Air Diffusion Research Articles

Singlet oxygen generation for selective oxidation of emerging pollutants in a flow-by electrochemical system based on natural air diffusion cathode.

The decay of free radicals involved in side reactions is one of the challenges faced by electrochemical degradation of organic pollutants. To this end, a non-radical oxidation system was constructed by a natural air diffusion cathode (ADC) and a Ti-based dimensional stable anode coated by RuO2 (RuO2-Ti anode) for cathodic hydrogen peroxide activation by anodic chlorine evolution. The ADC fabricated by the carbon black of BP2000 produced a stable concentration of hydrogen peroxide of 339.94mg L-1 (current efficiency of 73.4%) without aeration, which was superior to the cathode made by the XC72 carbon black. The flow-by ADC-RuO2 system consisted of an ADC and a RuO2-Ti anode showed high selectivity to aniline (AN) compared to benzoate (BA) in a NaCl electrolyte, whose degradation efficiencies were 97.72% and 1.3%, respectively. Rapid degradations of a mixture of emerging pollutants and AN were also observed in the ADC-RuO2 system, with pseudo-first-order kinetic constants of 0.51, 1.29, 0.89, and 0.99min-1 for Bisphenol A (BPA), tetracycline (TC), sulfamethoxazole (SMX) and AN, respectively. Quenching experiments revealed the main reactive oxygen species for the pollutant degradation was singlet oxygen (1O2), which was also identified by the electron spin resonance (ESR) analysis. Finally, the steady-stable content of 1O2 was quantitatively determined to be 6.25 × 10-11M by the method of furfuryl alcohol (FFA) probe. Our findings provide a fast, low energy consumption and well controlled electrochemical oxidation method for selective degradation of organic pollutants. H2O2 generated on an air diffusion cathode by naturally diffused O2, reacts with ClO- produced from chloride oxidation on the RuO2-Ti anode to form singlet oxygen (1O2). The electrochemical system shows an efficient oxidation to electron-rich emerging pollutants including bisphenol A, tetracycline, sulfamethoxazole and aniline, but a poor performance on the electron-deficient compounds (e.g., benzoate).

Application of jetventurimixer for developing low-energy-demand and highly efficient aeration process of wastewater treatment

In biological wastewater treatment, the oxygen supply in an aeration tank is the most important factor for removing organic pollutants, but it takes a large amount of electricity to generate the oxygen supply required. The Jetventurimixer (JVM) is a device that applies Bernoulli’s principle, and the difference in flow rate pressure through the impeller is generated by the rotational force. Due to this physical mechanism, this device can supply oxygen in the atmosphere to the bioreactor without additional power. In this study, the JVM-based aeration process was developed for more efficient water treatment that demands lower energy. Parameters were measured for validating the efficiency and lower power demands, including the oxygen mass transfer characteristics and power efficiency. The results indicated that all parameters related to the oxygen mass transfer characteristics were advanced in performance by more than 200 % compared to those of the conventional air diffuser. In the case of power efficiency, it was confirmed that performance was 153–176 % higher. Therefore, it was confirmed that the JVM provides high-efficiency and low-energy benefits to the aeration process and, based on these advantages, the developed system seems to require further studies and validation for application to the water treatment system.

Plant-wide modeling of a metropolitan wastewater treatment plant to reduce energy consumption and carbon footprint.

A real metropolitan wastewater treatment plant (RWWTP) serving a population equivalent of 1.55 million was modeled to reduce energy consumption and carbon footprint (CFP). An approach was proposed to handle the dilution factor and partial aeration due to discontinuous air diffuser locations in the Bardenpho-5 configuration. Various operational, structural, and configurational modifications were evaluated. Results indicated that management scenarios might provide conflicting outcomes for different targets. Reduced energy consumption may not result in lower CFP at the same time. Moreover, operational changes that would impact total nitrogen (TN) concentrations and N2O release may significantly impact CFP. A policy of using a modified Bardenpho-5 process with reduced internal recycle (IR) ratio, waste activated sludge (WAS), and return activated sludge (RAS) flow rates provided the lowest CPF. Modified Bardenpho-5 process and replacing belt thickeners with gravity thickeners supplied the highest savings in energy consumption. Overall, up to 14% and 20% reductions were possible in the energy consumption and CFP of the plant, respectively. The RWWTP may save up to 10% in energy expenses annually by operational modifications.

Electrochemical Synthesis of Hydrogen Peroxide Catalyzed by Carbon Nanotubes with Surface Co-NX Sites and Encapsulated Co Nanoparticles.

The exploitation of M-NX sites, where M is a transition metal atom, is widely regarded as an effective catalytic strategy to promote the oxygen reduction reaction (ORR). In addition, some studies have shown that transition metal nanoparticles (M-NPs) coated with carbon layers can improve the reactivity of ORR and ameliorate the overpotential of the reaction. In this study, we synthesized carbon nanotubes with single-atom Co-NX active sites, Co-NPs outside the tube, and Co-NPs wrapped in the tube by the complexation-pyrolysis synthesis method and explored the role of the particles and Co-NX sites through different pickling steps. The catalyst synthesized with the new stratagem in this study shows outstanding selectivity and also ORR activity. Furthermore, a natural air diffusion electrode fabricated using this material can produce H2O2 at 323 mg L-1 h-1 under neutral conditions without oxygen aeration.

Experimental study of an innovative perforated air diffuser at real scale conditions

The European regulations are demanding more than ever to reduce the energy consumption for buildings and at the same time to raise the Indoor Environmental Quality to a higher standard. This challenge implies that the occupants inside the building should benefit from at least the same thermal comfort conditions at a lower energetical cost. The purpose of this research is to improve the performance of the air diffusers ventilation devices with the purpose of obtaining a more efficient mixing of the airflow from the air diffuser towards the ambient air. In this regard, an innovative cross shaped orifices perforated panel is analysed and compared to a regular panel with circular orifices. The experimental approach was carried out in a climatic chamber. The indoor thermal comfort was assessed at the same time by means of two different experimental devices, namely a thermal manikin and Comfort Sense equipment. The equivalent temperature was assess using the thermal manikin. The panels were also evaluated from the noise levels and pressure losses points of view. By evaluating the PMV and PPD thermal comfort indexes, the results highlighted a more comfortable ambience for a specific person in the room for the cross shaped lobed perforated panel in comparison to the circular shaped perforated panel. Furthermore, it seems that the special geometry of the lobed perforated panel does not generate supplementary noise. The pressure losses of the airflow through the perforated panels were reduced as well.

Energy-Efficient H2O2 Electro-production Based on an Integrated Natural Air-Diffusion Cathode and Its Application

Given the low oxygen mass transfer rate and high aeration energy consumption, the traditional two-electron oxygen reduction reaction (ORR) is restricted. In this study, the integrated natural air diffusion cathode (INAC) and a reactor configuration with the horizontal scale facing to air (FTA) demonstrated highly selective H2O2 production for the removal of organic contaminants. Simply synthesized by shaping the mixture of carbon black and polytetrafluoroethylene, the INAC exhibited not only massive pores in all directions for sufficient mass transfer but also the integrated configuration for low charge transfer resistance. Based on the oxygen mass transfer models, for the ORR reaction kinetics, the interface oxygen concentration index was higher than 40, contributing to the high current efficiency of H2O2 production (>90%). The oxygen diffusion model can provide the quantitative description of H2O2 synthesis for porous electrode optimized design. Combining the INAC with the reactor configuration with the FTA mode for free additional O2/air source supply, the electrical efficiency per order was lower than 0.14 kWh m–3, and the removal rate of sulfonamides per unit current could reach 11 mg min–1 A–1, reaching the best reports. This ultraefficient process equipped with the INAC and the FTA mode provides a meaningful practical application prospect for wastewater treatment.

Removal of sulfamethazine by a flow-Fenton reactor with H2O2 supplied with a two-compartment electrochemical generator

A novel continuous-flow H2O2 electrochemical generator using a natural air diffusion electrode (NADE) as the cathode was designed and the two compartments of the generator were separated by a cation exchange membrane. The reactor did not require aeration, which saved aeration energy consumption. The reactor showed good performance in generating H2O2 up to 50.8 mg/h/cm2 with the energy consumption of 25.2 kWh/kg H2O2, and maintained a high current efficiency of about 70–94% in the current density range of 20 to 100 mA/cm2. The yield of H2O2 and current efficiency remained high and stable in a wide pH range of 3 ∼ 9. H2O2 produced in the generator was delivered to a flow-Fenton reactor for the occurrence of the Fenton reaction and the degradation of sulfamethazine (SMT), which avoided the problem of excessive generation and ineffective consumption of H2O2 in the electro-Fenton process and improved the utilization rate of H2O2. Moreover, due to the introduction of H2O2 solution with low pH to the flow-Fenton reactor, the pH of the working solution did not need adjustment. The flow-Fenton process achieved 99% of SMT removal, 90% of H2O2 utilization rate, and 54% of TOC removal within 20 min under the optimum conditions. The degradation of several other contaminants (2,4-dichlorophenoxyacetic acid, tetracycline and carbamazepine) was investigated and all of the removals were maintained above 97%. The study is promising for the practical electrochemical production of H2O2 and application of flow-Fenton for contaminants degradation.

Numerical and Experimental Study on the Indoor Climate in a Classroom with Mixing and Displacement Air Distribution Methods

One main challenge of air distribution in classrooms is to guarantee ventilation performance under different usage conditions. In this study, the indoor climate in summer and winter conditions with different occupancy densities in the classroom is presented. Thermal condition measurements of a half-size classroom were performed in a test room with four air suppliers: wall-grilles, ceiling diffusers, perforated duct diffusers, and displacement ventilation. Those measured data were used for CFD validation of the whole classroom. With CFD simulations, indoor climate parameters with different air diffusers are compared in summer and winter conditions. The results show that displacement ventilation gives the best performance in the occupied zone. The air change efficiency can be reached with displacement ventilation of 1.4 and of only 1 with the other three air diffusers. The air velocities were reasonably low (<0.3 m/s), and the indoor was quite uniform with ceiling diffusers, which is another well-performing solution for classrooms. Corridor wall-grilles give uniform thermal conditions but can have high velocities (0.4 m/s) on the perimeter side of the room space. The air distribution from the perforated duct diffuser is unstable, which causes high local draft (over 20%) in the occupied zone.

Experimental and numerical study of the flow dynamics and thermal behavior inside a car cabin: Innovative air diffusers and human body plumes interactions

In confined spaces, such as vehicle cabins, airflow and temperature distribution are the most critical factors affecting thermal comfort and pollutant dispersion. To develop innovative and energy-efficient HVAC systems, a deep understanding of the interaction of the jet flow from the air diffusers on the development process of the human thermal plume became essential to improve the knowledge of airflow patterns for optimizing ventilation system design, thermal comfort, and, indirectly, the energy efficiency. The human thermal plume is one of the most challenging phenomena to capture with optical measurement methods and validate with complex numerical models, given its unsteady nature governed by the buoyancy forces. This study aims to validate the interaction of jet flows from classical and innovative air diffusers on the thermal plume by comparing measured data and numerical simulation results. This validation was made with a specific approach by comparing PIV fields from measurements and CFD results with boundary conditions of air velocity distribution from LDV data. The PIV measurements for flow distributions at the air vents and the thermal plume of an advanced thermal manikin in the driver’s seat were performed in a 1:1 scale mock-up of a Renault Megane car cabin in a climatic chamber. The results obtained with both methods showed good agreement regarding air velocity ranges and distributions. Despite the confined cabin space restricting the development of the thermal plume, a difference in maximum velocities of 0.08 m/s was observed when the distance between the top of the head and the ceiling was doubled. With innovative air diffusers, air velocity distribution showed a more uniform flow than classical diffusers.

Partially enclosed air curtain dust control technology to prevent pollution in a fully mechanized mining face

To mitigate the effect of coal dust on the health of workers and the work environment, a new type of partially enclosed air curtain device for dust control is proposed; its dust control effect was numerically simulated in this study. The results show that after the dust control air curtain device has been turned on, a partially enclosed dust control air chamber is formed in the shearer driver’s working area. Although the air chamber affects the air flow velocity and diffusion trajectory at the 1.4–2.0 m height in the coal mining area, it does not affect the safe operation of the entire tunnel ventilation system. Simultaneously, the air chamber prevents the dust generated at the dust source from entering the shearer driver’s working area; with a dust control efficiency of 61.8%, the quantity of dust is successfully reduced. The diffusion of particles to the downwind side reduces the diffusion distance of ultra-high-concentration dust by approximately 35 m. This technology effectively improves the working environment for coal mine operators (particularly for shearer drivers), reduces risks, and provides operators with a safe and clean production environment. Moreover, this technology can provide new ideas for dust prevention and control methods in other restricted spaces.

Fiber-bundle-based 2D Raman and Rayleigh imaging for major species and temperature measurement in laminar flames.

In this Letter, we introduce a novel fiber-bundle-based 2D Raman and Rayleigh imaging system for 2D measurements of major species mole fractions and temperature in flames. A cascade of dichroic mirrors and bandpass filters separate the Raman signal associated with each major species and direct it to a custom-built four-inputs/one-output fiber bundle. The single output of the fiber bundle allows simultaneous detection of four species by using a single back-illuminated CCD camera. The novel imaging system combined with a pulse-burst laser operated at 10 kHz and a 10 kHz optical shutter is characterized from measurements in a Mckenna burner and then applied to a flame stabilized over a Santoro burner. The work is, to the best of our knowledge, the first demonstration of 2D measurements of temperature and major species (i.e., N2, O2, H2, and H2O) in H2-air diffusion flames at atmospheric pressure.

Nb2CTx MXenes functionalized Co−NC enhancing electrochemical H2O2 production for organics degradation

Cobalt-dispersed nitrogen-doped carbon nanotubes supported on oxygen-terminated Nb2CTx MXenes (Co−NC/MXenes) are successfully constructed, in which ZIF-67 are in-situ grown on Nb2CTx and then converted to Co−NC followed a pyrolysis process. The introduction of oxygen-terminated Nb2CTx MXenes can effectively regulate the structure of Co−NC and induces a strong interaction between Nb2CTx and Co−NC, promoting H2O2 electrosynthesis via two-electron (2e−) oxygen reduction reaction (ORR) with high selectivity. Moreover, the assembled device with Co−NC/MXenes as cathode enables an accumulated H2O2 concentration of 4.8 wt% even under natural air diffusion. When combined with the dual-cathode system, the device achieves excellent total organic carbon (TOC) removal towards organic dyes (50 mg L−1) and sulfamethoxazole (20 mg L−1). This work provides a direction for the precise construction of 2e− ORR catalysts and expands an emerging application of the dual-cathode technique.

Effects of feeding mode on the performance, life span and greenhouse gas emissions of a vertical flow macrophyte assisted vermifilter

This study was conducted to investigate the impact of intermittent feeding on performance, clogging, and gaseous emission on macrophyte assisted vermifiltration (MAVF) based treatment system. Synthetic slaughterhouse wastewater was applied to two different integrated vertical flow based MAVFs. Triplicates were used throughout the study. Eisenia fetida earthworms were added to MAVFs, and Carex muskingmenis plants were planted. Wastewater was applied to the reactors on 1) intermittent (8 h/day) (IMAVF) and 2) continuous (24 h/day) (CMAVF) basis. The average chemical oxygen demand, total nitrogen, and total phosphorous removals achieved by the IMAVF were 80.2 ± 1.6%, 53.9 ± 1.3% and 66.5 ± 1% respectively, and 68.3 ± 1.3%, 61.2 ± 1.4%, and 60.5 ± 1.4% by the CMAVF, respectively. The diffusion of air to the bedding of IMAVFs during no-flow conditions facilitated higher organics oxidation, adsorption of phosphorous, nitrification, and ammonification. At the end of the study, hydraulic conductivity of IMAVF and CMAVF were found to be 0.036 cm/s and 0.037 cm/s, respectively. CO2, CH4 and N2O emissions from IMAVF were 245.5 ± 38.0 mg C/m2, 5.0 ± 4.6 mg C/m2 and 2513.5 ± 2629.9 μg N/m2 respectively, while CO2, CH4 and N2O emissions from CMAVF were 123.3 ± 14.5 mg C/m2, 74.8±45.2 mg C/m2 and 328.4 ± 93.4 μg N/m2, respectively. Intermittent application of influent could be considered for improving the performance and lifespan of MAVFs, causing lower environmental footprints.

Evaluation of Conditions to Improve Biomass Production by Submerged Culture of Ganoderma sp.

In the present investigation, the conditions for in vitro submerged culture of a native strain of Ganoderma sp. were evaluated. Different culture medium ingredients, inoculum concentrations, inoculation methods, configuration, and airflows were evaluated to improve biomass production. The addition of thiamine and olive oil to the culture medium increased biomass production, as well as inoculating 6.6 g/L since there are no significant differences in biomass growth according to inoculum origin (pre-inoculum, discs or with spores). The best configuration of the 3 L stirred tank bioreactor was using three impellers and a porous air diffuser of 0.25 volume per volume per minute (vvm), the dry biomass concentration was 22.6 g/L after 12 days of cultivation at 30 °C, much higher than other investigations. This study provides relevant information for pilot-scale production of this fungus for future secondary metabolites. The culture medium was optimized, and it was defined that the concentration and origin of the inoculum did not influence the growth of Biomass, but the aeration and the configuration of the system allowed the establishment of protocols for the cultivation of Ganoderma sp.

Ventilation impacts on infection risk mitigation, improvement of environmental quality and energy efficiency for subway carriages

Subway carriages are enclosed for extended periods of time, with a high density of passengers. Providing a safe, healthy, and comfortable cabin environment is a great challenge, particularly during the COVID-19 pandemic. An increase in ventilation rate can potentially reduce infection probability, which may result in worsening environmental quality (e.g., thermal comfort) and larger energy consumption. Thus, exploring the trade-off among infection risk, environmental quality (with regard to ventilation, thermal comfort, and air quality), and energy consumption is important to optimize ventilation systems for carriages. The effect of different supply air parameters (e.g., velocity and temperature) and ventilation modes of mixing ventilation (MV) & Supply air from the Floor and Return air from the Ceiling (SFRC) was studied. The questionnaires were analyzed to explore passenger dissatisfaction with the carriage environment using a MV system. Simulations were performed to predict the velocity, temperature, and CO2 concentration fields. In addition, the comprehensive benefit was evaluated by analytic hierarchy process (AHP), based on infection probability from the revisited Wells–Riley equation, Air Diffusion Performance Index (ADPI), Predicted Mean Vote (PMV), Pollutant Removal Effectiveness (PRE) and energy consumption estimated by cooling load (Lcool). Compared with MV, the optimized SFRC provided softer draft sensation and decreased CO2 concentration by 42%. The SFRC achieved better comprehensive benefits, with an infection risk reduced to 0.4%, ADPI of 80%, PMV approaching zero, PRE up to 16, and energy efficiency increased by 30%. This work contributes to the optimal design of subway carriage ventilation systems in the post-epidemic era.

Engineering a concordant microenvironment with air-liquid-solid interface to promote electrochemical H2O2 generation and wastewater purification

Electroreduction of O2 to H2O2 provides an appealing route for both renewable energy storage and wastewater purification. Although grand endeavors are devoted into synthesizing high-performance electrocatalysts, the understanding and engineering of local microenvironment around reactive sites are also critical. Herein, a concordant gas/liquid microenvironment with plentiful air–liquid-solid interfaces is constructed and evaluated, which not only mediates the harmonious transport of O2, H+ and electron (especially reducing the O2 diffusion layer thickness and raising O2 local concentration to accelerate O2 transport), but also induces massive highly active triphase boundary sites for high-rate H2O2 electro-generation. Consequently, even under natural air diffusion, the cathode with the polytetrafluoroethylene proportion of 20% achieves a preeminent H2O2 productivity (40.7 mg h−1 cm−2 at 100 mA cm−2, corresponding to the maximum H2O2 concentration of 813.8 mg L-1) with superior current efficiency (64.2%). Long-term electrolysis stability and reusability indicate the practicability of the air-breathing cathode without the energy-intensive external aeration. Efficient purification of dye wastewater by the modified cathode meets the expectation, showing its huge potential in environmental protection. This work deeply elucidates the effect mechanism of a concordant gas/liquid microenvironment with abundant air–liquid-solid interfaces, which has considerable guiding significance for similar gas-involving electrocatalysis.

Effects of H2 Addition and CO2 Dilution on the Methane–Air Diffusion Flame in a Coflow Burner

Effects of H2 Addition and CO2 Dilution on the Methane–Air Diffusion Flame in a Coflow Burner

Cellular scaffolds based on multiwalled carbon nanotubes interpenetrating conductive metal-organic frameworks as efficient eelectrocatalysts in microbial fuel cells

Sluggish kinetics of the cathodic oxygen reduction reaction (ORR) is one of the major challenges hindering the development of microbial fuel cells (MFCs). In this work, a three-dimensional (3D) cellular scaffolds structure is fabricated by in-situ growth of conductive Ni/Co-catecholate bimetal metal-organic frameworks (MOFs) on multiwalled carbon nanotubes (NiCo-CAT/MWCNTs). Such specific structure successfully achieves favorable electronic channels and fast charge-transfer capacity and displays an ultra-low ohmic internal resistance of 7.27 Ω. Meanwhile, NiCo-CAT/MWCNTs exhibit a superior ORR half-wave potential (−0.442V vs. Hg/HgCl2), onset potential (−0.064V vs. Hg/HgCl2) and high limiting current density (8.25 mA cm−2), which exceed that of commercial Pt/C. In the MFC with the NiCo-CAT/MWCNTs cathode, the maximum power density is 130% higher than Pt/C cathode. The outstanding performance of MFC is mainly due to the optimized electronic structure and fully exposure of the Ni, Co synergistic catalytic active sites. In addition, oxygen permeability is greatly improved by electrospun polyvinylidene fluoride (PVDF) air diffusion layer replacing the traditional carbon cloth cathode. This study provides a new perspective for MFCs performance improvement by ORR conductive MOFs catalysts.

Liquid Core Waveguide Cell with In Situ Absorbance Spectroscopy and Coupled to Liquid Chromatography for Studying Light-Induced Degradation

In many areas, studying photostability or the mechanism of photodegradation is of high importance. Conventional methods to do so can be rather time-consuming, laborious, and prone to experimental errors. In this paper we evaluate an integrated and fully automated system for the study of light-induced degradation, comprising a liquid handler, an irradiation source and exposure cell with dedicated optics and spectrograph, and a liquid chromatography (LC) system. A liquid core waveguide (LCW) was used as an exposure cell, allowing efficient illumination of the sample over a 12 cm path length. This cell was coupled to a spectrograph, allowing in situ absorbance monitoring of the exposed sample during irradiation. The LCW is gas-permeable, permitting diffusion of air into the cell during light exposure. This unit was coupled online to LC with diode array detection for immediate and automated analysis of the composition of the light-exposed samples. The analytical performance of the new system was established by assessing linearity, limit of detection, and repeatability of the in-cell detection, sample recovery and carryover, and overall repeatability of light-induced degradation monitoring, using riboflavin as the test compound. The applicability of the system was demonstrated by recording a photodegradation time profile of riboflavin.

A Comprehensive Derivation and Application of Reference Values for Benchmarking the Energy Performance of Activated Sludge Wastewater Treatment

Wastewater treatment plants (WWTPs) are facing challenges concerning the service’s effectiveness and reliability, as well as the efficiency and sustainability of resource utilization, where energy represents one of the higher costs in activated sludge (AS) treatment. This paper presents the latest developments in the new energy performance indices (PXs) we have been developing for benchmarking, i.e., assessing and improving the performance of this widely used treatment. PXs compare the energy consumption with the energy requirements for the carbon and nitrogen removals needed for the plant’s compliance with the discharge consents (the closer they are, the better the performance). PXs are computed by applying to the state variables a performance function that is defined by the reference values for excellent, acceptable, and unsatisfactory performance. This paper shows the rationale for selecting the state variables for the AS energy performance and the comprehensive derivation of the equations to determine the reference values for energy consumption, which incorporate the effect of key parameters (flows, concentrations, and operating conditions). Reference values for the operating conditions affecting the energy performance are also proposed. A sensitivity analysis identified the key parameters for improving the aeration performance: α, F, and SOTE for air diffusers, and α and N0 for mechanical aerators. Fourteen Portuguese urban WWTPs (very diverse in size and inflows) were analyzed, and aeration (0.08–1.03 kWh/m3) represented 25–80% of total energy consumption (0.23–1.30 kWh/m3). The reference values for excellent performance were 0.23–0.39 kWh/m3 (P25–P75) for AS systems with air diffusers and 0.33–0.80 kWh/m3 for those with mechanical aerators. A comprehensive application in one WWTP (16–18 d solids retention time) showed the system’s ability at identifying which operating conditions to adjust (to F/M ratio lower than 0.09 d−1 and decreasing aeration during the low season) to improve the energy performance/savings while maintaining the treatment’s effectiveness and reliability.