Microplastics are a type of plastic waste that has received increasing attention in recent
years. Microplastics enter the environment from various sources. An important source is
the treated wastewater that comes from municipal wastewater treatment plants.
Constructed wetlands can be considered as an alternative to conventional municipal
treatment plants. Constructed wetlands utilize the properties of plants, soil, and
microbial communities to treat wastewater. Due to the large number of microplastics in
municipal wastewater, the question arises about the possible effects on the efficiency of
the wastewater treatment processes. The influence of microplastics on the operation and
efficiency of constructed wetlands has not been sufficiently researched and is not yet
fully understood.
The effects of microplastics on efficiency were investigated in a laboratory constructed
wetland with a subsurface horizontal flow. We determined ammonium, nitrite and
nitrate nitrogen, chemical oxygen demand, biochemical oxygen demand, total organic
carbon, orthophosphate, chloride and pH before and after the microplastics addition. We
added two types of microplastics that are often found in wastewater – polyethylene
microbeads from cosmetics and polyacrylonitrile synthetic fibers. We also monitored
the efficiency of microplastic retention.
The results showed that the constructed wetland operates well and effectively removes
carbon, nitrogen and phosphorus compounds. After the addition of microplastics, there
were no changes in the removal of carbon compounds, but we observed greater changes
in the removal of nitrite nitrogen and the removal of orthophosphate. The laboratory
constructed wetland effectively retained almost all of the added microplastics. Most of
the microplastics accumulated in the initial part of the sediment of the constructed
wetland.
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