WATER AND WATER PURIFICATION TECHNOLOGIES. SCIENTIFIC AND TECHNICAL NEWS

USE OF TEXTURED SURFACES FOR CONDENSATION OF WATER VAPOUR AND MIST

Oleksiy Myronyuk, Che Li — Mon, 01 Apr 2024 00:00:00 +0300

Producing purified water from air moisture is feasible even in arid areas where humidity is intermittent. This method relies on a condenser, usually cooler than the surroundings, where water condenses. Many studies use materials with diverse hydrophobicity, making it hard to pinpoint surface effects on condensation. Thus, comparing hydrophobic and hydrophilic surfaces with identical textures is crucial. The aim of this work is to determine the effect of gyrophobic metal surfaces on the processes of water collection from steam. Experiments in this work were conducted in a close chamber in the environment of water fog produced by the fog machine at the room temperature. It was shown that hydrophilic surfaces enhance water vapor condensation efficiency by up to 38% compared to hydrophobic ones. In this work, the femtosecond laser treatment was used to produce channel-shaped textures with a truncated trapezoidal cross-section, measuring 15 µm at the upper base, 45 µm at the lower base, and 22 µm in height. These textures were further extended by the development of aluminum oxide crystal inlays, ranging from 30-60 nm, due to metal oxidation from the laser's high-temperature interaction. Extended exposure to these textures in room environment naturally increases their water repellency. Contact angles can reach 148°, nearing the 154° efficiency achieved with stearic acid treatment. However, heating to 380 °C eliminates the hydrophobic layers, resulting in complete hydrophilisation. Textured hydrophilic surfaces prove most effective for condensate collection, outperforming hydrophobic surfaces by up to 28%. Additionally, microtexture orientation matters: a vertical orientation boosts condensate collection by 34% compared to horizontal orientation. The results may be useful in the development of water harvesting equipment for naturally dry regions, or place where extensive water purification is required.

DIGITALIZATION OF WATER VENDING MACHINES

Rostyslav Mudryk, Yevhen Orestov — Mon, 01 Apr 2024 00:00:00 +0300

Vending, the sale of goods and services through automated systems, has gained worldwide popularity as a convenient and low-maintenance method of commerce or service delivery. With its wide range of applications, vending can be used in almost all areas of commercial and social life. This article is dedicated to studying the impact of digitalization on the operation of water vending machines. These machines represent a modern way of obtaining safe and physiologically complete drinking water. Their advantage lies in autonomous operation without the constant presence of servicing personnel. This is achieved by replacing filters and maintenance tasks carried out on a time-based logic basis. However, time-based logic does not account for actual volumes of purified water, leading to over expenditure on servicing some machines and untimely maintenance, resulting in a deterioration of water quality for others. This study investigates the impact of digitalization on optimizing service costs and the cost price of water purification. It is shown that through digitalization, the maintenance logic was changed to volume-based, resulting in reduced expenses on replacement filters (51%), servicing (13%), and collection (17%). Collectively, these factors reduced the cost of water by 20%. The decrease in cost enhances the profitability of the vending machine network. With a fixed water price, this is the only way to increase profitability and attract investors, consequently popularizing water vending machines. Subsequent research will focus on seeking alternative filters, materials, and water preparation technologies to achieve even greater machine autonomy. By assessing the established impact of digitalization on water vending machine operations, a predictive cost of water is calculated, assuming compliance with all operational requirements. The predicted cost reduction amounts to 39%, providing economic justification for future research endeavors.

PERSISTENT ORGANIC POLLUTANTS: SOURCES, MIGRATION IN ECOSYSTEMS, REMOVAL METHODS IN WASTEWATER TREATMENT AND REMEDIATION OF SOILS AND NATURAL WATER

Marta Litynska — Mon, 01 Apr 2024 00:00:00 +0300

Persistent organic pollutants are among the most dangerous pollutants due to their resistance to destruction in natural conditions, the ability to migrate in ecosystems, bioaccumulation, biomagnification and significant harmful effects on health. Persistent organic pollutants include organochlorine pesticides, polychlorinated naphthalenes, polychlorinated biphenyls, polybrominated diphenyl ethers, polycyclic aromatic hydrocarbons, etc. Even in small amounts, these compounds can cause endocrine disorders and have a carcinogenic effect. Most of these compounds are exclusively of anthropogenic origin. Although the Stockholm Convention has severely restricted the production and use of persistent organic pollutants, many soils and water bodies are already contaminated with these compounds, and some banned substances continue to be produced as byproducts of industrial processes. Also, although the lists of substances prohibited for production are periodically updated, a large number of compounds, which by their properties are persistent organic pollutants, have not yet entered these lists. There are many methods for removing persistent organic pollutants from water, but most of them are insufficiently effective or lead to the generation of large quantities of contaminated waste that need to be disposed of. Photocatalysis is the most promising method of wastewater treatment that contains persistent organic pollutants. Unlike coagulation, adsorption, biological treatment and nanofiltration/reverse osmosis, this method avoids the generation of solid and liquid waste contaminated with these pollutants. In the case of remediation of polluted waters and soils, the main methods are bioremediation and adsorption, since these methods can immobilize persistent organic pollutants directly in the ecosystem without taking soil or water for treatment.

ADSORPTION REMOVAL OF CU (II) USING NI-MODIFIED SILICA GEL

Mon, 01 Apr 2024 00:00:00 +0300

The contamination of surface and groundwater with heavy metals represents a significant threat to environmental safety and the health of living organisms. Consequently, the development of new technologies and the improvement of existing ones to clean water bodies from toxicants of various kinds represents an important task. One of the factors influencing the choice of treatment method is the concentration of the pollutant. It is advisable to use adsorption methods for the post treatment of water environmental to the levels of maximum permissible concentrations. In the context of the implementation of adsorption methods, the selection of sorbents that combine high efficiency and low cost with ease of preparation represents an important factor. The aim of this work is to produce a sorbent based on commercial silica gel and nickel oxide. For its synthesis, the thermolysis method was chosen. A series of materials with varying mass ratios of NiO to SiO₂ was produced: 1:1 and 0.5:1. The presence of crystalline nickel oxide on the amorphous surface of SiO₂ was confirmed by X-ray diffraction analysis. The main parameters of the porous structure were determined by the method of low-temperature nitrogen adsorption/desorption. With an increase in the amount of the deposited oxide layer, the specific surface area and pore volume of the obtained samples decrease by 1.5-2.5 times compared to the original SiO₂. At the same time, the general character of the mesoporous structure is preserved. The optimal conditions for the removal of Cu (II) ions by nickel-containing composites based on silica gel (pH ~ 5.5; sorption time - 1 hour) were investigated. The adsorption kinetics is adequately described by a pseudo-second-order model, which indicates a high affinity of copper for the surface of such samples. It was demonstrated that the modification of the SiO₂ surface with nickel oxide results in an enhancement of the sorption capacity of materials with respect to Cu (II) ions. The maximum value of copper sorption on the synthesised samples is 10 times higher than on the original SiO₂.

ADSORPTIVE AND PHOTOCATALYTIC PROPERTIES OF THE ZnO/BENTONITE/Ag HETEROJUNCTION

Oleksiy Klimenkov, Iryna Ivanenko — Mon, 01 Apr 2024 00:00:00 +0300

The degradation of organic wastewater pollutants from diverse sources represents a critical scientific challenge, particularly in light of the escalating demand for dyes across various industries. Addressing this challenge entails the exploration of efficient and eco-friendly methods to convert organic pollutants into benign and straightforward compounds, leveraging state-of-the-art photocatalysts. The synthesis was conducted via the novel sol-gel method. Structural, crystalline, elemental and phase parameters were analyzed using X-ray analysis, chemical surface characteristics investigated through infrared spectroscopy, band gap determination performed via diffuse reflectance spectroscopy, and evaluation of adsorption and photocatalytic activity carried out for the semiconductor photocatalyst ZnO and heterojunctions incorporating bentonite. The synthesized photocatalysts were employed for the removal of malachite green dye. Equilibrium studies for adsorption were conducted using Langmuir and Freundlich isotherms, revealing a superior fit with the Langmuir model. The maximum adsorption capacity was determined as 70.4 mg/g using the Langmuir equation. Kinetic parameters indicated that the adsorption of malachite green on bentonite followed a first-order kinetics model where k₁=0,152 min^-1. The photodegradation efficiency of ZnO, ZnO/bentonite, and Zn/bentonite/Ag was investigated by static experiment under ultraviolet irradiation. Within 60 minutes, a 99.4% photodegradation of the malachite green solution at a concentration of 100 mg/L was achieved using the ternary heterojunction photocatalyst. Remarkably, within just 10 minutes in the presence of the ternary composite, a degree of photocatalytic degradation reaching 72% was attained, which significantly exceeds the results of the binary heterojunction photocatalyst. Thus, the synthesized heterojunction exhibits notable photocatalytic activity, particularly evident within short time intervals. A proposed mechanism for the photocatalytic degradation of malachite green is outlined based on existing literature sources.