Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-03-20
2001-10-23
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S616000, C210S617000, C210S630000, C210S631000, C210S912000
Reexamination Certificate
active
06306302
ABSTRACT:
THIS INVENTION relates to a process for treating water. More particularly, the invention relates to a process for treating raw water having anions consisting of sulphur and oxygen dissolved therein.
According to the invention there is provided a process for treating water having anions comprising sulphur and oxygen dissolved therein, the process comprising the steps of:
subjecting said anions to an anaerobic biological reduction whereby they are converted to sulphide (S
=
) anions to produce dissolved sulphide anions in the water;
subjecting the sulphide anions, produced in the water by the anaerobic biological reduction, to a biological oxidation whereby the dissolved sulphide ions are oxidized to elemental sulphur to produce suspended elemental sulphur in the water; and
separating from the water the suspended elemental sulphur produced in the water, the anaerobic biological reduction and the biological oxidation being effected simultaneously in the presence of each other in at least one common reaction stage in which there are oxidizing conditions which permit the biological oxidation to take place without preventing the anaerobic biological reduction from taking place.
Naturally separating the sulphur from the water will typically involve separating also some suspended biomass from the water.
The dissolved anions consisting of sulphur and oxygen may be selected from the group consisting of:
SO
4
═
;
SO
3
═
;
S
2
O
5
═
;
S
2
O
3
═
;
S
4
O
6
═
;
S
2
O
4
═
;
S
4
O
8
═
; and
mixtures thereof.
The raw water may also contain dissolved S
=
anions.
While the oxidizing conditions may be achieved by dissolving one or more chemical oxidizing agents such as nitrate anions and/or nitrite anions or preferably oxygen, eg in the form of air, in the water, other oxidizing means can naturally be used, if convenient, such as irradiation with light to cause biological photosynthetic anaerobic oxidation. The oxidizing agent may be added to the reaction stage separately from the raw water or, particularly if it is a nitrate or nitrite, it may be present in the raw water. Sulphite anions, which can arise from acid rain, can also act, similarly to nitrate or nitrite anions, as an oxidizing agent for the biological oxidation. When the oxidation agent is air, the process may include the step of aerating the reaction stage.
In particular, the oxidation conditions in the reaction stage may be achieved by dissolving a chemical oxidizing agent in the water, the chemical oxidizing agent being selected from:
nitrate anions;
nitrite anions;
elemental oxygen; and
mixtures thereof.
Furthermore, the water in the reaction stage may be subjected to irradiation which permits photosynthetic anaerobic biological oxidation to contribute to the oxidizing conditions which permit the biological oxidation of the dissolved sulphide ions to elemental sulphur.
In a particular embodiment of the invention, expected to occur frequently in practice, the raw water, prior to the treatment thereof, may contain dissolved anions consisting of sulphur and oxygen which are selected from SO
4
=
(sulphate) and SO
3
=
(sulphite) anions, the reaction stage being subjected to irradiation and the water containing elemental oxygen as a chemical oxidizing agent dissolved therein so that both an aerobic biological oxidation of dissolved sulphide anions, and a photosynthetic anaerobic biological oxidation of dissolved sulphide anions, to form elemental sulphur in the water, take place.
For the anaerobic biological reduction may be used suitable microorganisms of the genera:
Desulfomaculum;
Desulfomonas;
Desulfobulbus;
Desulfosarcina;
Desulfobacterium;
Desulforomas;
Desulfobacter;
Desulfovibrio;
Desulfococcus; and
Desulfonema, a suitable example being
Desulfovibrio desulfuricans.
For the biological oxidation may be used suitable microorganisms of the genera:
Thiobacillus;
Thiomicrospira;
Sulfolobus; and
Thermothrix,
a suitable example being
Thiobacillus thiooxidans.
For the biological photosynthetic anaerobic oxidation in the presence of light or irradiation a suitable microorganism is
Chlorobium limicola form a Thiosulphatophilum
, the anaerobic oxidation taking place according to the following biological reaction:
It should be noted that the biological conversion of sulphate anions to sulphide anions involves sulphite anions as intermediates, Thus, the water to be treated may often contain sulphite anions, which, as indicated above, can arise from acid rain, as well as sulphate anions, the sulphite anions also being converted to sulphide anions. Furthermore SO
2
-rich gases emanating from power stations can be dissolved in water to form H
2
SO
3
solutions, which can be treated.
The biological oxidation- and biological reduction reactions of the present invention will take place in the presence of a suitable metabolizable carbon source, ie an energy source, examples of which are:
sugar, as in waste sugar water;
lactate, as from lactic acid in milk products;
ethanol;
methanol;
producer gas, containing hydrogen and carbon monoxide;
methane burned in a reducing atmosphere to convert it to hydrogen and carbon monoxide; and, in general, water containing organic materials such as sewage or cheese whey.
While the process can in principle be carried out batchwise, it is conveniently continuous, water to be treated being fed continuously to the reaction stage and being continuously withdrawn therefrom, elemental sulphur and biomass being separated from the water withdrawn from the reaction stage, conveniently in a sedimentation stage as described hereunder. More particularly, the process may be carried out on a continuous basis, there being a continuous feed of raw water to the common reaction stage and the anaerobic biological reduction and the biological oxidation take place continuously in the common reaction stage, water containing elemental sulphur and biomass being continuously withdrawn from the reaction stage and continuously fed to a sludge separation stage, separate from the reaction stage, where the continuous separation of the elemental sulphur, together with biomass, from the watertakes place, the method including continuous recirculation of part of the separated sulphur and biomass, sufficient to maintain a suspended solids content in the reaction stage of 2-50 g/l.
The reaction stage may be provided in a packed-bed reactor or fixed-bed reactor, packed with a solid medium which can act as a support for the growth thereon of microorganisms, or it can be a suspended growth reactor containing suspended solids forming a microorganism support for the growth of microorganisms thereon, or it can be in the form of a fluidized bed having fluidized particles which are granules of biomass, or fluidized particles which act as a microorganism support for supporting growing microorganisms, the water being treated in each case by being passed through the bed, in the latermost case upwardly and acting to fluidize the bed. Instead the reaction stage may be provided by a completely mixed reactor, or by a plug-flow- or a slug-flow reactor, or a baffled-flow reactor or a gas-lift reactor. Conveniently, however, the process may, as indicated above, include a separation stage such as a sedimentation stage, downstream of the reaction stage in the direction of flow of water being treated, elemental sulphur and optionally other suspended solids such as bio mass being precipitated and settled in the sedimentation stage, and being optionally recycled through the reaction stage to act as a microorganism support. If desired, however, the sulphur can, instead, be subjected to flotation instead of settling, to separate it from the water in the separation stage. The age of any biomass separated may be 2-30 days.
In the reaction stage, process parameters should be provided which permit, and indeed encourage and promote, the biological oxidation and the biological reduction reactions of the present invention. Such process parameters include:
a dissolved oxygen content in the water being treated of
Gerber Andries
Maree Johannes Philippus
CSIR
Klarquist & Sparkman, LLP
Prince Fred
Simmons David A.
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