The use of engineered wetlands to treat recalcitrant wastewaters

Abstract

Constructed wetlands provide good removals of BOD, COD, suspended solids, heavy metals, and pathogens from wastewaters being treated in them. However, although they are widely used in cold climates, winter operability often presents problems, and they normally only remove part of nitrogen and phosphorus nutrients in wastewaters being treated in them. What is needed was a new type of constructed wetland which removes nutrients as well as it does other contaminants, which operates better in cold weather, and which is able to handle especially difficult‐to‐treat wastewaters. The answer may be found with engineered wetlands, a type of constructed wetland in which process conditions and/or operations are modified, manipulated and/or controlled, in contrast to the more passive operation of ordinary constructed wetlands. Although the names ≪engineered wetland≫ and ≪constructed wetland≫ are sometimes used interchangeably, it is appropriate to define the former more narrowly by limiting the engineered wetland designation to apply only to the less passive situation. All engineered wetlands are constructed wetlands, but not all constructed wetlands are engineered ones. Constructed wetland systems may be ≪engineered≫ in many ways. For example, influent streams may be varied in flow rate (or periodically turned off); effluents from various points in the wetland system may be recycled to other points, ordinary substrates may be replaced with special ones having specific qualities (e.g., the ability to permanently chemically adsorb certain pollutants from wastewaters passing through them); things may be added at certain points (e.g., heat, chemicals, air); and/or wetland vegetation may be selected for its phytoremediating properties. This paper describes a new sub‐surface flow (SSF) engineered wetland biological/environmental technology (ecotechnology) known as BioReactor Engineered Wetland for wastewater treatment (BREW). It presents the results from bench scale, mesocosm testing which show that ammonia nitrogen and phosphate removals can be increased greatly with engineered wetlands.