A two-stage subsurface vertical flow constructed wetland for high-rate nitrogen removal

Abstract

By using a two-stage constructed wetland (CW) system operated with an organic load of 40 gCOD.m(-2).d(-1) (2 m2 per person equivalent) average nitrogen removal efficiencies of about 50% and average nitrogen elimination rates of 980 g N.m(-2).yr(-1) could be achieved. Two vertical flow beds with intermittent loading have been operated in series. The first stage uses sand with a grain size of 2-3.2 mm for the main layer and has a drainage layer that is impounded; the second stage sand with a grain size of 0.06-4 mm and a drainage layer with free drainage. The high nitrogen removal can be achieved without recirculation thus it is possible to operate the two-stage CW system without energy input. The paper shows performance data for the two-stage CW system regarding removal of organic matter and nitrogen for the two year operating period of the system. Additionally, its efficiency is compared with the efficiency of a single-stage vertical flow CW system designed and operated according to the Austrian design standards with 4 m2 per person equivalent. The comparison shows that a higher effluent quality could be reached with the two-stage system although the two-stage CW system is operated with the double organic load or half the specific surface area requirement, respectively. Another advantage is that the specific investment costs of the two-stage CW system amount to 1,200 EUR per person (without mechanical pre-treatment) and are only about 60% of the specific investment costs of the singe-stage CW system.

The Impact of Pulsing Hydrology and Fluctuating Water Table on Greenhouse Gas Emissions from Constructed Wetlands

“…It is typically used in vertical subsurface flow (VSSF) CWs, where it increases the aeration and nitrification rate, elimination of biological oxygen demand (BOD) and chemical oxygen demand (COD), promotes advanced C utilization by bacteria, and supports more effective NH 4 , total N, and total P removal (Kadlec and Knight 1996;Healy et al 2007;Langergraber et al 2008). In horizontal subsurface flow (HSSF) CWs, pulsing water regimes enhance removal of BOD, COD, NH 4 , and total N (Vymazal and Masa 2003;Caselles-Osorio and Garcia 2007).…”

Entwicklung eines neuen Designs für 2-stufige vertikal durchströmte bepflanzte Bodenfilter

“…Während des über 4-jährigen Betriebs des 2-stufigen Bodenfilters waren die Medianwerte der Zulaufkonzentrationen 340 mg BSB 5 /L (Anzahl der Analysen: 146, 95 % Konfidenzintervall 9 mg BSB 5 /L), 510 mg CSB/L (181, 11), 64.5 mg NH 4 -N/L (181, 1.3) und 77.9 mg Nges/L (181, 1.5 (Langergraber et al, , 2008. Die Ablaufkonzentrationen und Reinigungsleistungen des 2-stufigen Bodenfilters waren bei Ablaufwassertemperaturen von > 8°C unabhängig von der Temperatur und sehr konstant (ÖKOREAL und BOKU-SIG, 2007).…”

Simulating vertical flow wetlands using filter media with different grain sizes with the HYDRUS Wetland Module

“…This system is designed for full nitrification and high nitrogen elimination. The design is based on the specific area needed with 1 m² per people equivalent (PE) for each stage, i.e., in total 2 m² per PE (Langergraber et al, 2008;Langergraber et al, 2009b;Langergraber et al, 2014).…”