Coagulant residual monitors perform on-line chemical analyses of residual coagulant to indicate whether something is affecting the coagulant dose. Adjusting the dose is one way to reduce the amount of residual aluminum in finished water. Although coagulant residual monitors do not directly determine whether an overfeed or underfeed occurs, they do provide a useful tool for optimizing water treatment. Aluminum salts neutralize electric charges and thereby facilitate floc formation. Streaming-current detectors operate on line to measure the charged environment of the particle and colloid, and can also be used to adjust the coagulant dosage accordingly.
Efficient flocculation is a key process in controlling residual aluminum.
The speed and efficiency of this reaction is determined partly by the pH of the water. Manipulating the water's pH to favor the formation of hydroxide floc helps to ensure that much of the aluminum will be removed in the form of floc during sedimentation and filtration. Finally, operating filters to produce water with turbidity below the 0.1-ntu range minimizes the amount of aluminum floc particles in finished water. Using Coagulant Aids. In some circumstances, coagulant aids such as activated silica, polyelectrolytes, weighing agents, and absorbents can reduce alum usage.