• Energy Research

The aim of this paper is to provide insight into research and activities of in situ remediation to remove petroleum hydrocarbon pollutants from a contaminated aquifer’s sediment, located near two radial collector wells of a water supply system. It was decided that the most appropriate method for remediation of this aquifer’s sediment is in situ bioremediation because it is clean, efficient and sustainable technology. Before the start of the bioremediation process, it was necessary to isolate and cultivate the microorganisms present at the contamination site, so they could be later applied in the bioremediation process. The samples before and after the bioremediation were studied using both GC and GC × GC–MS to determine how the concentrations of contaminants changed over time. Additionally, in this paper, a spatiotemporal representation of the change in hydrocarbon content by depth within the zone of the highest contamination over time is shown. After 12 months of bioremediation, the hydrocarbon content in the samples decreased by 82.0%, and based on GCxGC-MS analysis, the order of degradation of various hydrocarbon groups was as follows: steranes (99.6%), isoprenoids (98.4%), benzene derivatives (98.4%), alkanes (97.2%), and terpenes (49.3%). The exponential decay model showed the greatest decomposition rate of hydrocarbons occurred at depths of 8–10 m, with an average decay constant of 0.227, independent of the initial concentration of hydrocarbons. To the best of our knowledge, to date, the described approach has not been applied to an aquifer (the simultaneous treatment of groundwater and its associated sediment layers).

The problem of wastewater has long been ubiquitous and has great consequences for the environment and its inhabitants. Microbial fuel cells (MFCs) have enormous potential for the treatment of wastewaters polluted with azo dyes. The amount of energy that can be produced from a single-chamber MFC is sufficient to perform decolorization and degradation of such dyes, which are widely used in the textile industry. This study on the azo dye, reactive black 5 (RB5), provides an alternative method through three parallel-connected MFCs to obtain electricity that directly serves for the dye's electrochemical degradation. We examined degradation followed by decolorization of RB5 using Fe and Pt electrodes, together with H2O2, to achieve the electro-Fenton process. The amount of voltage produced (295 mV), the current density (276 mA m-3) and the power density (50 mW m-3) were sufficient to degrade 25 mg L-1 RB5 dye with 0.5 mM H2O2 in just 2 h. The dye degradation mechanism was investigated using UV-VIS, FT-IR and HPLC-MS/MS. The ecotoxicity of the degradation products was assessed using a bacterial model, Aliivibrio fischeri. These tests showed that there was successful degradation of the dye to products whose toxicity is less than that of RB5.