Effect of cell structure and heat pretreating of the microorganisms on performance of a microbial fuel cell.

While microbial fuel cells are being considered as a tool for energy saving in wastewater treatment facilities, such applications in oil refineries pose a challenge due to harder acclimation of microorganisms. In this research, the effect of heat pretreating mixed culture microorganisms (MCM), and cell cross section, on the performance of a novel cell design with two cross sections (single chamber microbial fuel cells, with circular: SCMFC_CC and rectangular: SCMFC_RC cross section) fed batched with refinery wastewater were investigated. First, using original and heat pretreated MCM, the performance of SCMFC_CC in terms of chemical oxygen demand (COD) removal and electricity production was investigated. Then, using only the heat pretreated MCM, the electricity production of SCMFC_RC was measured and compared with that of SCMFC_CC. Heat pretreatment of MCM improved maximum open circuit voltage (OCV) and maximum power density generated by 14% and 16%, respectively. However, heat pretreatment reduced COD removal by about 4%. The performance of SCMFC_CC in terms of maximum OCV and power density compared to SCMFC_RC was improved by 41% and 279%, respectively. Heat treatment of MCM increases the electricity generation of the cell, while reducing the performance of COD reduction due to decreasing the microorganism varieties in the MCM.

Microbiome assembly and stability during start-up of a full-scale, two-phase anaerobic digester fed cow manure and mixed organic feedstocks.

Carbon transformations during anaerobic digestion are mediated by complex microbiomes, but their assembly is poorly understood, especially in full-scale digesters. Gene-centric metagenomics combining functional and taxonomic classification was performed for an on-farm digester during start-up. Cow manure and organic waste pre-treated in a hydrolysis tank were fed to the methane-producing digester and the volatile solids loading rate was slowly increased from 0 to 3.5 kg volatile solids m-3 d-1 over one year. The microbial community in the anaerobic digester exhibited a high ratio of archaea, which were dominated by hydrogenotrophic methanogens. Bacteria in the anaerobic digester had a high abundance of genes for ferredoxin cycling, H2 generation, and more metabolically complex fermentations than in the hydrolysis tank. In total, the results show that a functionally stable microbiome was achieved quickly during start-up and that the microbiome created in the low-pH hydrolysis tank did not persist in the downstream anaerobic digester.

Oily wastewater treatment by a continuous flow microbial fuel cell and packages of cells with serial and parallel flow connections.

This study reports the results of the application of microbial fuel cells (MFC) in refinery wastewater (RW) treatment. In this research, the effect of hydraulic retention time (HRT), and scale-up on the performance of a novel expandable modular design of single-chamber MFC (SCMFC) has been investigated. In the first part of the paper, the effect of HRT on chemical oxygen demand (COD) removal and electricity generation was examined. The generated steady open-circuit voltage (OCV) was 785 mV at HRT 90 h, and the provided maximum power density (PD) was 113 mW/m2 at HRT 15 h. At HRT of 45 h, COD removal increased up to 87% via an increase in the HRT. In the second part, the scale-up of SCMFC was investigated by serial (SFC) or parallel (PFC) connecting the outlets and inlets of fluid flows. The average produced OCV was 760 mV in PFC mode, and average produced PD in PFC and SFC modes were 97 and 75.6 mW/m2, respectively. COD removal in SFC and PFC modes were reported to be 89 and 42%, respectively. Compared to PFC mode, SFC mode was more efficient in terms of COD removal and coulombic efficiency. However, it produced lower PD compared to PFC mode. It is possible to control the quality and capacity of wastewater treatment by using combining the SFC and PFC mode connections in packages of MFCs.

Base-catalysed decomposition of polychlorinated biphenyls in transformer oils by mixture of sodium hydroxide, glycerol and iron.

In this research, a method based on base-catalysed decomposition (BCD) was developed using sodium hydroxide and glycerol for dechlorination of transformer oils with low levels of polychlorinated biphenyls (PCBs). PCB removal and dechlorination efficiencies were measured by gas chromatography and the silver nitrate titration method, respectively. PCB dechlorination and removal efficiencies after 4 h at 250°C and in the presence of iron were 97.4% and 99.8%, respectively. However, in the absence of iron the same efficiencies were calculated to be 79.4 and 99.7%, respectively. The dielectric loss factor of oil refined at 250°C was 0.0064 and did not meet the required standards to be reused in the transformers. However, that refined at 200°C satisfied the standards with acceptable conversion rates. Use of iron, besides increasing conversion rates, changed the mechanism of the reaction from nucleophilic substitution to a combination of hydrodechlorination and nucleophilic substitution. In the presence of iron, highly chlorinated PCBs were converted to less chlorinated PCBs, and this caused the concentration of less chlorinated PCBs to reach a peak and then decline thereafter. The production of PCB 36 confirmed this. However, in the absence of iron particles, all changes in the PCB concentration curves were downward.

Hot water extraction with in situ wet oxidation: kinetics of PAHs removal from soil.

Finding environmentally friendly and cost-effective methods to remediate soils contaminated with polycyclic aromatic hydrocarbons (PAHs) is currently a major concern of researchers. In this study, a series of small-scale semi-continuous extractions--with and without in situ wet oxidation--were performed on soils polluted with PAHs, using subcritical water (i.e. liquid water at high temperatures and pressures, but below the critical point) as the removal agent. Experiments were performed in a 300 mL reactor using an aged soil sample. To find the desorption isotherms and oxidation reaction rates, semi-continuous experiments with residence times of 1 and 2 h were performed using aged soil at 250 degrees C and hydrogen peroxide as oxidizing agent. In all combined extraction and oxidation flow experiments, PAHs in the remaining soil after the experiments were almost undetectable. In combined extraction and oxidation no PAHs could be detected in the liquid phase after the first 30 min of the experiments. Based on these results, extraction with hot water, if combined with oxidation, should reduce the cost of remediation and can be used as a feasible alternative technique for remediating contaminated soils and sediments.

Hot water extraction with in situ wet oxidation: PAHs removal from soil.

We are reporting the results of a small-scale batch extraction with and without in situ wet oxidation of soils polluted with polycyclic aromatic hydrocarbons (PAHs) using subcritical water (liquid water at high temperatures and pressures but below the critical point as the removal agent). Two types of soil; one spiked with four PAHs, and an aged sample were used. Experiments were carried out in a 300 ml volume reactor in the batch mode. In each experiment, the reactor was filled with 45-50 g of soil and 200-220 ml of double distilled water. For extraction without oxidation, the reactor was pressurized with nitrogen, while for those with the oxidation, an oxidizing agent (air, oxygen or hydrogen peroxide) was used. The extraction only experiments were carried out at 230, 250 and 270 degrees C for spiked soil samples, and at 250 degrees C for aged soil samples, while all of the combined extraction and oxidation experiments were carried out at 250 degrees C. Removal of PAHs from spiked soil in extraction-only experiments was from 79 to 99+% depending on the molecular weight of the PAH. This was in the range of 99.1% to excess of 99.99% for the combined extraction and oxidation. While 28-100% of extracted PAHs can be found in water phase in case of extraction alone, this reduces to a maximum of 10% if the extraction is combined with oxidation. With aged soil similar or comparable results were obtained. Based on these results, extraction with hot water, if combined with oxidation, would probably reduce the cost of post treatment for the water and can be used as a feasible alternative technique for remediation of contaminated soils and sediments.