulphate by controlling the redox potential in the reactor at a value below -300 mV (against an Ag/AgCl reference electrode), or below -97 (against a H.sub.2 reference electrode). Also disclosed is process for the biological treatment of an aqueous solution containing sulphides and/or mercaptans in an aerobic reactor, wherein the solution is treated in the presence of bacteria of the new species Methylophaga sulfidovorans.

Abstract: The invention provides a process for removing polyamine chelating agents from aqueous solutions comprising oxidising the chelating agents with oxygen in the presence of an equivalent amount of a transition metal such as iron, followed by biologically reducing the chelates in the presence of an electron donor, and optionally by membrane filtration. The biological reduction is carried out with denitrifying and/or sulphate-reducing bacteria.

Abstract: An installation and a method are described for the treatment of a gas containing hydrogen sulphide, the gas (1) being washed in a first gas scrubber (5) with an alkaline wash liquid and the spent wash liquid (4) being treated in an aerobic reactor (6) with oxygen in the presence of sulphide-oxidising bacteria and the effluent (9) from the aerobic reactor (6) being re-used as wash liquid (3) and the elementary sulphur formed during the treatment with oxygen being removed from the effluent (19), the effluent (13) from which sulphur has been removed being treated in an anaerobic reactor (17) with sulphate-reducing bacteria and returned to the aerobic reactor (6). The installation and the method can also be used for simultaneous removal of SO.sub.2, COS, CS.sub.2, NH.sub.3 and HCN.

Abstract: A process and a device for purifying flue gas containing nitrogen oxides, in which the flue gas is scrubbed with a circulating scrubbing liquid which contains a transition metal chelate such as Fe (II) EDTA and the complex formed from nitrogen oxide and transition metal chelate and/or spent transition metal chelate is regenerated biologically in the presence of an electron donor, nitrogen oxide being reduced to molecular nitrogen. The biological reactor can be combined with the gas scrubber. The electron donor is, for example, hydrogen or methanol, but may also be sulphite which originates from sulphur dioxide in the flue gas.