Municipal wastewater treatment has become a complex process, due to numerous industrial facilities located in and around settlements, making their wastewater highly irregular in composition. Industrial wastewater requires a combination of the existing methods and improvement of the whole treatment process. The main approaches that can be used in municipal wastewater treatment plants are discussed below.
Mechanical treatment is used for cleaning of virtually all wastewater. Its essence is clarification, sedimentation, filtration and centrifugation. These methods allow to remove up to 60-80% of impurities contained in the wastewater in undissolved and partly colloidal state.
Biological wastewater treatment is considered to be one of the simplest and the most accessible method. It is based on the natural ability of ecosystems to recycle the substances by microbes. Biological treatment can remove the smallest suspended solid particles which remain in the wastewater after mechanical treatment.
Chemical treatment is the removal of contaminants by chemical reactions. These reactions begin with the introduction of special substances acting as reagents into wastewater. A good example is the oxidation-reoxidation reaction which causes precipitation of contaminants for filtration.
Physico-chemical methods of treatment are adsorption, crystallization, flotation, extraction, coagulation and others.
Neutralization of wastewater is another method, which can be performed by using one of the following techniques:
- Mixing of acidic and alkaline wastewater in equalization tanks;
- Mixing wastewater with reagents in balancing tanks;
- Filtration of wastewater through various materials (dolomite, marble, limestone, etc.).