Sewage enhanced bioelectrochemical degradation of petroleum hydrocarbons in soil environment through bioelectro-stimulation.

The impact of readily biodegradable substrates (sewage and acetate) in bioelectroremediation of hydrocarbons (PW) was evaluated in a bench-scale soil-based hybrid bioelectrochemical system. Addition of bioelectro-stimulants evidenced efficient degradation than control operation. Acetate and sewage were exhibited power density of 1126 mW/m2 and 1145 mW/m2, respectively, which is almost 15 % higher than control (without stimulant, 974 mW/m2). Increased electrochemical activity was correlated well with total petroleum hydrocarbons (TPH) degradation through addition of acetate (TPHR, 525 mg/L, 67.4 %) and sewage (TPHR, 560 mg/L,71.8 %) compared to the control operation (TPHR, 503 mg/L, 64.5 %). Similarly, chemical oxygen demand (COD) reduction was also enhanced from 69.0 % (control) to 72.1 % and 74.6 % with acetate and sewage, respectively. Sewage and acetate also showed a positive role in sulfates removal, which enhanced from 56.0 % (control) to 62.9 % (acetate) and 72.6 % (sewage). This study signifies the superior function of sewage as biostimulant compared to acetate for the bioelectroremediation of hydrocarbons in contaminated soils.

Review on the production of medium and small chain fatty acids through waste valorization and CO2 fixation.

The developing approaches in the recovery of resources from biowastes for the production of renewable value-added products and fuels, using microbial cultures as bio-catalyst have now became promising aspect. In the path of anaerobic digestion, the microorganisms are assisting transformation of a complex organic feedstock/waste to biomass and biogas. This potentiality consequently leads to the production of intermediate precursors of renewable value-added products. Particularly, a set of anaerobic pathways in the fermentation process, yields small-chain fatty acids (SCFA), and medium-chain fatty acids (MCFA) via chain elongation pathways from waste valorization and CO2 fixation. This review focuses on the production of SCFA and MCFA from CO2, synthetic substrates and waste materials. Moreover, the review introduces the metabolic engineering of Escherichia coli and Saccharomyces cerevisiae for SCFAs/MCFAs production. Furtherly, it concludes that future critical research might target progress of this promising approach as a valorization of complex organic wastes.

Characterization of Cellobiohydrolases from Schizophyllum commune KMJ820.

A novel cellobiohydrolase (CBH)-generating fungi have been isolated and categorized as Schizophyllum commune KMJ820 based on morphology and rDNA gene sequence. Cellulose powder was used as carbon source, the total enzyme activity was 11.51 U/ml is noted; which is among the highest amounts of CBH-generating microbes studied. CBH have been purified to homogenize, with pursual of serial chromatography using S. commune supernatants and two different CBHs were found; CBH 1 and 2. The filtered CBHs showed greater activity (V max = 51.4 and 20.8 U/mg) in contrast to CBHs from earlier studies. The MW (molecular weights) of S. commune CBH 1 and 2 were verified to be approximately 50 kDa and 150 kDa, respectively, by size exclusion chromatography. Even though CBHs have been evaluated from other sources, but S. commune CBH is prominent in comparison to other CBHs by its high enzyme activity.

Effects of dissolved organic phase composition and salinity on the engineered sulfate application in a flow-through system.

Engineered sulfate application has been proposed as an effective remedy to enhance the rate-limited biodegradation of petroleum-hydrocarbon-contaminated subsurface environments, but the effects of dissolved organic phase composition and salinity on the efficiency of this method are unknown. A series of flow-through experiments were conducted for 150 days and dissolved benzene, toluene, naphthalene, and 1-methylnaphthalene were injected under sulfate-reducing and three different salinity conditions for 80 pore volumes. Then, polycyclic aromatic hydrocarbons (PAHs) were omitted from the influent solution and just dissolved benzene and toluene were injected to investigate the influence of dissolved phase composition on treatment efficiency. A stronger sorption capacity for PAHs was observed and the retardation of the injected organic compounds followed the order of benzene < toluene < naphthalene < 1-methylnaphthalene. Mass balance analyses indicated that 50 and 15% of toluene and 1-methlynaphtalene were degraded, respectively. Around 5% of the injected naphthalene degraded after injecting > 60 PVs influent solution, and benzene slightly degraded following the removal of PAH compounds. The results showed substrate interactions and composition can result in rate-limited and insufficient biodegradation. Similar reducing conditions and organic utilization were observed for different salinity conditions in the presence of the multi-component dissolved organic phase. This was attributed to the dominant microbial community involved in toluene degradation that exerted catabolic repression on the simultaneous utilization of other organic compounds and were not susceptible to changes in salinity.

Removal of petroleum hydrocarbons and sulfates from produced water using different bioelectrochemical reactor configurations.

Produced water (PW) is a wastewater generated in large quantities from the extraction of oil and gas. PW found to have high amounts of dissolved solids (TDS) and residual petroleum hydrocarbons causing considerable damage to the environment. PW also contains sulfates in significant amounts, due to which treating this wastewater is essential prior to discharge. The present study was aimed for bioelectrochemical treatment of PW and simultaneous bioelectrogenesis in the two most studied configurations viz., single and dual chamber microbial fuel cells (MFCs). The study evidenced treatment of recalcitrant pollutants of PW. Both MFCs were operated by keeping similar operating conditions such as anode chamber volume, hydraulic retention time (HRT) for batch mode of operation, electrode materials, inlet characteristics of PW and ambient temperature. Among both configurations, dual chamber MFC showed higher efficiency with respect to bioelectrogenesis (single chamber - 789 mW/m2; dual chamber - 1089 mW/m2), sulfates removal (single chamber - 79.6%; dual chamber - 93.9%), total petroleum hydrocarbons removal (TPH, single chamber - 47.6%; dual chamber - 53.1%) and chemical oxygen demand degradation (COD, single chamber - 0.30 kg COD/m3-day (COD removal efficiency, 54.7%); dual chamber - 0.33 kg COD/m3-day (COD removal efficiency, 60.2%)). Evaluated polarization behavior of both MFCs were also evidenced the effective response of the electroactive anodic biofilm.

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

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 TPHR per L (320 mg TPH per L) and 356 mg TPHR 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.

Sorption of benzene and naphthalene on (semi)-arid coastal soil as a function of salinity and temperature.

Considerable activities from the oil and natural gas sector have risen some concerns about the pollution of soil and groundwater by petroleum hydrocarbons (PHCs) in (semi)-arid coastal regions. The understanding of the fate and transport of PHCs in these regions is therefore necessary to develop strategies for remediation. To quantify the sorption rates of PHCs in (semi)-arid coastal soil environments, we conducted a series of controlled-laboratory batch experiments under variable temperature and salinity conditions. The soil samples were collected from the eastern coast of Qatar which is near the two largest off-shore oil and natural gas fields of the country (North Gas and Al-Shaheen Oil Fields), and the volatile benzene and naphthalene were used as PHCs. The characterization of soil samples showed sand classification with the texture class of sabkha and saline beach sandy soils with calcite as potential dominant mineral. The concentrations of dissolved chloride and sodium were found to be high (> 400 mg L-1) with a chloride-to­sodium ratio of about 1.7. The results of sorption experiments showed that the rates of naphthalene sorption were more than for benzene, where the initial aqueous concentrations of benzene and naphthalene were reduced at equilibrium due to sorption by about 14-25% and 65-79%, respectively. This difference was attributed mainly to the organic carbon-water partitioning coefficient which is higher for naphthalene. The sorption rate experiments showed that sorption was stronger for benzene under higher salinity and lower temperature conditions. The sorption of naphthalene was not affected by the change in salinity but increased by 18% when the temperature decreased from 35 to 5 °C. A sorption kinetic model was also applied to define the sorption behavior of benzene and naphthalene for the coastal soil collected in Qatar and the best fits were achieved with the Langmuir sorption isotherm.

Cylindrical graphite based microbial fuel cell for the treatment of industrial wastewaters and bioenergy generation.

Cylindrical graphite microbial fuel cell (MFC) configuration designed by eliminating distinct casing and membrane was evaluated for bioelectrogenesis and treatment of real-field wastewaters. Both petroleum refinery wastewater (PRW) and Labanah whey wastewater (LW) were used as substrates, and investigated for electricity generation and organic removal under batch mode operation. PRW showed higher bioelectricity generation (current and power generation of 3.35mA and 1.12mW at 100Ω) compared to LW (3.2mA and 1.02mW). On the contrary, higher substrate degradation efficiency was achieved using LW (72.76%) compared to PRW (45.06%). Superior function of MFC operation in terms of volumetric power density (PRW, 28.27W/m3; LW, 23.23W/m3) suggesting the feasibility of using these wastewaters for bioelectricity generation. Large sources of wastewater that generating in the Middle-East countries have potential to produce renewable energy from the treatment, which helps for the sustainable wastewater management and simultaneous renewable energy production.

Induced bioelectrochemical metabolism for bioremediation of petroleum refinery wastewater: Optimization of applied potential and flow of wastewater.

Hybrid based bioelectrochemical system (BES) configured with embedded anode and cathode electrodes in soil was tested for the bioelectrochemical degradation of petroleum refinery wastewater (PRW). Four applied potentials were studied to optimize under batch mode operation, among which 2 V resulted in higher COD degradation (69.2%) and power density (725 mW/m2) during 7 days of operation. Further studies with continuous mode of operation at optimized potential (2 V) showed that hydraulic retention time (HRT) of 19 h achieved the highest COD removal (37%) and highest power density (561 mW/m2). BES function with respect to treatment efficiencies of other pollutants of PRW was also identified with respect to oil and grease (batch mode, 91%; continuous mode, 34%), total dissolved salts (batch mode, 53%; continuous mode, 24%) and sulfates (batch mode, 59%; continuous mode, 42%). Soil microenvironment in association with BES forms complex processes, providing suitable conditions for efficient treatment of PRW.

Enhanced treatment of petroleum refinery wastewater by short-term applied voltage in single chamber microbial fuel cell.

Electrochemically active anodic biofilm that has adapted under mild applied potentials in the range 100-500 mV was evaluated for its improved bioelectrogenesis and bioelectrochemical treatment of petroleum refinery wastewater (PRW) in a single chamber air cathode microbial fuel cell (MFC). MFC operation with 500 mV as supplemental voltage has exhibited a maximum power density of 132 mW/m2, which was three times higher than control MFC (45 mW/m2). Similarly, highest substrate removal efficiency (48%) was also obtained with the MFC of 500 mV, followed by 300 mV (37%), 100 mV (32%) and control (27%). Adaptation under applied potential conditions also exhibited enhanced degradation efficiency of diesel range organics (DROs)/straight chain-alkanes. The strategy efficiently reduced DROs with the maximum efficiency of 89% (500 mV), which is almost 50% higher than that of the control system (59%), demonstrating the effectiveness of using supplemented voltage in treating PRW.

Experimental investigation of the influence of grain geometry on residual NAPL using synchrotron microtomography.

The objective of this work was to investigate the impact of grain geometry (size and shape) of porous media on the morphology of residual NAPL. Synchrotron microtomography was used to obtain maps of residual NAPL in multiphase systems. High-resolution, three-dimensional images of natural sand systems, comprising a range of grain sizes and shapes were imaged and analyzed. Findings indicate that residual NAPL saturation is influenced by the shapes of grains of the porous medium more than their sizes. In systems composed of grains with similar sphericity and angularity, residual saturations are independent of median grain sizes at the same operating regime (capillary-controlled regime in this work). Residual saturations tend to increase as the system comprised more angular or non-spherical grains where relatively large NAPL blobs are entrapped in such systems. While volumes of individual blobs tend to decrease as grain size decreases, grain geometry has more profound effects on the morphology of the residual NAPL blobs. Within a system composed of grains with similar shape characteristics, total NAPL-water interfacial area increases as grain sizes decrease where a large number of small blobs are trapped. Total meniscus NAPL-water interfacial area exhibits a linear relation with total interfacial area where it tends to increase as grain sizes decrease. However, while meniscus interfacial areas of individual blobs are highly influenced by pore geometry; residual blobs trapped in pores with complex geometry tend to have higher meniscus interfacial areas due to their branched nature which increases contacts with the wetting phase.

Impact of wettability on pore-scale characteristics of residual nonaqueous phase liquids.

The objective of this paper was to investigate the impact of wettability of porous media on pore-scale characteristics of residual nonaqueous phase liquids (NAPLs). Synchrotron X-ray microtomography was used to obtain high-resolution three-dimensional images of fractionally wet sand systems with mean grain size of 250 microm. Pore-scale characteristics of NAPL blobs such as volume, lengths, interfacial areas, and sphericity index were computed using three-dimensional image processing algorithms. Four systems comprised of 100, 50, 25, and 0% NAPL-wet mass fractions containing the residual NAPL were imaged and analyzed. Findings indicate that spatial variation in wettability of porous media surfaces has a significant impact on pore-scale characteristics of residual NAPL blobs in saturated porous media systems. As the porous media comprises more water-wet surfaces, residual NAPL blobs increase in size and length due to the entrapment at large pore bodies. NAPL-water interfacial areas tend to increase as the NAPL-wet surface fractions increase in the systems. Overall residual NAPL saturations are less in fractionally wet systems and increase as the systems become more NAPL-wet or water-wet.

A pore-scale investigation of a multiphase porous media system.

Pore-scale processes govern fundamental behavior in multiphase porous media systems. A high-resolution, three-dimensional image of the interior of a multiphase porous media system was obtained using synchrotron X-ray tomography. The system was imaged at a resolution of 12.46 mum following entrapment of the nonwetting phase at residual saturation. First, the physically representative network structure of the porous media system is extracted from the void space. This provides a direct mapping of the pore bodies and throats and enables pore-level calculations of coordination numbers, aspect ratios, and pore body and throat correlations. Next, algorithms developed to calculate properties of the entrapped nonwetting phase, such as volume, sphericity, interfacial area, and orientation, are applied to the residual nonwetting phase blobs. Finally, correlations between the pore network structure and nonwetting phase characteristics are examined. As expected, it was found that the nonwetting phase was trapped primarily in the largest pore spaces, the pore bodies with the highest aspect ratios, and the pore bodies with the highest coordination numbers. This work shows that, while there may be limitations related to the ability to capture REV-sized domains for some of the multiphase flow properties and phenomena, high-resolution X-ray tomography is able to provide the high quality datasets needed to observe and quantify the pore-scale phenomena and processes that govern multiphase flow in unconsolidated porous media systems.