WO2001002304A1

WO2001002304A1 - Method and device for removal of environmental contaminants from water

Info

Publication number: WO2001002304A1
Application number: PCT/US2000/017697
Authority: WO
Inventors: Xiaoguang Meng; George P. Korfiatis
Original assignee: Stevens Institute of Technology
Current assignee: Stevens Institute of Technology
Priority date: 1999-07-02
Filing date: 2000-06-28
Publication date: 2001-01-11
Anticipated expiration: 2002-01-02
Also published as: AU6056900A

Abstract

A water filtration unit capable of removing heavy metals and pesticides from raw water is provided. A method for removing heavy metals and pesticides from raw water is also provided.

Description

METHOD AND DEVICE FOR REMOVAL OF ENVIRONMENTAL CONTAMINANTS FROM WATER

Background of the Invention

Concern over the safety of drinking water sources is a worldwide focus . Drinking water in developed countries such as the United States is monitored by local, state and federal regulatory agencies to assure it is free of dangerous environmental contaminants such as heavy metals and pesticides. Some of these contaminants, such as arsenic, are associated with human health effects such as cancer.

Heavy metals and pesticides are now ubiquitous in the environment, being found routinely in food and water. Many of the heavy metal compounds such as chromium, lead, mercury, cadmium, and arsenic are of particular concern in potable water, with specific government regulations addressing the issue of drinking water quality. Although industrial sources of some of the heavy metals such as lead, mercury, and arsenic have been greatly reduced or eliminated in the United States and other industrialized nations, environmental contamination is still a problem in developing countries around the world. In fact, arsenic levels in drinking water sources in some underdeveloped countries pose a significant risk to human health. As a result, there has been worldwide attention focused on ways to remove heavy metals and pesticides from drinking water sources.

Conventional treatment processes for removal of heavy metals from water are generally based on chemical precipitation and coagulation followed by conventional sand filtration (Dupont, A. 1986. Lime Treatment of Liquid Waste Containing Heavy Metals, Radionuclides and Organics, 7th edition, Washington D.C., pp. 306-312; Eary, L.E. and D. Rai . 1988. Environ . Sci . Technol . 22:972-977 ; Cheng, R.C. et al . 1994. J. AWWA 86:79-90). Sand filtration alone is not effective in removing heavy metals, especially arsenic and chromate, mainly because sand filter media have a low sorptive capacity for heavy metals. However, if the filter sand surface is coated with iron or aluminum hydroxide, the adsorption capacity of the filter media can be significantly enhanced (Meng, X.G. 1993. Effect of Component Oxide Interaction on the Adsorption Properties of Mixed Oxides , Ph.D. Thesis, Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY) .

In column studies, research has shown that cationic metals (Cu, Cd, Zn and Pb) can be removed effectively by sand and granular activated carbon coated with ferric oxide

(Benjamin, M. 1992. Metal Treatment at Superfund Si tes by

Adsorptive Fil tration, EPA/540/F-92/008 ; Jarog, D. et al .

1992. Adsorption and Fil tra tion wi th Oxide-Coa ted Granular Activated Carbon, ACS Meeting, San Francisco, CA, pp. 711-714; Edwards, M. and M. Benjamin. 1989. J^". Water Pollut . Control Fed. 61:1523-1533) . However, during these processes, sand and activated carbon have to be coated periodically prior to their placement in the filter. Further, the adsorptive capacity of the ferric oxide coating is much lower than that of fresh ferric hydroxide precipitate.

Microfiltration (Martin, J.F. et al . 1991. J. Air Waste Manage . Assoc . 41:1653-1657) and adsorption and magnetic filtration (Chen, W.Y. et al . 1991. Res . J. Water Pollut . Control Fed . 63:958-964) have also been studied as means of removing heavy metals from water. The microfiltration process includes precipitation and filtration in two steps. The main difference between this process and the traditional precipitation and filtration treatment is that the heavy metal precipitates are removed directly through a membrane filter, eliminating the coagulation step. In the adsorption and magnetic filtration process, heavy metals are adsorbed onto fine magnetic particles coated with ferrihydrite . The magnetic particles are then collected using a magnetic filter. Finally, the magnetic particles are regenerated by metal desorption and then reused.

In a Japanese patent (JP 10192849) , a bath water purifier is described that consists of a purifying material which is a mixture of a chelating agent in lumps of water soluble resin. When water contacts the resin mixture, the chelating agent is released and it then dissolves gradually. Heavy metal ions are removed by the chelating agent.

A German patent (DD 69089) , describes purifying arsenic compound contaminated water by adsorptive filtration after adding chlorine and adsorbent to form adsorbing flocculate in a filter bed. A metal hydroxide compound, iron hydroxide, is used as a flocculent and arsenic compounds deposit. The flocculent-arsenic mixture is then separated in a filter bed. Dermatas and Meng (1996. Removal of Arsenic Down to Trace Levels by Adsorptive Fil tration, 2nd Specialized Conference on Pretreatment of Industrial Wastewaters, Athens, Greece, pp. 191-198) developed an iron injection-sand filtration process for selective removal of arsenic from water. The process involved continuous injection of small amounts of iron solution into a packed-bed sand filter during filtration. Arsenic was removed down to trace levels in this single step process .

A water filtration unit has now been developed for removal of arsenic and other heavy metals, as well as pesticides, from drinking water. The units are designed for use in places without water distribution systems and with no power supplies, such as small villages in underdeveloped countries . Summary of the Invention

An object of the present invention is a water filtration unit which comprises a contained sand bed and a sedimentation chamber which is sized so that it can be placed within said container for the sand bed and which comprises a plurality of openings passing completely through the sidewall of said sedimentation chamber so that water can pass through said openings .

Another object of the present invention is a water filtration system that includes a coagulant compound which comprises an oxidizing agent and a coagulant and said water filtration unit.

Yet another object of the present invention is a method for removal of heavy metals and pesticides from raw water which comprises collecting raw water and mixing it with a coagulant compound, pouring the raw water coagulant mixture into a water filtration unit comprising a contained sand bed and a sedimentation chamber so that the raw water is filtered and heavy metals and pesticides are removed.

Detailed Description of the Invention

Much of the prior work on the removal of heavy metals from drinking water has focused on development of complex or large-scale water treatment systems for use on municipal water systems. A water filtration unit has now been developed that filters water and removes arsenic as well as other heavy metals and pesticides down to trace levels. The system uses a coagulant compound that is a mixture of a coagulant and an oxidizing agent, a unique filter device and a simple filtration process that does not require input of a power supply.

The water filtration unit comprises a contained sand bed and a sedimentation chamber which is sized so that it can be placed within said contained for the sand bed and which comprises a plurality of openings passing through the sidewall of said sedimentation chamber so that water can pass through the openings . The sand bed can be contained in any suitable container such as a column, bucket or other suitable container. For use by a single family, the sand bed can be contained in a bucket. The sand bed in this case need be only about six inches deep. In the case where a number of families or a small community are served by the unit, a container capable of handling a larger volume of water can be constructed from barrels or columns, for example. "Raw water" containing the arsenic or other heavy metals and pesticides is collected in any suitable container and mixed with a coagulant compound which comprises a coagulant and an oxidizing agent. Examples of the coagulants that can be used in this device would include but not be limited to ferric sulfate and ferric chloride. In one embodiment, the ferric sulfate concentration in the coagulant is in the range of 10 to 30 ppm. Examples of the oxidizing agents that are useful include but not be limited to potassium permanganate, sodium hypochlorite, calcium hypochlorite, and hydrogen peroxide. In one embodiment, the potassium permanganate concentration in the coagulant compound is in the range of 0.5 to 2.5 ppm. The coagulant compound may be in solid form, such as a powder or tablet, or a solution. In the case of arsenic removal from water, the arsenite [As (III)] and arsenate [As (V) ] ions are adsorbed by the coagulant solids. For example, permanganate in the coagulant converts As (III) to

As (V) , ferrous (Fe⁺²) ions to ferric hydroxides and manganous

(Mn⁺²) ions to manganic oxides or hydroxides. The As (V) ions are removed by the ferric hydroxide formed from the ferric sulfate and ferrous ions. After thorough mixing of the raw water and the coagulant compound, the raw water-coagulant mixture is poured into the sedimentation chamber of the water filtration unit.

The sedimentation chamber is sized so that it can be placed inside of the container for the sand bed. The sedimentation chamber is placed on top of the sand bed. The use of the sedimentation chamber protects the sand bed from being disturbed by pouring of the water and also acts as a basin for most particles that can settle out of the raw water. To treat water so that heavy metals and pesticides are removed, the raw water-coagulant mixture is poured into the sedimentation chamber of the filtration unit after mixing in the collection container. Most of the coagulant particles settle at the bottom of the sedimentation chamber. The clarified water then passes through the sand bed to complete the removal of the solids from the raw water. The filtered water then passes out of the bottom of the sand bed and the filtered or cleaned water is collected for use as drinking water. Experiments have shown that more than 95% of arsenic is removed from raw water when treated with this filtration unit. Results of other experiments testing removal of lead, chromium, mercury and a pesticide, dieldrin, from raw water are presented in Table 1.

Claims

What is claimed is:

1. A water filtration unit comprising (a) a contained sand bed and (b) a sedimentation chamber which is sized so that it can be placed within the container for the sand bed and which comprises a plurality of openings passing through a side wall of said sedimentation chamber so that water can pass through said openings and onto the sand bed.

2. A water filtration system comprising the water filtration unit of claim 1 and a coagulant compound which is mixed with collected raw water before it is poured into the filtration unit.

3. A method for removal of heavy metals and pesticides from raw water comprising: (a) collecting raw water and mixing the raw water with a coagulant compound;

(b) pouring the raw water coagulant compound mixture into a water filtration unit of claim 1 so that the raw water is filtered and heavy metals and pesticides are removed.