Conventional Chemical Cleaning Research Articles

Sustainable control of organic-inorganic combined fouling of electroactive ultrafiltration membrane during electrocatalytic-driven self-cleaning process: Mechanism and implications

Organic-inorganic combined fouling of membrane is a tough problem that restrained its application in water treatment, which was insufficient and non-sustainable to be alleviated by conventional chemical cleaning. Herein, a facile and sustainable control strategy was developed to mitigate biopolymer-Ca2+ combined fouling for an electroactive metal-organic framework ultrafiltration membrane. Bovine serum albumin (BSA) and sodium alginate (SA) were selected as model biopolymer. The results showed BSA and SA fouling both accelerated with increasing Ca2+ concentration (0–1.0 mM) via calcium bridging action and hydraulic cleaning was insufficient to restore flux (flux recovery < 7 %). By comparison, flux can be fully recovered by applying electricity to all combined fouling, suggesting membrane presented outstanding self-cleaning performance. According to the free radical quenching test and physicochemical property of biopolymer, fouling control mechanism was revealed because in-situ electro-generated OH and O2− free radicals caused decomplexation of biopolymer and Ca2+, and then degraded biopolymer into smaller and less hydrophobic fragments that repulsed membrane. Extended Derjaguin–Landau–Verwey–Overbeek theory further unveiled the foulants-membrane interaction shifted from attraction to repulsion after self-cleaning. This strategy has the advantages of low chemical cleaning reagents and energy consumption, which may provide the guidance for sustainable control of organic-inorganic combined membrane fouling.

The Effects of Surface Oxidation and H-Termination Processes Applied to Si Using Electrolytic Hydrogen Peroxide Solution to The Produced Cu/p-Si Schottky Contact Parameters

By using electrolytic hydrogen peroxide (H2O2) solution, oxidation and H-termination processes were applied to the p-Si crystal surface, which will be used for Cu/p-Si Schottky contact production, in a selective and controlled manner. Before the oxidation and H-termination processes, the p-Si(100) wafer used in this study was subjected to conventional chemical cleaning, and ohmic contact was made using pure aluminum (99.99%) metal on its back surface. The p-Si/Al with ohmic back contact was divided into three parts. A rectifying contact was immediately made to the front surface of one of them by using pure copper (99.98%) metal and called the REF (Reference) sample. The front surface of one of the remaining two p-Si/Al parts was oxidized, and the front surface of the other was H-Terminated. Rectifier contacts were made for both using pure copper (99.98%) metal and were named MIS (metal-insulator-semiconductor) and SP (surface passivated), respectively. Current-voltage (I-V) measurements of Schottky diodes of REF, MIS, and SP samples were performed at room temperature and in the dark. From the obtained data, the ideality factor (n), barrier height (Fbo), and series resistance (Rs) values of the samples were determined. As a result of the investigations, it was observed that the surface oxidation and H-Termination processes caused a decrease in the rectification factor and Fbo values of MIS and SP samples. These interesting situations were interpreted by the double-layer theory, which Bardeen predicted could exist on the surface of a semiconductor crystal and contribute to its work function.

Green Solvent Cleaning Removes Irrecoverable Foulants from End-of-Life Membranes in Membrane Bioreactors: Efficacy and Mechanisms.

Removal of irrecoverable foulants, which cannot be removed by conventional chemical cleaning, from end-of-life (EOL) membranes remains a substantial challenge due to the strong interaction between the foulants and membrane matrix. Herein, we developed a green solvent cleaning strategy based on Hansen solubility parameters to achieve the removal of irrecoverable foulants from the EOL polyvinylidene fluoride (PVDF) membranes serving for 6 years in a large-scale membrane bioreactor (MBR). We selected methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (MDMO) as the green solvent due to its strong interaction with the PVDF material, which might enable the substitution of binding sites of irrecoverable foulants. After the MDMO cleaning, the water permeance of the EOL membrane recovered from 47.6 ± 4.7 to 390.9 ± 8.2 L m-2 h-1 bar-1 (with a flux recovery ratio of ∼100%), with its rejection ability and stability maintained. The main components of irrecoverable fouling were humic acid-like substances revealed by spectroscopic characterization. Molecular dynamic simulation further elucidated the cleaning mechanisms: the strong interaction of MDMO-PVDF enabled substitution of binding sites of irrecoverable foulants by MDMO, followed by desorption of the irrecoverable foulants from PVDF and diffusion of the irrecoverable foulants into the bulk phase of MDMO. Evaluation in a lab-scale MBR treating real municipal wastewater verified the reusability of green solvent cleaned-EOL membranes. This study provides a novel, effective, and green cleaning strategy to remove irrecoverable foulants and prolong the service life of membranes in MBRs, facilitating sustainable wastewater treatment using membrane-based processes.

Novel sodium percarbonate-MnO2 effervescent tablets for efficient and moderate membrane cleaning

Membrane flux recovery efficiency and durability are two key factors closely associated with the practical application for membrane cleaning process. However, conventional chemical membrane cleaning method by soaking the whole membrane module in highly concentrated chemical reagents has prominent drawbacks including the low mass transfer efficiency of reagents, long period of washing time, and the potential threat to membrane structure. Herein, for the first time, we report a facile approach to fabricate the sodium percarbonate-MnO2 effervescent tablets which show bubbling reaction to release oxygen and free radicals when being dispersed in water for membrane cleaning. Due to the synergistic effect of MnO2 and sodium percarbonate, the tablets are highly effective to clean the membrane fouled by humic acid within 5 min, with the terminal membrane flux being recovered from 0.50 to 0.95, and the irreversible fouling resistance being reduced by more than 90%, which is prominently more efficient than the conventional chemical cleaning methods. Moreover, even by consecutive membrane fouling and cleaning for 6 times, the membrane flux and filtration efficiency of the membrane could still be kept almost constant, and the moderateness of this membrane cleaning method was also verified by the systematic microscopic analysis. For mechanism study, results of Electron Spin Resonance (ESR) and quenching experiments indicated that the high-efficiency and robust durability of sodium percarbonate-MnO2 (SPC-MnO2) system for membrane cleaning was mainly attributed to the abundantly generated hydroxyl radicals and secondary free radicals (i.e. carbonate radicals). Conclusively, compared with the conventional membrane cleaning method with liquid cleaning reagents, the novel SPC-MnO2 system with remarkable advantages in terms of convenience and membrane cleaning performance demonstrated high potential for the wide application in practice.

Periodic chemical cleaning with urea: disintegration of biofilms and reduction of key biofilm-forming bacteria from reverse osmosis membranes

Biofouling is one of the major factors causing decline in membrane performance in reverse osmosis (RO) plants, and perhaps the biggest hurdle of membrane technology. Chemical cleaning is periodically carried out at RO membrane installations aiming to restore membrane performance. Typical cleaning agents used in the water treatment industry include sodium hydroxide (NaOH) and hydrochloric acid (HCl) in sequence. Rapid biofilm regrowth and related membrane performance decline after conventional chemical cleaning is a routinely observed phenomenon due to the inefficient removal of biomass from membrane modules. Since extracellular polymeric substances (EPS) make up the strongest and predominant structural framework of biofilms, disintegration of the EPS matrix should be the main target for enhanced biomass removal. Previously, we demonstrated at lab-scale the use of concentrated urea as a chemical cleaning agent for RO membrane systems. The protein denaturation property of urea was exploited to solubilize the proteinaceous foulants, weakening the EPS layer, resulting in enhanced biomass solubilization and removal from RO membrane systems. In this work, we investigated the impact of repeated chemical cleaning cycles with urea/HCl as well as NaOH/HCl on biomass removal and the potential adaptation of the biofilm microbial community. Chemical cleaning with urea/HCl was consistently more effective than NaOH/HCl cleaning over 6 cleaning and regrowth cycles. At the end of the 6 cleaning cycles, the percent reduction was 35% and 41% in feed channel pressure drop, 50% and 70% in total organic carbon, 30% and 40% in EPS proteins, and 40% and 66% in the peak intensities of protein-like matter, after NaOH/HCl cleaning and Urea/HCl cleaning, respectively. 16S ribosomal RNA (rRNA) gene sequencing of the biofilm microbial community revealed that urea cleaning does not select for key biofouling families such as Sphingomonadaceae and Xanthomonadaceae that are known to survive conventional chemical cleaning and produce adhesive EPS. This study reaffirmed that urea possesses all the desirable properties of a chemical cleaning agent, i.e., it dissolves the existing fouling layer, delays fresh fouling accumulation by inhibiting the production of a more viscous EPS, does not cause damage to the membranes, is chemically stable, and environmentally friendly as it can be recycled for cleaning.

A Probiotic-Based Sanitation System for the Reduction of Healthcare Associated Infections and Antimicrobial Resistances: A Budget Impact Analysis.

Healthcare associated infections (HAIs) and antibiotic resistance have high social and economic burdens. Healthcare environments play an important role in the transmission of HAIs. The Probiotic Cleaning Hygiene System (PCHS) has been shown to decrease hospital surface pathogens up to 90% vs. conventional chemical cleaning (CCC). This study compares PCHS to CCC as to reduction of HAIs and their severity, related antibiotic resistances, and costs. Incidence rates of HAIs/antibiotic resistances were estimated from a previously conducted multicenter pre-post (6 months CCC + 6 months PCHS) intervention study, after applying the propensity score matching technique. A budget impact analysis compared the current scenario of use of CCC with future scenarios considering increasing utilization of PCHS, from 5% to 50% in the next five years, from a hospital perspective in Italy. The cumulative incidence of HAI was 4.6% and 2.4% (p < 0.0001) for CCC (N = 4160) and PCHS (N = 4160) (OR = 0.47, CI 95% 0.37–0.60), with severe HAIs of 1.57% vs. 1% and antibiotic resistances of 1.13% vs. 0.53%, respectively. Increased use of PCHS over CCC in Italian internal medicine/geriatrics and neurology departments in the next 5 years is expected to avert at least about 31,000 HAIs and 8500 antibiotic resistances, and save at least 14 million euros, of which 11.6 for the treatment of resistant HAIs. Innovative, environmentally sustainable sanitation systems, like PCHS, might substantially reduce antibiotic resistance and increase protection of health worldwide.

Spatial variation of fouling behavior in high recovery nanofiltration for industrial reverse osmosis brine treatment towards zero liquid discharge

Nanofiltration (NF), as a cost-efficient pre-concentrating process, has been incorporated into Zero Liquid Discharge (ZLD) treatment system to improve economic feasibility. However, NF is required to operate with an extremely high recovery rate to achieve ZLD, which could cause severe and complex membrane fouling.Understanding the variation of fouling behavior with increase in recovery rate is crucial for the development of effective fouling control strategy. Spatial variation of fouling behavior in a 3-stage NF used for industrial RO brine treatment towards ZLD was investigated in present study. Distinctive fouling characteristics were observed in each operation stage. Membrane fouling was dominated by organics at lead stage, which could be completely removed via simple base cleaning. Scaling by deposition of bulk crystallization occurred on fouling layer at middle stage, which required a combination of acid and base cleaning for its removal. At the tail stage, more refractory scaling by surface crystallization accompanied by irreversible silica and ferric fouling led to the formation of fouling layer that was resistant to conventional chemical cleaning. Significant humics in preformed fouling layer could have facilitated the occurrence of surface crystallization. Minor elements present in the feed such as silica, humics and iron could cause significant fouling and alter preformed fouling layer that induced more complex and refractory fouling/scaling as recovery rate increased.

Novel H2O2–MnO2 system for efficient physico-chemical cleaning of fouled ultrafiltration membranes by simultaneous generation of reactive free radicals and oxygen

The novel H2O2–MnO2 system was developed to achieve highly efficient membrane cleaning for both fouled PVDF and PES membranes in this study. Compared with conventional chemical cleaning process in which the whole membrane module had to be soaked in highly concentrated solution of chemical reagent for long period of time, the H2O2–MnO2 cleaning process conducting for only 5 min in 0.5 wt% H2O2 solution could achieve more than 95% recovery of permeate flux and almost total removal of the irreversible foulants. More importantly, the permeate flux and filtration efficiency of the membrane could be still kept stable after 6 runs of consecutive fouling and cleaning. Based on the systematic microscopic analyses, Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FTIR), as well as the quenching experiments with different free radical scavengers, the outstanding performance of H2O2–MnO2 system was attributed to the generation of both free radicals and abundant oxygen simultaneously, leading to the physico-chemical membrane cleaning. Conclusively, the newly developed H2O2–MnO2 system demonstrated noteworthy advantages on efficient membrane cleaning, and exhibited highly potential for the wide application in practical water treatment process.

Membrane backwash cleaning using CO2 nucleation

Low pressure membranes, such as ultrafiltration (UF), are widely used in water treatment applications, including the pretreatment of reverse osmosis desalination. UF membranes produce a water of superior quality, in addition to reducing the footprint and the use of chemicals, compared to conventional methods. However, membrane fouling remains a major drawback, and frequent membrane cleanings are required to maintain the flux of water and its quality. Typically, after a series of backwashes using an UF permeate, a chemical cleaning process is applied to fully recover the membrane's permeability. However, frequent chemical cleanings negatively affect the lifetime of the membrane, the environment, and increase operational costs. Here, we introduce a novel cleaning method that uses a solution saturated with CO2 to clean the membranes through the backwash step. As the pressure drops, the CO2 solution becomes supersaturated, and bubbles start to nucleate within the membrane pores and on its surface, resulting in the effective removal of the deposited fouling material. These foulants are further helping the nucleation process as they are considered as imperfection sites with high creation and growth of bubbles. Investigations performed for different synthetic feed solutions of organic compounds (sodium alginate), colloidal matter (silica) and sea salts, at different concentrations, show that our new physical cleaning process using CO2 is more performant than the regular backwash using Milli-Q water. We obtain a 100% flux recovery, in a short time, even under severe irreversible fouling conditions. Based on these results, we conclude that replacing water by a solution saturated with CO2 for the backwash cleaning of filtration membranes provides significant benefits to existing cleaning processes, and represent a promising alternative for improving and lowering the frequency of conventional chemical cleaning methods.

Impact of a probiotic-based hospital sanitation on antimicrobial resistance and HAI-associated antimicrobial consumption and costs: a multicenter study.

PurposeAntimicrobial resistance (AMR) is one of the major threats to human health, and the high frequency of resistant pathogens in the hospital environment can contribute to the transmission of difficult-to-treat health care-associated infections (HAIs). We recently reported that, compared with conventional chemical cleaning, the use of a microbial-based sanitation strategy (Probiotic Cleaning Hygiene System [PCHS]) was associated with remodulation of hospital microbiota and reduction of HAI incidence. Here, we aimed to analyze the impact of PCHS on AMR and related effects, such as HAI-associated antimicrobial drug consumption and costs.Patients and methodsFive Italian hospitals, enrolled in a multicenter study where conventional sanitation methods were replaced with PCHS, were included in the analysis. The study period included a 6-month observation for each sanitation type. Surface microbiota AMR was analyzed using microarray, nested PCR, antibiogram, and microdilution tests. Drug consumption data and related costs were obtained from the medical records of all hospitalized patients affected by HAIs.ResultsPCHS use was associated with up to 99% decrease of the AMR genes harbored by surface hospital microbiota, independently of the resistance types originally present in each individual setting (Pc<0.01). Functional assays confirmed the molecular data, demonstrating a 33%–100% decrease of resistant strains depending on the antibiotic type. Antimicrobial drug consumption associated with HAI onset showed a global 60.3% decrease, with a 75.4% decrease of the associated costs.ConclusionThe spread of AMR in the hospital environment can be limited by the use of sanitation methods to remodulate the hospital microbiota, leading to lower antimicrobial consumption and costs. This approach might be considered as part of broader infection prevention and control strategies.

Surface treatment and profile characterization of p-type graded band gap AlGaN material for preparing high performance photocathode

Ar+ sputtering was applied for exploring the graded band gap profile and the effectiveness of surface contaminations removal, especially the oxide, of the AlGaN material for preparing high performance photocathodes. The X-ray photoelectron spectroscopy scan(XPS) and spectral curves fitting indicated that after conventional chemical cleaning, there were still large amount of carbon and oxygen on surface, where the oxide mainly included gallium oxide and aluminum oxide. After Ar+ sputtering for 0.5min and 1min, these carbon and oxygen were both completely removed from surface and the proportion of Al changed from original 29.8% to 36.7% and 37.8%, respectively, more suitable to the solar blind detection. The variation trend of Al and Ga from surface to bulk confirmed the graded band gap profile of this AlGaN material, which would introduce built-in electric field for preparing high performance photocathode.

Optimisation and performance of NaClO-assisted maintenance cleaning for fouling control in membrane bioreactors

Based on conventional chemical cleaning and physical backflush methods, a novel in situ chemical backflush method, i.e., chemically assisted maintenance cleaning with NaClO as the principal reagent, was developed for membrane fouling control in membrane bioreactors (MBRs). The results demonstrated that, compared with a control MBR with water backflush, the use of low NaClO loads had few adverse effects on nutrient removal; on the contrary, the exposure to NaClO enhanced the denitrification performance of the MBR as a result of the formation of sludge granules. Measurements of transmembrane pressure (TMP) showed that an NaClO backflush at 0.2 ppm could achieve effective membrane fouling control in MBRs. Ex situ backflush tests showed that an NaClO backflush enhanced the detachment of biopolymers from the fouled membranes compared with a water backflush. Comparative 16S rRNA sequencing showed differing bacterial community composition in the fouling layers of the two MBRs. Specifically, the NaClO backflush could suppress filament-caused membrane fouling (i.e., lowered the abundance of Thiothrix eikelboomii in the fouling layers). Both the water and NaClO backflush resulted in significant increases in the pure water permeability of the membranes as a result of the enlargement of membrane pores. The results of Fourier transform infrared spectrometry indicated that the frequent NaClO backflush did not change the functional groups of the active layer of the membranes significantly. This study could provide an alternative for the implementation of membrane cleaning in MBR plants.

Effect of Calcium and Magnesium Ions on Calcium Oxalate Formation in Sugar Solutions

During the concentration of sugarcane juice, there is continuous deposition of nonsugar impurities on the surface of evaporator units. Because the scale deposit has a low thermal conductivity, its accumulation impairs heat transfer and eventually renders the process uneconomical owing to reduced throughput. Calcium oxalate is the main intractable scale formed in factories that process sugarcane. It is not removed by conventional chemical cleaning methods. This paper describes studies on the apparent solubility product of calcium oxalate in the presence of sugar and calcium and magnesium ions at different temperatures and pH's. A solubility product model was obtained that states that the apparent solubility product of calcium oxalate decreases with increasing temperature and sugar concentration, but increases with increasing pH. The model was able to predict calcium oxalate solubility changes in raw sugarcane factory processes, indicating that the apparent solubility product of calcium oxalate declines rapidly through the evaporator set. The results also indicated that calcium oxalate solubility is increased in the presence of calcium and, in particular, magnesium ions.

Preparation of Sapphire for High Quality III-Nitride Growth

We developed a unique preparation technique to eliminate surface damage on the c-plane of sapphire and render it atomically flat. AFM images of c-plane sapphire annealed at 1380 °C for 1hour show terrace-like features with about 0.2 μm long terraces. The GaN layers grown by MBE on annealed sapphire have [0 0 2] symmetric and [1 0 4] asymmetric full width at half maximum (FWHM) of about 60 and 132 arcsec, respectively. This compares with 408 and 600 arcsec, respectively, for GaN grown on sapphire having gone through conventional chemical cleaning.

Evaluation of different cleaning techniques for oxygen-free high-conductivity copper

Oxygen-free high-conductivity copper is a candidate material for future electron/positron storage rings with beam currents in the range of ampere or more. The advantages being high electrical conductivity and good x-ray absorption. However, there are problems of fabrication and lack of extensive data on easy cleaning techniques for complicated shapes. We have over the last year gained considerable experience and understanding of the same. Techniques varying from conventional chemical cleaning, high-pressure hot-water jet cleaning, and vacuum bakeout, to novel methods such as CO2 snow cleaning, and wet bead blasting have been tried. The samples were evaluated for surface cleanliness by x-ray photoelectron spectroscopy. Data along with some analysis and interpretation are being presented.

Electrically enhanced separation processes: the basis of in situ intermittent electrolytic membrane cleaning (IIEMC) and in situ electrolytic membrane restoration (IEMR)

The basis of two innovative electrolytic techniques for the combating of membrane fouling during cross-flow microfiltration is described. The first, which we have termed “ in situ intermittent electrolytic membrane cleaning” or IIEMC, makes use of brief, intermittent electric field pulses to clean membranes without interruption of the separation process. Experimental studies of the filtration of dispersions of baker's yeast and titanium dioxide, chosen as model systems representing biological and inorganic process streams, show that this technique can improve overall membrane permeation rates by a factor of up to ten with only a modest electrical energy requirement. The second, which we have termed “ in situ electrolytic membrane restoration” or IEMR, is very effective at restoring membrane water permeation rates under mild chemical conditions. Used in combination, these techniques may obviate the requirement for membrane backflushing and conventional chemical cleaning.