Abstract:
A method for removing contaminants from fluids comprises contacting the fluid with an expanded material selected from popped corn, puffed rice and puffed wheat. The preferred expanded material is popped corn. The method is applicable to a wide range of organic and inorganic contaminants. Examples of contaminants include aromatic compounds such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo furans (PCDFs), polychlorinated dibenzo dioxins (PCDDs), carbamates, sulphonamides, dichlorodiphenyltrichloroethane (DDT), 2,4-dichlorophenoxyacetic acid (2,4-D), other compounds such as carbon disulphide, ethylene glycol and pesticides. Other examples include inorganic compounds or organo-metallic compounds, e.g. those containing aluminum, antimony, barium, cadmium, cobalt, chromium, copper, iron, lead, mercury, molybdenum, nickel, silver, tin, titanium, vanadium and zinc.

Description:
This is a continuation-in-part of Application No. 08/736 210 which was filed Oct. 25, 1996, now U.S. Pat. No. 5,830,363, which in turn claimed priority on now-lapsed provisional application 60/007,044 which was filed Oct. 25, 1995. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of removing chemical contaminants from waste streams. 
     BACKGROUND TO THE INVENTION 
     Large quantities of environmentally persistent compounds have been disposed of on land, air and water and which accumulate on land and in water. The term &#34;environmentally persistent&#34; includes those compounds which are only slowly degraded or not degraded at all in the natural environment. Many remain as potentially dangerous and toxic materials to plant and animal life. Others appear innocuous but the effects may be long term, e.g. causing mutations or lowering immunity to disease. Yet others promote the growth of unwanted species. Obvious blots on the landscape may be caused by deliberate or accidental release of large quantities of such compounds, e.g. as a result of rupture of containers or pipelines. More subtle is the deliberate use of chemicals which make their way to waterways, e.g. the use of pesticides on farmland, mine tailings ponds which seep into water courses. 
     There is growing concern over the contamination of land and water bodies, especially as it relates to the food chain and to the purity of drinking water. Various chemical methods have been used to convert toxic materials into relatively harmless materials. However, in cleaning up large contaminated bodies such methods tend to be extremely costly. It would be preferable to be able to use natural products in order to clean up contaminated bodies. 
     It is known to use natural materials such as sphagnum moss for absorbing materials such as oils from contaminated substrates such as soil. Absorption of the oils seems to be dependent upon the high surface area of the sphagnum moss. It is unsuitable, however for removing trace quantities of contaminants. Starch xanthates have also been used for removal of metals but carbon disulphide is released during the removal process. Cooked cereals, e.g. puffed rice, have been used to cause agglomeration of oil from the surface of water, as indicated by Arsenault et al in U.S. Pat. No. 4,969,774 which issued Nov. 13, 1990. Such a method is dependent on the oil floating on the water&#39;s surface. A method has been found which is particularly efficacious for removing very low concentrations of organic chemicals and heavy metals, which are dissolved or otherwise entrained in aqueous or gaseous fluids and is relatively inexpensive. Surprisingly it has been found that this absorption can be accommodated using commonly available materials which are derived from natural products. 
     SUMMARY OF THE INVENTION 
     Accordingly the present invention provides a method for removing contaminants from an aqueous or gaseous fluid comprising contacting the fluid with a puffed material selected from popped corn, puffed rice and puffed wheat. 
     Popped corn is the preferred material. 
     In one embodiment the fluid is water which is contaminated with a contaminant selected from organic compounds and metallic compounds. 
     In another embodiment the fluid is a gas contaminated with an organic compound. 
     Preferably, the method is for removing environmentally persistent contaminants from a body of water comprising contacting the water with popped corn for a time sufficient to remove a substantial portion of the contaminants, said contaminants being selected from the group consisting of pesticides, alkylene glycols, inorganic compounds with at least one metallic ion, organo-metallic compounds, organohalides, organosulphides and benzenoid solvents. 
     In one embodiment, the contaminants are in low concentrations, e.g. 5% or less. 
     In another embodiment, the fluid is contacted by the expanded material in a manner selected from the group consisting of i) immersing the expanded material in the body of water and removing contaminated expanded material from contact with the water and ii)passing the water through a bed of the expanded material. 
     The organic compounds may be simple compounds like carbon disulphide, aliphatic compounds like ethylene glycol or aromatic compounds like polychlorinated biphenyls (PCBs), polybrominated biphenyls, polychlorinated dibenzo furans (PCDFs), and dioxins, particularly chlorinated dioxins, including polychlorinated dibenzo dioxins (PCDDs). 
     The metallic compounds may be inorganic or organo-metallic compounds. The inorganic compounds contain metal ions, particularly the heavier metals. The breadth of metals which may be removed using the present invention is exemplified by metals such as aluminum, antimony, arsenic, barium, cadmium, cobalt, chromium, copper, iron, lead, mercury, molybdenum, nickel, selenium, silver, tin, titanium, vanadium, zinc. 
     Other examples of contaminants may be classified as pesticides, wood preservatives, bleaching agents used in the pulp and paper industry, and other chemical contaminants. 
     Examples of pesticides include dichlorodiphenyl-trichlorethane (DDT), 2,4-dichlorophenoxyacetic acid (2,4-D), sulphonamide pesticides, chlordane, malathion, maneb, methoxychlor, nicotine sulphate, rotenone, zineb, lindane, alachlor, pentachlorophenol, aldicarb, carbofuran, heptachlor, toxaphene, ethylene dibromide, dichloropropane and dibromochloropropane. 
     Examples of other organic contaminants include carbon tetrachloride, carbon disulphide , dichloroethane, dichloroethylene, trichloroethane, epichlorohydrin, trichloroethylene, tetrachloroethylene, vinyl chloride and benzenoid solvents such as benzene, toluene, ethyl benzene, xylene and dichlorobenzene. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention makes use of popped corn, puffed rice or puffed wheat. Popped corn is the preferred material. It is made from a particular type of corn known as popcorn, which has been bred for its qualities to &#34;pop&#34; when heated. It is understood that the latin name for such popcorn is zea mays everta. Two types of popcorn are used commercially, i.e. those known as the mushroom kind and the other known as the snowflake kind, the snowflake kind being relatively flat after popping, and the mushroom kind being bulky. Both kinds are useful in the present invention. The processes for expanding corn, rice and wheat to make popped corn, puffed rice and puffed wheat are known and involve rapid heating of the popcorn, rice or wheat. Heating is usually provided by contact of the appropriate variety of corn, rice or wheat with a hot fluid, e.g. air, oil. Expansion can also be attained by microwave or open flame methods. The expanded materials are sometimes available commercially as breakfast cereals or as snacks. 
     The expanded material may be reduced in size, e.g. by grinding or chopping in order to increase their surface area. It is not usually necessary to reduce the size of the expanded material, however. 
     These materials may be used for removing chemical contaminants from water bodies and soils. Examples of water bodies include mine tailings ponds, harbours, lakes, rivers, sewage streams, underground water. As indicated hereinbefore, the range of organic compounds for which the invention is believed effective is broad and includes compounds such as carbon disulphide, ethylene glycol, polychlorinated biphenyls (PCBs), dioxins, polychlorinated dibenzo furans (PCBFS) and polychlorinated dibenzo dioxins (PCDDs), pesticides, wood preservatives, pulp and paper bleaching compounds and the like. The range of metallic compounds is also broad and includes salts of metals, e.g. acetates, bromides, chlorides, nitrates, sulphates, sulphides, sulphites, bisulphites, and organo-metallic compounds, e.g. methylmagnesium iodide, metallic alkyls such as butyllithium, tetraethyl lead, triethyl aluminum, tetrabutyl titanate, dibutyl tin laurate, copper phthalocyanate, zineb, ethylmercuric acetate, stereato chromic chloride, ferrocene, nickel carbonyl. 
     Because the puffed cereal, i.e. popped corn, puffed rice and puffed wheat, contains entrapped air, they tend to float on water and therefore it is desirable to contain these materials in a water-permeable container. A container made of textile material or similar is suitable, e.g. a bag made from cotton, burlap, woven polyolefin tapes, which contains heavier-than-water material eg. glass beads, sand, stones or the like. This permits the puffed cereal to be brought in contact with the contaminants within the water body. The water is allowed to remain in contact with the water for a period of time, sometimes as little as a few minutes but sometimes as long as several days. Although the mechanism is not clearly understood, chemicals contaminants seem to be absorbed by the puffed cereal, thus removing them from the water body. The puffed cereal is then removed from the water body and may be disposed of, for example in landfill or dried and burned. Alternatively, the contaminated expanded material can be removed to a site where the contaminants may be recovered by chemical means for further processing. 
     In order to remediate contaminated soil it is usual to wash the soil. The present invention may be used to remove contaminants from the wash water. Alternatively the soil, puffed material and some water may be mixed in a suspension, slurry or the like and then the puffed material and soil be separated by flooding with water and allowing the soil to sink and the puffed material to float. As used herein the term &#34;soil&#34; includes sand and the like. 
     The present method using puffed cereal to remove contaminants seems to work not only in water bodies such as lakes, but also in relatively harsh conditions where the pH may be low, e.g. in mine tailings ponds. The water stream to be decontaminated need not be in situ as with a pond, tank or similar. The contaminated water may be passed, e.g. pumped over a bed of puffed material in a tower or other vessel in a manner similar to filtration. The necessary residence time in the puffed material bed can be easily determined by simple experimentation. 
     Although the method of the present invention is operable over a wide range of concentrations, there are far more situations where the concentration of contaminants is low, e.g. about 5% or less. It has been found that the method is effective even at extremely low initial concentrations of contaminants, e.g. as low as 10 parts per billion initial concentration. If will be understood that water bodies may be treated several times, each time with a fresh batch of expanded material, with the intention of lowering the concentration of contaminants with each treatment. 
     With gaseous fluid streams, the puffed cereal may be placed in a fluid bed and the contaminated fluid passed over the puffed cereal. In such a manner, contaminants such as solvents, carbon disulphide and paint fumes may be removed from air streams. 
     The invention may also be better understood by reference to the following examples, in which the popped corn was made from the mushroom kind and had a particle size range, after popping, of from 1.5 mm to 3 cm: 
    
    
     EXAMPLE I 
     Sample A of water, containing metal contaminants taken from an automotive plant was split into two sub-samples for testing and analysis. The first sub-sample was filtered through a filter and the resulting filtrate analyzed for concentrations of certain elements using a conventional inductively coupled plasma (ICP) procedure. Mercury concentrations were measured using conventional cold vapour flame techniques. The second sub-sample, weighing 238 g, was taken and to it was added 8.3 g of popped corn. The popped corn was stirred in the water sample for about 12 minutes. The second sub-sample was then filtered through a Whatman® No. 1 filter and the resulting filtrate analyzed for metal concentrations using the above-described analytical methods. The test results are shown in Table I. 
     
                       TABLE I______________________________________Concentration (ppm)           First Sample                     Second Sample______________________________________Boron           &lt;0.1      &lt;0.1Sulphur (as SO.sub.3)           18.3      18.3Cobalt          &lt;0.1      &lt;0.1Titanium        &lt;0.1      &lt;0.1Tin             &lt;0.1      &lt;0.1Iron            0.1       &lt;0.1Copper          &lt;0.1      &lt;0.1Chromium        &lt;0.1      &lt;0.1Molybdenum      &lt;0.1      &lt;0.1Nickel          &lt;0.1      &lt;0.1Vanadium        &lt;0.1      &lt;0.1Zinc            1.5       1.0Lead            &lt;0.1      &lt;0.1Barium          &lt;0.1      &lt;0.1______________________________________ 
    
     This example shows a reduction in zinc concentrations under the conditions of the experiment. Those elements with a concentration of &lt;0.1 ppm were below the detection limit of the analysis and no conclusion regarding removal could be made. 
     EXAMPLE II 
     A similar experiment to Example I was conducted with Sample B which was water run-off from a Toronto, Ontario location. Sample B was split into two sub-samples for testing and analysis; the first sub-sample was without treatment with popped corn and the second sub-sample was with treatment, i.e. 11.3 g popped corn to 317 g of the second sub-sample. The test results are shown in Table II. 
     
                       TABLE II______________________________________Concentration (ppm)           First Sample                     Second Sample______________________________________Titanium        0.069     0.033Arsenic         0.029     0.026Mercury         0.061     0.007Selenium        0.033     0.012Molybdenum      0.204     0.175Antimony        0.045     0.003Tungsten        0.029     0.017Zinc            1.11      0.136Bismuth         0.015     0.002______________________________________ 
    
     This example shows a reductions of metal concentrations of from 10, e.g. arsenic to about 90%, e.g. antimony, bismuth, mercury and zinc, starting from very low concentrations in the first instance. 
     EXAMPLE III 
     Sample C, which was effluent from a mine tailings pond was taken and split into two sub-samples for testing and analysis. Sample C contained about 5% wt./wt. sulphuric acid. The first sample was filtered through a Whatman® GFC No. 40 glass filter and the resulting filtrate analyzed for concentrations of nickel and ferrous ions using conventional ICP procedures. The second sub-sample, weighing 82.4 g, was taken and to it was added 2.5 g of popped corn. The popped corn was stirred in the second sub-sample. The second sample was then filtered through a Whatman® No. 1 filter and the resulting filtrate analyzed for concentrations of nickel and ferrous ions using conventional ICP procedures. The concentrations of nickel and ferrous ions in the first sample, i.e. before treatment, were 5 ppm and 1400 ppm respectively. The concentrations of nickel and ferrous ions in the second sample, i.e. after treatment with popped corn, were 0.266 ppm and 349 ppm respectively. This clearly demonstrates the efficacy of the present method even in harsh environments, i.e. with low pH. 
     EXAMPLE IV 
     Two further samples (D and E) of water, containing metallic salts were prepared from standard metal solutions and diluted with reverse osmosis deionized water. Two sub-samples of each were taken. The first sub-samples were analyzed for metal content without treatment with popped corn. The second sub-samples were analyzed after treatment with popped corn (120 g of water to 3 g of popped corn in each case). The metals were analyzed using conventional ICP procedures. The results are shown in Table III. 
     
                       TABLE III______________________________________         Sample D      Sample E         First   Second    First SecondConcentration (ppm)         Sample  Sample    Sample                                 Sample______________________________________Silver        0.2400  0.0741    0.0243                                 0.0030Aluminium     3.0000  2.9530    0.3166                                 0.0200Boron         3.0000  0.0408    0.2420                                 0.0100Barium        3.0000  0.0168    0.2457                                 0.0020Cadmium       3.0000  2.8650    0.2899                                 0.0050Cobalt        3.0000  2.6790    0.2810                                 0.0050Chromium      3.0000  0.0500    0.0050                                 0.0030Copper        3.0000  2.9840    0.2948                                 0.0050Iron          3.0000  2.2780    0.2829                                 0.0050Manganese     3.0000  0.0829    0.0050                                 0.0060Molybdenum    3.0000  0.0600    0.0060                                 0.0060Nickel        3.0000  1.9720    0.2998                                 0.0060Phosphorus    3.0000  2.9490    0.1997                                 0.0595Lead          3.0000  2.7730    0.2974                                 0.0060Tin           3.0000  1.2870    0.2420                                 0.0050Titaniuin     3.0000  2.0730    0.2889                                 0.0060Vanadium      3.0000  0.0060    0.2000                                 0.0200Zinc          3.0000  2.8730    0.3032                                 0.0052______________________________________ 
    
     These show varying degrees of removal of contaminants at two different initial concentration levels. Removal of up to 99% of the contaminants were realized. 
     EXAMPLE V 
     Three water samples F, G and H, containing polychlorinated biphenyls (PCBS) were taken. Each was split into two sub-samples. The first sub-samples were analyzed for PCBs without treatment with popped corn. The second sub-samples were analyzed for PCBs after contacting 101 g of the sub-sample with 2.7 g of popped corn. The PCBs were analyzed using EPA Method No. 508 for the determination of chlorinated pesticides in water by gas chromatography and electrocaptive detector. The concentrations of PCBs in the first sub-samples, i.e. before treatment, were 15 ppm, 3.0 ppm and 10.5 ppb for sub-samples F, G and H respectively. The concentrations of PCBs in the second sub-samples, i.e. after treatment with popped corn, were 0.00, 0.00 and 1.60 ppb for sub-samples F, G and H respectively, the first two being not measurable with the analytical method and the third being within the detection limit of the analytical method. This clearly demonstrates the efficacy of the present method for removing small concentrations of certain aromatic compounds. 
     EXAMPLE VI 
     Seven 100 ml water samples J, K, L, M, N, 0 and P, containing ethylene glycol were taken. Each sample was split into two sub-samples. The first of each of the sub-samples were analyzed for ethylene glycol without treatment with popped corn. The second of each sub-samples were analyzed for ethylene glycol after contacting the sub-sample with a small quantity of popped corn (in the range of about 2-3 g) for one minute. The ethylene glycol in samples J, K, L and M were measured using a Hach field kit and a standard COBAS colorimetric analysis with a UV visual detector. The detection limit for this method is about 10 ppm. The ethylene glycol in samples N, 0 and P were measured with a more sensitive gas chromatographic method, using a Hewlett Packard (trade mark) 5980 chromatograph with a polar 0.53 mm Carbowax (trade mark) biphasic column. The detection limit for this method is about 0.5 ppm. The results, in parts per million ethylene glycol, are shown in Table IV. 
     
                       TABLE IV______________________________________       First Sample                  Second SampleSample      (Initial concn.)                  (After treatment)______________________________________J           5000       &lt;300K           1000       &lt;25L           500        &lt;25M           100        &lt;25N           100        16O           50         7P           20         4______________________________________ 
    
     This clearly shows the efficiency of the method of the present invention with another simple organic compound. 
     EXAMPLE VII 
     Samples of water containing 1,1,1-trichloroethane were taken. Each sample was split into two sub-samples. The first of each of the sub-samples were analyzed for 1,1,1-trichloroethane without treatment with popped corn. The second of each of the sub-samples were analyzed for 1,1,1-trichloroethane after contacting the sub-sample with a small quantity of popped corn. The samples are identified by letters Q, R, S, T, U and V. Samples Q, R and S had a ratio of popped corn to water of 1:15; samples T and U had a ratio of popped corn to water of 1:30; and sample V had a ratio of popped corn to water of 1:60. In Sample Q, the popped corn was ground prior to mixing in the water sample. The initial concentration of 1,1,1-trichloroethane was 400 ppm in samples Q, R, S and T and 200 ppm in samples U and V. the percent removal of 1,1,1-trichloroethane was 95%, 93%, 95%, 89%, 76% and 46% for samples Q, R, S, T, U and V respectively. 
     EXAMPLES VIII 
     The experiment of Example V was repeated but with toluene as the contaminant. The samples are identified as QA, RA, SA, TA, UA and VA. The initial concentrations of toluene were 2000 ppm in samples QA, RA, SA and TA and 1000 ppm in samples UA and VA. The percent removal of toluene was 97%, 76%, 74%, 62%, 71% and 46% for samples QA, RA, SA, TA, UA and VA respectively.