Constructed wetlands for agricultural wastewater treatment

A 23-tank, 43 m , pilot-scale constructed wetland system was loaded daily with 136.2 liters of cattle feedlot wastewater to measure the nitrogen removal effectiveness and to compare this removal to nitrogen removal models. The 23-tanks were separated into six different treatment series, and the effects of four different total nitrogen (TN) loading rates were investigated with three different series surface areas and detention times. The four TN loading rates were 11.4, 8.0, 2.3, and 0.5 g TN/day. All four loading rates were tested in treatment series consisting of four tanks. Additionally, the 2.3 g TN/day loading rate was tested in a series with two tanks and a series with five tanks.

The removal of nitrogen constituents from wastewater is dominated by maximizing the permanent removal processes inherent to the nitrogen cycle. Although the nitrogen cycle is a complex interaction of biological and chemical phenomena, maximizing its inherent removal processes is attainable in the wetland environment. The primary facilitator of this nitrogen removal is the root-zone aeration of the predominantly anaerobic environment surrounding the wetland soil. Given proper amounts of dissolved oxygen, the microbiota of nitrification can oxidize ammonia to nitrate, and denitrification can take place in the anaerobic environment, ultimately removing nitrogen from the wastewater in the form of nitrogen gas. An additional permanent nitrogen removal pathway in wetlands is defined by the plant uptake of ammonia and/or nitrate. However, maximizing this removal pathway requires plant harvesting, which can be costly in the full scale wetland treatment settmg and does not always yield an appreciable amount of nitrogen removal.