Liquid purification or separation – Filter – Material
Reexamination Certificate
2003-03-10
2004-09-07
Walker, W. L. (Department: 1723)
Liquid purification or separation
Filter
Material
C210S502100, C210S661000, C210S688000, C422S070000, C502S404000
Reexamination Certificate
active
06786336
ABSTRACT:
This invention relates to a novel method of effective wastewater treatment using a novel composite biosorbent. More in particular, this invention relates to a new and effective method of wastewater treatment utilizing a chitosan-coated biosorbent to remove heavy metals from wastewater containing the same. In one embodiment this invention relates to a novel method for preparing a novel chitosan-coated biosorbent. In another embodiment this invention relates to a novel biosorbent composition.
In yet another embodiment, this invention presents a novel composite biosorbent prepared from a biological material with a high affinity for heavy metals. A chitosan-coated biosorbent has a high affinity for heavy metal adsorption. Chitosan is coated on to a support material, such as a ceramic support material, to provide support and stability to the biomaterial and to facilitate column flow conditions and enhance mass transfer characteristics of the biosorbent material.
BACKGROUND OF THE INVENTION
It is not uncommon for some industrial processes, businesses or even naturally occurring geographical or weather phenomena to produce aqueous waste streams which contain one or more undesirable heavy metals.
Conventional known methods of treating such aqueous waste streams contaminated with an undesired heavy metal(s) to remove one or more of the heavy metals include chemical precipitation as hydroxides or sulfides, chemical oxidation or reduction, evaporation, carbon adsorption, ion exchange, flotation, centrifugation and membrane separate technologies. The estimated cost of the treatment for heavy metal contaminated wastewater range from $0.20-2.00 per gallon approximately depending on the concentration and type of the metals present in the waste matrix. Despite the aforementioned, industries such as metal plating and finishing industries continue to seek higher efficiency and more cost-effective technologies for treating the above mentioned aqueous streams whereby the heavy metals are removed from the wastestreams containing the same.
OBJECTS OF THE INVENTION
It is an object of this invention to provide a novel biosorbent composition for the effective treatment of aqueous systems containing heavy metals.
It is an object of this invention to provide an improved process utilizing a novel biosorbent composition useful for the effective treatment of waste streams containing heavy metals.
It is an additional object of this invention to utilize a chitosan-coated support material as a biosorbent composition for the effective treatment of waste streams.
It is an additional object of this invention to produce a biosorbent composition by utilizing a support material and coating it with chitosan and its equivalents and the like.
It is a further object of this invention to provide a chitosan-coated ceramic substrate for use as a biosorbent composition in aqueous waste streams.
It is an object of this invention to provide an environmentally friendly process to remove undesirable heavy metals from wastewater.
These and other objects are provided in this invention which is described in more detail hereafter.
BRIEF SUMMARY OF THE INVENTION
This invention comprises a process for preparing a supported chitosan biosorbent useful for the treatment of wastewater which comprises preparing a ceramic support material, preparing a chitosan gel, and coating said chitosan gel to said ceramic support material. This invention further comprises a novel biosorbent composition as well as a process for preparing and utilizing a novel biosorbent utilizing chitosan, its equivalents and the like.
This invention also comprises a biosorbent composition comprising a support material coated with chitosan useful for treatment of wastewater.
This invention further comprises a process for treating aqueous systems containing heavy metals comprising adding a chitosan-coated biosorbent to an aqueous system.
This invention is further described in the detailed invention which follows.
DETAILED DESCRIPTION OF THE INVENTION
Chitosan has a structure chemically similar to cellulose. Chitosan has the repeating units of the saccharide pictured below.
Chitosan is a biomaterial derived from the deacetylation of chitin, a polysaccharide found in the exoskeleton of the shells of shrimp, crab and other arthropods.
Chitosan, useful for the practice of the instant invention described herein, is available from Aldrich Chemical (Aldrich Chemical Company Inc, 1001 W. Saint Paul Avenue, Milwaukee Wis. 53233-2641, USA).
Chitosans high affinity for metals adsorption is well documented in the literature. However, if chitosan is used in a flow column in its natural flake form, gelling and associated hydrodynamic flow problems arise due to the fact that the metal binding sites of the chitosan are not fully exposed for adsorption in its flake form. In order to overcome these problems, it has now been discovered that chitosan is coated on to a support material. It has further been discovered that support material facilitates column flow conditions and enhances mass transfer characteristics of the chitosan.
Support materials useful for the practice of the instant invention are appropriately selected so that the support material accepts and retains the chitosan gel of the instant invention for a sufficient time.
One embodiment of this invention comprises ceramic support materials coated with chitosan. Nonlimiting examples of ceramic support materials useful herein include alumina and silica (available from Aldrich Chemical Company, Inc., 1001 W.Saint Paul Avenue, Milwaukee, Wis. 53233-2641, USA and Sumitomo Chemical America, Inc., One California Street, Suit 2300, San Francisco, Calif. 94111, USA). Penile is also a support material useful for the practice of the instant invention.
A preferred support material is ultra fine ceramic alumina. Such useful ceramic alumina is available from Aldrich Chemical Company. Ultrafine ceramic alumina means having the property of particle size in the range of from about 10&mgr; to about 150&mgr;.
The process for coating chitosan on to a support material of this invention comprises producing a chitosan gel, producing a support material, and coating the chitosan on to the support material. Processes such as dip coating and spin coating are useful for coating the chitosan gel on to the support material.
The process of dip coating comprises the steps of preparing a ceramic substrate, preparing a chitosan gel, surface coating the ceramic substrate with chitosan, filtration of the coated biosorbent and coating a second surface coating of chitosan on the ceramic substrate.
A substrate to be utilized for dip coating can be prepared by drying a selected substrate (such as a ceramic substrate) in an oven and then storing the dried substrate in a desiccator. This substrate then can then be mixed with an acid. After acid treatment the substrate should be washed and dried again.
A chitosan gel to be utilized for dip coating can be prepared by adding about 3 to 10 grams of medium molecular weight chitosan to 100 ml of 10 wt % acid under constant stirring and heat addition a viscous mixture is formed.
The now prepared chitosan gel can then be coated on to the acid treated and dried substrate by diluting the chitosan gel with water under heat. The acid treated substrate can then be added to the diluted gel and stirred for about 36 hours.
After stirring, the contents are allowed to settle, and any clear liquid produced is filtered out under vacuum. The filtered material (chitosan biosorbent) should be washed with deionized water and dried in an oven at 55° C. under vacuum for 24 hours. The dried chitosan biosorbent can then be stored for a second coat of chitosan.
A second coating of chitosan can be applied by treating the once coated substrate again with chitosan-acid gel under constant stirring conditions for approximately 24 hours. Again, the mixture is allowed to settle. The supernatant liquid can then be decanted. The solid, pasty material recovered can then be treated with 125 ml of 1 N NaOH. This alkaline mixture should then be stirred aga
Boddu Veera M.
Smith Edgar Dean
Menon Krishnan S
The United States of America as represented by Secretary of the
Thompson & Coburn LLP
Walker W. L.
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