Journal of Environmental Engineering

The effect of influent chemical oxygen demand (COD), hydraulic retention time (HRT), and influent pH on COD removal efficiency and power generation was studied in a dual-chambered microbial fuel cell (MFC) having stainless-steel mesh electrodes and treating synthetic wastewater. Statistical models were formulated based on these three variables to predict the responses, namely COD removal efficiency and power generation, in MFC using a two-level full factorial design. It was observed from statistical analyses that all the three variables affected the COD removal efficiency, whereas proper combination of the operating variables was of utmost importance in enhancing power generation. Average influent COD concentration of $2200–2400\mathrm{mg}/\mathrm{L}$ and HRT of 22–25 h was found to be optimum for achieving optimal COD removal efficiency and power. Validation of the model’s predictions for treatment of synthetic wastewater revealed the efficacy of these models. Under optimal conditions when these MFCs were operated with a graphite plate cathode and using aerated distilled water and persulfate as cathodic electrolyte, respective volumetric power densities of 979 and $\mathrm{7,408}\mathrm{mW}/{\mathrm{m}}^3$ were observed.

This study evaluates the ability of biostimulation to enhance the bioremediation of soil contaminated with oily compounds as compared with natural attenuation. The soil was contaminated with 4% of diesel or biodiesel and biostimulated with phycocyanin (a proteic emulsifier extracted from the Spirulina platensis biomass), an inactive biomass of S. platensis, or ammonium sulfate. Experiments were conducted for 60 days, whereas the biodegradation was measured through the determination of carbon dioxide (${\mathrm{CO}}_2$) evolution and oils and grease. Higher ${\mathrm{CO}}_2$ evolution was observed in the soil contaminated with the biodiesel and phycocyanin as biostimulant (2,997.35 mg ${\mathrm{C}\text{-}\mathrm{CO}}_2$) and in the soil contaminated with diesel oil with the inactive biomass S. platensis as biostimulant (2,454.89 mg ${\mathrm{C}\text{-}\mathrm{CO}}_2$). The highest biodegradation was achieved by using phycocyanin as a biostimulant for biodiesel contamination (88.75%) or inactive biomass of S. platensis (63.89%) for diesel as contaminant. Natural attenuation resulted in the lower ${\mathrm{CO}}_2$ evolution of 386.5 and 282.5 mg ${\mathrm{C}\text{-}\mathrm{CO}}_2$ and biodegradation rates of 42.4 and 31.3% for biodiesel and diesel, respectively.

Pure aluminum (hydr)oxide (AlOOH) and AlOOH-amended sodalite exhibited good performance in column fluoride removal studies in terms of service time (time until breakthrough), energy required for operation, and cost. The long service times (2,000 and 1,370 bed volumes for pure AlOOH and AlOOH-amended sodalite, respectively) were due to the relatively large mass loading of AlOOH, as well as the formation of a very adsorptive amorphous AlOOH phase at a slightly acidic pH (5.3). There was significant aluminum release from the columns during the first 70 bed volumes, which was attributed to outflow of AlOOH particles. Subsequently, the effluent aluminum concentration stayed below $0.2\mathrm{mg}/\mathrm{L}$ until breakthrough, after which it increased, possibly due to fluoride-induced AlOOH dissolution and formation of aqueous aluminum–fluoride complexes. The pumping energy required to treat $1{\mathrm{m}}^3$ of water using AlOOH-amended sodalite in a community-scale filter (approximately $2.2\times {10}^{-2}\mathrm{kWh}/{\mathrm{m}}^3$) is two orders of magnitude lower than the energy required to operate electrocoagulation and reverse osmosis, and is favorable for the practical use of AlOOH-amended sodalite. In the absence of a continuous power supply, hydrostatic energy could also be used to run a community-scale filter using an elevated water tank. The relatively low cost of these materials (e.g., $1.05 to produce sufficient AlOOH-amended sodalite to treat $1{\mathrm{m}}^3$ of water) makes them appealing for use in developing regions. The overall materials costs can be further decreased by regeneration with 0.01 M sodium hydroxide.

Ganoderma lucidum’s potential to decolorize and detoxify malachite green (MG) was studied. A Plackett-Burman experimental design to select operational factors and conditions favoring decolorization associated with laccase activity was performed. The most influential variables based on this statistical optimization were temperature, rpm for flask agitation, inoculum percentage, and dye concentration. Based on these features, removal experiments for 96 h were performed. Following thr 96-h removal assays, it was demonstrated that viable biomass at different glucose concentrations was able to remove over 90% MG at a $10\mathrm{mg}/\mathrm{L}$ concentration, evidencing a positive correlation with laccase activity. Adsoprtion studies allowed to evidence acid pHs favored MG adsorption, with the Elovich model best describing the chimioadsorption phenomenon. Finally, it was demonstrated that MG ($10{\mathrm{mgL}}^{-1}$) without treatment was highly toxic for Lactuca sativa seed germination index (GI) ($<50\%$). This index increased when seeds were exposed to MG solution after it was treated with G. lucidum viable biomass (VB).