Acid red 27 decolourisation and simultaneous electricity generations by mixed bacterial cultures in microbial fuel cell

Abstract

Azo dyes are widely used in industries although poorly biodegradable and highly toxic. Poor existing wastewater treatment caused dye residues in industrial effluent to be discharged into neighbouring water bodies causing major distress to the environment. This study was carried out to identify the potential of using mixed bacterial culture system for efficient biodegradation of azo dye in single batch system and for potential electricity generation in microbial fuel cell (MFC). This study used single and mixed bacterial consortium in batch shake flask experiment to decolourize Acid Red azo dye (AR27) and for electricity generation in a dual-chamber MFC. Four bacterial strains coded as MF1, B2, ZL and CO were used. Morphological, biochemical and 16S rDNA sequence analyses of these bacteria were carried out. Phylogenetic analysis successfully confirmed the identity of strains MF1 and B2 as Klebsiella pneumoniae (MF1 and B2), CO as Bacillus cereus. However, ZL identification was inconclusive. Flask experiment of single strain showed that all single strains were able to degrade AR27 dye, where strain CO displayed 2 to 4-fold higher rate of dye removal compared to other strains. Compatibility test successfully showed that strains CO, MF1 and ZL were able to grow without antagonism effect whereas CO and B2 were competing with each other. Selection of the best mixed bacterial culture based on AR27 dye degradation showed that combination of strains CO, MF1 and ZL produced the best dye decolourisation rate and Chemical Oxygen Demand (COD) removal. Optimization study revealed that mixed culture of CO+MF1+ZL performed the best AR27 dye degradation in CDM medium when adjusted to pH 5.0-7.0, supplemented with 3 g/L yeast extract, 100 mg/L AR27 dye and incubated under static condition at 32 – 37°C. Under optimal conditions, 99% of 100 mg/L AR27 was removed at the rate of 4.21 mg/h. Sequential facultative anaerobic-aerobic condition demonstrated that the COD removal percentage increased from 57% to 69% when aerobic condition was introduced to the system. However, the amount of Total Polyphenolic Content (TPP) removed showed no significant difference. Assessment of potential electricity generation by CO+MF1+ZL mixed culture during AR27 dye removal in dual-chamber MCF demonstrated that the maximum generated open circuit voltage (OCV) was 567.7mV. Closed circuit voltage (CCV) across 5000 Ω external resistance generated was 39.7mV with maximum power density and current density of 0.26 mW/m2 and 6.6 mA/m2, respectively. In the application of mixed culture for dye removal in real textile wastewater, the voltage generated dropped to 232.38 mV for OCV and 13.9 mV for CCV with maximum power and current density generated 0.03 mW/m2 and 2.3 mA/m2, respectively. This was due to high pH value of textile wastewater. When textile wastewater was adjusted to pH 7, the voltage generated improved to 489.9 mV for OCV and 32.9 mV for CCV with maximum power and current density generated 0.18 mW/m2 and 5.78 mA/m2, respectively. This study showed that mixed culture of CO+MF1+ZL has a good potential for treating wastewater containing azo dye for simultaneous decolourization and electricity generation.