Method for removing hydrogen sulfide from aqueous streams

Waste water containing dissolved hydrogen sulfide is passed through a vessel containing redox resin which oxidizes the dissolved hydrogen sulfide to elemental sulfur which is removed from the waste water, preferably through filtration. The method of the present invention is also particularly desirable in that the redox-active resin may be restored to a high oxidation state by contacting the resin with an oxidizing fluid such as humidified air or oxygen. The restoration of the redox-active resin is particularly easy when the resin is disposed within a vessel as a membrane dividing the interior volume of the vessel into separate chambers: one chamber for the passage of the waste water and the other chamber for the passage of oxidizing fluid.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for removing hydrogen sulfide 
from waste water and in particular to a method employing redox resin 
material which can be used repeatedly as a result of continuous oxidation 
treatment. 
Industrial waste water containing hydrogen sulfide presents a significant 
pollution problem because of its high toxicity and unpleasant odor even at 
low concentrations. The treatment of such waste water is necessary before 
discharging it to the environment so as to reduce the hydrogen sulfide 
content to acceptable levels. The present invention is aimed at developing 
a simple and effective method of performing the removal of hydrogen 
sulfide from such waste water streams. 
In U.S. Pat. No. 4,076,621 issued Feb. 28, 1978 to I. C. Hardison, there is 
apparently disclosed a method of stripping hydrogen sulfide containing 
waste water with air and scrubbing the evolved gas with solutions 
containing iron chelate. The process which is described in this patent is 
a two stage process requiring a large equipment assembly for aeration of 
the waste water and a subsequent scrubbing operation. Spent chemicals 
employed in this process are neither recovered nor regenerated. 
Accordingly, this method requires high material costs because chemicals 
employed are spent and not recovered. 
In the text "Physicochemical Processes for Water Quality Control" by N. J. 
Weber (Wiley-Interscience 1972) the direct production of sulfur from 
hydrogen sulfide in an aqueous phase is apparently disclosed using 
oxidizing agents such as potassium permanganate, KMnO.sub.4. However, 
these oxidizing agents cannot be recovered, and accordingly, this method 
also requires high material costs and involves a potential pollution 
problem generated by the excess chemicals employed. 
Accordingly, it is seen that it is desirable to provide a method for 
removing hydrogen sulfide from waste water or other aqueous streams by 
means of processes which do not require the use of expendable chemical 
quantities nor the use of chemicals which, when employed in excess of 
stoichiometric requirements, can produce a pollution problem of their own. 
It is also seen that a method for hydrogen sulfide removal is desirable in 
which materials employed can be recycled, reconditioned or restored to 
reduce the cost of the method which would otherwise be attributable to 
spent chemical materials. 
SUMMARY OF THE INVENTION 
In accordance with a preferred embodiment of the present invention, a 
method for removing hydrogen sulfide from waste water or other aqueous 
solutions comprises passing the solution through a vessel containing at 
least one redox resin material having a high oxidation state, so that the 
waste water and resin are contacted with one another so as to thereby 
oxidize the dissolved hydrogen sulfide to produce elemental sulfur which 
is separated from the resulting aqueous solution through a process such as 
filtration. Sulfate and other oxidized sulfur species may also be formed 
as oxidation by-products. In accordance with another embodiment of the 
present invention the redox resin material is employed as a membrane 
dividing the vessel into two volumes. The hydrogen sulfide containing 
waste water is passed through a first volume and an oxygenating fluid is 
passed through the second volume. In particular, the oxidizing fluid may 
simply comprise humidified air or oxygen itself. It is therefore 
accordingly seen that the instant method provides reusable materials for 
the oxidation of the dissolved hydrogen sulfide and it is efficient, 
effective and economical. 
Accordingly, it is an object of the present invention to provide a method 
for removing hydrogen sulfide from waste water and other aqueous streams. 
It is also an object of the present invention to provide a hydrogen sulfide 
removal method employing recyclable chemical materials which may be easily 
restored to a high oxidation state. 
Furthermore, it is an object of the present invention to employ redox resin 
materials as a catalyst for the oxidation of hydrogen sulfide in dissolved 
aqueous solutions. 
Lastly it is an object of the present invention to provide a process for 
the production of elemental sulfur.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates one embodiment of the present invention in which waste 
water containing hydrogen sulfide is passed through vessel 10 containing 
at least one redox resin material, preferably in the form of redox resin 
pellets 11. Waste water passed through vessel 10 is therefore brought in 
contact with the pellets which are preferably present in a high oxidation 
state so as to oxidize the dissolved hydrogen sulfide, thereby producing 
elemental sulfur which may be removed from the treated waste water 
solution by means of filter 12. However, other means for removing 
elemental sulfur may be employed. These means include centrifugation, 
floatation or sedimentation. However, the use of filters is preferred 
because of the high solid content, small space requirement and low cost of 
separation achieved by filtration. 
After the oxidation process is complete, the spent redox resin pellets may 
be regenerated by passing oxygen or air through the chamber. In this way 
the resin pellets may be recycled and used repeatedly, thereby minimizing 
material costs for the processes of the present invention. To provide 
continuous operation, a plurality of vessels may be configured in a 
parallel arrangement so that some may be recharged as others are operating 
and vice versa. 
Passing air and wastewater simultaneously through the bed containing redox 
resins is also a possible method for redox resin regeneration. 
Additionally, simultaneous oxidation of hydrogen sulfide and regeneration 
of the resin is possible through the use of redox-active membranes. A 
schematic diagram illustrating this process is shown in FIG. 2. In this 
diagram a redox-active membrane 13 is employed to divide vessel 10 into 
two volumes. Waste water containing hydrogen sulfide is passed through one 
of these volumes while humidified oxygen or air or other oxidizing fluid 
is passed through the other volume so that these two fluid streams contact 
opposite sides of the membrane. In this embodiment, hydrogen sulfur in the 
waste water is oxidized to sulfur at the surface of the membrane. The flow 
of oxygen or air on the other side of the membrane maintains the redox 
resin membrane at a high oxidation state. 
It should also be pointed out that the process of the present invention may 
be refined through the repeated application of the present process to the 
treated waste water. Accordingly, the process of the present invention may 
also be practiced in a plurality of stages in which the treated product 
from one stage is supplied to the vessel of a subsequent stage. 
The redox resin of the present invention may be prepared by polymerization 
of redox-active substances such as vinylhydroquinone or polymers 
containing redox-active substances such as quinones, benzoquinones, 
naphthoquinones, anthraquinones and others. Such a process is taught by 
Erzin, Updegraff and Cassidy in "Electrochange Polymer III. Polymers and 
Copolymers of Vinylhydroquinone", (Journal of the American Chemical 
Society, Vol. 75, page 1610 (1953). The redox resin may also be easily 
produced by attaching redox-active ions to ion exchange resins in an ion 
exchange process. Effective ions for oxidizing hydrogen sulfide to sulfur 
include organometallic compound such as iron complexed with chelating 
agents such as ethylenediaminetetraacetic acid (EDTA), 
N-hydroxyethylethylene diaminetriacetic acid (HEDTA), nitrilotriacetic 
acid (NTA), and diethylenetriaminepentaacetic acid (DPTA). 
Removal of hydrogen sulfide and the production of elemental sulfur has been 
demonstrated in an experiment employing the redox resin prepared by 
equilibrating an ion exchange resin with a 0.1 molar sodium ferric/EDTA 
solution. 
Accordingly, from the above, it may be appreciated that the method of the 
present invention achieves the objectives stated. In particular, the 
method of the present invention provides a means for the production of 
elemental sulfur from hydrogen sulfide containing solutions. Furthermore, 
the present invention provides for minimum loss of chemical quantities 
during the operation of the present invention. Because of the ability to 
restore the chemicals employed to a high oxidation state, the present 
invention results in a process having minimal material costs. Furthermore 
the cost of the equipment employed in the present invention is low. The 
method of the present invention results in negligible addition of chemical 
quantities to the treated solution. While those skilled in the art will 
recognize that oxidized sulfur species such as sulphate, sulphite and 
thiosulphate may nonetheless be present in the end product of the present 
invention, it will also be appreciated that the toxicity of the end 
product has been greatly reduced by the removal of H.sub.2 S. Finally, it 
is noted that the restoration of the redox resin catalyst to a high 
oxidation state is readily achieved through a low cost process which may 
employ air as the oxidizing fluid. 
While the invention has been described in detail herein, in accordance with 
certain preferred embodiments thereof, many modifications and changes 
therein may be effected by those skilled in the art. Accordingly, it is 
intended by the appended claims to cover all such modifications and 
changes as fall within the true spirit and scope of the invention.