Electrified biotrickling filters as tertiary urban wastewater treatment

Abstract

Nitrification-denitrification is a well-established method in wastewater treatment plants (WWTPs). Ammonium (NH4+) is oxidized to nitrate (NO3-) using oxygen (O2) as electron acceptor (nitrification) and NO3- is further reduced to dinitrogen gas (N2) under anoxic conditions using organic matter as electron donor (denitrification) [1]. However, secondary effluents can occasionally contain excessive nitrogen content [2].

Biofilters can be a suitable technology to reach the nitrogen standards, but the lack of electron donors in urban wastewater might hinder the performance of denitrification [3,4]. Microbial electrochemical technologies (MET) have been postulated as a promising alternative for nitrogen removal [5]. Full ammonium removal was reported for the first time in 2008 in METs [6]. Thereafter, different configurations have been studied. For example, simultaneous nitrification-denitrification was promoted in an aerated biocathode [7] or the integration of bioelectrochemical nitrogen removal in a WWTP configuration [8], among others. Following the principle of integrating METs into existing wastewater treatment technologies, electrified biotrickling filters (e-biofilters) aims at upgrading the current biotrickling filters by incorporating a submerged, electrified zone to promote bioelectrochemical denitrification [9]. Consequently, e-biofilters maintains nitrification activity and promotes denitrification processes in wastewaters with a low Carbon/Nitrogen ratio, such as secondary wastewaters. For this reason, this work assesses for the first time the application of an e-biofilter to treat the secondary effluent of an urban WWTP