Performance Evaluation of a Floating Treatment Wetland in an Urban Catchment

Abstract

Floating Treatment Wetland (FTW) systems are purpose-built devices designed to replicate the water treatment processes that occur in and around naturally occurring floating vegetated islands. FTWs can be used to improve the water quality of water storage ponds by contributing to water treatment processes through adhesion, filtration, nutrient uptake (direct use by plants), and sequestration. This paper presents the results of a twelve-month investigation into the pollution removal performance of a FTW receiving stormwater runoff from a 7.46 ha urban residential catchment. As anticipated, there was a high degree of variation in FTW treatment performance between individual rainfall events. Overall pollution removal performance was calculated to be 80% for Total Suspended Solids (TSS), 53% for Total Phosphorous (TP), and 17% for Total Nitrogen (TN) for a FTW footprint of 0.14% of the contributing catchment. TSS and TP concentrations were found to be significantly reduced after FTW treatment. The minimum FTW footprint to catchment size ratio required to achieve regulated nutrient removal rates was calculated to be 0.37%. Sum of loads calculations based on flow resulted in pollution load reductions of TSS 76%, TP 55%, and TN 17%. Pollution treatment performance (particularly for TN) was found to be affected by low influent concentrations, and highly-variable inflow concentrations. The study demonstrated that FTWs are an effective treatment solution for the removal of pollution from urban stormwater runoff.

Field Evaluation of the Nutrient Removal Performance of a Gross Pollutant Trap (GPT) in Australia

“…The highly variable results found in this study are likely to be a result of highly variable, and/or low concentration pollution inflows. This result has also been found in previous studies [19,20,22,23]. Results that were less than the limits of detection (LoD) for that particular test, have been shown as 50% of the LoD.…”

“…These include: Event Mean Concentration (EM-Equation (1)), Average Concentration Removal Efficiency (Avg.CRE-Equation (2)), and Efficiency Ratio (E-Equation (3)) [17][18][19]. The value of CRE as an effective metric has been reduced as a reliable metric since minor variation (˘1 mg/L) observed in the analytical variability has significant influence on the metric at low influent concentrations, and so ER has been used as the primary metric in this study [19,20]. Prior to statistical testing, concentrations of TSS, TN and TP were log transformed (Equation (4)) to achieve normality (Ryan-Joiner p > 0.01).…”

Nitrate Removal by Floating Treatment Wetlands Amended with Spent Coffee: A Mesocosm-Scale Evaluation

“…FTWs provide water treatment for NO 3 -N, total N (TN), ammonium-N (NH 4 -N), total microcystin-LR, E. coli, and total P (TP) (Chauzat and Faucon, 2007;Jones et al, 2017;Keizer-Vlek et al, 2014;Mercado-Borrayo et al, 2015;Saeed et al, 2014Saeed et al, , 2016Tanner and Headley, 2011;Winston et al, 2013;Xian et al, 2010). Specifically, FTWs reduce the TN, TP, and total suspended solids (TSS) in influent by 4% to 88%, 8% to 53%, and 5% to 80%, respectively (Borne et al, 2013;Lane et al, 2016;Nichols et al, 2016;White and Cousins, 2013). FTWs are also cost-effective compared to traditional surface flow treatment wetlands (Koustas and Selvakumar, 2003;Tyndall and Bowman, 2016), which allows this BMP to be more affordable for low-income communities.…”

“…While FTWs have had great success in nutrient removal, nutrient reductions have been highly variable among studies. Those differences are attributed to the variability of plant type, maturity, study length, FTW placement, hydraulic retention time (HRT), surface coverage, and loading concentration (Borne et al, 2013;Lane et al, 2016;McAndrew et al, 2016;Nichols et al, 2016;White and Cousins, 2013). Therefore, improved understanding of the NO 3 -N removal processes in FTWs is critical for improving the design and efficiency of this BMP.…”

Stormwater Treatment Evaluation of a Constructed Floating Wetland after Two Years Operation in an Urban Catchment

“…This paper describes the results of a two-year field study undertaken to evaluate the pollution removal performance of a CFW designed to treat stormwater runoff from an existing urban development in Queensland, Australia. Preliminary results of this study were presented in Nichols et al [11] and Schwammberger et al [12].…”