Procedure for determining maximum sustainable power generated by microbial fuel cells

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.     

Uranium immobilization by sulfate-reducing biofilms grown on hematite, dolomite, and calcite

Biofilms of sulfate-reducing bacteria Desulfovibrio desulfuricans G20 were used to reduce dissolved U(VI) and subsequently immobilize U(IV) in the presence of uranium-complexing carbonates. The biofilms were grown in three identically operated fixed bed reactors, filled with three types of minerals: one noncarbonate-bearing mineral (hematite) and two carbonate-bearing minerals (calcite and dolomite). The source of carbonates in the reactors filled with calcite and dolomite were the minerals, while in the reactor filled with hematite it was a 10 mM carbonate buffer, pH 7.2, which we added to the growth medium. Our five-month study demonstrated that the sulfate-reducing biofilms grown in all reactors were able to immobilize/reduce uranium efficiently, despite the presence of uranium-complexing carbonates.     

Drawbacks in the use of the Biuret method for determination of the same protein in differently treated fish samples

There was a considerable difference in absorption (due to proteins) at 540 nm between fresh fish and frozen, thawed fish flesh using the Biuret method on the same raw material on the same day. This difference was increased after a day, giving lower results.     

Simultaneous evaluation of effective diffusion coefficients of the substrates in a biofilm with a novel experimental method

In this study, a pure culture of Zoogloea ramigera was grown as a film on active carbon particles in a differential fluidized bed biofilm reactor (DFBBR) as a novel experimental system for the application of diffusion-reaction models. The effective diffusion coefficients of the essential substrates; glucose, ammonium ion and oxygen in the active biofilm were simultaneously calculated. The values of effective diffusion coefficients in the active biofilm to those in water varied between 13–34, 48–96 and 28–48% for glucose, ammonium ion and oxygen, respectively, at different biofilm densities, which is in fair agreement with the literature.     

Immobilization of U(VI) from oxic groundwater by Hanford 300 Area sediments and effects of Columbia River water

Regions within the U.S. Department of Energy Hanford 300 Area (300 A) site experience periodic hydrologic influences from the nearby Columbia River as a result of changing river stage, which causes changes in groundwater elevation, flow direction and water chemistry. An important question is the extent to which the mixing of Columbia River water and groundwater impacts the speciation and mobility of uranium (U). In this study, we designed experiments to mimic interactions among U, oxic groundwater or Columbia River water, and 300 A sediments in the subsurface environment of Hanford 300 A. The goals were to investigate mechanisms of: 1) U immobilization in 300 A sediments under bulk oxic conditions and 2) U remobilization from U-immobilized 300 A sediments exposed to oxic Columbia River water. Initially, 300 A sediments in column reactors were fed with U(VI)-containing oxic 1) synthetic groundwater (SGW), 2) organic-amended SGW (OA-SGW), and 3) de-ionized (DI) water to investigate U immobilization processes. After that, the sediments were exposed to oxic Columbia River water for U remobilization studies. The results reveal that U was immobilized by 300 A sediments predominantly through reduction (80-85%) when the column reactor was fed with oxic OA-SGW. However, U was immobilized by 300 A sediments through adsorption (100%) when the column reactors were fed with oxic SGW or DI water. The reduced U in the 300 A sediments fed with OA-SGW was relatively resistant to remobilization by oxic Columbia River water. Oxic Columbia River water resulted in U remobilization (∼7%) through desorption, and most of the U that remained in the 300 A sediments fed with OA-SGW (∼93%) was in the form of uraninite nanoparticles. These results reveal that: 1) the reductive immobilization of U through OA-SGW stimulation of indigenous 300 A sediment microorganisms may be viable in the relatively oxic Hanford 300 A subsurface environments and 2) with the intrusion of Columbia River water, desorption may be the primary process resulting in U remobilization from OA-SGW-stimulated 300 A sediments at the subsurface of the Hanford 300 A site.     

Analysis of tapered preforms in cold upsetting

Upset forging is usually carried out with a sequence of stages and the tapered preforms are commonly used. The preforms should be free from flash formation and buckling injuries. In this paper, the results that depend on elastic–plastic finite element analysis of taper upset forging are given. The buckling analysis was realized by using the Modified Riks method. For a given upset ratio which is the ratio of unsupported length to diameter of the initial billet, reduction in the height of the billet and the diameter ratio are the important design parameters in taper upsetting. For several values of the design parameters, the analysis has been carried out and the results have been compared with the results of the well-known Meyer's experiment and Gökler's suggestions. In the analysis, the perfectly square end (ideal billet case) and the end with face inclination angle were considered as two different end conditions of the billet. The results for the ideal billet case are in good-agreement with Meyer's results. The end-face inclination angle, which is a significant imperfection on the billet, reduces the limits of allowable upset ratio. It has been observed that although the tapered header dies designed at the limits suggested by Meyer produce flashless preforms, in some of the cases, injuries due to buckling are not eliminated. However, Gökler's suggested limits provide elimination of both flash formation and injuries due to buckling.     

The effects of conceptual change texts accompanied with animations on overcoming 11th grade students’ alternative conceptions of chemical bonding

This paper aims to determine the effect of conceptual change texts accompanied with computer animations on 11th grade students’ understanding and alternative conceptions related to chemical bonding. One experimental group (EG; N = 28) and one comparison group (CG; N = 30) were used in the study. While the comparison group taught traditional instruction, the experimental group received conceptual change text accompanied with computer animations instruction. Chemical bonding achievement test was applied as pre-test, post-test and delayed test to collect data. The results of the study indicated that while there is no statistically significant difference between groups in pre-test, performance of EG students is greater than the CG ones in post-test and delayed test. And also, the EG students are better in remediating their alternative conceptions related to chemical bonding. Based on the study, it is concluded that conceptual change texts combined with computer animations can be effective instructional tools to improve students’ conceptual understanding of chemical concepts.     

Antimicrobial Particulate Silver Coatings on Stainless Steel Implants for Fracture Management

We have used particulate silver coating on stainless steel to prevent in vivo bacterial infection. Stainless steel is commonly used as an implant material for fracture management. The antimicrobial use of silver has been well documented and studied, therefore the novelty of this research is the use of a particulate coating as well as facing the real world challenges of a fracture repair implant. The variable parameters for applying the coating were time of deposition, silver solution concentration, voltage applied, heat treatment temperature between 400 to 500 °C and time. The resultant coating is shown to be non-toxic to human osteoblasts using an MTT assay for proliferation and SEM images for morphology. In vitro silver release studies of various treatments were done using simulated body fluid. The bactericidal effects were tested by challenging the coatings with P. aeruginosa in a bioreactor and compared against uncoated stainless steel. A 13-fold reduction in bacteria was observed at 24 hours and proved to be statistically significant.     

Analysis of voltage and frequency-dependent series resistance and interface states of Al/ZnCo2O4: Gelatin/n-Si diode

Journal of Materials Science: Materials in Electronics - In this work, which aims to investigate the capacitance and conductance properties of ZnCo2O4-doped Gelatin, 5% ZnCo2O4-doped Gelatin film...     

Use of Fenton oxidation to improve the biodegradability of a pharmaceutical wastewater

The applicability of Fenton's oxidation to improve the biodegradability of a pharmaceutical wastewater to be treated biologically was investigated. The wastewater was originated from a factory producing a variety of pharmaceutical chemicals. Treatability studies were conducted under laboratory conditions with all chemicals (having COD varying from 900 to 7000 mg/L) produced in the factory in order to determine the operational conditions to utilize in the full-scale treatment plant. Optimum pH was determined as 3.5 and 7.0 for the first (oxidation) and second stage (coagulation) of the Fenton process, respectively. For all chemicals, COD removal efficiency was highest when the molar ratio of H(2)O(2)/Fe(2+) was 150-250. At H(2)O(2)/Fe(2+) ratio of 155, 0.3M H(2)O(2) and 0.002 M Fe(2+), provided 45-65% COD removal. The wastewater treatment plant that employs Fenton oxidation followed by aerobic degradation in sequencing batch reactors (SBR), built after these treatability studies provided an overall COD removal efficiency of 98%, and compliance with the discharge limits. The efficiency of the Fenton's oxidation was around 45-50% and the efficiency in the SBR system which has two reactors each having a volume of 8m(3) and operated with a total cycle time of 1 day, was around 98%, regarding the COD removal.