Method for removing toxic substances in water

#This invention is directed to a method and system which removes several regulated, toxic mineral and organic precursor substances from drinking water or wastewater by causing them to be absorbed and adsorbed onto sulfur-activated sponge iron particles, which may be referred to as “sulfur-modified iron”. Specifically, the method and system removes from water trace amounts of (1) dissolved, colloidal, and particulate arsenic, selenium, and lead; and (2) naturally-occurring organic compounds (TOC, total organic carbon in the water), which, when oxidized, form “disinfection byproducts”; and (3) other potentially harmful minerals.

#The subject matter of this invention is related to some extent to that of U.S. Pat. Nos. 4,940,549 and 5,200,082, which are directed to removal of selenium from agricultural drain water and from refinery effluents and other industrial waste waters. See also U.S. Pat. Nos. 5,575,919, 5,866,014 and 6,093,328.

#The process of the present invention is particularly concerned with removal of arsenic and other toxic metals, and lowering the level of TOC from drinking water, using some of the same steps which were found efficacious in removal of selenium in the above referenced patents.

#FIG. 1 is a schematic flow chart of the use of a preparation of sulfur-modified iron according to a batch process.

#FIG. 2 is a schematic flow chart of a prior-art water treatment process/plan indicating the addition of a flow-through treatment reactor according to the present invention. In each of FIGS. 1 and 2 the contact vessel can be understood to be either a mixed container or a gravity filter-like contactor (upflow or downflow) or a fluidized bed contactor. Further, mixing in a fully-mixed reactor is unnecessary to obtain full benefit of the SMI treatment for removal of contaminants.

#FIG. 3 illustrates a reactor according to an embodiment of the present invention for producing sulfur-modified iron.

#As specified above, the method of the present invention removed trace amounts of certain toxic substances or precursors to toxic substances in drinking water. This process depends upon the creation or use of a solid medium with a very high surface area produced from finely-divided metallic elemental iron called “sulfur-modified iron” herein, as explained above. The medium is generated by forming an oxidized iron surface in water in the presence of finely-defined elemental sulfur or other sulfur-bearing compounds such as manganese sulfide.

#Accordingly, FIG. 3 illustrates a preferred method for the creation of sulfur-modified iron. A reaction vessel 10 is filled with water at 12. Next, a fluid is introduced at 14 to bring the mixture to a predetermined pH level, which for one preferred embodiment is in a range of pH between 5.0 and 8.5, more broadly, about 3.5 to about 10. In addition, heat may be introduced or recovered by heat exchanger 30 as appropriate to bring the water into an acceptable temperature range. Normal process temperatures range from 34° F. to near boiling. As noted below, some elevation of temperature above standard (room) temperature has been found effective in facilitating a lesser reaction time.

#A modified method is described below following the examples, by which minimal water is used and the exothermic nature of the reaction is used to speed the reaction and substantially to dry the mixture at completion of the reaction.