Chapter 3 - Long-term performance and feasibility of using constructed wetlands for treatment of emerging and nanomaterial contaminants in municipal and industrial wastewater

Abstract

There are growing concerns about the emerging contaminants originating from the pharmaceuticals and personal care products, plasticizers, flame retardants, surfactants, certain pesticides, endocrine-disrupting contaminants, disinfection by-products, perfluorinated compounds, and engineered nanomaterials. These contaminants are discharged into surface water through municipal, industrial, and agricultural wastewater and stormwater flows. They can be toxic to humans and ecosystems and pose high carcinogenic risks. Traditional wastewater treatment processes (WWTPs) cannot completely remove many organic emerging contaminants, but in most cases, they are released to surface water bodies. Therefore, the WWTP effluents need further treatment before they are discharged to surface water to protect water sources from contamination. The well-designed and well-maintained constructed wetlands have high potential for secondary and tertiary treatment of wastewater and stormwater, and thus, they can treat water to high standards and recycle water. The constructed wetlands consist of water, plant species, substrate/sediment, and native microorganisms, where the complex physical and biogeochemical systems control the volatilization, sorption, sedimentation, phytodegradation, plant uptake, and microbial degradation of contaminants. The performance of constructed wetlands depends on the designs and parameters of constructed wetlands, selection of plant species, substrate/sediment, hydraulic retention time, type of contaminants, and seasonal variability. Based on the water flow, position of plant growth, and water flow path, the constructed wetlands are classified as (1) surface flow constructed wetland, (2) horizontal subsurface flow constructed wetlands, and (3) vertical subsurface flow constructed wetlands. The combination of different types of constructed wetlands may build hybrid constructed wetland systems that have higher removal efficiency than individual constructed wetlands.