Integrated electro-anammox process for nitrogen removal from wastewater

Conventional biological nutrient removal (BNR) requires a large footprint and high-energy consumption to ensure nitrification conditions for ammonia oxidation and denitrification conditions for the reduction of nitrates to diatomic nitrogen gas (N-2). Alternatively, anaerobic ammonia-oxidizing (anammox) bacteria are able to accelerate this treatment by directly converting ammonia to N-2 in the presence of nitrite only. However, their growth in mainstream treatment is very slow, which prevents its full-scale implementation. In this study, a new electro-bioreactor was designed to enhance the anammox reaction during wastewater treatment. The proposed reactor configuration, which takes advantage of a low direct current (DC) application, has a smaller footprint with less organic and oxygen requirements. To demonstrate its effectiveness, synthetic wastewater was used to feed a completely mixed continuous flow electro-bioreactor with anammox species and compared to a traditional anammox bioreactor (control). At the same hydraulic retention time (HRT), the electro-bioreactor reached steady-state conditions twice faster (3 months). The results show that the intermittent DC field improved the simultaneous removal of NH4+ -N and NO2--N by 90% and 89%, respectively. The system significantly enhanced the key enzyme generation and cellular metabolism involved in the anammox reactions, which subsequently led to superior removal of nitrogen. Fluorescent in situ hybridization (FISH) revealed the dominance of anammox microbial population in the electro-bioreactor over denitirifiers despite elevated carbon concentrations. Furthermore, anammox activity was maintained in the electrobioreactor at low temperatures. The electro-bioreactor offers potential cost-effective large-scale application of the anammox mainstream process for enhanced removal of nitrogen from wastewater in the cold season.