Biofilm control in water by a UV-based advanced oxidation process

An ultraviolet (UV)-based advanced oxidation process (AOP), with hydrogen peroxide and medium-pressure (MP) UV light (H₂O₂/UV), was used as a pretreatment strategy for biofilm control in water. Suspended Pseudomonas aeruginosa cells were exposed to UV-based AOP treatment, and the adherent biofilm formed by the surviving cells was monitored. Control experiments using H₂O₂ or MP UV irradiation alone could inhibit biofilm formation for only short periods of time (<24 h) post-treatment. In a H₂O₂/filtered-UV (>295 nm) system, an additive effect on biofilm control was shown vs filtered-UV irradiation alone, probably due to activity of the added hydroxyl radical (OH?). In a H₂O₂/full-UV (ie full UV spectrum, not filtered) system, this result was not obtained, possibly due to the germicidal UV photons overwhelming the AOP system. Generally, however, H₂O₂/UV prevented biofilm formation for longer periods (days) only when maintained with residual H₂O₂. The ratio of surviving bacterial concentration post-treatment to residual H₂O₂ concentration played an important role in biofilm prevention and bacterial regrowth. H₂O₂ treatments alone resulted in poorer biofilm control compared to UV-based AOP treatments maintained with similar levels of residual H₂O₂, indicating a possible advantage of AOP.     

Biofilm problems in dental unit water systems and its practical control

Dental chair units (DCUs) contain integrated systems that provide the instruments and services for a wide range of dental procedures. DCUs use water to cool and irrigate DCU-supplied instruments and tooth surfaces during dental treatment. Water is supplied to these instruments by a network of interconnected narrow-bore (2–3 mm) plastic tubes called dental unit waterlines (DUWLs). Many studies over the last 40 years demonstrated that DUWL output water is often contaminated with high densities of micro-organisms, predominantly Gram-negative aerobic heterotropic environmental bacteria, including Legionella and Pseudomonas species. Untreated DUWLs host biofilms that permit micro-organisms to multiply and disperse through the water network and which are aerosolized by DCU instrument use, thus exposing patients and staff to these micro-organisms, to fragments of biofilm and bacterial endotoxins. This review concentrates on how practical developments and innovations in specific areas can contribute to effective DUWL biofilm control. These include the use of effective DUWL treatment agents, improvements to DCU supply water quality, DCU design changes, development of automated DUWL treatment procedures that are effective at controlling biofilm in the long-term and require minimal human intervention, are safe for patients and staff, and which do not cause deterioration of DCU components following prolonged use.     

Biofilm formation on copper and its control by inhibitor/biocide in cooling water environment

The present study has successfully identified the nitrate reducing bacteria present in the cooling water system and also investigated the performance of industrially applied biocide and inhibitor on the bacterial inhibition. In order to carry out the objective of this study, facilities and methods such as 16S rRNA gene sequencing, Lowry assay, SEM, EIS, ICP-MS and weight loss analysis were being utilized. In this study, two out of the five morphologically dis- similar colonies identified through 16S rRNA gene sequencing, namely the Massilia timonae and the Pseudomonas, were being utilized in the biocorrosion study on copper metal. From the surface analysis using SEM demonstrated the phenomenon of biofilm formation on the copper surface. 2-methylbenzimidazole has the addition of methyl group in the diazole ring position of benzimidazole it has create basicity environment and inhibit the metal deterioration. Meanwhile, it is also deducible from the EIS and protein analysis that com- bination of biocide with either of the inhibitors gives rise to better biocorrosion suppression (0.00178 mpy and 0.00171mpy) as compared to the sole effect of either biocide or inhibitor (0.00219 mpy, 0.00162 and 0.00143). Biocorrosion system biocide with MBM was found to exhibit 65% corrosion inhibition efficiency. Moreover, adoption of 2-Methylbenzimidazole seems to display better performance as compared to Multionic 8151, which is adopted in cooling water system.     

Chemiluminescence-assisted study on a peracetic acid-based advanced oxidation process activated with cobalt phosphide

In recent years, the elimination of organic pollutants using advanced oxidation processes (AOPs) based on peracetic acid (PAA) has drawn increasing attention due to the high oxidative potential and low byproducts. However, to explore more efficient and stable PAA-based AOPs, there is still great room for study on the activation of PAA and degradation mechanism in the reaction process. In this study, a new PAA-based AOP activated by metal–organic framework-derived cobalt phosphide (CoP) and accompanied by chemiluminescence (CL) behaviour was explored. The CoP/PAA system could efficiently degrade 99.98% of RhB (20 mg L⁻¹) within 5 min at pH 7 compared with the conventional Co₃O₄/PAA system (merely 17.29%), and the degradation process was matched well with the pseudo-first-order kinetic, and the kinetic constants was ~23.7 times higher than that of Co₃O₄ (0.546 min⁻¹ for CoP vs. 0.023 min⁻¹ for Co₃O₄). In the CoP/PAA/RhB process, the CL intensity was related to the concentration of ¹O₂, O₂^•– and acetyl peroxyl radicals [CH₃C(O)OO• and CH₃C(O)O•]. Therefore, CL analysis, combined with quenching tests and electron paramagnetic resonance analysis, was used to study the degradation mechanism in detail, and ¹O₂ was confirmed as the dominant contributor for the dye degradation.     

Biofilm formation in water cooling systems

Biofilm formation on stainless steel samples immersed in cooling water has been evaluated by exposing metal samples to cooling seawater for 30 days. Anaerobic bacteria were then at 1.6 × 10⁶/cm², with sulphate-reducing species predominating. Aerobic bacteria and fungi were 2600 and 140/cm², respectively. After 60 days, numbers of aerobic microorganisms remained constant whereas the count of anaerobic microorganisms had increased to 1.8×10⁹/cm². Scanning electron microscopy showed the presence of morphologically different microorganisms in deposits and as a mucilaginous net. No signs of corrosion were detected on the stainless steel surface.The authors are with the Departamento de Engenharia Bioquimica Centro de Tecnologia, Bloco E. Universidade Federal do Rio de Janeiro Ilha do Fundão, 21941-900 Rio de Janeiro, Brazil     

Biofilm formation in drinking water affected by low concentrations of phosphorus

Abstract: There are geographical regions where microbial growth in drinking waters is limited by phosphorus instead of organic carbon. In these drinking waters even a low amount of phosphorus can strongly enhance microbial growth. The formation of biofilm can be limited by low availability of phosphorus in drinking waters with low content of phosphorus. The formation of biofilms on polyvinyl chloride plates was studied in laboratory experiments with water containing 48 microg/L assimilable organic carbon and 0.19 microg/L microbially available phosphorus. We found that low additions of phosphate (1-5 microg/L PO4(3-)-P) to water increased microbial growth in the water and in the biofilm. The effect of phosphorus on microbial growth could be detected by determining either the microbial cell production or the content of ATP in biofilms. Also, in steady-state biofilms, microbial concentrations were higher with phosphorus addition as enumerated by heterotrophic plate counts on R2A-agar and acridine orange direct counting. This work confirms the earlier findings of the importance of phosphorus for microbial growth in humic-rich drinking waters.     

ADD CONTROL: advanced control solutions for waste water treatment

Instrumentation, control, and automation (ICA) in wastewater treatment enables the improvement of treatment plant performance without structural modifications of the plant. Even for wastewater treatment plants (WWTPs) meeting all criteria with respect to effluent concentrations and sludge disposal, ICA can be of interest as it can help to reduce energy consumption and operating costs of the plant. Simulations are a useful and cost-effective tool for designing and evaluating different control strategies. Simulation strategies developed with existing WWTP-specific simulation packages are based on ideal sensor and actuator behavior because signal noise and potential sensor and actuator failures are not considered. Real sensor and actuator behavior including failures, however, needs to be accounted for to ensure robust controller performance despite disturbances in sensor and actuator behavior. The ADD CONTROL project aims to design, implement, and validate a new simulation tool that allows for designing and testing “practical” control solutions. A multi-layer modeling architecture is proposed for the simulation tool to represent the hierarchical architecture for automation and control in full-scale WWTPs, and to separate mathematical modeling of components related to the treatment process from components describing instrumentation and actuation devices, and components related to automation and control. The developed simulation tool is implemented based on the TORNADO framework for modeling and virtual experimentation and the WEST^? product suite.     

Inhibition of proline oxidation by water stress

The conversion of proline to glutamic acid and hence to other soluble compounds (proline oxidation) proceeds readily in turgid barley (Hordeum vulgare) leaves and is stimulated by higher concentrations of proline. This suggests that proline oxidation could function as a control mechanism for maintaining low cellular levels of proline in turgid tissue. In water-stressed tissue, however, proline oxidation is reduced to negligible rates. These results are consistent with the idea that proline accumulation results from inactivation by water stress of normal control mechanisms. It seems likely that inhibition of proline oxidation is necessary in maintaining the high levels of proline found in stressed barley leaves.     

Dynamics of electron transfer in the oxidation of water by chlorophyll a dimer

The observed temperature dependence of the rate constant for reduction of (Chl a.2H2O)2+. by water is fitted to a theoretical expression for the rate of an intramolecular electronic radiationless transition. The theory assumes a single effective mediating mode and the best-fit value for the frequency of this mode is omega(m) = 680 cm(-1), which corresponds to high-frequency, intermolecular librations in water. From an explicit calculation of the nonadiabatic-coupling matrix element, an average electron-transfer distance of 11 A is obtained, consistent with molecular dimensions available for this system.     

Biofilm formation by the yeast Rhodotorula mucilaginosa: process,repeatability and cell attachment in a continuous biofilm reactor

Yeast biofilms contribute to quality impairment of industrial processes and also play an important role in clinical infections. Little is known about biofilm formation and their treatment. The aim of this study was to establish a multi-layer yeast biofilm model using a modified 3.7 l bench-top bioreactor operated in continuous mode (D = 0.12 h^?1). The repeatability of biofilm formation was tested by comparing five bioprocesses with Rhodotorula mucilaginosa, a strain isolated from washing machines. The amount of biofilm formed after 6 days post inoculation was 83 μg cm^?2 protein, 197 μg cm^?2 polysaccharide and 6.9 × 10⁶ CFU cm^?2 on smooth polypropylene surfaces. Roughening the surface doubled the amount of biofilm but also increased its spatial variability. Plasma modification of polypropylene significantly reduced the hydrophobicity but did not enhance cell attachment. The biofilm formed on polypropylene coupons could be used for sanitation studies.     

Biofilm formation by the yeast Rhodotorula mucilaginosa: process, repeatability and cell attachment in a continuous biofilm reactor

Yeast biofilms contribute to quality impairment of industrial processes and also play an important role in clinical infections. Little is known about biofilm formation and their treatment. The aim of this study was to establish a multi-layer yeast biofilm model using a modified 3.7 l bench-top bioreactor operated in continuous mode (D = 0.12 h(-1)). The repeatability of biofilm formation was tested by comparing five bioprocesses with Rhodotorula mucilaginosa, a strain isolated from washing machines. The amount of biofilm formed after 6 days post inoculation was 83 μg cm(-2) protein, 197 μg cm(-2) polysaccharide and 6.9 × 10(6) CFU cm(-2) on smooth polypropylene surfaces. Roughening the surface doubled the amount of biofilm but also increased its spatial variability. Plasma modification of polypropylene significantly reduced the hydrophobicity but did not enhance cell attachment. The biofilm formed on polypropylene coupons could be used for sanitation studies.     

Photosynthetic water oxidation: towards a mechanism

This mini-review outlines the current theories on the mechanism of electron transfer from water to P680, the location and structure of the water oxidising complex and the role of the manganese cluster. We discuss how our data fit in with current theories and put forward our ideas on the location and mechanism of water oxidation.     

Proton release during successive oxidation steps of the photosynthetic water oxidation process: stoichiometries and pH dependence.

Flash-induced absorption changes of pH-indicating dyes were investigated in photosystem II enriched membrane fragments, in order to retrieve the individual contributions to proton release of the successive transitions of the Kok cycle. These stoichiometric coefficients were found to be, in general, noninteger and to vary as a function of pH. Proton release on the S0----S1 step decreases from 1.75 at pH 5.5 to 1 at pH 8, while, on S1----S2 the stoichiometry increases from 0 to 0.5 in the same pH range and remains close to 1 for S2----S3. These findings are analyzed in terms of pK shifts of neighboring amino acid residues caused by electrostatic interactions with the redox centers involved in the two first transitions. The electrochromic shift of a chlorophyll, associated with the S transitions, responding to local electrostatic effects was investigated under similar conditions. The pH dependence of this signal upon the successive transitions was found correlated with the titration of the proton release stoichiometries, expressing the electrostatic balance between the oxidation and deprotonation processes.     

Recent developments in research on water oxidation by photosystem II

Photosynthetic water oxidation chemistry at the unique manganese-calcium complex of photosystem II (PSII) is of fundamental importance and serves as a paragon in the development of efficient synthetic catalysts. A recent crystal structure of PSII shows the atoms of the water-oxidizing complex; its Mn4CaO5 core resembles inorganic manganese-calcium oxides. Merging of crystallographic and spectroscopic information reverses radiation-induced modifications at the Mn-complex in silico and facilitates discussion of the O-O bond chemistry. Coordinated proton movements are promoted by a water network connecting the Mn4CaO5 core with the oxidant, a tyrosine radical and one possibly mobile chloride ion. A basic reaction-cycle model predicts an alternating proton and electron removal from the catalytic site, which facilitates energetically efficient water oxidation.     

Detection of advanced oxidation protein products in patients with chronic kidney disease by a novel monoclonal antibody

Abstract

Advanced oxidation protein products (AOPP) as a biomarker of oxidative stress has been demonstrated in chronic kidney disease (CKD) patients; however, current methods to detect the accumulation of AOPP in serum and in tissues are limited and unreliable. This study generated a monoclonal antibody (mAb) designated 3F2, that reacts specifically with hypochlorous acid (HOCl)-modified proteins, but not with the native forms or with other types of oxidative modifications. Notably, mAb 3F2 recognizes the AOPP deposited in renal tissues of AOPP-treated rats and of patients with different kinds of CKD. Moreover, this mAb can almost completely inhibit the production of reactive oxygen species in RAW264.7 cells induced by AOPP (p < 0.001). In conclusion, mAb 3F2 can be used to detect AOPP specifically in serum and in tissues, and this antibody can potentially provide an important tool and new insight into research on diseases related to oxidative stress.     

Detection of advanced oxidation protein products in patients with chronic kidney disease by a novel monoclonal antibody

Advanced oxidation protein products (AOPP) as a biomarker of oxidative stress has been demonstrated in chronic kidney disease (CKD) patients; however, current methods to detect the accumulation of AOPP in serum and in tissues are limited and unreliable. This study generated a monoclonal antibody (mAb) designated 3F2, that reacts specifically with hypochlorous acid (HOCl)-modified proteins, but not with the native forms or with other types of oxidative modifications. Notably, mAb 3F2 recognizes the AOPP deposited in renal tissues of AOPP-treated rats and of patients with different kinds of CKD. Moreover, this mAb can almost completely inhibit the production of reactive oxygen species in RAW264.7 cells induced by AOPP (p < 0.001). In conclusion, mAb 3F2 can be used to detect AOPP specifically in serum and in tissues, and this antibody can potentially provide an important tool and new insight into research on diseases related to oxidative stress.     

Saliva plays a dual role in oxidation process in stomach medium

The aim of this study was to evaluate the role of saliva in the oxidation process under the acidic condition of the stomach. Saliva specimens played varied roles in the lipid peroxidation process of heated muscle tissue in simulated gastric fluid: pro-oxidant effects, no effects, and antioxidant effects. To elucidate these differences, selected saliva components were examined. The pseudoperoxidase activity of lactoperoxidase increased lipid peroxidation, while thiocyanate and nitrite-reduced lipid peroxidation. The effect of a saliva specimen on lipid peroxidation was correlated with the concentration of nitrite in the specimen, but not with that of other saliva components. The inhibitory effect of nitrite may be due to its conversion to NO. Elucidation of the antioxidant effect of saliva on co-oxidation of d-alpha-tocopherol in gastric fluid, demonstrated that saliva alone cannot protect d-alpha-tocopherol from co-oxidation, although it partially protected against lipid peroxidation. The presence of red wine polyphenols in stomach medium totally inhibits food lipid peroxidation and d-alpha-tocopherol co-oxidation.     

Control of Listeria monocytogenes in a Biofilm by Competitive-Exclusion Microorganisms

Biofilms from drains in food processing facilities with a recent history of no detectable Listeria monocytogenes in floor drains were cultured for microorganisms producing antilisterial metabolites. A total of 413 microbial isolates were obtained from 12 drain biofilm samples and were assayed at 15 and 37°C for activities that were bactericidal or inhibitory to L. monocytogenes, by two agar plate assays. Twenty-one of 257 bacterial isolates and 3 of 156 yeast isolates had antilisterial activity. All 24 isolates which produced metabolites inhibitory to L. monocytogenes were assayed for antilisterial activity in coinoculated broth cultures containing tryptic soy broth with yeast extract (TSB-YE). A five-strain mixture of 10³ CFU of L. monocytogenes/ml and 10⁵ CFU of the candidate competitive-exclusion microorganism/ml was combined in TSB-YE and incubated at 37°C for 24 h, 15°C for 14 days, 8°C for 21 days, and 4°C for 28 days. Substantial inhibition of L. monocytogenes growth (4 to 5 log CFU/ml) was observed for nine bacterial isolates at 37°C, two at 15 and 8°C, and three at 4°C. The inhibitory isolates were identified as Enterococcus durans (six isolates), Lactococcus lactis subsp. lactis (two isolates), and Lactobacillus plantarum (one isolate). The anti-L. monocytogenes activity of these isolates was evaluated in biofilms of L. monocytogenes on stainless steel coupons at 37, 15, 8, and 4°C. Results revealed that two isolates (E. durans strain 152 and L. lactis subsp. lactis strain C-1-92) were highly inhibitory to L. monocytogenes (growth inhibition of >5 log₁₀ CFU of L. monocytogenes/cm²). These two bacterial isolates appear to be excellent competitive-exclusion candidates to control L. monocytogenes in biofilms at environmental temperatures of 4 to 37°C.