Furthermore, the process of coagulation uses higher viscosity fluids to treat the water. There are typically two types of viscous fluids found in these processes: Netwonian and Thixotropic.
Newtonian fluids have a viscosity that does not change based on the mechanical stress applied to it while thixotropic fluids have viscosity that changes under the application of mechanical stress or shear. Thixotropic viscosity is also known as shear thinning, and the viscosity reduces over time as the fluid shears. For this reason, it is important to select a pump product that is compatible with higher viscosities.
While the coagulation process is exceptionally critical, it can also be costly. Costliness is primarily determined by how much chemical is used in the process. While polymer may be more expensive by weight, it can be more efficient than an inorganic salt. Polymer efficacy can be increased by preparing the proper polymer volume to ensure it can fully react with the process water, which in turn reduces polymer usage and may have a cost advantage over the inorganic salt.
Inorganic chemicals require the water treatment operator to strike a balance which requires accurate dosing of chemicals. Too much chemical would likely require pH correction; while not enough chemical may lead to additional processing time to reach the desired condition.
Coagulation processes are time intensive and for that reason can be expensive. It is important for water treatment plants to optimize their process with cost effective technologies. Measurement devices such as Streaming Current Detectors measure net charge density of particles in a sample of water. These devices help improve and streamline coagulation processes because it measures in real time how well the process is working.
Additionally, flash mixing can be a major constraint for agitators in coagulation processes. Flash mixing in the coagulation process requires vigorous flow in a very short time period, typically less than one minute. For this reason, it is important to select a suitable motor and impeller to achieve the desired results.
While coagulation is primarily a chemical process; flocculation is the clumping of particles primarily via a physical process. Once the coagulation process has taken place, the flocculation process begins with agitation or mixing of the fluid. This allows some of the suspended solids to begin to bond together and grow in size into larger clumps. This process is assisted by the addition of flocculants and mixers.
After the colloidal particles have had their charge neutralized, mixing of the process fluid allows more of these particles to come together. The goal of this process is for the grouped particles to achieve a state in which they can be most easily filtered out of the water.
Mixing of the process water with the addition of adding flocculants allows for the colloidal particles to stick and form bigger and bigger clumps. The challenge with this process is that you must stir the fluid without separating the particles. For this reason, it is important to consider the mixing shear on the fluid.