Cleaning Protocol Research Articles

“Glucono-delta-lactone” as a substrate for preparation of new magnetically recoverable nanocatalyst for the environmentally benign synthesis of novel azo linked 3-methyl-isoxazol-5-ones

Silica-coated Fe3O4 nanoparticles bound to Glucono-delta-lactone (GDL) magnetic nanoparticles (Fe3O4@SiPr@GDL MNPs) were prepared and characterized by TEM, EDX, TGA/DTG, Zeta Potential, BET, FE-SEM, XRD, FTIR and VSM. Fe3O4@SiPr@GDL MNPs have been shown to be effective catalysts for the synthesis of the isoxazol-5(4H)-one system. The advantages of this method are efficiency, clean protocol, easy handling, high yield, shorter reaction time and availability of catalyst. The catalyst can be rapidly recovered and reused for six cycles with almost constant activity. The newly synthesized compounds were characterized by 1H NMR, 13C NMR and FTIR spectra and elemental analysis.

PIDA-Catalysed oxidative C–C bond cleavage for the direct synthesis of benzoic acids and antibacterial studies of the amides derivatives

A hypervalent iodine, (diacetoxyiodo)benzene (PIDA) catalysed facile synthesis of benzoic acids has been developed from aromatic ketone through oxidative C–C bond cleavage. A series of aromatic ketones get converted to the corresponding aromatic acid via oxime intermediate. Additionally, we have also utilized the resulted benzoic acid for the amide compounds using drug intermediate and studied the antibacterial activities. The use of hypervalent iodine, milder reaction conditions, good to high yields, clean protocols, the biological application are the notable features of the method.

COVID-19 cleaning protocol changes, experiences, and respiratory symptom prevalence among cleaning services personnel.

Cleaning protocols were changed in response to the COVID-19 pandemic with unknown occupational health impacts. There is evidence that COVID-19 transmission risks from contaminated surfaces are low and that exposure to cleaning products can increase risks of work-related asthma. The study objective was to investigate relationships between reported COVID-19-related changes in cleaning protocols and prevalence of asthma-related respiratory symptoms for asthmatic and non-asthmatic janitors and maids. A secondary objective was to characterize experiences of respiratory symptoms associated with cleaning and barriers to personal protective equipment (PPE) use. Employees from two Tucson-based maid service companies (approximately 30 personnel in total) and one Phoenix-based school district (>300 janitors/custodians) were invited to participate in a written survey and/or a one-on-one interview in Spanish or English. Fisher's exact tests (α = 0.05) were used to test for statistically significant associations between reported respiratory symptoms by self-reported physician-diagnosed asthma status and changes in cleaning protocols. Interviews were transcribed and then analyzed by at least two researchers in English or Spanish. Eighty-three percent reported that cleaning protocols had changed during COVID-19, with the two most reported changes including increased cleaning frequency (92%) and change of application type (e.g., fog, spray, wipe) (53%). There was a statistically significant association between multiple respiratory symptoms and self-reported physician diagnosed asthma. Reporting a type of application change (e.g., fog, spray, wipe) and being awakened during the night by attack/episode of cough were statistically significantly associated (p = 0.04). Interviews elucidated respiratory issues related to fogging devices. This study provides preliminary evidence that changes in cleaning and disinfection protocols during COVID-19 (namely, the use of fogging/mechanical spraying devices) may have had negative impacts on the health of workers in the cleaning industry with little benefit to reducing COVID-19 risks. Further research is needed to evaluate the generalizability of our findings across larger geographical areas and to develop guidance for employers and employees on how to protect and promote respiratory health.

Selected physical and chemical cleanings remove biofilm in seawater membrane distillation without causing pore wetting

Membrane distillation (MD) is an emerging process with a proven ability to recover freshwater from streams with a wide range of salinities. However, MD is susceptible to biofouling. This study explores the efficiency of different cleaning strategies in biofilm removal during seawater MD. Hydraulic cleaning and chemical cleanings with 0.3%w w−1 ethylenediaminetetraacetic acid (EDTA), 0.3%w w−1 NaOCl, and 3%w w−1 citric acid were tested. The results showed that permeate flux recovery increased in the order of hydraulic cleaning <3%w w−1 citric acid <0.3%w w−1 NaOCl ≈0.3%w w−1 EDTA. Membrane cleanings substantially reduced the thickness of the residual biofilm layer and decreased its bacterial concentration and resistance to vapor pressure. The post-cleaning permeate conductivities were low suggesting that employed cleaning protocols did not cause pore wetting of hydrophobic polytetrafluoroethylene microporous (0.22 μm) membrane, and membrane rejection properties remained stable.

Effects of Processing-Induced Contamination on Organic Electronic Devices.

Organic semiconductors are a family of pi-conjugated compounds used in many applications, such as displays, bioelectronics, and thermoelectrics. However, their susceptibility to processing-induced contamination is not well understood. Here, it is shown that many organic electronic devices reported so far may have been unintentionally contaminated, thus affecting their performance, water uptake, and thin film properties. Nuclear magnetic resonance spectroscopy is used to detect and quantify contaminants originating from the glovebox atmosphere and common laboratory consumables used during device fabrication. Importantly, this in-depth understanding of the sources of contamination allows the establishment of clean fabrication protocols, and the fabrication of organic field effect transistors (OFETs) with improved performance and stability. This study highlights the role of unintentional contaminants in organic electronic devices, and demonstrates that certain stringent processing conditions need to be met to avoid scientific misinterpretation, ensure device reproducibility, and facilitate performance stability. The experimental procedures and conditions used herein are typical of those used by many groups in the field of solution-processed organic semiconductors. Therefore, the insights gained into the effects of contamination are likely to be broadly applicable to studies, not just of OFETs, but also of other devices based on these materials.

Easy cleaning plus stable activation of glassy carbon electrode surface by oxygen plasma

Glassy carbon (GC) electrodes are widely used in electroanalytical applications especially in bioelectrochemistry. Their use starts with an efficient surface cleaning and activation protocol, mostly based on surface polishing steps. We studied the use of an oxygen plasma exposure of GC electrodes to replace common polishing procedures. The cyclic voltammetry (CV) responses of ferrocyanide and ferrocene-dimethanol were used to compare brand new, surface-polished and plasma-treated GC electrodes. Plasma treatment induces CV responses with improved features, close to theoretical values, as compared to other methods. The plasma effects were quasi-stable over a week when electrodes were stored in water, this being explained by increased surface energy and hydrophilicity. Furthermore, when electroreduction of diazonium was performed on GC electrodes, the surface blockade could be removed by the plasma. Thus, a short oxygen plasma treatment is prone to replace polishing protocols, that display person-dependent efficiency, in most of the experiments with GC electrodes.

A Life-Cycle of Ni in Proton Exchange Membrane Fuel Cells

The usage of Proton Exchange Membrane Fuel Cells (PEMFCs) in the automotive industry is currently limited by the price, performance, and durability of a platinum catalyst. Alloying with nickel provides lower cost and enhances activity. However, the membrane electrode assembly (MEA) performance is, in practice, much lower than expected from liquid laboratory experiments on the catalyst layer. One of the identified issues is Ni leaching from nanoparticles (NPs) and subsequent Ni poisoning of the Nafion membrane.Here, we use Wide-Angle X-ray Scattering (WAXS) and X-ray Absorption Near-Edge Structure (XANES) to follow Ni dissolution from the catalyst layer and its movement in the MEA. We shine (synchrotron) light on the full life cycle of Ni, starting from (i) characterization of the catalyst powder, followed by (ii) the changes in catalyst composition during the ink-making process and (iii) membrane coating and finishing with (iv) NP characterization and Ni tracking during the operation of MEAs.Proper incorporation of PtNi catalyst requires modification of all the aforementioned steps that are otherwise well optimized for pure Pt catalyst. It is even more critical for shape-controlled octahedra (oh) PtNi NPs as their activity is closely related to their structure [1]. Highly active oh-PtNi NPs are usually made from precursors such as Nickel(II) bis(acetylacetonate). Using EDX, we find precursor residues in catalyst powders that dissolve upon further processing and add to membrane poisoning. We conclude that we need to develop a cleaning protocol that would remove all Ni residue while retaining the nanoparticle shape.During ink-making, high ionomer concentrations and elevated temperatures promote Ni dissolution from the catalyst, which can, in turn, poison the membrane even before the MEA is put in use. With the WAXS technique, we track the dissolution during ink-making and MEA operation by following changes in lattice parameter, showing the dynamics and the extent of Ni dissolution in each step of aging.Furthermore, we use angle-resolved XANES to track the movement of dissolved Ni. We show that Ni ions are getting reduced back to metallic form within the MEA, likely due to hydrogen crossover. The presence of such a metal band in the membrane blocks proton conductivity and decreases performance [2]. That is why it is crucial to set manufacturing and operational boundaries to prevent dissolution.For this reason, we follow WAXS total scattering intensity during oxidation and reduction cycles to understand the Ni dissolution dynamics during operation. We find that limiting both upper and lower potential cycling limits greatly reduces the redox extent and subsequent dissolution. It is, therefore, possible to find and understand the trade-off between high power density and dissolution in operational cells.Even though this work looks at the Ni life cycle, the presented techniques and conclusions are transferable to all multimetallic high-performance PEMFC catalysts.

SERS Sensing of Dopamine with Fe(III)-Sensitized Nanogaps in Recleanable AuNP Monolayer Films.

Sensing of neurotransmitters (NTs) down to nm concentrations is demonstrated by utilizing self-assembled monolayers of plasmonic 60nm Au nanoparticles in close-packed arrays immobilized onto glass substrates. Multiplicative surface-enhanced Raman spectroscopy enhancements are achieved by integrating Fe(III) sensitizers into the precisely-defined <1nm nanogaps, to target dopamine (DA) sensing. The transparent glass substrates allow for efficient access from both sides of the monolayer aggregate films by fluid and light, allowing repeated sensing in different analytes. Repeated reusability after analyte sensing is shown through oxygen plasma cleaning protocols, which restore pristine conditions for the nanogaps. Examining binding competition in multiplexed sensing of two catecholamine NTs, DA and epinephrine, reveals their bidentate binding and their interactions. These systems are promising for widespread microfluidic integration enabling a wide range of continuous biofluid monitoring for applications in precision health.

Synthesis of polymerizable quaternary ammonium bromides and their efficacy against pathogenic and food spoilage bacteria

Despite rigorous cleaning and sanitization protocols, food manufacturing facilities can harbor persistent microorganisms that can cause post processing contamination leading to food safety and food spoilage issues. Of particular concern are ‘growth niches’, regions within a manufacturing facility more likely to accumulate water and debris because they are outside the zones of routine cleaning and sanitization. Such growth niches present a challenge in controlling post-processing microbial contamination which can affect the safety and shelf life of foods and beverages. In recent years, researchers have explored using antimicrobial and nonfouling coatings to control microbial persistence and cross contamination. A challenge in identifying effective coatings is the limited research on efficacy of antimicrobial monomers (suitable for polymerization into antimicrobial coatings) on microorganisms relevant in food safety and spoilage. In this work, we synthesize and characterize the efficacy of five antimicrobial quaternary ammonium bromide (QAB) monomers against pathogenic and food spoilage organisms. The QAB monomers are end-capped with dihydroxy moieties suitable for subsequent polymerization into antimicrobial polyurethanes and polyesters. N,N-bis(2-hydroxyethyl)-N-methyl-N-R-1-ammonium bromides (R= -octan {C8QAB}, -decan {C10QAB}, -dodecan {C12QAB}, -hexadecan {C16QAB}, -octadecan {C18QAB}) were synthesized and characterized using spectral techniques (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy). Minimum inhibitory concentrations were determined against relevant food safety and food spoilage bacteria Listeria monocytogenes, Salmonella Typhimurium, Escherichia coli, and Pseudomonas poae. Sixteen and eighteen carbon length QAB monomers inhibited growth of L. monocytogenes and P. poae at a concentration of 3 ppm, while sixteen carbon length QAB monomerinhibited growth of Salmonella Typhimurium at 26 ppm and against Escherichia coli at 13 ppm. Quaternary ammonium compounds capped with polymerizable end groups such as those reported here offer an opportunity to reduce persistence and cross-contamination of food pathogens and food spoilage bacteria with particular relevance in growth niches outside of routine cleaning and sanitization regimens.

Evaluation of cleaning and disinfection protocols for commercial farm equipment following a foreign animal disease outbreak

AbstractThis study evaluated the microbiocidal efficacy of a cleaning and disinfection (C&amp;D) treatment using stainless‐steel coupons applied to three common types of animal mortality transport vehicles when exposed to agricultural conditions. Metal test coupons, inoculated with bacteriophage MS2, were affixed to the undercarriage of three types of animal mortality transport vehicles at various locations. Coupons were grimed by maneuvering the test vehicles down a series of wet dirt roads. Coupons were attached and extracted at various points to evaluate C&amp;D performance with and without grime. C&amp;D efficacy using a water‐supplied pressure washing system and a dilute sodium hypochlorite (NaOCl) solution was determined by comparing the difference in recovered viable virus between positive control coupons and test coupons. The results demonstrated a relatively high surface decontamination efficacy, with all but one location showing &gt;5 log reduction of MS2. Coupons located on the roll‐off truck's inside‐back bumper contained the highest level of grime and resulted in a 4 log reduction of MS2. There was no significant difference in C&amp;D efficacy across vehicle types, but locations impacted by grime and lack of accessibility achieved lower efficacies on average. These findings suggest that common C&amp;D protocols, when applied to farm mortality transport vehicles, are effective. Hard‐to‐access locations containing high levels of grime may be candidates for additional targeted treatment.

IMPACT OF ENVIRONMENTAL CLEANING AND DISINFECTION PRACTICES ON INFECTION CONTROL OUTCOMES IN SAUDI ARABIAN HEALTHCARE SETTINGS: A SYSTEMATIC REVIEW AND META-ANALYSIS

IMPACT OF ENVIRONMENTAL CLEANING AND DISINFECTION PRACTICES ON INFECTION CONTROL OUTCOMES IN SAUDI ARABIAN HEALTHCARE SETTINGS: A SYSTEMATIC REVIEW AND META-ANALYSIS

Decontamination of biofilm-contaminated implant surfaces: An in vitro evaluation.

The aim of the present study was to evaluate the cleaning efficacy of two mechanical and two chemical protocols in the decontamination of implant surfaces. In total, 123 commercially available implants were mounted in plastic models mimicking peri-implant circumferential intra-bony defects. A multispecies biofilm was grown on implant surfaces. Mechanical (air-polishing (AP), rotating titanium brush (TiB)) and chemical decontamination (alkaline electrolyzed water, N-acetyl-L-cysteine) protocols were used. Cleaning efficacy in terms of residual biofilm area, chemical surface properties, and bacterial counts were analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and quantitative polymerase chain reaction. Surface decontamination protocols including use of an AP device or a rotating TiB were superior in terms of biofilm removal and in reducing atomic% of Carbon on implant surfaces when compared to methods restricted to wiping with gauze. The use of chemical agents as adjuncts to the mechanical cleaning protocols provided no relevant overall benefit over saline. No treatment modality, however, resulted in complete biofilm removal. Air-polishing and rotating TiB were more effective implant surface decontamination protocols than wiping with gauzes. Use of chemical agents did not improve cleaning efficacy.

Comparison of bond strength to three restorative materials after contamination and the use of two cleaning agents

Statement of problemScientific data on the decontamination effectiveness of a newly introduced cleaning agent are lacking. PurposeThe purpose of this in vitro study was to evaluate and compare the tensile bond strength (TBS) of 3 different restorative bonding surfaces after contamination with saliva following different cleaning protocols. Material and methodsA total of 192 disk specimens were made out of 3 materials (n=64); Katana Avencia (A), Katana Zirconia (Z), and e.max CAD (L). The bonding surfaces of all disks were polished, steam cleaned, and then pretreated by following the recommended protocol for each material. The specimens of each group were divided into 4 subgroups (n=16). The first subgroup served as the reference (R), where no contamination was applied. The 3 other subgroups were contaminated with saliva and subsequently rinsed with water for 20 seconds and dried with oil- and water-free air spray. They were then either not treated with any cleaning method (0), cleaned with Katana Cleaner (K), or cleaned with Ivoclean (I). The bonding surfaces of the specimens were perpendicularly luted to plexiglass tubes filled with dual-polymerizing composite resin (Clearfil DC Core) with resin cement (Panavia V5) after the recommended surface conditioning. Each subgroup was further subdivided into 2 groups: stored in 37 °C water for 3 days or subjected to thermal-cyclic loading for 150 days with 37 500 thermal cycles (7500 per month), temperature 5 to 55 °C, and dwell time of 30 seconds. All specimens were subjected to TBS testing in a universal testing machine. Three-way ANOVA was applied. A significant interaction (P<.01) was detected between the 3 different variables (material, treatment, aging). After significant interactions had been revealed by 3-way ANOVA, additional statistical analysis was performed by using separate 2-way ANOVAs, then separate 1-way ANOVAs followed by the Tukey-HSD test for post hoc pairwise comparisons among groups (α=.05 for all tests). All specimens underwent failure mode analysis after TBS testing ResultsAll specimens survived the storage with thermocycling except for group Z-0, where all specimens debonded during thermocycling. The mean ±standard deviation TBS values ranged from 18.3 ±5.3 MPa to 34.0 ±5.4 MPa after 3 days and from 6.7 ±5.5 MPa to 26.9 ±5.4 MPa after 150 days. ConclusionsContaminated groups that did not receive any cleaning had significantly lower TBS. Thermocycling had a negative effect on the TBS but was not statistically significant for all groups. Using the same cleaning method, the restorative material did had a significant effect on the TBS after 150 days.

Contaminated Equipments: A Source of Hospital Acquired Infections among Patients at Critical Areas of Holy Family Hospital, Rawalpindi

Introduction: A nosocomial infection is contracted within a period of 48 hours following admission to a hospital or within 48 hours after being discharged from the hospital. Patients in the intensive care unit (ICU) are vulnerable to infections due to various factors, including their pre-existing medical conditions, medical procedures such as surgery, intubation, and catheterization, as well as their potential exposure to microorganisms from fellow patients. In addition to this, the presence of contaminated equipment represents a significant contributor to the occurrence of hospital-acquired infections caused by multidrug-resistant organisms among patients in critical areas. Methods: This cross-sectional study was conducted in coronary care and critical areas of Holy Family Hospital, Rawalpindi. A total of 415 samples were processed at the microbiology laboratory over a 4 month period from which 112 were swabs taken from equipment of the Medical, Surgical and Pediatric intensive care Units (MICU, SICU, and PICU) and the Coronary Care Unit. The remaining 303 samples were blood, urine, tracheal secretions/tips, pus and Foley tip cultures received in the microbiology laboratory from MICU, SICU, CCU and PICU. Samples were cultured on the appropriate media and observed after the required period. Results: High levels of contamination (58.03%) were identified on a wide range of healthcare equipment. The total of infected patients were 37.6%. Most common infection site was the respiratory tract. Acinetobacter spp. was the most predominant isolate among patients in MICU, SICU and CCU while Klebsiella spp. was the predominant isolate from the PICU. Conclusion: A significant degree of contamination is observed across a diverse array of healthcare equipment. Nevertheless, the prevalence of contaminated instruments and the subsequent potential for acquiring a healthcare-associated infection (HAI) can be significantly mitigated through the consistent implementation of cleaning, disinfection, and sterilization protocols for medical equipment. Keywords: hospital acquired infections, Contamination, equipment, pathogens.

The role of mixing and surface hydrophobicity on the operation of a continuous tubular slug flow crystalliser for lysozyme

Continuous crystallisation is currently seen as a more economic and efficient alternative compared to standard techniques for the purification of biopharmaceutical proteins. Despite being promising as continuous crystalliser platforms, tubular slug flow crystallisers pose their challenges due to the tendency of proteins to accumulate at solid surfaces, to form amorphous precipitates at high protein concentrations and to undergo slow diffusive mass transport. This work investigates the effect of equipment surface chemistry and physical mixing on the design and operability of a tubular slug flow crystalliser for lysozyme under laminar flow conditions (Re ∼ 1). Firstly, glass tubes with different surface functional groups, –OH or –CH3, with water contact angles between 9° and 99°, were investigated. CH3 surfaces resulted in a up to 33% delayed onset of nucleation, demonstrating lower heterogeneous nucleation rates, and therefore are better suited to prevent fouling. However, a surface chemistry-independent deposition of lysozyme was found, altering the water contact angle by up to 56°, resulting in an unstable slug flow and a reduction of the onset of nucleation by up to 11.5-fold. To achieve a stable slug flow and controlled nucleation, the surface functional groups were recovered by implementing surface-specific cleaning protocols comprising NaOH or liquid detergent. To overcome poor mixing and amorphous precipitation, a two-step mixing approach, consisting of an intermediate mixing step was developed. This novel mixing approach reduced the mixing time from > 10 min to < 10 s, allowing the achievement of an instantaneous homogeneous solution under laminar flow conditions. Overall, the findings of this study are therefore of crucial relevance to the future design and operation of tubular slug flow crystallisers as purification platforms for biopharmaceutical proteins.

Microbial Transport by a Descending Ice Melting Probe: Implications for Subglacial and Ocean World Exploration.

Ocean Worlds beneath thick ice covers in our solar system, as well as subglacial lakes on Earth, may harbor biological systems. In both cases, thick ice covers (>100 s of meters) present significant barriers to access. Melt probes are emerging as tools for reaching and sampling these realms due to their small logistical footprint, ability to transport payloads, and ease of cleaning in the field. On Earth, glaciers are immured with various abundances of microorganisms and debris. The potential for bioloads to accumulate around and be dragged by a probe during descent has not previously been investigated. Due to the pristine nature of these environments, minimizing and understanding the risk of forward contamination and considering the potential of melt probes to act as instrument-induced special regions are essential. In this study, we examined the effect that two engineering descent strategies for melt probes have on the dragging of bioloads. We also tested the ability of a field cleaning protocol to rid a common contaminant, Bacillus. These tests were conducted in a synthetic ice block immured with bioloads using the Ice Diver melt probe. Our data suggest minimal dragging of bioloads by melt probes, but conclude that modifications for further minimization and use in special regions should be made.

Development and Control of Biofilms: Novel Strategies Using Natural Antimicrobials.

Separation membranes have a wide application in the food industry, for instance, in the clarification/fractionation of milk, the concentration/separation of selected components, and wastewater treatment. They provide a large area for bacteria to attach and colonize. When a product comes into contact with a membrane, it initiates bacterial attachment/colonization and eventually forms biofilms. Several cleaning and sanitation protocols are currently utilized in the industry; however, the heavy fouling of the membrane over a prolonged duration affects the overall cleaning efficiency. In view of this, alternative approaches are being developed. Therefore, the objective of this review is to describe the novel strategies for controlling membrane biofilms such as enzyme-based cleaner, naturally produced antimicrobials of microbial origin, and preventing biofilm development using quorum interruption. Additionally, it aims to report the constitutive microflora of the membrane and the development of the predominance of resistant strains over prolonged usage. The emergence of predominance could be associated with several factors, of which, the release of antimicrobial peptides by selective strains is a prominent factor. Therefore, naturally produced antimicrobials of microbial origin could thus provide a promising approach to control biofilms. Such an intervention strategy could be implemented by developing a bio-sanitizer exhibiting antimicrobial activity against resistant biofilms.

Early care and education after COVID-19: A perspective

This perspective highlights the experiences and observations of an early care and education researcher reentering the field after the lifting of COVID-19 restrictions in the USA. Specifically, this perspective highlights the struggles of children, teachers, early care and education leaders, and the system itself as early care and education attempts to return to normal post COVID-19. Children exhibit behavioral, social, cognitive, and physical challenges. Teachers are burned out from grueling cleaning and safety protocols and caring for children who have missed the benefits of early care and education socialization during the pandemic. Leaders are struggling to keep a stable workforce and fill many roles in the childcare site. This perspective details firsthand experiences and recent relevant literature to describe these struggles.

Three-Dimensional Printed Resin: Impact of Different Cleaning Protocols on Degree of Conversion and Tensile Bond Strength to a Composite Resin Using Various Adhesive Systems.

The present investigation tested the effect of cleaning methods and adhesives on the tensile bond strength (TBS) of a resin-based composite luted to a temporary 3D printed resin. Substrates (n= 360) were printed using a Rapidshape D20II and cleaned with a butyldiglycol-based solution, isopropanol, or by centrifugation. Specimens were air-abraded with Al2O3 (mean particle size 50 µm) at 0.1 MPa followed by pretreatment (n = 30/subgroup) with: (1) Clearfil Ceramic Primer (CCP); (2) Clearfil Universal Bond (CUB); (3) Scotchbond Universal Plus (SUP) or 4. Visio.link (VL) and luted to PanaviaV5. TBS (n = 15/subgroup) was measured initially (24 h at 37 °C water) or after thermal cycling (10,000×, 5/55 °C). The degree of conversion (DC) for each cleaning method was determined prior and after air-abrasion. Univariate ANOVA followed by post-hoc Scheffé test was computed (p < 0.05). Using Ciba-Geigy tables and chi-square, failure types were analyzed. The DC values were >85% after all cleaning methods, with centrifugation showing the lowest. CCP pretreatment exhibited the lowest TBS values, with predominantly adhesive failures. The combination of CCP and centrifugation increased the TBS values (p < 0.001) compared to the chemical cleaning. CUB, SUP, and VL, regardless of cleaning, can increase the bond strength between the 3D printed resin and the conventional luting resin.

Nitrogen recovery from sludge centrate by membrane contactor: Influence of operating parameters and cleaning conditions

In urban wastewater treatment, the sludge generated is treated by anaerobic digestion, to be subsequently dehydrated by centrifuges. Currently, the liquid fraction obtained in this dehydration process is recirculated at the head of the treatment plant. However, its high nitrogen and phosphorus content makes it an effluent with high added value. The recovery of these nutrients could be an excellent alternative for the production of fertilizers or other industrial applications. In this study, the use of a liquid-liquid phase membrane contactor is presented as a favorable solution for the recovery of ammoniacal nitrogen from sludge centrated. The polypropylene hollow fiber membrane was evaluated considering its ammonia removal and recovery capacity. For this, different parameters were evaluated: the influence of the type and concentration of the acid solution, the wastewater pH, the flow rates of feeding and the acid stripping solution, and the contact time. Results showed that with a contact time of 65 min, ammonia removal and recovery percentages of the order of 90% were achieved. The flow rates of the stripping and feed solutions together with the acid concentration did not have a significant influence on the removal but on the recovery. Concerning used acid, sulphuric and phosphoric acid solutions achieved better results than nitric acid solution. The most critical parameter was the pH, obtaining the highest removal and recovery of ammonium at the highest pH. Finally, a stable cleaning protocol was obtained, between preventive and moderate cleanings to avoid severe cleanings, keeping the membrane at its maximum capacity.