This invention relates in general to water treatment but specifically to methods and compositions for rectifying the land which water passes over, around or through in a manner that simultaneously reinforces the compressive strength of the land while retentively filtering certain toxic waste from the water.
Mining, excavation, drilling operations, processing of hazardous or offensive waste materials, disposal of combustion by-products, and other industrial or municipal activities have reached critical proportion in modern day society. As a consequence thereof, the quality of the environment in many geographical areas has become of such great concern that highly restrictive laws and regulations have been promulgated to protect our land, water and other natural resources.
In an attempt to comply with these laws, many products and processes have been developed to curtail further environmental destruction. Very few of these techniques, however, serve to rectify pre-existing environmental problems, particularly those problems associated with certain ground water passages such as abandoned mine shafts, pits and waterway bottoms of streams, lakes, ponds and spillways.
The prior art waste treatment processes tend to be complex and expensive ancillary stages to the actual production of goods and services that fuel our economy and often times burden the consumer with ever increasing cost in the way of increased prices and/or taxes. For example, batch waste treatment plants have been developed to retard infusion of hazardous waste into the local water system, but offer little rectification to pre-existing contamination. Additionally, such plants require collection and disposal of the extracted waste, which in turn creates additional cost to consumers. Disposal of the waste often transfers the problem to yet another geographical site where the expensive cycle may in-part be repeated.
More specifically, the U.S. Environmental Protection Agency in implementing the hazardous waste control program under the Resource Conservation and Recovery Act of 1976, promulgated in 1980 a series of regulations. The regulations require that sludges, slurries and other liquid wastes containing specified hazardous materials be pretreated, stabilized and dewatered prior to disposal in landfills. Additionally, the toxicity of the wastes must be measured and maintained at certain acceptable levels. One primary goal of these requirements is to achieve a non-flowing consistency to the waste. Accordingly, either the liquid content is reduced or the solid content is increased to eliminate the presence of free-standing liquid prior to final disposal in a landfill, and a number of proprietary means for dewatering, chemical fixation, solidification or combinations thereof have been developed.
Among the prior art methods for "chemical fixation" are those which detoxify, immobilize, insolubilize, or otherwise render the waste material suitably fixed and less hazardous for ultimate disposal in landfills as for example by ocean dumping, etc. U.S. Pat. No. 3,837,872 discloses a method for treating liquid wastes by adding an aqueous solution of alkali metal silicate and silicate setting agent, which converts the waste into a chemically and physically stable solid product. Other prior art chemical fixations which will be familiar to those skilled in the art are achieved through "encapsulation", "crystalline capture", and "pseudo mineralization".
The term "solidification" is employed in the waste treatment art to describe transformations of flowable waste residues into solid physical forms which are more stable for storage, earthen or ocean disposal, transportation, or re-use in construction such as highway pavement. For example, U.S. Pat. No. 3,980,558 discloses a method for treating liquid wastes by adding a solidification agent consisting essentially of hydraulic cement. Although such solidification does not directly convert or change the hazardous potential of the waste, it does create a barrier between the waste particles and the environment, limiting permeability of the waste and reducing the amount of surface area exposed to any diffusing waste. Oftentimes, drying, filtration or other forms of dewatering are categorized as solidification. U.S. Pat. No. 4,518,508 describes a solidification which involves cement, an absorbent material, and a powdered alkali metal silicate.
Conventional chemical fixations and solidifications have many shortcomings not the least of which is their inability in certain applications to provide suitable end products. Generally, prior art fixation and solidification techniques are only suitable for sludges and slurries containing substantial solids contents. For example, dewatering techniques frequently cannot achieve acceptable solid forms on slurries because of the difficulty in preventing reversion back to the original state. Moreover, the absorbed liquid phase of many fixed or solidified wastes can often be repatriated under the mechanical pressure which occurs in landfills or during handling and transportation. Attempts at compensating for these shortcomings through the infusion of special additives, binders or adsorbents has been expensive, impractical, and led to cumbersome duplicity in waste processing from one site to the next.
"Stabilization" is essentially a pretreatment process which alters waste to prevent further chemical reactions, e.g. the use of lime in biological sludges to kill or inactivate micro-organisms so that the sludge will not undergo further biological decomposition. Although stabilization is often considered a form of chemical fixation, there are subtle differences in the two. Nevertheless, many of the previously described problems are attendant to prior art forms of stabilization waste treatments.
Also, early methods of waste treatment which employed simple absorption techniques such as the addition of vermiculite, or solidification by large quantities of Portland cement to insure no free standing water after curing, gave rise to large volumetric increases in the material being disposed of. Although the system afforded the rapid setting rates essential to continuous processes, the disposal itself was prohibitively expensive as a consequence of excessive landfill utilization.
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