Wastewater Treatment

Wastewater treatment is an essential industrial process that needs to be undertaken, so as to remove harmful and toxic elements from the water before its reuse or release into the environment. The treatment process involves the use of various physical, chemical, and biological procedures. Some of the associated problems with wastewater are foaming, solid accumulation, high BOD, sludge de-watering, heavy metals, and offensive odor. Polyelectrolytes for wastewater treatment are considered one of the best chemical processes

Role of polyelectrolytes in wastewater treatment

Polyelectrolytes are organic polymer chains with an electrolyte group on every repeat unit. Based on the electrolyte group present in the chain, polyelectrolyte treatments are categorized into anionic, cationic, and non–ionic species. Polyelectrolytes discharge water with chemical-physical and biological characteristics which do not have a detrimental impact on the environment. Specially for reusing water, polyelectrolytes have been used to combat water scarcity. This organic polymer chain with a repeat electrolyte group dissolved in a polar solvent, hence charged due to the dissociation of small counterions which leave behind a charged micro ion.

Cationic polyelectrolytes have a positively charged group for use in the coagulation of negatively charged flocs through electrostatic interactions. These are useful in various processes of effluent /wastewater treatment, depending upon their molecular weight and charge density.

Anionic polyelectrolytes have a negatively charged group on each repeating unit, acrylamide-based polymers being the most available type. They are widely useful as flocculants, rheology modifiers, and adhesives and are immensely used in municipal wastewater and effluent treatment. Anionic flocculants are also used in enhanced oil recovery, decoloring, paper making, mineral processing, etc.

Polyelectrolyte treatment based on application

These are formulated in a way so as to be used as coagulants and flocculants as well as sludge dewatering agents in wastewater treatment plants.

Flocculants: Flocculants are chemicals responsible for bringing about secondary settling and sludge dewatering. They carry active groups with a charge which helps in counterbalancing the charge of the particles. These can be used in water treatment on their own or in combination with coagulants. It adsorbs on particles and causes destabilization either by bridging or charge neutralization. These may be categorized according to the charge density and molecular weight.

Coagulants: Coagulants are referred to as chemicals that are used to help in the removal of colour and turbidity present in untreated, raw water. Particles get settled down in the form of floc, which is then removed in downstream clarification or filtration treatment processes. These coagulants are either organic or inorganic based on their formulations. Organic coagulants are used for the treatment of water with low suspended solid content and they partly or completely replace the inorganic coagulants. These chemicals are appreciated for their attributes like quick flocculation, precise pH value, etc.