Biostimulation of heterotrophic-autotrophic denitrification in a microbial electrochemical system using alternating electrical current

In this study, a novel integrated anoxic bioreactor with an electrochemical system was developed for heterotrophic-autotrophic denitrification using alternating current. The obtained results were revealed that sinusoidal and triangular waveforms were more effective than the square wave for enhancing the heterotrophic-autotrophic denitrification process efficiency. The nitrate removal efficiency was significantly decreased by increasing frequency ranges from 10 to 50 Hz. The system performance had an optimum response at 4 peak-to-peak voltage (Vpp). Nitrate reduction occurred at longer reaction times in higher voltage values (6, 8, and 10 Vpp). It was demonstrated that both heterotrophic and autotrophic bacteria coexist in the heterotrophic-autotrophic denitrification bio-electroreactor induced by the alternating current. The most probable numbers were determined 5.2 × 106 and 5.2 × 104 for heterotrophic and autotrophic denitrification bacteria, respectively. Pseudomonas spp., Nesterenkonia spp., Bacillus spp., and Brevibacillus spp. were determined using 16S rRNA, as the most abundant denitrifiers present in the system. Accordingly, it is concluded that heterotrophic-autotrophic denitrification supplied with low-frequency low-voltage alternating current could be a promising technique for water treatment contaminated with nitrate.