Optimal Cleaning Procedure Research Articles

Evaluation of Membrane Fouling Control for Brackish Water Treatment Using a Modified Polyamide Composite Nanofiltration Membrane.

In northwest China, the limited amount of water resources are classified mostly as brackish water. Nanofiltration is a widely applied desalination technology used for brackish water treatment; however, membrane fouling restricts its application. Herein, we modified the membrane with triethanolamine (TEOA) and optimized the operating conditions (transmembrane pressure, temperature, and crossflow velocity) to control the nanofiltration membrane fouling by brackish water. Based on the physiochemical characteristics and desalination performance of the prepared membranes, the membrane modified with 2% TEOA (MPCM2) was identified as the optimal membrane, and 0.5 MPa, 25 °C, and 7 cm/s were identified as the optimal operating conditions through a series of nanofiltration experiments. Moreover, the membrane cleaning procedure for fouled MPCM2 was further determined, and a two-step cleaning procedure using ethylene diamine tetraacetic acid disodium followed by HCl with a permeance recovery rate of 98.77% was identified as the optimal cleaning procedure. Furthermore, the characterizations of the fouled and cleaned MPCM2 showed that the optimized cleaning procedure could recover the properties of MPCM2 to near virgin. This study is of great significance for the long-term stable operation of nanofiltration processes in brackish water treatment to ensure the supply of healthy water in the water-deficient areas of northwest China.

An evaluation of cleaning methods, preservation and specimen stages on trace elements in modern shallow marine ostracod shells of Sinocytheridea impressa and their implications as proxies

Trace elements of marine shells are important tools for reconstructing past ocean conditions, which are usually obtained through empirical calibrations with ocean parameters. For example, Mg/Ca ratios of ostracod shells have been linked to ocean temperature. However, some uncertainties usually arise from extraneous impacts, such as the selection of cleaning methods, specimen ontogenetic stage and shell preservation. Here, we present an evaluation of trace elements (Ca, Mg, Sr, Na, Al and Fe) in a shallow marine ostracod, Sinocytheridea impressa, and their potential utility as paleoceanographic proxies. We investigated single-shell variability of trace-element-to‑calcium ratios through Inductively Couple Plasma Mass Spectrometry (ICP-MS). In addition, the internal distribution of trace-elements was studied by Electron Probe Micro Analysis (EPMA) and Flow-Through Time-Resolved Analysis (FT-TRA). We conducted these analyses on ostracod specimens of different life stages and preservation conditions, subject to different cleaning methods, to resolve the suitability of this species as a new paleoenvironmental archive. Based on cleaning tests, we observe that clays stuck to the shells are the major contaminants in our specimens. We report an optimal cleaning procedure using sodium hypochlorite, which reduced the adherence of clays to the organism without significantly dissolving adult and juvenile calcite. We additionally find that the internal Mg distribution of S. impressa specimens is different for adults and the oldest stage of juveniles, namely A-1, with only the former having an enriched inner Mg layer. Therefore, precautions should be taken when combining life stages for trace-element analysis. While Sr and Mn are found to be mostly homogenous throughout all shells, the distribution of Na was found to be heterogeneous, which suggests that the incorporation of Na is controlled by a different mechanism than Mg, Sr and Mn. Finally, we report that transparent and opaque shells show similar Mg/Ca, Sr/Ca and Na/Ca ratios, unlike Mn/Ca and Fe/Ca, which suggests that opaque shells result from Mn- and Fe-enriched porewaters and Mn-enriched waters from the Pearl River. Our combined analysis suggests that Mg, Sr and Mn of adult S. impressa are incorporated into the carbonate matrix during calcification, and may therefore be suitable proxies of important environmental variables such as temperature and aqueous elemental concentrations.

Validation of a Fouling Measurement Procedure

The combustion of fuels usually involves the emission of particulate matter (PM) and occurrence of fouling and slagging phenomena, which are among the common drawbacks. In the case of fouling, the particles accumulate on the surfaces of certain devices, such as heat exchangers and electrostatic precipitators, leading to a reduction in their efficiencies. Identifying the shape of the layer of such particles can help develop solutions to these problems, such as the realization of an optimal cleaning procedure or the prevention of deposition on the critically affected areas. This study proposes a fouling measurement procedure that can be used to determine the thickness and profile of a particle/ash layer deposited on a surface. The system and methodology are validated by evaluating the accumulation of particles on the inner surface of a chimney during 40 h of operation and an electrostatic precipitator after 10 h of operation. The thickness of the PM layer is below 0.5 mm for the first case and above this value for the electrostatic precipitator. The worst case estimated uncertainty of the procedure is ±2%.

Oil Refinery Heat Exchanger Network Cleaning Scheduling Strategy with Unit Cleanability Consideration

Heat exchanger networks (HENs) play an important role in the chemical industries. Unfortunately, fouling is inevitable in heat exchangers operation. Therefore, the optimal cleaning procedure is required to restore heat exchangers' performance periodically. A systematic cleaning scheduling strategy for the heat exchanger network in an oil refinery is proposed in this work. There are 11 operating heat exchangers in an oil refinery to be reviewed. Different cleaning decision scenarios based on the overall heat transfer coefficient are explored for optimal cleaning schedule performance. The daily number of exchangers available to be cleaned i.e., the unit cleanability, is investigated while minimizing the energy consumption and the additional heat requirement due to the offline heat exchanger under cleaning procedure. The HEN performance and the energy-saving from the cleaning procedures are benchmarked with the uncleaned HEN. The results indicate that the cleaning procedure significantly increases the HEN performance and simultaneously reduces the heat requirement if compared to the untreated HEN benchmark. The possible conflicting situation is discussed when some heat exchangers are waiting to be cleaned due to the unit cleanability restriction, which allows the overall heat transfer coefficient to be below the allowed limit. Therefore, nonconflicting cleaning scheduling is also addressed in this work by relaxing the unit cleanability limit. Furthermore, the optimal cleaning schedule is also suggested for user reference. In this work, the optimum cleaning schedule with minimum energy consumption and maximum energy saving could be achieved when cleaning decision limit is set at 40% decrease of overall heat transfer coefficient. In the contrast, the lowest number of cleaning procedures is associated with 90% decrease in the overall heat transfer coefficient as the cleaning decision limit.

Effects of cleaning procedures on the long-term corrosion behavior of bronze artifacts of the cultural heritage in outdoor environment.

The cleaning of metallic artworks is a crucial step for their preservation. Cleaning operations generally aim at removing deposits and corrosion layers, and all the non-stable and potentially reactive phases formed as a consequence of the interaction of the metal with the environment. Thus, all secondary-formed compounds and layers that can undermine the overall preservation of the artwork, both from the esthetic and the corrosion point of view, should be removed. On the other hand, superficial stable patinas contributing to the artistic and historic value of the objects and that may provide protection to the metallic surface should be preserved. The optimal cleaning procedure should be able to promote a long-term improvement of the corrosion resistance of the surfaces. Therefore, the long-term monitoring of the corrosion behavior of the cleaned surfaces with electrochemical techniques could provide valuable information for the selection of the optimal methodology. In this work, five cleaning procedures have been applied to five bronze sculptures. The cleaned surfaces have been characterized following a multi-analytical and non-invasive approach, and the long-term evolution of their corrosion behavior has been monitored by means of on-site non-invasive linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements for more than 2years.

Laser cleaning of Cu-based artefacts: laser/corrosion products interaction

<p class="Abstract">This study aims to develop a low invasive and selective laser cleaning procedure for the removal of reactive corrosion products on Cu-based artefacts without damage the substrate. In a preliminary step, laser cleaning was performed on two typologies of artificially corroded copper reference samples. The effect of the variation of laser parameters as pulse duration and output power, was thus evaluated on an oxide layer, simulating a protective patina, and a hydroxychloride layer, simulating a reactive corrosion products layer to be removed. The optimized cleaning procedure was validated on an archaeological artefact, a bronze coin. Morphological, microchemical and microstructural characterizations were performed by means of optical microscopy, confocal microscopy, field emission scanning electron microscopy, X-Ray diffraction and Raman spectroscopy, before and after laser cleaning. The experimental findings show that laser cleaning, in optimized conditions, can reduce the thickness of the hydroxychloride layers slightly affecting the oxide layers. The difference in the interaction with laser radiation of these two layers seems to be mainly related to the difference in grain size and porosity. Notwithstanding these encouraging results, in order to define the real feasibility of the laser cleaning procedure, a further validation on real artefacts is mandatory due to the variation in thickness and composition of the corrosion products formed during long-lasting uncontrolled degradation processes.</p>

Permeability recovery of fouled forward osmosis membranes by chemical cleaning during a long-term operation of anaerobic osmotic membrane bioreactors treating low-strength wastewater

Anaerobic osmotic membrane bioreactor (AnOMBR) has gained increasing interests in wastewater treatment owing to its simultaneous recovery of biogas and water. However, the forward osmosis (FO) membrane fouling was severe during a long-term operation of AnOMBRs. Here, we aim to recover the permeability of fouled FO membranes by chemical cleaning. Specifically speaking, an optimal chemical cleaning procedure was searched for fouled thin film composite polyamide FO (TFC-FO) membranes in a novel microfiltration (MF) assisted AnOMBR (AnMF-OMBR). The results indicated that citric acid, disodium ethylenediaminetetraacetate (EDTA-2Na), hydrochloric acid (HCl), sodium dodecyl sulfate (SDS) and sodium hydroxide (NaOH) had a low cleaning efficiency of less than 15%, while hydrogen peroxide (H2O2) could effectively remove foulants from the TFC-FO membrane surface (almost 100%) through oxidizing the functional group of the organic foulants and disintegrating the colloids and microbe flocs into fine particles. Nevertheless, the damage of H2O2 to the TFC-FO membrane was observed when a high cleaning concentration and a long duration were applied. In this case, the optimal cleaning conditions including cleaning concentration and time for fouled TFC-FO membranes were selected through confocal laser scanning microscope (CLSM) and scanning electron microscopy (SEM) images and the flux recovery rate. The results suggested that the optimal cleaning procedure for fouled TFC-FO membranes was use of 0.5% H2O2 at 25 °C for 6 h, and after that, the cleaned TFC-FO membrane had the same performance as a virgin one including water flux and rejection for organic matters and phosphorus during the operation of AnMF-OMBR.

An investigation of the deposition of ceria on silica by quartz crystal microbalance: Observations on the effect of many body interactions

Interaction of ceria and silica is important in a wide variety of applications such as Chemical Mechanical Polish (CMP). In this work, a Quartz Crystal Microbalance (QCM) and mathematical modeling and simulations are used to investigate the dynamics of the attachment of ceria and silica under different flow rate, colloid concentration and pH conditions. The well-known DLVO forces of interaction were successfully used to distinguish between favorable and unfavorable conditions for the attachment of ceria and silica, and to develop a cleaning procedure to obtain reproducible data when using QCM for studying charged particles. The use of the optimized cleaning procedure as well as careful selection of the experimental conditions such as flow rate and concentration led to the important experimental observation that deposition of ceria particles onto silica surface is affected by many body particle–particle interactions in the bulk that can hinder the ability of the ceria particles to successfully attach to the silica surface. These experimental results could not be predicted by using a convection-diffusion-migration model which incorporates a single particle-surface DLVO interaction energy but ignores particle–particle interactions in the bulk. This is an important finding that permits the determination of the proper conditions for applications such as CMP and post CMP cleaning.

New approach of long-term modification of Topas® to acquire surface hydrophilicity for chromosome spreading

A modified and improved photografting procedure of Topas® surface hydrophilization is investigated in order to obtain stable modification of the polymer for long term storage. The achieved hydrophilicity and monitoring of the wettability during one month of storage are presented as well as a description of the optimal cleaning procedure and storage conditions to maintain the modified surface. Three minutes of oxygen plasma activation followed by 4min of acrylic acid UV-photografting at 50°C leads to the most stable hydrophilicity that was characterized by an initial water contact angle of 53.5°±1.2°. Storage of the modified material in cold water at 4°C and refraining from ultrasonic cleaning limit water contact angle increase to 5° over 30 days. In comparison with pristine hydrophobic Topas, the proposed treatment improves chromosome spreading ability significantly.

The study of Si(5 5 12) cleaning in the ultra-high vacuum conditions

The LEED patterns, electronic structure and morphology of Si(5 5 12) substrate surface were studied after different temperature cleaning procedures: high temperature (1250 oC), low temperature (900 oC) and cleaning at 800 oC in low silicon atom flow. The low temperature annealing without using of Si flow has been determined as the optimal cleaning procedure for Si(5 512) substrate.

Dissolved organic carbon in rainwater: Glassware decontamination and sample preservation and volatile organic carbon

The efficiency of different methods for the decontamination of glassware used for the analysis of dissolved organic carbon (DOC) was tested using reported procedures as well as new ones proposed in this work. A Fenton solution bath (1.0 mmol L −1 Fe 2+ and 100 mmol L −1 H 2O 2) for 1 h or for 30 min employing UV irradiation showed to combine simplicity, low cost and high efficiency. Using the optimized cleaning procedure, the DOC for stored UV-irradiated ultra-pure water reached concentrations below the limit of detection (0.19 μmol C L −1). Filtered (0.7 μm) rain samples maintained the DOC integrity for at least 7 days when stored at 4 °C. The volatile organic carbon (VOC) fraction in the rain samples collected at two sites in São Paulo state (Brazil) ranged from 0% to 56% of their total DOC content. Although these high-VOC concentrations may be derived from the large use of ethanol fuel in Brazil, our results showed that when using the high-temperature catalytic oxidation technique, it is essential to measure DOC rather than non-purgeble organic carbon to estimate organic carbon, since rainwater composition can be quite variable, both geographically and temporally.

An Optimized Freeze-Fracture Replication Procedure for Human Skin

This in vitro study aimed at substantial modification of the freeze-fracture replication technique (FFRT) which should result in an optimal visualization of the ultrastructure of human skin. The technique was modified in two ways: firstly, the conventional sample holders such as gold cups and copper plates were replaced by silver cylinders (83.5% silver, 16.5% copper) resulting in almost perpendicular cross fractures through the skin. Secondly, the replica cleaning procedure was optimized through the following sequence of treatments. Firstly, a mild tissue destruction was obtained by simultaneous lipid solvation and water extraction with absolute methanol (20 h), followed by protein denaturation with dimethyl sulfoxide (DMSO, 24 h). Subsequently, a final treatment was given using an alkaline sodium hypochlorite solution (20% KOH/13% NaClO; 1:3 v/v, 4 d). After rinsing the replicas for 45 min in aqua bidest, they were mounted on copper grids and examined in the transmission electron microscope (TEM). The combination of the unorthodox fracturing method and the optimized cleaning procedure yielded large, practically undamaged and very clean replicas of near perpendicular cross fractures through human skin. Common handicaps related to current freeze-fracture procedures when applied to skin, such as incomplete cleaning and fragmentation of replicas and oblique or irregular fracturing planes, can largely be avoided in this way. In this paper a complete description of the method is given, and a number of advantages are illustrated with the aid of TEM micrographs.