STORMWATER POLYMERS DESCRIPTION
Tramfloc offers a complete line of stormwater polymers for water clarification of stormwater runoff. The stormwater polymers product line includes a series of synthetic organic polymers which possess a progressive degree of anionic or cationic charge. These stormwater polymers are designed for use as primary coagulants or as flocculants for clarifying stormwater runoff. Previously, stormwater was directed to ponds, lakes, streams and other large bodies of water, both fresh and sea water, while bypassing POTW. Today, regulators demand that stormwater runoff be treated with stormwater polymers to remove objectionable contaminants such as FOG, TPH, dirt, metals and other debris which might adversely impact the water quality of the receiving water body. The regulators now mandate improved environmental quality by accepting only stormwater runoff which has been treated with stormwater polymers before discharge into a public waterway.
WATER CLAIRIFICATION PRINCIPLES – How to Treat with Stormwater Polymers
The purpose of stormwater clarification is to remove the suspended particles which are adsorbed from rainwater falling upon asphalt and concrete pavement, dirt, sand mineral stock piles, leaks of both benign and hazardous liquids and the like contaminants. Such removal is necessary to prevent over loading the POTW or private WWTP with various suspended solids. Because larger particles such as sand are removed quite easily by settling, the basic problem of clarification is to remove the stabilized colloidal particles which will not settle naturally. Leaf litter and other naturally occurring organic material help to stabilize the suspended solids and make clarification more difficult. The application of stormwater polymers is even more crucial under these circumstances. The colloidal particle may consist of clay and silt, color bodies, precipitated iron or manganese oxides, and even bacteria and algae and other organic species.
Coagulation is generally taken to mean the neutralization of particle charges and the initial collision and coalescence of two or more particle to form “micro-flocs” due to natural Brownian movement in the body of the water. Coagulation is only the first step of clarification with stormwater polymers because the mico-flocs that are formed are still virtually invisible and too small to settle in a sedimentation basin. Gentle stirring of the water is then applied to cause further collisions of the mico-flocs, so that further growth occurs into floc particles of sufficient size to settle rapidly in a sedimentation basin. This growth, due to externally applied movement, is termed flocculation. Stormwater polymers aid greatly in this flocculation process because they possess numerous sites on the same polymer chain which can absorb additional colloidal particles so that a bridging action occurs.
CATIONIC POLYMERS FOR STORMWATER
Cationic organic polymers of appreciable charge density like DMDAAC based cationic flocculants are primary stormwater polymers just as are the conventional inorganic coagulants, alum and iron salts, which hydrolyze to form inorganic cationic polymers. They cannot be added to water without neutralization of all of part of the negative charge on the colloidal particles which results in coagulation. Since they are relatively high molecular weight polyelectrolytes, these stormwater polymers aid flocculation by their bridging action and are more effective in this respect than the hydrolyzing inorganic coagulants. However, because the molecular weights of stormwater polymers usually decrease as the cationic charges increase, frequently, they are less effective bridging agents then nonionic and anionic organic polymers.
Cationic organic coagulants may be used alone as stormwater polymers or in conjunction with lesser amounts of inorganic coagulants in much the same way as when both alum and iron salts must be used to clarify water. Much depends upon the total mixing time available. The organic cationic polymers have a relatively slow destabilization time (time required for adsorption, charge neutralization and initial floc formation) as compared to the inorganic coagulants. Since existing plants are designed for inorganic coagulants, the most effective and economical application of stormwater polymers in existing plants is usually to use from 0.25 to 3 ppm of organic polymers to replace 40-60% of the alum or iron salts previously used. The use of the inorganic coagulant speeds the total destabilization time to accommodate the short mixing times encountered. The use of the organic polymer reduces treatment costs considerably.
In several systems it has been possible to feed the stormwater polymers into the raw water line far enough upstream from the plant to obtain several hours of additional mixing time in the line. In such cases, as little as 0.5 ppm of the stormwater polymers has improved clarification considerably and eliminated the use of alum and activated silica as well as lime. Even when stormwater polymers is used with alum, it is usually better to feed it into the raw water line ahead of the rapid mix to obtain a maximum of mixing time. It is also sometimes advantageous to premix the stormwater polymers solution with the inorganic coagulant solution. However these factors do not hold true with nonionic or anionic organic polymers which function by bridging action alone.
NONIONIC AND ANIONIC STORMWATER POLYMERS
Nonionic, anionic and even weakly cationic organic polymers function basically as flocculants or stormwater polymers rather than as primary coagulants. They have little or no effect in neutralizing negative particle changes, but instead function by improving the bridging action of the primary coagulants. Because of their very high molecular weight, they are much more efficient bridging agents then the cationics and are used primarily to produce much larger and tougher flocs to overcome serious flocculation and floc carryover problems. Stormwater polymers are more frequently employed in industrial water clarification plants where high rate up flow clarifiers are the rule and filters are frequently omitted. Because of improved flocculation with the stormwater polymers, they frequently permit appreciable dosage reduction of alum or other primary coagulants but not usually as much as can be obtained with strongly cationic polymers, Their primary purpose usually is to improve results rather than to reduce treatment costs. Nonionic polymers are perhaps the most reliable coagulant aids inasmuch as drastic overdoses have little or no effect on zeta potential. However, over treatment is still possible since good flocculation does not occur if more than 50% of the particle surface is covered by a general or stormwater polymers.
Anionic polymers frequently give the best bridging action because their polymer chains are more uncoiled and therefore exposed to a greater number of separate particles when added to the water. They also have the highest molecular weights which are indicative of longer chain lengths. Anionic stormwater polymers may function as primary coagulants when the colloidal particles are positively charged such as occurs in lime or lime-soda softening processes. In these processes, when pure calcium carbonate precipitates, it carries a negative charge. However, when calcium carbonate precipitates with magnesium or even in the presence of considerable magnesium still in solution, the particles have a positive charge. For this reason,Tramfloc® 100 Series stormwater polymers have widespread use as coagulants for softening applications.
When nonionic or anionic organic polymers are used as coagulant aids with inorganic coagulants, dosages in the range of 0.1 to 0.5 ppm are most frequently employed. Dosages from 0.1 to 0.2 are usually sufficient for most waters. Like most coagulant aids, these stormwater polymers are usually most effective when fed shortly after the primary coagulant or at the point of initial floc formation.
FEEDING ORGANIC STORMWATER POLYMERS
Detailed instructions for dissolving and feeding each of the Tramfloc stormwater polymers products discussed herein are given in individual product bulletins which are available upon request or via our website, www.tramfloc.com. A few general principles, however, apply to all stormwater polymers. They have very large molecules and are effective only when they are thoroughly mixed and dispersed with the water to be treated so that all colloidal particles can be contacted evenly. Absorption of too little or too much stormwater polymers some particles results in incomplete coagulation or flocculation. Adsorption of too much stormwater polymers on some particles can result in the destabilization of these particles on the positive or negative side depending upon the type of polymer used. This is the most frequent cause of the haze that is left in some settled waters. The haze can best be eliminated and more uniform coagulation obtained by using more dilution water with stormwater polymers solution prior to application and by using multiple addition points to provide more rapid distribution of the large polymer molecules throughout the stormwater polymers that is being applied.