Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-07-30
2001-11-13
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S603000, C210S605000, C210S610000, C210S630000, C210S631000, C210S747300, C210S903000, C210S906000, C210S912000, C435S262500
Reexamination Certificate
active
06315904
ABSTRACT:
THIS INVENTION relates to the treatment of water. More particularly, the invention relates to the treatment of waste water. Still more particularly, the invention relates to a process for treating sulphate-containing waste water.
According to the invention, there is provided a process for treating sulphate-containing waste water, which process comprises
introducing a feedstock comprising sulphate-containing waste water, into a pond;
subjecting the sulphate-containing waste water to biological sulphate reduction in the pond, thereby to convert dissolved sulphate anions to dissolved sulphide anions; and
withdrawing treated waste water, containing the dissolved sulphide anions, from the pond.
In order to effect the biological sulphate reduction in the pond, a metabolizable carbon source may also be introduced into the pond, with the metabolizable carbon source mixing with the waste water in the pond, and with metabolization thereof by organisms involved in the biological sulphate reduction occurring. The metabolizable carbon source may comprise an organic carbon source which exhibits a high chemical oxygen demand (‘COD’). The organic carbon source may be an effluent or waste product comprising organic material dissolved, suspended and/or carried in waste water, such as sewage, settled sewage, settled sewage solids, tannery waste water, brewery waste water, starch manufacture waste water, and paper pulp waste water. These waste waters provide metabolizable organic carbon and the necessary organisms for the biological sulphate reduction in the pond, although, naturally, the pond can, at least in principle, be seeded with suitable microorganisms for the biological sulphate reduction in the pond.
The pond may be a facultative pond. In particular, it may be a facultative pond having an anaerobic compartment, eg an anaerobic pit upflow digester. The pond may thus contain an oxygenated surface layer of water. The oxygenated surface layer of water may be provided by withdrawing treated waste water from the pond, subjecting it to polishing, in a polishing stage, for photosynthetic oxygen production, for reoxidation of residual sulphides, and for removal of nitrates and phosphates, and returning a portion of the algae-rich oxygenated polished waste water to the pond as the surface layer. Instead, or additionally, the pond may be fitted with surface aerators to provide, or to assist in providing, the oxygenated surface layer of water in the pond.
The polishing stage may comprises a high rate algal pond. The process may include passing polished waste water, containing algal biomass, from the high rate algal pond to a harvesting stage where algal biomass is harvested or separated from the polished waste water.
The sulphate-containing waste water may be a sulphate-containing metalliferous, ie metal-containing, waste water from which the metal component has been removed. The process may thus include pre-treating a sulphate-containing metalliferous waste water to remove dissolved metal cations therefrom, and using the resultant pre-treated sulphate-containing, metal-lean, waste water as the feedstock to the pond. However, at least in principle, it is possible, if desired, to treat such a metal- and sulphate-containing waste water directly in the facultative pond, in which case there will be settling of metal sulphide sludges in the anaerobic compartment of the pond.
The sulphate-containing metalliferous waste water may be mine effluent or waste water containing dissolved heavy metal cations, such as ferrous cations, and the dissolved sulphate anions. Instead, however, the waste water can be any other dissolved sulphate-containing waste water, such as zinc refinery waste water. These waste waters may also be acidic.
The pretreatment of the metalliferous waste water to remove the metal cations therefrom, may include adding a sulphide compound to the waste water in a mixing stage, with the sulphide compound reacting with the dissolved metal cations to form the corresponding insoluble metal sulphides, allowing the metal sulphides to precipitate from the waste water, and separating the precipitated metal sulphides from the waste water in a separation stage, eg in a settler.
The sulphide compound may be in liquid or gaseous form. For example, it may be hydrogen sulphide.
In one embodiment of the invention, at least part of the sulphide compound added to the mixing stage may be that obtained by withdrawing treated sulphide-containing waste water from the pond; stripping gaseous components, including hydrogen sulphide and carbon dioxide, therefrom in a stripping stage; returning the stripped waste water to the pond; mixing the gaseous hydrogen sulphide with the feedstock; and passing the carbon dioxide to the high rate algal pond as a nutrient. However, in another embodiment of the invention, at least part of the sulphide compound added to the mixing stage may instead or additionally be that obtained by withdrawing treated sulphide-containing waste water from the pond, and mixing it directly with the feedstock.
Instead, however, the sulphide compound added to the mixing stage may be obtained from an external source. The process may then include withdrawing sulphide-containing waste water from the pond, recovering sulphur therefrom as a product, and returning the sulphide-lean waste water to the pond.
The process may include removing a metal sulphide sludge from the separation stage, and feeding the sulphate-containing waste water from the separation stage directly to the pond. However, if desired, the process may include treating the waste water from the separation stage in an alkalinity generating stage, to increase the alkalinity thereof, and returning a portion of this waste water to the mixing stage, to increase the alkalinity of the waste water, eg to neutralize the feedstock waste water. The alkalinity generating stage may comprise a stress reactor, which may be in the form of a high rate algal pond. The process may then include feeding at least some of the algal biomass harvested in the harvesting stage, to this high rate algal pond. The process may also include withdrawing pre-treated algal-containing waste water from this high rate algal pond; separating algal biomass therefrom; returning this biomass to the high rate algal pond, and then feeding the sulphate-containing waste water to the facultative pond.
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Boshoff Genevieve Ann
Duncan John Richard
Rose Peter Dale
Van Hille Robert Paul
James Ray & Associates
Prince Fred
Simmons David A.
Water Research Commission
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