Integrated bio-electrogenic process for bioelectricity production and cathodic nutrient recovery from azo dye wastewater

Microbial electrochemical treatment (MET) process was designed to evaluate complete mineralization of partially treated dye effluent obtained from anoxically operated Periodic discontinuous batch reactor (PDBR) for simultaneous bioelectricity generation and recovery of nutrients. In MET bioreactor, anode and cathode chambers were fed with designed synthetic wastewater (DSW) and PDBR dye effluents. The dye metabolite (NH₄⁺) will be converted to nitrates by the activity of aerobic biocatalyst present in cathode chamber to be used as biofertilizer. Dye removal of 90.2% was observed with good electrogenic activity (voltage (OCV)/current; 395 mV/1.77 mA). The mineralization of dye and its intermediates were assessed by reduction in overall toxicity from 23% to 4%. Chemical oxygen demand (COD) removal efficiency of 75% (anode) and 88% (cathode) were observed in correspondence to higher azoreductase (18.7 U; 48 h) and dehydrogenase (1.66 μg/ml of toluene; 24 h) enzyme activities which correlated well with metabolic activities of biocatalyst. Bioelectrocatalytic behavior of mixed biocatalyst on the basis of redox catalytic currents and prevalence of redox mediators signified the specific function of electron transfer toward dye mineralization. The results obtained suggest that the use of MET can considerably degrade toxic pollutants and provides nitrate rich solution (biofertilizer). Utilization of recovered nutrients directly to farms without any energy intensive methods is reported in this communication.