Electrical Stimulation Improves Microbial Salinity Resistance and Organofluorine Removal in Bioelectrochemical Systems

Abstract

cFed batch bioelectrochemical systems (BESs) based on electrical stimulation were used to treat p-fluoronitrobenzene (p-FNB) wastewater at high salinities. At a NaCl concentration of 40 g/liter, p-FNB was removed 100% in 96 h in the BES, whereas in the biotic control (BC) (absence of current), p-FNB removal was only 10%. By increasing NaCl concentrations from 0 g/liter to 40 g/liter, defluorination efficiency decreased around 40% in the BES, and in the BC it was completely ceased. p-FNB was mineralized by 30% in the BES and hardly in the BC. Microorganisms were able to store 3.8 and 0.7 times more K ؉ and Na ؉ intracellularly in the BES than in the BC. Following the same trend, the ratio of protein to soluble polysaccharide increased from 3.1 to 7.8 as the NaCl increased from 0 to 40 g/liter. Both trends raise speculation that an electrical stimulation drives microbial preference toward K ؉ and protein accumulation to tolerate salinity. These findings are in accordance with an enrichment of halophilic organisms in the BES. Halobacterium dominated in the BES by 56.8% at a NaCl concentration of 40 g/liter, while its abundance was found as low as 17.5% in the BC. These findings propose a new method of electrical stimulation to improve microbial salinity resistance.O rganofluorine compounds, especially fluorinated aromatic compounds, are widely used in the production of adhesives, pesticides, dyes, pharmaceuticals, refrigerants, and surfactants (1). They were found to inhibit enzymes, modify cell-to-cell communication, and disrupt membrane transport as well as energy generation processes (2). Due to their high toxicity and recalcitrance, conventional biological methods fail to efficiently remove organofluorine from wastewaters (1, 3). On the other hand, bioelectrochemical treatment has been proved to be an effective method to minimize refractory properties of typical p-fluoronitrobenzene-contaminated organofluorine wastewater (4).Salinity poses another serious challenge to the treatment of such organofluorine-containing wastewater. Typically, addition of strong acid or alkali to adjust the pH during production processes results in high salt concentrations in organofluorine wastewaters. As an example, salinity concentrations from an organofluorine industry effluent in China typically fluctuate between 2 and 3%, with a maximum of 5%. Conventional physicochemical treatment processes for salinity wastewater are energy intensive and costly. Although biological processes have been recommended for salinity wastewater treatment (5, 6), high salinity may cause cell plasmolysis and even the death of microorganisms due to osmotic pressure increases (7,8). To address this issue, wastewaters are always diluted, which results in a meaningless freshwater consumption and increases operational cost (5). An enhancement of microbial salinity resistance would enable implementation of biological methods for salinity wastewater treatment, which could be succeeded by acclimatization and enrichment of haloduric or halophilic strains (5). H...

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