A microbial fuel cell configured for the remediation of recalcitrant pollutants in soil environment

Abstract

A pristine soil environment supports a healthy soil biodiversity, which is often polluted with recalcitrant compounds. The bioelectrochemical remediation of the contaminated soils using bioelectrochemical systems (BESs) is gaining significant attention with respect to the restoration of the soil ecosystem. In this direction, a microbial fuel cell (MFC, an application of BES), was employed for the treatment of total petroleum hydrocarbons (TPHs) in a soil microenvironment at three ranges of pollution (loading conditions - 320, 590 and 840 mg TPH per L). TPHs degraded effectively in the soil-electrode vicinity in the range of 158 mg TPH_R per L (320 mg TPH per L) and 356 mg TPH_R per L (840 mg TPH per L). The study also demosntrated a maximum bioelectrogenesis of 286.7 mW m^-2 (448 mV at 100 Ω) at the highest TPH loading concentration studied (840 mg TPH per L). The conditions prevailing in the soil MFC also facilitated the removal of sulfates (114 mg SO₄ ^2- per L; 62.64%) and the removal of total dissolved solids (910 mg TDS per L, 12.08%) at an 840 mg TPH per L loading condition. The pH of the outlet wastewater prevailing in the mild alkaline range of 7.6 and 8.4, along with improved sulfate and TPH removal in the respective conditions suggested suitable conditions for sulfate-reducing bacteria (SRB). This study also signified the sustainability of the process for the effective treatment of hydrocarbon contaminated soil that also generates green energy.

Fig. 1. Degradation of the total petroleum hydrocarbons during the three loading conditions of the (a) soil MFC and in the (b) control operations. Cycle numbers 1–3 represent 320 mg TPH per L, 4–6 represent 590 mg TPH per L and 7–8 represent 840 mg TPH per L.

Fig. 2. Pattern of the diesel range organic (DRO) degradation in the bioelectroremediation process and respective control operations. (a) Total concentration of the DROs, (b) DRO removal concentration and DRO removal efficiency and (c) concentrations of diverse DROs in the MFC and control operation.

Fig. 3. (a) Bioelectricity generation potential of the soil-based microbial fuel cell depicting the voltage generation during the three TPH loading conditions with a 100 ohms resistor. (b) Polarization behavior of the MFC under operation using the three TPH loading conditions.

Fig. 4. Evaluation of the sustainable performance of the soil MFC during the three TPH concentrations. (a) Anodic and cathodic potentials as well as the (b) sustainable power and resistance value at a relative decrease in the anodic potential (RDAP) point.

Fig. 5. Sulfate removal pattern registered in the (a) soil MFC and (b) control operations during the three loading conditions of the petroleum-based hydrocarbons. Cycle numbers 1–3 represent 320 mg TPH per L, 4–6 represent 590 mg TPH per L and 7–8 represent 840 mg TPH per L.

Fig. 6. (a) Removal of the total dissolved solids (TDS) during the three loading conditions of TPH in the soil MFC. (b) Outlet TDS values evaluated in the soil MFC and control operations (the dotted line represents the value of the inlet TDS). (c) Change in pH (from inlet pH of 7.82). Cycle numbers 1–3 represent 320 mg TPH per L, 4–6 represent 590 mg TPH per L and 7–8 represent 840 mg TPH per L.