Simulating phosphorus removal from a vertical-flow constructed wetland grown with C. alternifolius species

Authors: OUYANG, YING - Mississippi State University; CUI, LIHUA - South China Agricultural University; Feng, Gary; Read, John

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2015
Publication Date: 1/14/2015
Publication URL: http://handle.nal.usda.gov/10113/60734
Citation: Ouyang, Y., Cui, L., Feng, G.G., Read, J.J. 2015. Simulating phosphorus removal from a vertical-flow constructed wetland grown with C. alternifolius species. Ecological Engineering. 77:60-64.

Interpretive Summary: Phosphorus (P) is an essential nutrient to all forms of life in aquatic ecosystems. However, elevated P in surface waters could cause eutrophication of aquatic ecosystems and impair water for drinking, industry, agriculture, and recreation. Vertical flow constructed wetlands (VFCWs) can purify P contaminated wastewaters before they discharge into streams and rivers. Although several mathematical models have been developed to estimate the removal efficiency of contaminants from the constructed wetlands, they are, in general, not suitable for predicting P purification from the VFCWs. A team of scientists used the commercially available STELLA (Structural Thinking, Experiential Learning Laboratory with Animation) software to develop and test a simulation model that would predict the fate, transport, and removal of P from wastewaters in a VFCW. The model, which included P uptake dynamics during growth of an important wetland plant species, Cyperus alternarius, was calibrated and validated through a set of experimental data in prior testing. Tests of the model application involved several wetting and drying cycles with wastewater of known quality. The simulation results revealed a major mechanism for P removal from wastewater in the VFCW was P adsorption by the soil substrate, which accounted for 53% of total P as compared with 14% and 0.5% for leaching and plant uptake, respectively. The STELLA model developed in this study appears to be a useful tool for water resource managers to estimate P removal efficiency from vertical flow constructed wetlands.

Technical Abstract: Vertical flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewater and stormwater. The aim of this study was to develop a STELLA (Structural Thinking, Experiential Learning Laboratory with Animation) model for estimating phosphorus (P) removal in an artificial VFCW (i.e., a substrate column with six zones) associated with a growing C. alternifolius species under a wetting (wastewater) -to-drying ratio of 1:3. The model was calibrated and validated by our experimental data with very good agreements prior to its applications. Simulations showed that the rate of soluble P (SP) leaching was highest at the top zone (i.e., Zone 1) and decreased gradually with increasing zone number due to the adsorption, clogging, and uptake when the SP flowed through the zones. The simulations further revealed that the best time for an optimal removal of SP from the wastewater was within the first week (168h) because the adsorption capacity of the substrate in the VFCW was highest at this time period. Additionally, the rate of SP leaching through zones followed the water flow pattern: breakthrough during wetting period and cessation during drying period. In general, the cumulative amounts of total P (TP) were in the following order: adsorption (53.3%) > leaching (13.5%) > uptake (0.49%). The rate of SP uptake by roots decreased with the column depth and occurred because more active roots were distributed in the top zones. Our study suggested that adsorption of P was a major mechanism for P removal from the VFCW system.