this case, polymers that are anionic and nonionic(usually anionic to a slight extent when placed in water) become attached at a number of adsorption sites to the surface of the particles found in the wastewater. A articles become intertwined with other bridged particles during the flocculation process. The si nsional particles grows un particle removal is to be achieved by the formation of particle-polvmer bridges. the initial mixing of the olvmer and the wastewater containing the particles to be removed must be accomplished in a matter of second Fig. 6-2 Particles in wastewa Panicle with adsorbed polymer efinition sketch for interparticle bridging about by perikinetic or orthokinetic fiocculation Charge Neutralization and Polymer Bridge Formation. The third type of polyelectrolyte action may be classified as a charge neutral ization and bridging phe oolvelectrolvtes of extremely high molecular weight. Besides lowering the surface charge on the particle, these polyelectrolytes also form particle bridges as described above Particle Destabilization and Removal with Hydrolyzed Metal lons In contrast with the aggregation brought about by the addition of chemicals that act as counterions, electrolytes, and polymers, aggregation brought about by the addition of alum or ferric sulfate is a more complex process. To understand particle destabilization and the removals achieved with hydrolyzed metal ions, it will be instructive to consider first the formation of metal ion hydrolysis products. Operating ranges for action of metal salts and the importance of initial mixing are also considered in light of the formation of these particles Formation of Hydrolysis Products. In the was thought that free al products are responsible. Although the effect of these hydrolysis products is only now appreciated, it is interesting to note that their chemistry was first elucidated in the early 1900s by Pfeiffer(1902-1907 Bjerrum(1906-1920), and Wemer(1907)(Thomas, 1934). It should be noted that the complex compounds group of surrounding molecules or ions by coordinate co known as ligands and the atoms attached directly to the metal ion are called ligand donor atoms Ligand compounds of interest in wastewater treatment include carbonate(CO32). chloride(C1). hydroxide (OH). ammonia(NH3) and water(H2O). In addition, a number of the coordination compounds are also amphoteric in that they can exist both in strong acids and in strong bases Over the past 50 vears. it has been observed that the intermediate hydrolysis reactions of Al(llD) are much more complex than would be predicted on the basis of a model in which a base is added to the solution. At the present time the complete chemistry for the formation of hydrolysis reactions and products is not well understood. A hypothetical model, proposed by Stumm for Al(lD), is useful for the purpose of illustrating the complex reactions involved. A number of alternative formation sequences have also been proposed Before the reaction proceeds to the point where a negative aluminate ion is produced, polymerization as depicted in the following formula will usually take place The possible combinations of the various hydrolysis products are endless, and their enumeration is not the purpose here. What is important, however, is the realization that one or more of the hydrolysis products and/or polymers may be responsible for the observed action of aluminum or iron Further. because the hydrolysis reactions follow a stepwise process. the effectiveness of alumin iron will vary with time. For example, an alum slurry that has been prepared and stored will it is added to a wastewater Action of Hydrolyzed Metal lons. The action of hydrolyzed metal ions in bringing about the destabilization and removal of colloidal particles may be divided into the following three categories6-5 this case, polymers that are anionic and nonionic (usually anionic to a slight extent when placed in water) become attached at a number of adsorption sites to the surface of the particles found in the wastewater. A bridge is formed when two or more particles become adsorbed along the length of the polymer. Bridged particles become intertwined with other bridged particles during the flocculation process. The size of the resulting three-dimensional particles grows until they can be removed easily by sedimentation. Where particle removal is to be achieved by the formation of particle-polymer bridges, the initial mixing of the polymer and the wastewater containing the particles to be removed must be accomplished in a matter of seconds. Charge Neutralization and Polymer Bridge Formation. The third type of polyelectrolyte action may be classified as a charge neutralization and bridging phenomenon, which results from using cationic polyelectrolytes of extremely high molecular weight. Besides lowering the surface charge on the particle, these polyelectrolytes also form particle bridges as described above. Particle Destabilization and Removal with Hydrolyzed Metal Ions In contrast with the aggregation brought about by the addition of chemicals that act as counterions, electrolytes, and polymers, aggregation brought about by the addition of alum or ferric sulfate is a more complex process. To understand particle destabilization and the removals achieved with hydrolyzed metal ions, it will be instructive to consider first the formation of metal ion hydrolysis products. Operating ranges for action of metal salts and the importance of initial mixing are also considered in light of the formation of these particles. Formation of Hydrolysis Products. In the past, it was thought that free A13+ and Fe3+ were responsible for the effects observed during particle aggregation; it is now known, however, that their hydrolysis products are responsible. Although the effect of these hydrolysis products is only now appreciated, it is interesting to note that their chemistry was first elucidated in the early 1900s by Pfeiffer (1902-1907), Bjerrum (1906-1920), and Wemer (1907) (Thomas, 1934). It should be noted that the complex compounds are known as coordination compounds, which are defined as a central metal ion (or atom) attached to a group of surrounding molecules or ions by coordinate covalent bonds. The surrounding molecules or ions are known as ligands, and the atoms attached directly to the metal ion are called ligand donor atoms. Ligand compounds of interest in wastewater treatment include carbonate (CO3 2- ), chloride (C1- ), hydroxide (OH), ammonia (NH3), and water (H2O). In addition, a number of the coordination compounds are also amphoteric in that they can exist both in strong acids and in strong bases. Over the past 50 years, it has been observed that the intermediate hydrolysis reactions of Al(III) are much more complex than would be predicted on the basis of a model in which a base is added to the solution. At the present time the complete chemistry for the formation of hydrolysis reactions and products is not well understood. A hypothetical model, proposed by Stumm for Al(III), is useful for the purpose of illustrating the complex reactions involved. A number of alternative formation sequences have 'also been proposed. Before the reaction proceeds to the point where a negative aluminate ion is produced, polymerization as depicted in the following formula will usually take place. The possible combinations of the various hydrolysis products are endless, and their enumeration is not the purpose here. What is important, however, is the realization that one or more of the hydrolysis products and/or polymers may be responsible for the observed action of aluminum or iron. Further, because the hydrolysis reactions follow a stepwise process, the effectiveness of aluminum and iron will vary with time. For example, an alum slurry that has been prepared and stored will behave differently from a freshly prepared solution when it is added to a wastewater. Action of Hydrolyzed Metal Ions. The action of hydrolyzed metal ions in bringing about the destabilization and removal of colloidal particles may be divided into the following three categories: Fig. 6-2