What are wastewater treatment plants not capable of?
Wastewater treatment plants play a key role in protecting water resources; however, municipal wastewater treatment plants, without further upgrades, are not capable of removing all pollutants completely. This is not due to a technological “failure,” but because these systems were originally designed for different types of loads.
Conventional municipal wastewater treatment plants are primarily designed to remove organic matter, suspended solids, nitrogen and phosphorus compounds, and to provide disinfection. These pollutants typically occur in large quantities and can be efficiently treated using mechanical, biological, and chemical processes. The original objective was to prevent oxygen depletion in receiving waters, reduce public health risks, and limit further pollution of surface waters.
New times, new pollutants
In recent decades, an increasing number of micropollutants have appeared in wastewater. These include pharmaceutical residues, hormones, pesticides, perfluorinated compounds, industrial chemicals, and microplastics. Although often present at extremely low concentrations, they are persistent and difficult to degrade, allowing them to partially or fully pass through conventional treatment processes.
Why is the capability of wastewater treatment plants limited?
One of the root causes is that conventional wastewater treatment plants were not designed or optimized to remove these substances, but rather to eliminate suspended solids, organic pollution (BOD, COD), and nutrients (N, P). These systems target a relatively small number of parameters occurring in large quantities. In contrast, pharmaceutical residues, hormones, pesticides, perfluorinated compounds, industrial chemicals, and microplastics occur only in trace concentrations (µg–ng/L) and in a wide variety of chemical forms.
The number of micropollutants reaches tens or even hundreds of thousands, making their individual removal practically impossible—especially since many of them can transform during treatment and form degradation products. Therefore, only general, non-selective solutions can be applied.
Technology is too expensive
Advanced technologies do exist—such as activated carbon filtration, ozonation, and membrane processes—that are capable of removing or degrading a large proportion of micropollutants. However, these technologies are extremely costly and require significant energy and operational expenditure. As a result, they are typically applied only in specific industrial wastewater treatment scenarios, since there is currently neither economic justification nor regulatory pressure for their widespread use at municipal treatment plants.
Limitations of prevention
From an environmental protection perspective, prevention has therefore gained increasing importance, alongside public awareness and decision-maker education. If hazardous or poorly degradable substances did not enter wastewater systems in the first place—through proper pharmaceutical collection or industrial pre-treatment—the pollutant load on receiving waters could be significantly reduced. However, this is not solely a matter of intent, as hormones and pharmaceutical residues enter wastewater via human excretion, which cannot be eliminated.
Summary
Wastewater treatment is therefore not a miracle solution, but rather a final line of defense that does not provide complete protection, due to technical, economic, and regulatory constraints. Unfiltered and undegraded dissolved pollutants from chemical and pharmaceutical industries leave the system with treated effluent, while microplastics and heavy metals are released into the environment via sewage sludge.
