Wastewater Treatment: BJAAM's B-CLEAR^™ Family of Products

In the field of wastewater treatment, many techniques are available to help remove contaminants, reduce or eliminate the hazardous nature of the effluent, and prepare the water for release into the environment. Most of these techniques are multi-step, and require considerable time and extensive handling to accomplish the task of removing suspended solids, oils, and metal ions from the water. Even if the problem of time and handling are alleviated, a significant problem remains. For most of the methods available, the residues from these treatments are still classified as a hazardous waste. Currently, the accepted best available treatment for most of these residues is to stabilize them in a matrix that will not allow any leaching of hazardous materials into the surrounding environment. This requires an extra manipulation that adds time and even more cost to the operations of already overburdened treatment facilities. However, using the appropriate formulation from the B-CLEAR^™ family of wastewater treatment products, these laborious, multi-step processes can be reduced to a simple and efficient operation that clarifies the contaminated water in a single step, and yields a non-leachable, non-hazardous solid as the only by-product.

Wastewaters contain a mixture of suspended solids, dissolved metals, ions, and organic contaminants. The science of wastewater treatment is predicated on the concept of precipitating these species out of solution into an aggregated mass that either floats on the surface where it can be skimmed off, or sinks to the bottom where it can be removed by filtration or decantation. The process of forming that solid is called flocculation, and the solid that forms is called a floc (actually short for floccule, although the term is no longer used). The mechanism of flocculation is complex, and involves the presence of extremely tiny colloidal particles (<1 micron) and dissolved ions. All particles exert forces, both attractive and repulsive, on each other. For colloidal particles, the attractive forces are much weaker than the repulsive forces; that fact, coupled with their extremely small size, allows them to remain suspended in solution. However, under the right conditions, the attractive forces can be strengthened and the repulsive forces shielded so that floc can be formed.

The traditional approach to purifying wastewaters containing particulate, oils, and dissolved metals involves flocculating these contaminates. This is accomplished by successively adjusting the wastewater conditions to the point where each particular class of contaminant will become insoluble and agglomerate into a small mass that can be removed from the much larger volume of purified water.

The first step usually consists of adjusting the water to acidic conditions to break any oil emulsions that may exist. Most of the oil will float to the top of the tank where it can be removed by skimming. A cationic polymer (called a flocculant) is typically added at this point to attract negatively charged species in the water, as well as any remaining oil. When the polymer performs properly, it flocculates into a mass that can be removed from the water by decantation and filtration. The water must be tested to be sure that enough oil has been removed to achieve appropriate standards. If it does not pass this test, the treatment is repeated until it does. This process is often time consuming, because a certain amount of trial and error is frequently required to find the right polymer for generating a floc that is dense enough to separate the oil. Often the polymer/oil interaction is not particularly strong. Since oil and water do not mix, whereas like materials are readily soluble with each other, the oil tends to associate with the polymer chains because they are more similar to the oil than the water. However, since the polymer is polar enough to be soluble in water, it becomes only slightly more desirable as a partner for the oil than the water. If enough water washes through the polymer/oil floc, the two will separate. Such a floc is unlikely to pass the leachability test for hazardous materials.

Once the water has passed the tests for residual organics, it is taken to another holding tank and made caustic to precipitate any dissolved heavy metals. This step again is time consuming, and requires the use of large quantities of base material to elevate the pH of the wastewater. Anionic polymers are then added to collect the metals and flocculate them into a separable solid. The polymers available for this task are usually quite good, and for heavy metals under the proper circumstances, claims of non-leachability are probably valid. But again, the time and monetary investment is considerable.

Finally the water is separated and tested to insure that the metal species have been eliminated. If heavy metal treatment is successful, the wastewater is then neutralized and released. Unfortunately, the sludges left from such operations are enriched in heavy metals, oils and greases. Typically, these sludges are hazardous.

A much better alternative is a one-step system that accomplishes all of these procedures in a very short period of time, with no additional chemicals required. The B-CLEAR^™ line of products accomplishes these goals in a single vessel in minutes instead of hours. With the B-CLEAR^™ products, all of the contaminant materials settle to the bottom of the vessel as a floc that can be easily filtered and disposed of as a non-hazardous waste.

The B-CLEAR^™ line is a series of dry powders composed of minerals, acids, bases and polymers blended into complex and carefully controlled formulations. The B-CLEAR^™ products take a wastewater stream through each of the treatment steps that a traditional system would use. The process occurs quickly and sequentially without the need for extra holding tanks or constant supervision. This is accomplished by employing the different solubility rates of each of the ingredients so that they become active at just the right time to accomplish the task at hand.

The acidic portion of the formulation goes into solution first. The result is a reduction of the pH of the water, which breaks any oily emulsions. Cationic (positively charged) polymers then attract the oil and some of the sparingly soluble, negatively charged species such as phosphate or sulfate. The montmorillonite clay particles also participate as an absorbent for the oil.

The base components go into solution next, taking the pH high enough to trigger the removal of any metals from solution as insoluble hydroxides. These combine with the polymers and clay to form a thick, easily separated mass.

There are additional benefits afforded by the clay. Many materials used to absorb wastewater contaminants do their job by purely mechanical means, and do not actually bond the offending material very strongly. Flyash, for instance, simply absorbs the offending molecules to its surface, holding them there by very weak intermolecular forces. In contrast, clay - and specifically bentonite clay - is extremely effective at removing certain cationic components from wastewater. Bentonite has a remarkable affinity for metals, particularly heavy metals in solution. These metals become bound in the clay through the process of ion exchange, which is driven by electrostatic attractive forces between the metal ion contained in solution, and the anionic surfaces of the clay particles.

Ion exchange is a process whereby charged ions are exchanged for one another on a solid support. It is the principle involved in the softening of water in commercial and residential water treatment systems. The bentonite used in B-CLEAR^™ is an anionic (negatively charged) solid. This negative characteristic is a consequence of unbalanced oxide ions in the clay's molecular structure. In any system, negatively charged particles must be balanced by pairing with positively charged ions. In this system, especially at the high pH involved, most of the anionic oxide sites are paired with sodium or calcium ions. However, these ions are very soluble in water and are constantly changing positions within the clay structure. Heavy metals, on the other hand, are much less soluble in water under alkaline conditions. Furthermore, they form a much stronger bond with the bentonite than either the sodium or calcium ions. Whenever a heavy metal ion encounters a loosely -bonded sodium ion residing on a clay surface, it replaces it. The resulting heavy metal cation/clay association is stronger, because the charge to radius ratio of the heavy metal cations is greater, thereby favoring the development of more highly localized charge density on those cations. Such cations possess fewer molecules of water in their hydration spheres, and consequently are more strongly attracted to the negatively charged clay surface (i.e. - via powerful electrostatic attractive forces). Under these conditions, the heavy metal cations are essentially completely immobilized.

Normally, such binding action would be quite adequate to accomplish the removal of this portion of the waste. However, given today's environmental standards, the toxic leachability of the resultant waste is also extremely important. An additional advantage of the B-CLEAR^™ system is that it forms easily de-watered sludges which pass the TCLP leach test. The non-leachable characteristic of the final floc is a consequence of two additional properties of the B-CLEAR^™ system: first, under the right conditions, clay particles are attracted to each other; and secondly, the resultant clay/floc mass can form a pozzolanic (cementitious) material. These two properties allow for the isolation of the contaminants by a process that we refer to as microencapsulation. The fact that clay particles can be attracted to each other is a very interesting phenomenon in colloidal science. Basic physics tell us that like-charged bodies repel each other and oppositely charged bodies attract each other. In the absence of such charge interactions, molecules and atoms are still weakly attracted to one another by a second set of forces often referred to as Van der Waals forces, named after the Dutch scientist who first postulated them. These Van der Waals forces are much weaker than the electrostatic forces involved in the charge interactions. So in a simple colloid solution, (roughly any system of particles whose diameters are < 1 micron) such as suspended clay particles, the particles stay suspended because the repulsive forces between the particles exceed the attractive Van der Waals forces. With just clay in solution, the sodium cations that counterbalance the negatively charged surface sites are well hydrated. In this highly shielded state, they can drift quite far from the surface of the clay particle. Under these conditions, if two clay particles begin to approach each other, they will be repulsed as both particles possess significant numbers of negative (like) charges. However, when treating with B-CLEAR^™ , extra B-CLEAR^™ chemical is added to make the solution quite over-saturated with cations. Under these conditions, the extra cations are less fully hydrated and are forced into tighter association with the clay surface. Consequently, the clay particles begin to act as if they have no charge (i.e. - the cations are so close to the clay surface, the particles act as if they were neutral). The weakly attractive Van der Waals forces then take over and pull the clay particles toward each other. When they get close enough together, they bond to one another. This gathering together of the individual particles is the beginning of the process of flocculation. To some degree, all of the species in solution are affected by both Van der Waals and the electrostatic forces, not just the clay particles. Inevitably, the positively charged polymer molecules and their absorbed contaminants also get bound in this floc and precipitate out of solution as the clay floc grows.

The final property requiring attention is the pozzolanic nature of the clay. This property is key in the B-CLEAR^™ approach to removing waste contaminants from solution. The term pozzolan (sometimes spelled pozzuolan) is derived from the name of the Italian village Pozzuoli, found near the base of Mt. Vesuvius. During the time of the Roman Empire, volcanic ash from this area was mixed with water and lime to make a cement mortar. That mortar was used in the construction of most of the ruins that still exist in Rome. Today, we define pozzolans as silicon and aluminum-based materials that can react with lime to form rock-hard, non-porous solids when mixed with water in the right proportions. Theses reactions are often called pozzolanic reactions. There are many materials available today that fit this definition. Examples are fly ash, pumice, opaline shales, diatomaceous earth, and, of course, bentonite clays. In fact, Portland cement uses this same type of reaction to cure into its final form. Pozzolanic reactions occur when lime and pozzolanic materials combine to form the permanent, covalent bond that define a solid structure. In an idealized fashion, these reactions fall into three categories:

These chemical equations define the formulation of calcium silicates, aluminates and aluminosilicates from the reaction between lime and the silicon and aluminum oxides that are basic constituents of the pozzolans. In the B-CLEAR^™ formulations that involve them, the inorganic bases in solution are believed to react with the bentonite clay as it flocculates according to the equations described above. In this way, they form very intractable solid particles that precipitate from solution. Once formed, these particles are amazingly resistant to leaching under TCLP test conditions.

Summarizing, we can describe the operation of B-CLEAR^™ in the following way. First the acidic component of B-CLEAR^™ causes oily contaminants to coalesce and separate from the water. Next, the polymeric cationic portion of the formulation attracts any remaining oil and larger, more highly charged anions (such as phosphate and sulfate). Finally, the basic component helps precipitate metallic hydroxides and drives the system to a fully flocculated condition. This condition results when cationic polymer molecules (with any absorbed oil) and metallic ions are all attracted to the clay. Any unprecipitated heavy metal cations still remaining in solution will ion-exchange with the sodium on the clay and become strongly bound to the clay structure. The resulting mass is a complex mixture of encapsulated contaminants and clay solids held together by Van der Waals and electrostatic forces. The clay particles then begin to bond together, entrapping the other components and surrounding them completely. Once the pozzolanic reactions begin between the lime and the bentonite, the process of microencapsulation is complete. The water is clear, and the entire process is over in just minutes.

At this point, the flocculated and solidified waste mass is non-leachable. This has been tested in independent laboratories for an assortment of formulations in the B-CLEAR^™ family of products. The contaminants are microencapsulated and are surrounded by a barrier of clay particles making it nonreactive to external leaching.