Biofouling is referred to as the unwanted deposition and growth of biofilms. This phenomenon can occur in an extremely wide range of situations, from the colonisation of medical devices to the ...production of ultra-pure, drinking and process water and the fouling of ship hulls, pipelines and reservoirs. Although biofouling occurs in such different areas, it has a common cause, which is the biofilm. Biofilms are the most successful form of life on Earth and tolerate high amounts of biocides. For a sustainable anti-fouling strategy, an integrated approach is suggested which includes the analysis of the fouling situation, a selection of suitable components from the anti-fouling menu and an effective and representative monitoring of biofilm development.
•After over 50 years, research has failed to answer fundamental questions related to MIC.•Research has not provided tools for detection of MIC in the field.•There are no systematic programs to ...mitigate and prevent MIC.•Both require advancement of reliable and predictive MIC models.•It is suggested that proactive, integrated approaches be used for MIC prevention and mitigation.
Microbially influenced corrosion (MIC), is acknowledged to be the direct cause of catastrophic corrosion failures, with associated damage costs ranging to many billions of US$ annually. In spite of extensive research and numerous publications, fundamental questions relating to MIC remain unanswered. The following review provides an overview of current MIC research and stresses the lack of information related to MIC recognition, prediction and mitigation. The review establishes a link between management decisions and root causes. A holistic, proactive approach to MIC is suggested in which an entire system is considered, monitored and improved.
Biofouling causes performance loss in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane operation for process and drinking water production. The development of biofilm formation, ...structure and detachment was studied in-situ, non-destructively with Optical Coherence Tomography (OCT) in direct relation with the hydraulic biofilm resistance and membrane performance parameters: transmembrane pressure drop (TMP) and feed-channel pressure drop (FCP). The objective was to evaluate the suitability of OCT for biofouling studies, applying a membrane biofouling test cell operated at constant crossflow velocity (0.1 m s−1) and permeate flux (20 L m−2h−1).
In time, the biofilm thickness on the membrane increased continuously causing a decline in membrane performance. Local biofilm detachment was observed at the biofilm–membrane interface.
A mature biofilm was subjected to permeate flux variation (20 to 60 to 20 L m−2h−1). An increase in permeate flux caused a decrease in biofilm thickness and an increase in biofilm resistance, indicating biofilm compaction. Restoring the original permeate flux did not completely restore the original biofilm parameters: After elevated flux operation the biofilm thickness was reduced to 75% and the hydraulic resistance increased to 116% of the original values. Therefore, after a temporarily permeate flux increase the impact of the biofilm on membrane performance was stronger. OCT imaging of the biofilm with increased permeate flux revealed that the biofilm became compacted, lost internal voids, and became more dense. Therefore, membrane performance losses were not only related to biofilm thickness but also to the internal biofilm structure, e.g. caused by changes in pressure.
Optical Coherence Tomography proved to be a suitable tool for quantitative in-situ biofilm thickness and morphology studies which can be carried out non-destructively and in real-time in transparent membrane biofouling monitors.
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•In-situ imaging of biofilm thickness and structure.•Flux decline related to biofilm thickness and biofilm compaction.•Biofilm compaction caused by temporary permeate flux increase.•Reduced membrane performance by biofilm compaction after high flux operation.•Highest hydraulic resistance may be caused by the thinnest biofilm.
Extracellular polymeric substances are the construction materials for microbial aggregates such as biofilms, flocs ("planktonic biofilms") and sludge. Their major components are not only ...polysaccharides but also proteins and in some cases lipids, with minor contents of nucleic acids and other biopolymers. In the EPS, biofilm organisms can establish stable arrangements and function multicellularly as synergistic microconsortia. The matrix facilitates the retention of exoenzymes, cellular debris and genetic material; it can be considered as a microbial recycling yard. Gradients can develop due to the physiological activity and the fact that diffusive mass transport prevails over convective transport in the matrix. Biofilm cells tolerate higher concentrations of many biocides. The EPS matrix sequesters nutrients from the water phase. In photosynthetic communities, EPS molecules can function as light transmitters and provide photons to organisms located deeper in a microbial mat. The EPS matrix is a dynamic system, constructed by the organisms and responding to environmental changes. It enables the cells to function in a manner similar to multicellular organisms.
Hydraulic resistance of biofilms Dreszer, C.; Vrouwenvelder, J.S.; Paulitsch-Fuchs, A.H. ...
Journal of membrane science,
02/2013, Letnik:
429
Journal Article
Recenzirano
Biofilms may interfere with membrane performance in at least three ways: (i) increase of the transmembrane pressure drop, (ii) increase of feed channel (feed-concentrate) pressure drop, and (iii) ...increase of transmembrane passage. Given the relevance of biofouling, it is surprising how few data exist about the hydraulic resistance of biofilms that may affect the transmembrane pressure drop and membrane passage. In this study, biofilms were generated in a lab scale cross flow microfiltration system at two fluxes (20 and 100Lm−2h−1) and constant cross flow (0.1ms−1). As a nutrient source, acetate was added (1.0mgL−1 acetate C) besides a control without nutrient supply. A microfiltration (MF) membrane was chosen because the MF membrane resistance is very low compared to the expected biofilm resistance and, thus, biofilm resistance can be determined accurately. Transmembrane pressure drop was monitored. As biofilm parameters, thickness, total cell number, TOC, and extracellular polymeric substances (EPS) were determined, it was demonstrated that no internal membrane fouling occurred and that the fouling layer actually consisted of a grown biofilm and was not a filter cake of accumulated bacterial cells. At 20Lm−2h−1 flux with a nutrient dosage of 1mgL−1 acetate C, the resistance after 4 days reached a value of 6×1012m−1. At 100Lm−2h−1 flux under the same conditions, the resistance was 5×1013m−1. No correlation of biofilm resistance to biofilm thickness was found; Biofilms with similar thickness could have different resistance depending on the applied flux. The cell number in biofilms was between 4×107 and 5×108 cellscm−2. At this number, bacterial cells make up less than a half percent of the overall biofilm volume and therefore did not hamper the water flow through the biofilm significantly. A flux of 100Lm−2h−1 with nutrient supply caused higher cell numbers, more biomass, and higher biofilm resistance than a flux of 20Lm−2h−1. However, the biofilm thickness after 4 days at a flux of 100Lm−2h−1 (97μm) was in the same order of magnitude as the thickness of a biofilm at a flux of 20Lm−2h−1 (114μm). An increase of flux caused an increased biofilm resistance while a decrease of flux caused a decreased resistance. The effect was reversible. It is suggested that the biofilm resistance is mainly attributed to EPS, probably due to the tortuosity (“hair-in-sink-effect”) of the biopolymers to water molecules travelling across the biofilm. The data show clearly that biofilm resistance (6×1012m−1) was high compared to the intrinsic resistance of the employed MF membrane (5×1011m−1). However, in nanofiltration (intrinsic membrane resistance ca. 2×1013m−1) and reverse osmosis membranes (intrinsic resistance ca. 9×1013m−1), the biofilm will not contribute significantly to the overall resistance.
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► The resistance of the biofilm reaches values up to 50 × 1012 m−1. ► Effect of growing biofilms dominated that of bacterial filter cakes at same density. ► The resistance was not caused by the biofilm cells but by the EPS matrix. ► No correlation between biofilm thickness and resistance could be found. ► The flux impacted the trans membrane biofilm resistance.
Biofilm formation causes performance loss in spiral-wound membrane systems. In this study a microfiltration membrane was used in experiments to simulate fouling in spiral-wound reverse osmosis (RO) ...and nanofiltration (NF) membrane modules without the influence of concentration polarization. The resistance of a microfiltration membrane is much lower than the intrinsic biofilm resistance, enabling the detection of biofilm accumulation in an early stage. The impact of biofilm accumulation on the transmembrane (biofilm) resistance and feed channel pressure drop as a function of the crossflow velocity (0.05 and 0.20 m s−1) and feed spacer presence was studied in transparent membrane biofouling monitors operated at a permeate flux of 20 L m−2 h−1. As biodegradable nutrient, acetate was dosed to the feed water (1.0 and 0.25 mg L−1 carbon) to enhance biofilm accumulation in the monitors. The studies showed that biofilm formation caused an increased transmembrane resistance and feed channel pressure drop. The effect was strongest at the highest crossflow velocity (0.2 m s−1) and in the presence of a feed spacer. Simulating conditions as currently applied in nanofiltration and reverse osmosis installations (crossflow velocity 0.2 m s−1 and standard feed spacer) showed that the impact of biofilm formation on performance, in terms of transmembrane and feed channel pressure drop, was strong. This emphasized the importance of hydrodynamics and feed spacer design. Biomass accumulation was related to the nutrient load (nutrient concentration and linear flow velocity). Reducing the nutrient concentration of the feed water enabled the application of higher crossflow velocities. Pretreatment to remove biodegradable nutrient and removal of biomass from the membrane elements played an important part to prevent or restrict biofouling.
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•Biofouling increased both transmembrane resistance and feed channel pressure drop.•Largest problems occurred at high crossflow velocity in presence of a feed spacer.•An increase of crossflow velocity caused a stronger biofilm formation.•Biomass accumulation was related to the nutrient load.•Current membrane practice increased the impact of biofouling on performance.
The benefit of an implantable cardioverter-defibrillator (ICD) in patients with symptomatic systolic heart failure caused by coronary artery disease has been well documented. However, the evidence ...for a benefit of prophylactic ICDs in patients with systolic heart failure that is not due to coronary artery disease has been based primarily on subgroup analyses. The management of heart failure has improved since the landmark ICD trials, and many patients now receive cardiac resynchronization therapy (CRT).
In a randomized, controlled trial, 556 patients with symptomatic systolic heart failure (left ventricular ejection fraction, ≤35%) not caused by coronary artery disease were assigned to receive an ICD, and 560 patients were assigned to receive usual clinical care (control group). In both groups, 58% of the patients received CRT. The primary outcome of the trial was death from any cause. The secondary outcomes were sudden cardiac death and cardiovascular death.
After a median follow-up period of 67.6 months, the primary outcome had occurred in 120 patients (21.6%) in the ICD group and in 131 patients (23.4%) in the control group (hazard ratio, 0.87; 95% confidence interval CI, 0.68 to 1.12; P=0.28). Sudden cardiac death occurred in 24 patients (4.3%) in the ICD group and in 46 patients (8.2%) in the control group (hazard ratio, 0.50; 95% CI, 0.31 to 0.82; P=0.005). Device infection occurred in 27 patients (4.9%) in the ICD group and in 20 patients (3.6%) in the control group (P=0.29).
In this trial, prophylactic ICD implantation in patients with symptomatic systolic heart failure not caused by coronary artery disease was not associated with a significantly lower long-term rate of death from any cause than was usual clinical care. (Funded by Medtronic and others; DANISH ClinicalTrials.gov number, NCT00542945 .).
Limited data suggest a benefit of population-based screening for cardiovascular disease with respect to the risk of death.
We performed a population-based, parallel-group, randomized, controlled ...trial involving men 65 to 74 years of age living in 15 Danish municipalities. The participants were randomly assigned in a 1:2 ratio to undergo screening (the invited group) or not to undergo screening (the control group) for subclinical cardiovascular disease. Randomization was based on computer-generated random numbers and stratified according to municipality. Only the control group was unaware of the trial-group assignments. Screening included noncontrast electrocardiography-gated computed tomography to determine the coronary-artery calcium score and to detect aneurysms and atrial fibrillation, ankle-brachial blood-pressure measurements to detect peripheral artery disease and hypertension, and a blood sample to detect diabetes mellitus and hypercholesterolemia. The primary outcome was death from any cause.
A total of 46,611 participants underwent randomization. After exclusion of 85 men who had died or emigrated before being invited to undergo screening, there were 16,736 men in the invited group and 29,790 men in the control group; 10,471 of the men in the invited group underwent screening (62.6%). In intention-to-treat analyses, after a median follow-up of 5.6 years, 2106 men (12.6%) in the invited group and 3915 men (13.1%) in the control group had died (hazard ratio, 0.95; 95% confidence interval CI, 0.90 to 1.00; P = 0.06). The hazard ratio for stroke in the invited group, as compared with the control group, was 0.93 (95% CI, 0.86 to 0.99); for myocardial infarction, 0.91 (95% CI, 0.81 to 1.03); for aortic dissection, 0.95 (95% CI, 0.61 to 1.49); and for aortic rupture, 0.81 (95% CI, 0.49 to 1.35). There were no significant between-group differences in safety outcomes.
After more than 5 years, the invitation to undergo comprehensive cardiovascular screening did not significantly reduce the incidence of death from any cause among men 65 to 74 years of age. (Funded by the Southern Region of Denmark and others; DANCAVAS ISRCTN Registry number, ISRCTN12157806.).
Clinical outcomes following coronary computed tomography–derived fractional flow reserve (FFRCT) testing in clinical practice are unknown.
This study sought to assess real-world clinical outcomes ...following a diagnostic strategy including first-line coronary computed tomography angiography (CTA) with selective FFRCT testing.
The study reviewed the results of 3,674 consecutive patients with stable chest pain evaluated with CTA and FFRCT testing to guide downstream management in patients with intermediate stenosis (30% to 70%). The composite endpoint (all-cause death, myocardial infarction, hospitalization for unstable angina, and unplanned revascularization) was determined in 4 patient groups: 1) CTA stenosis <30%, optimal medical treatment (OMT), and no additional testing; 2) FFRCT >0.80, OMT, no additional testing; 3) FFRCT ≤0.80, OMT, no additional testing; and 4) FFRCT ≤0.80, OMT, and referral to invasive coronary angiography. Patients were followed for a median of 24 (range 8 to 41) months.
FFRCT was available in 677 patients, and the test result was negative (>0.80) in 410 (61%) patients. In 75% of the patients with FFRCT >0.80, maximum coronary stenosis was ≥50%. The cumulative incidence proportion (95% confidence interval CI) of the composite endpoint at the end of follow-up was comparable in groups 1 (2.8%; 95% CI: 1.4% to 4.9%) and 2 (3.9%; 95% CI: 2.0% to 6.9%) (p = 0.58) but was higher (when compared with group 1) in groups 3 (9.4%; p = 0.04) and 4 (6.6%; p = 0.08). Risk of myocardial infarction was lower in group 4 (1.3%) than in group 3 (8%; p < 0.001).
In patients with intermediate-range coronary stenosis, FFRCT is effective in differentiating patients who do not require further diagnostic testing or intervention (FFRCT >0.80) from higher-risk patients (FFRCT ≤0.80) in whom further testing with invasive coronary angiography and possibly intervention may be needed. Further studies assessing the risk and optimal management strategy in patients undergoing first-line CTA with selective FFRCT testing are needed.
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To examine the 3.5 year prognosis of stable coronary artery disease (CAD) as assessed by coronary computed tomography angiography (CCTA) in real-world clinical practice, overall and within subgroups ...of patients according to age, sex, and comorbidity.
This cohort study included 16,949 patients (median age 57 years; 57% women) with new-onset symptoms suggestive of CAD, who underwent CCTA between January 2008 and December 2012. The endpoint was a composite of late coronary revascularization procedure >90 days after CCTA, myocardial infarction, and all-cause death. The Kaplan-Meier estimator was used to compute 91 day to 3.5 year risk according to the CAD severity. Comparisons between patients with and without CAD were based on Cox-regression adjusted for age, sex, comorbidity, cardiovascular risk factors, concomitant cardiac medications, and post-CCTA treatment within 90 days. The composite endpoint occurred in 486 patients. Risk of the composite endpoint was 1.5% for patients without CAD, 6.8% for obstructive CAD, and 15% for three-vessel/left main disease. Compared with patients without CAD, higher relative risk of the composite endpoint was observed for non-obstructive CAD hazard ratio (HR): 1.28; 95% confidence interval (CI): 1.01-1.63, obstructive one-vessel CAD (HR: 1.83; 95% CI: 1.37-2.44), two-vessel CAD (HR: 2.97; 95% CI: 2.09-4.22), and three-vessel/left main CAD (HR: 4.41; 95% CI :2.90-6.69). The results were consistent in strata of age, sex, and comorbidity.
Coronary artery disease determined by CCTA in real-world practice predicts the 3.5 year composite risk of late revascularization, myocardial infarction, and all-cause death across different groups of age, sex, or comorbidity burden.
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