Given the current emphasis on the environment, scientists are seeking to purify contaminated waters in ways that do not further contaminate air, water, or earth. The trend is toward recycling all natural resources, including water, by using natural systems, such as constructed treatment wetlands. Wetlands are the most biologically productive ecosystems on the earth and are home to a multitude of plants and animals including those that are uncommon in other ecosystems since wetlands are areas where the soil is saturated with water with resulting anaerobic or low-oxygen conditions. Due to their high biological activities, wetlands can utilize essential nutrients that occur in wastewater for additional biological productivities, and transform many of the common pollutants into harmless byproducts. Because of these properties of wetlands, the intentional construction of wetlands to provide habitat and water quality functions began. Historically, natural wetlands have been used as convenient wastewater discharge sites for as long as sewage has been collected. The relatively recent development of wetland treatment technology blooms in response to the Clean Water Act of 1972 (Cole, 1998). Since then, this natural technology seems to have firmly established roots.
In North America, constructed treatment wetland systems have been designed predominantly for large-scale treatment of municipal wastewater. In 1993, a survey of more than 300 wetland cells treating municipal wastewater in North America was conducted to evaluate the average performance for the mix of system types. In this survey, biochemical oxygen demand (BOD) was reduced 73% to 8 mg/L, total suspended solids were cut 72% to 13 mg/L, total nitrogen was reduced 53% to 4.5 mg/L, and total phosphorus was cut 56% to 1.7 mg/L (Cole, 1998). This tremendous reduction has this alternative innovative technology to become one of major treatment forces, and since 1986, these systems have been treating millions of gallons of municipal wastewater a day. In addition to municipal wastewater, constructed wetlands have also been built to treat other types of wastewaters, including acid mine drainage, industrial wastewater, agricultural and storm water runoff, and effluent from livestock operations.
The petroleum industry is one of the pioneers using constructed wetlands to treat a variety of wastewater from refineries and fuel storage tanks. Amoco has been treating pretreated process wastewater at its oil refinery since 1975, and Chevron has operated treatment wetlands since 1988 (Cole, 1998). Other than the petroleum industry, the food-processing industry and the pulp and paper industry have also conducted extensive pilot-scale projects or have built many full-scale treatment wetland systems. According to Robert Kadlec as quoted in Cole (1998), “Every major industry is implementing wetland technology in one way or another”.
Constructed treatment wetland systems have also been built to treat livestock wastewater. Wastewaters from feed lots, dairy barns, swine barns, poultry operations, and similar activities tend to have high solids, and high NH4+ and organic nitrogen concentrations. It is necessary to reduce the concentrations of these materials in a preliminary treatment step, so agricultural livestock wastewater generally passes through a solid separation system first to reduce organic matter content before wastewater enters the storage lagoon. Lagoons are deep earthen structures to provide sufficient storage for degradation to take place. Due to financial considerations, anaerobic lagoons are commonly selected to serve this purpose, and it is also considered as the most efficient process to deal with livestock wastewater. The wastewater is then treated physically and biologically in constructed treatment wetlands. The major components of constructed treatment wetlands include plants, detritus, soils, bacteria, and animals. These components interact with each other and also physical parameters such as water depth, temperature, pH, and dissolved oxygen concentration, and make the wastewater treatment process possible.
Comments or questions, email 