Towards the optimisation of ceramic-based microbial fuel cells: A three-factor three-level response surface analysis design.

Microbial fuel cells (MFCs) are an environment-friendly technology, which addresses two of the most important environmental issues worldwide: fossil fuel depletion and water scarcity. Modelling is a useful tool that allows us to understand the behaviour of MFCs and predict their performance, yet the number of MFC models that could accurately inform a scale-up process, is low. In this work, a three-factor three-level Box-Behnken design is used to evaluate the influence of different operating parameters on the performance of air-breathing ceramic-based MFCs fed with human urine. The statistical analysis of the 45 tests run shows that both anode area and external resistance have more influence on the power output than membrane thickness, in the range studied. The theoretical optimal conditions were found at a membrane thickness of 1.55 mm, an external resistance of 895.59â€¯Ω and an anode area of 165.72 cm2, corresponding to a maximum absolute power generation of 467.63 µW. The accuracy of the second order model obtained is 88.6%. Thus, the three-factor three-level Box-Behnken-based model designed is an effective tool which provides key information for the optimisation of the energy harvesting from MFC technology and saves time in terms of experimental work.

Synthesis of low cost organometallic-type catalysts for their application in microbial fuel cell technology.

Microbial fuel cells (MFCs) are a promising technology that generates electricity from several biodegradable substrates and wastes. The main drawback of these devices is the need of using a catalyst for the oxygen reduction reaction at the cathode, which makes the process relatively expensive. In this work, two low cost materials are tested as catalysts in MFCs. A novel iron complex based on the ligand n-phenyledenparaethoxy aniline has been synthesized and its performance as catalyst in single chamber MFCs containing ionic liquids has been compared with a commercial inorganic material such as Raney nickel. The results show that both materials are suitable for bioenergy production and wastewater treatment in the systems. Raney nickel cathodes allow MFCs to reach a maximum power output of 160 mW.m-3 anode, while the iron complex offers lower values. Regarding the wastewater treatment capacity, MFCs working with Raney nickel-based cathodes reach higher values of chemical oxygen demand removal (76%) compared with the performance displayed by the cathodes based on Fe-complex (56%).

Ionic liquid technology to recover volatile organic compounds (VOCs).

Volatile organic compounds (VOCs) comprise a wide variety of carbon-based materials which are volatile at relatively low temperatures. Most of VOCs pose a hazard to both human health and the environment. For this reason, in the last years, big efforts have been made to develop efficient techniques for the recovery of VOCs produced from industry. The use of ionic liquids (ILs) is among the most promising separation technologies in this field. This article offers a critical overview on the use of ionic liquids for the separation of VOCs both in bulk and in immobilized form. It covers the most relevant works within this field and provides a global outlook on the limitations and future prospects of this technology. The extraction processes of VOCs by using different IL-based assemblies are described in detail and compared with conventional methods This review also underlines the advantages and limitations posed by ionic liquids according to the nature of the cation and the anions present in their structure and the stability of the membrane configurations in which ILs are used as liquid phase.

Microalgae as substrate in low cost terracotta-based microbial fuel cells: Novel application of the catholyte produced.

In this work, the by-product generated during the operation of cylindrical MFCs, made out of terracotta material, is investigated as a feasible means of degrading live microalgae for the first time. In addition to the low cost materials of this design, the reuse of the solution produced in the cathode renders the technology truly green and capable of generating bioenergy. In this study, the effect of a light/dark cycle or dark conditions only on the digestion of live microalgae with the catholyte is investigated. The results show that a combination of light/dark improves degradation and allows algae to be used as substrate in the anode. The addition of 12.5mL of a 1:1 mix of catholyte and microalgae (pre-digested over 5days under light/dark) to the anode, increases the power generation from 7µW to 44µW once all the organic matter in the anode had been depleted.

Effect of circulatory assistance on premature death and long-term prognosis.

BACKGROUND: Patients undergoing urgent heart transplantation (HT) have a poorer prognosis and more long-term complications. The objective of this study was to compare the preoperative course in patients undergoing urgent HT according to the need for preoperative intra-aortic balloon counterpulsation (IABP). MATERIALS AND METHODS: We studied 102 consecutive patients including 23 patients with IABP who underwent urgent HT between January 2000 and September 2006. We excluded patients who received combination transplants, those who underwent repeat HT, and pediatric patients who underwent HT. The statistical methods used were the t test for quantitative variables and the chi(2) test for qualitative variables. A logistic regression model was constructed to assess the possible relationship between IABP and other variables on premature death within 30 days after HT. RESULTS: Mean (SD) patient-age was 50 (10) years. No significant differences were observed in baseline characteristics between the IABP and the non-IAPB groups. The IABP patient group had higher rates of acute graft failure (45.5% vs 35.4%; P = .46) and premature death (18.8% vs 14.8%; P = .67) and shorter long-term survival (40.6 [34.9] vs 54.5 [43.7] mo; P = .30). Multivariate analysis demonstrated no association between the need for IABP and increased frequency of premature death. CONCLUSIONS: Use of IABP is not associated with premature or late death. We recommend use of IABP in patients with acute decompensated heart failure to stabilize them before HT.

Effect of clinical trials on survival after heart transplantation.

UNLABELLED: The application of clinical trials (CTs) to daily practice is based on the assumption that the patients included in these trials are similar to those seen on a daily basis. We performed a retrospective study to evaluate patient survival depending on whether they were included in a CT. We studied 217 patients who underwent heart transplantation (HT) between January 2000 and September 2006. We excluded patients who received combination transplants, those who underwent repeat HT, and pediatric patients who underwent HT. In total, 54 patients were included in a CT and 163 were not (NCT). The statistical tests included the t test, the chi(2) test and the Kaplan-Meier method. RESULTS: Patients in the NCT group were in worse condition at HT, with a greater percentage of inotropic treatments pre-HT (36% vs 17%; P = .005), emergency transplants procedures (30% vs 13%; P = .01), and worse functional status pre-HT (P = .03). The NCT group exhibited lower survival (80.37% vs 87.04%; P = 0.13, log-rank test). There were no significant differences in the other analyzed variables. CONCLUSIONS: Patients included in CTs tend to have better long-term survival rates, for several reasons: patients in the CT group were more stable at HT (selection bias), and the close follow-up of patients in CTs makes it more likely that any complication will be detected and treated early (follow-up bias).

Influence of traditional cardiovascular risk factors in the recipient on the development of cardiac allograft vasculopathy after heart transplantation.

BACKGROUND: Cardiac allograft vasculopathy (CAV) is the leading cause of death heart transplant (HT) recipients after the first year. We assessed the influence of cardiovascular risk factors (CVRFs) in HT recipients on the development of CAV after 1 year of follow-up. MATERIALS AND METHODS: From 2001 to 2005, we studied 72 patients who received a HT and survived for at least 1 years. All patients underwent coronary arteriography and intravascular ultrasonography at 1 year after HT. Cardiac allograft vasculopathy was defined as intimal proliferation of 0.5 mm or more. The analyzed CVRFs were age, sex, body mass index, diabetes mellitus, hypertension, dyslipidemia, and smoking. We also considered the heart disease that was the reason for HT. The statistical tests used in the univariate analysis were the t and chi(2) tests. Logistic regression was performed with the variables obtained at univariate analysis. RESULTS: Mean (SD) recipient age at HT was 51 (9) years. Eighty patients (90.5%) were men. Dyslipidemia was significantly associated with a greater incidence of CAV at 1 year (68.3% vs 41.9%; P = .03). Ischemia, as opposed to all other causes, was also significantly associated with CAV (69.4% vs 44.4%; P = .03). Older age, hypertension, smoking history, and high body mass index were associated with a higher incidence of CAV, albeit without statistical significance. At multivariate analysis, dyslipidemia was the most significant CVRF (P = .045) for the development of CAV. CONCLUSIONS: Recipient dyslipidemia is a risk factor for the development of CAV in HT. The remaining traditional CVRFs are more weakly associated with CAV. After HT close monitoring of recipients with pretransplantation CVRFs is essential for early detection of CAV.

Impact of smoking on survival after heart transplantation.

INTRODUCTION: Smoking is an important risk factor in any population group. According to previous studies, having been a smoker before heart transplantation (HT) confers a greater likelihood of developing any type of tumor or other complication after HT. Our objective was to determine the impact of having been a smoker before HT on survival, respiratory complications during the postoperative period, and long-term tumor development. MATERIALS AND METHODS: After excluding combined transplantations, pediatric transplantations, and retransplantations, we retrospectively reviewed 288 HT performed between November 1987 and September 2006. We divided patients into nonsmokers (including those who quit smoking more than 1 year before HT (n = 163), exsmokers for less than 1 year (n = 76), and those who smoked until HT (n = 49). The statistical tests were chi-square, Student t, analysis of variance (ANOVA), and Kaplan-Meier curves. RESULTS: There were more male patients among smokers and exsmokers than nonsmokers (93.9% vs 96.1% vs 82%, respectively; P = .003). There were no differences in baseline characteristics between the groups. Exsmokers remained intubated for a longer time than smokers or nonsmokers (33.4 +/- 44.6 vs 14.2 +/- 7.3 vs 17.9 +/- 19.2, respectively; P = .05). We observed the same trend in recovery unit stay (7.9 +/- 10.5 days vs 4.4 +/- 1.88 days vs 4.84 +/- 3.49 days, respectively; P = .021). The development of any type of tumor was also more frequent among smokers and exsmokers, although not significantly. The survival rate was similar in nonsmokers and exsmokers, although higher than in smokers (89.57 vs 92.11% vs 81.63%, respectively; P = .031). We did not observe differences in the causes of death. CONCLUSIONS: Patients who smoke or have smoked until shortly before HT showed a poorer prognosis and a longer recovery unit stay. There was also a trend to increased tumor development.