ABSTRACT
This chapter discusses the principal processes, constraints, and design and operation parameters which control organic load and nutrient removal in the basic types of constructed wetlands (CW). While many physical processes act and interact to reduce and remove pollutants from wastewater, many of the nutrient and organic matter removal effects of CWs are dominated or influenced by microbial activity. The main mechanisms for dissolved organic matter removal from wastewater streams are off-gassing of metabolic products such as CO2 and CH4. Aerobic transformation consumes organic matter in the presence of molecular oxygen producing carbon dioxide, water, and energy. Biodegradable organic matter, nitrogen, and phosphorus are common wastewater contaminants which must be addressed by treatment systems before re-use or discharge back to the environment. The net removal of contaminants is the sum of many processes, including sedimentation, filtration, precipitation, volatilization, adsorption, plant uptake, and various microbial processes influencing carbon, nitrogen, and phosphorus cycles, among others.
