Wastewater is used water that contains dirt and impurity includes substances such as human waste, food scraps, oils, soaps and chemicals. Businesses and industry also contribute to the amount of contaminated water that has to be cleaned. The main purpose of wastewater treatment is to remove as many suspended solids as possible before releasing the remaining water, known as effluent, to the environment. Solid material decomposes, which decreases oxygen, which is required by plants and animals.
Approximately 60% of suspended particles are removed from wastewater during "primary treatment." Aerating (stirring up) the wastewater to restore oxygen is also part of this treatment. More than 90% of suspended particles are removed during secondary treatment. If wastewater is not treated correctly, it can have a severe influence on the environment and human health. These can impact fish and wildlife species, oxygen levels decreased, beach closures and limits on recreational water usage, limitations on fish and shellfish harvesting, and occurring drinking water contamination.
Coagulation and flocculation are used to remove suspended particulates from water in waste water treatment. Although the concepts of coagulation and flocculation are frequently interchanged, or the term "flocculation" is used to define both, they are two separate processes.
Coagulation is the process of destabilizing colloids by removing the forces that hold them apart. Cationic coagulants lower the negative charge (zeta potential) of colloids by providing positive electric charges. As a result, the particles collide, resulting in the formation of larger particles (flocks). As a result, coagulation entails the development of smaller, more compact aggregates.
Meanwhile, Flocculation is a gentle mixing stage that transforms submicroscopic microfloc into visible suspended particles. When microfloc particles collide, they join together to form pin flocs, which are larger, visible flocs. Additional collisions and interactions with added inorganic polymers (coagulant) or organic polymers increase the size of the floc. Water is ready for sedimentation once the floc has acquired its optimal size and strength. One of chemicals used in the flocculation process is Polyaluminium chloride (PAC) which is used in the treatment of drinking potable water and wastewater treatment.
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