The environment is considered as a composite term for the condition in which organisms live. Pollution of the environment is one of the most fatal ecological crisis to which we are subjected today. Earlier these amenities were pure, undisturbed and uncontaminated for living organisms. But situation is reverse today. The impurities present in water are threat to life. The impurities present in water and wastewater is decisive factor for selection of treatment scheme. Impurities are present in water in dissolved and suspended form. The suspended impurities present in water are non- biodegradable in nature. So it is necessary to remove suspension in water and wastewater. The coagulation-flocculation method is sustainable solution for different kind of surface water, ground water, synthetic water and industrial effluents. In conventional method, inorganic coagulants are used for coagulation-flocculation. But major drawbacks are high dosage of inorganic coagulants, poor results and large quantities of sludge generation. So, organic polyelectrolytes were introduced in conjunction with inorganic coagulants for the treatment of water and wastewater.

Treatment plants are faced with the challenge of stricter regulations and higher standards for finished water quality. New developments in control strategies and instrument design have overcome some of the previous limitations of monitoring and controlling the coagulation process. An online floc analyzer provides valuable information on the dynamics of particle aggregation subsequent to coagulation. Optimizing coagulation will form floc that is large and easily settled. Fractal analysis has suggested that diffusion and collision of colloidal particles limit particle aggregation. So, proper mixing is a major factor influencing floc formation.

Polyelectrolytes - the flocculation agents

Polyelectrolytes are chemical flocculants used in water treatment; they act mainly in the coagulation-flocculation stage and in the conditioning/thickening of the sludge line. Polyelectrolytes show many applications in fields, such as in water treatment as flocculation agents, in ceramic slurries as dispersant agents, and in concrete mixtures as super-plasticizers. Polyelectrolytes are long chain organic polymers often having molecular weights in excess of one million and are either natural or synthetic in origin. The term “polyelectrolyte” was introduced to include those polymers which, by some ion-producing mechanism, can become converted to a polymer molecule having electrical charges along its length. The electrical charges arise from, the presence of ionizable functional groups along the polymer chain. Polyelectrolytes are, therefore, polymeric-electrolytes, i.e., having characteristics of both polymers and electrolytes.

Commercial polyelectrolytes used in the aggregation of suspended matter are water-soluble. They may come in granular forms, in form of powder, or as highly-viscous liquids. All existing polyelectrolytes have a tendency to degrade when stored over a period of time – For a particular product, such a period is usually stated by the manufacturer. In general, the more dilute a polyelectrolyte solution is, the faster the degradation, which probably involves the breaking up of the long chains, resulting in decreasing viscosity.

Extent of utilization of polyelectrolytes

The use and importance of polyelectrolytes is increasing rapidly. The number of manufacturers producing these materials is likewise increasing. Synthetic polyelectrolytes have found considerable applications in the following broad areas:

Process industries

Industrial wastewater treatment

Water treatment

Domestic wastewater treatment

Commercially available polyelectrolytes include PolyDimethylammonium chloride (PolyDADMAC), Polyacrylic acid (PAA), and Polystyrene sulfonate. Commercial grades of polyelectrolytes (PAAs) are available from Dow Chemical (Duramax, Tamol, Romax, Dowex), Rohm and Haas (Acusol, Acumer), BASF (Dispex®, Magnafloc®), and Arkema (Rheoslove, Terrablend). Specific uses of polyelectrolytes in process industries include clarification of raw sugar juice in the sugar industry; separation of gypsum from wet process phosphoric acid; settling improvement in coal-washer operation; increasing thickener capacity in wet process cement manufacture; separation of clay impurities from hot borax streams; improving the quality of metal deposition in the electrolytic refining or electrowinning of copper and zinc; improvement of thickening operations in uranium processing, and so on. Polyelectrolytes can also be used to treat industrial wastewater. The fight against river pollution is getting more and more intense, and industries need all the help they can get. Polyelectrolytes are becoming an increasingly important factor in resolving these pollution issues. In the future, polyelectrolytes will have a greater impact on industrial wastewater treatment than on municipal wastewater treatment. This might be due to the fact that industrial wastewater treatment plants are not subject to the same constraints as municipal wastewater treatment plants. As such, industrial waste treatment plant designers may be more focused on reducing overall treatment plant costs than on whether those savings result from capital investments or operating costs.