Integrating a microbial electrochemical system into a classical wastewater treatment configuration for removing nitrogen from low COD effluents

Abstract

The scaling-up process of microbial electrochemical technologies (METs) may require an initial investment for constructing completely new infrastructure. In contrast, adapting METs to equipment already present in wastewater treatment plants (WWTP) can be an attractive alternative to accelerate their implementation. In this study we evaluated the viability of adapting a classical oxic–anoxic chamber system to a membrane-free microbial electrochemical system in order to remove both nitrogen and organic matter. We simulated this configuration on a 22 L reactor with two chambers in the absence of any separation membrane. The working electrode acted as the electron source for denitrifying microorganisms and was placed in the first chamber. The system was able to support the nitrifying activity without external aeration and at oxygen levels below 2 mg L⁻¹. The influent, a synthetic medium with ammonium as the sole nitrogen source, was fed at COD/N ratios from 2 to 4. Up to 19 g NO₃⁻ N m⁻³ TCC per day were reduced at a COD/N ratio of 4, with a denitrification efficiency of 93% and a nitrogen removal efficiency of 81%. The system's capacity for nitrifying and denitrifying was strongly dependent on both the COD/N ratio and the working electrode potential. A massive sequencing study revealed the greater abundance of denitrifying genera such as Opitutos, Methyloversa and Zoogloea at the cathode. Nitrifying genera such as Nitrosomonas and Nitrospira were found in the reactor, the latter being enriched at the anode. In this study we demonstrate that the classical configuration of activated sludge systems can be turned into a MET to treat wastewater. We suggest the implementation of this air-free hybrid configuration in WWTP as an alternative method to remove nutrients from effluents with low levels of organic matter.