Liquid purification or separation – Processes – Utilizing electrical or wave energy directly applied to...
Reexamination Certificate
2000-01-26
2002-10-29
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Utilizing electrical or wave energy directly applied to...
C210S702000, C210S767000, C210S903000, C210S906000
Reexamination Certificate
active
06471873
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrolytic techniques for treating and purifying contaminated aqueous solutions and remediating soil in situ by irrigating the soil and then treating the resulting contaminated aqueous solution electrolytically. As used herein, the term “contaminated aqueous solutions” refers to bulk aqueous solutions containing concentrations of colloidal particles, heavy metals, phosphate-containing species, micro-organisms, nitrogenous species, soluble organic matter, dissolved solids such as inorganic mineral salts, or any combination thereof.
BACKGROUND OF THE INVENTION
Purifying Contaminated Aqueous Solutions
Present state-of-the-art techniques for treating and purifying contaminated aqueous solutions, such as sanitary wastewater, drinking water, groundwater and landfill leachate, primarily involve bio-oxidative techniques. Application of these bio-oxidative techniques is limited by serious problems. U.S. Pat. No. 5,853,588 to Molof, et al., notes that transient conditions generate a chemical imbalance which does not allow for adequate phosphate removal. U.S. Pat. No. 5,514,277 to Khudenko describes factors that complicate anaerobic digestion in standard biological treatment.
Conventional wastewater treatment, as presently practiced, typically involves three stages, namely, primary, secondary and tertiary treatment. Some form of sludge is usually generated at each stage. Sludge is mainly a material of bacterial origin formed at all three stages of conventional treatment but largely produced from the bio-oxidative (secondary) treatment stage. Sludge, a highly viscous concentrate of settled colloidal suspension with a mushy or mud texture, is the solids material which settles out during various stages of conventional wastewater treatment and which has to be processed and dewatered prior to being hauled off site for disposal.
Conventional Wastewater Treatment Stages
Primary treatment is the first stage of the process using mechanical methods to separate and remove sand, grit and larger solids from the influent (untreated or fresh wastewater). Screens, settling tanks and skimming devices are commonly used to effectuate the separation. The solid material which settles out in this process is generally referred to as “primary sludge”.
Secondary treatment follows primary treatment and typically involves bio-oxidative techniques for reducing suspended, colloidal and dissolved organic matter in the effluent emanating out of primary treatment. Bio-oxidation, at best, produces sludge and usually performs less than ideally in practice due to a number of operational problems, such as toxic loading and temperature depressions. Activated sludge and trickling filters are two of the most common means of secondary treatment. In secondary treatment, wastewater typically passes through a series of holding and aeration tanks and ponds to further remove floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection, typically by chlorination, is the final step in secondary treatment.
Tertiary treatment encompasses the additional treatment of effluent beyond that of primary and secondary treatment methods, generally by chemical or physico-chemical means. It involves selected biological, physical and chemical separation processes to remove additional pollutants such as nitrogen and phosphorous. Examples of tertiary treatment include activated carbon treatment, removal of ammonia by anaerobic denitrification, removal of phosphates by liming, and germicidal treatment by ozonolysis, ultraviolet irradiation and chlorination. All such tertiary treatments are usually very expensive to operate and most often require the addition of chemical agents which always leave some unpleasant residue in the effluent.
Conventional tertiary treatment to remove ammonia cannot proceed by the direct transformation of ammonia to nitrogen gas, but must proceed by anaerobic denitrification whereby ammonia is oxidized to terminal nitrate ion and then anaerobically converted back to nitrogen gas.
A basic problem with anaerobic denitrification is that wastewater is typically poor in carbon compounds. Biological tertiary treatment to remove ammonia requires additional carbonaceous input to insure sufficient presence of carbon to support the bacteria that carry out the treatment. Such addition of carbon results in the further production of residual solids (often referred to as “tertiary sludge”). Phosphate removal accomplished by liming also produces additional tertiary sludge.
The concentrated solids residue remaining after secondary or tertiary treatment is further processed for reuse and/or disposal. Residual solids which purportedly meet certain health and safety criteria are called “biosolids” and can be recycled as fertilizer/soil conditioner, burned to produce energy, or made into other useful products. Residual solids which do not meet such criteria are called “sludge” and must be hauled off site for disposal by means other than land application. The final solids by-product of conventional wastewater treatment systems falls within the category of sludge.
Problems with Conventional Wastewater Treatment
U.S. Pat. No. 5,837,142 to Mullerheim further describes the problems and complications associated with conventional wastewater treatment systems, which involve biological digestion of wastewater in the liquid phase. As indicated by Mullerheim, the digestion process is susceptible to disturbances of flow, nutrient loadings, temperature, chemical content, accumulated sludge levels and other influences. Digestion requires long retention times in large tanks. Close supervision of the process by skilled operators is often required for acceptable performance, although such supervision is no guarantee of a good outcome. In secondary treatment, organic nitrogenous wastes are not entirely removed by the processes, but rather, are converted into soluble nitrate compounds that could potentially pollute surface and ground waters.
The proper disposal of sludge has become a major problem by virtue of its ability to collect and retain heavy metals and toxic chemicals present in a waste stream, as well as its daunting physical properties and large water content. Incineration, landfilling, and ocean dumping all have major flaws and are strictly regulated. Due to the presence of bacteria in sludge, the impact of the disposal of sludge by land application is the likely invasion of the soil by heavy metals, toxic chemicals and pathogenic agents, in which case groundwater can be contaminated and can spread disease causing bacteria.
The problems and complications associated with conventional wastewater treatment systems are also encountered in the treatment and purification of other contaminated aqueous solutions.
Non-biological Processes
Products and processes developed for treating wastewater and other contaminated aqueous solutions by non-biological means have not found widespread use. Such approaches have involved electrolysis; the use of incineration; chemical treatment with coagulants, flocculants, adsorbants, filter aids and oxidants; radiation from nuclear sources; and physical treatments such as air flotation, filtration and centrifuging. Chemical and incineration approaches have been very expensive and energy intensive, often producing chemical laden sludges and air contaminants, which in themselves present a pollution problem. Filtration has been relatively unsuccessful because of the inability to achieve high rates of solids removal without fouling of the filters and frequent need for backwashes which in themselves create a disposal burden.
Electrolytic Removal of Contaminants
Various methods have been reported for electrolytically removing contaminants from aqueous solutions. U.S. Pat. No. 5,531,865 to Cole describes a method using an electrolytic apparatus wherein the electrodes include at least one elongate cathode and one or more elongate sacrificial floc-forming anodes aligned parallel with the cathode. The method described
Greenberg Bernard
Sulner Andrew
Gottlieb Rackman & Reisman P.C.
Hoey Betsey Morrison
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