Enhanced bioelectrochemical nitrogen removal in flow through electrodes

In the past decade, bioelectrochemical systems (BESs) have been studied extensively for the generation of power and maximizing power densities. In recent years, it was noticed that BESs applications can critically improve wastewater treatment. Most of the previous BESs work has used varied reactor geometry and configuration, wastewater composition, electrolyte solution, and constant electrode size to maximize power generation. However, there is limited research investigating the influence of increased electrode size on the wastewater treatment process. We investigated the effect of increased electrode surface area on wastewater treatment effi-ciency and studied the mechanism of nitrogen removal. In this study, we developed a flow-through electrode in a 3-electrode bioelectrochemical reactor. The anodic biofilms were enriched on electrodes for one week. Following the anodic enrichment period, the reactor was operated in a semi-continuous mode with raw domestic waste-water. To investigate the wastewater treatment efficiency, the chemical oxygen demand (COD), total nitrogen (TN), ammonia (NH3-N), nitrite (NO2-N), and nitrate (NO3-N) concentrations were measured. We found that increased surface area of anode did not significantly contribute to COD removal rate, most likely indicating the limits of BES. On the other hand, the TN removal rate increased proportionally to the surface area of the anode in the BES. We also found that outlet NO3-N and NO2-N concentrations were 1.2 +/- 0.2 and 3.2 +/- 0.9 mg/L, respectively. Our results indicated that it is possible to remove COD and TN simultaneously. Analysis of the microbial community structure showed that nitrogen removal was dominated by sulfidogenesis, anodic ammonia oxidation, autotrophic and heterotrophic denitrification as well as reducing NO3-N to NO2-N using Geo-bacter species in our system.

Automated summary

Increasing electrode surface area can enhance TN removal rate, while it has a limited impact on COD removal rate in BES. Our results demonstrate the feasibility of simultaneous COD and TN removal in the BES system. Microbial community structure analysis revealed that nitrogen removal was mainly influenced by sulfidogenesis, anodic ammonia oxidation, autotrophic and heterotrophic denitrification processes.