Substances that endanger biological treatment
Biological wastewater treatment is based on the metabolic activity of bacteria, archaea, and other microorganisms. These organisms are highly sensitive to toxic compounds; therefore, both the type and concentration of pollutants entering the treatment plant are critical factors.
Due to lack of knowledge or irresponsibility, some users discharge substances into the sewer system that can damage the biological processes of municipal wastewater treatment plants or harm mechanical system components. Furthermore, most treatment technologies are not suitable for removing many dissolved pollutants (e.g. pharmaceutical residues, heavy metals, complex chemical compounds). As a result, a significant portion of these substances ultimately enters the environment through treated wastewater or sewage sludge.
The key to preventing harmful substances from entering sewer networks lies in industrial wastewater pre-treatment, while for municipal wastewater it is public awareness and continuous wastewater quality monitoring. Together, these measures can ensure the long-term sustainable operation of wastewater treatment plants.
Heavy Metals
Heavy metals—such as mercury, cadmium, lead, and chromium—even at low concentrations inhibit enzymatic processes, thereby reducing the efficiency of organic matter degradation, nitrification, and denitrification.
Solvents and Pharmaceuticals
Industrial organic solvents, phenols, pesticides, and certain pharmaceutical residues can also be toxic, especially when they enter the system as shock loads.
Acids and Alkalis
Extreme pH values—acidic or highly alkaline wastewater—damage microbial communities, as most treatment plant microorganisms function optimally near neutral pH. High salinity can cause similar problems by inducing osmotic stress, particularly in industrial wastewater. Extreme pH fluctuations also reduce the service life of mechanical equipment.
Coarse Solids
The machinery of wastewater treatment plants—pumps, screens, screws, blowers, and mixers—is sensitive to both physical and chemical stress beyond certain limits. Coarse solids such as textiles, wet wipes, plastic films, and hygiene products cause blockages, shaft entanglement, and mechanical failures. These materials not only increase maintenance demands but can also raise energy consumption.
Oils and Particles
Fats, oils, and grease (FOG) form deposits in pipelines, on tank walls, and on mechanical components, reducing hydraulic capacity and accelerating corrosion. Sand and other abrasive particles increase wear, especially in pumps, fittings, and valves.
Oxidizing Agents
Chemically aggressive substances—such as acids, alkalis, and oxidizing agents—cause corrosion, significantly shortening the service life of metal components.
Summary
Damage to biological processes leads to reduced treatment efficiency, while mechanical damage results in increased operational and maintenance costs and operational disturbances. The composition, toxicity, and harmfulness of wastewater entering a treatment plant via sewer networks or direct discharge is ultimately the responsibility of the user.
