Effects of process operating conditions on the autotrophic denitrification of nitrate-contaminated groundwater using bioelectrochemical systems

Abstract

Nitrates have been detected in groundwater worldwide, and their presence can lead to serious groundwater use limitations, especially because of potential health problems. Amongst different options for their removal, bioelectrochemical systems (BESs) have achieved promising results; in particular, attention has raised on BES-driven autotrophic denitrification processes. In this work, the performance of a microbial electrolysis cell (MEC) for groundwater autotrophic denitrification, is assessed in different conditions of nitrate load, hydraulic retention time (HRT) and process configuration. The system obtained almost complete nitrate removal under all conditions, while nitrite accumulation was recorded at nitrate loads higher than 100mgNO3−L−1. The MEC system achieved, in different tests, a maximum nitrate removal rate of 62.15±3.04gNO3−-Nm−3d−1, while the highest TN removal rate observed was 35.37±1.18gTNm−3d−1. Characteristic of this process is a particularly low (in comparison with other reported works) energy consumption: 3.17·10−3±2.26·10−3kWh/gNO3—N removed and 7.52·10−2±3.58·10−2kWhm−3 treated. The anolyte configuration in closed loop allowed the process to use less clean water, while guaranteeing identical performances as in other conventional configurations.