Do wastewater pollutants impact oxygen transfer in aerated horizontal flow wetlands?

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2020-03, Vol.383, p.123173, Article 123173
• Main Authors: Boog, Johannes, Nivala, Jaime, Kalbacher, Thomas, van Afferden, Manfred, Müller, Roland A.
• Format: Article
• Language: English
• Subjects: Aeration; Alpha factor; Constructed wetland; Domestic sewage; Environmental Sciences; Nature-based technology; Numerical process modeling
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2019.123173

[Display omitted] •Oxygen absorption experiments were conducted in a gravel column with real wastewater.•α linearly decreased with increasing CODs concentration.•Numerical process model was extended with α=f(CODs).•Reduction of treatment efficacy due to changes in oxygen transfer was simulated. Aerated treatment wetlands are an increasingly recognized nature-based technology for wastewater treatment that relies heavily on mechanical aeration. Although aeration-mediated oxygen transfer into the wastewater can be impeded by wastewater pollutants, little is known about the link between the volumetric oxygen mass transfer coefficient kLa and the organic carbon concentration of the wastewater in aerated wetlands. In this study, oxygen transfer experiments were carried out in a lab-scale gravel column using clean water and wastewater from a pilot-scale horizontal flow (HF) aerated wetland treating domestic sewage. The α-factor, which describes the ratio of the volumetric oxygen mass transfer coefficient kLa in wastewater to clean water, was reduced by increasing soluble chemical oxygen demand (CODs). The derived regression equation α=1.066-1.372E-3mgCODsL-1 was incorporated into a numerical process model to simulate the impact of the reduced oxygen transfer on a hypothetical HF aerated wetland. The simulations revealed that α and treatment efficacy for nitrogen were substantially reduced by CODs at low aeration (kLa of 1 h−1) and high influent wastewater strength (CODs of 300 mg L−1). At the same kLa and influent CODs concentration, longitudinal gradients of α and concentrations for dissolved oxygen (DO), NH4-N and NOx-N in the simulated wetland were shifted up to 21% of wetland length downstream. These effects decreased with increasing kLa and were found to be negligible at kLa > 3 h−1, which corresponds to an air flow rate of approximately 400 L m−2 h−1. Following this, higher organic carbon concentrations can reduce oxygen transfer in HF aerated wetland systems, thus resulting in decreased treatment efficacy.