WATER AND WATER PURIFICATION TECHNOLOGIES. SCIENTIFIC AND TECHNICAL NEWS

TOWARDS MODELS COMPLEXITY IN WATER USAGE AND TREATMENT OPTIMISATION PROBLEMS

Arcady Shakhnovsky — Mon, 03 Jul 2023 00:00:00 +0300

The paper addresses water recycling in process industry, inter alia, the issues of mathematical models’ complexity problem in the “process integration”-based structural optimization of sustainable water usage and treatment networks. The nature of addressing structural optimization problems requires iteratively querying individual process models, which are incorporated as objective functions and constraints within the optimization model, throughout the process of finding a solution, therefore the goal was to explore the intricacy of mentioned models. Within the framework of the research, the impact of complexity of water network constituent parts models on the optimization performance was investigated by Monte Carlo method for one step of the optimization procedure, as well as for the optimization procedure as a whole. Units’ models in form of algebraic equations (for direct equation calculation case), algebraic equations (for root search), ordinary differential equations (for Cauchy initial value problem with a case of two differential equations), ordinary differential equations (for boundary value problem), and partial differential equations (for two spatial variables) were examined with an analysis of their applicability for optimization purposes. The justification for employing both deterministic "counter-current mass transfer" models and statistical polynomial "input-output" steady-state algebraic models were established for addressing the specific problems under investigation. As the case study, special polynomial model was constructed based on the experimental design / response surface methodology and the dynamics simulation results on adsorption wastewater treatment within the packed bed column ﬁlled with activated carbon. Central composite rotatable design was formulated and subsequently executed using computational experimentation methods for the parametric identification of a nonlinear polynomial model. The evaluation confirmed that the constructed model exhibits satisfactory predictive accuracy.

SHARED AUTOMATIC DRINKING WATER TREATMENT AND DISPENSING SYSTEMS AND METHODS OF THEIR OPTIMIZATION

Rostyslav Mudryk, Tetiana Mitchenko — Mon, 03 Jul 2023 00:00:00 +0300

Access to clean and safe drinking water is a fundamental human right. However, in many parts of the world, water scarcity and contamination pose significant challenges. To address these issues, shared automatic drinking water treatment and dispensing systems have emerged as innovative solutions. The article is devoted to the problem of access to safe, physiologically complete drinking water in collective systems of water preparation and sale, namely in water vending machines. Since such machines are a relatively new solution, the search for rational ways of adapting existing technologies is relevant and necessary for their widespread implementation. The article discusses the peculiarities of preparation and sale of water in the network of existing vending machines. It was established that automatic machines are autonomous multifunctional systems, the effectiveness of which depends on the balanced operation of all elements. Formulated requirements for the operation of automatic machines in autonomous conditions, namely, regarding water quality, automatic machine productivity, and the duration of its operation without operator intervention. A comparison of the requirements with operational data showed a discrepancy in water quality (in terms of hardness, pH, dry residue), productivity (10 times higher than required), duration of operation without an operator (4 times shorter than specified in the requirements). Factors influencing the operation of vending machines are formulated, namely: water preparation technology, number of stages, resource of filter elements, volume of water for own needs, combination of payment methods, time or volume logic of service. To achieve the proposed requirements, solutions have been developed, the effectiveness of which will be investigated in the course of further work. It was noted that a mandatory condition for the successful solution of the tasks set is digital control of the operation of the machine.

DECOMPOSITION MECHANISM AND DISSOCIATION CONSTANTS OF BICARBONATE IONS

Serhii Kontsevoi — Mon, 03 Jul 2023 00:00:00 +0300

Using carbonic acid to explain pH changes in aqueous solutions is invalid due to its undetectability under normal temperature and pressure conditions. Instead, two reversible reactions involving the decomposition of HCO₃^- ions into OH^- and CO₂ or H⁺ and CO₃^2- should be employed. The second reaction (H-mechanism) is well known as the basis for the second dissociation constant of “carbonic acid”. For the first reaction (OH-mechanism), the formula has been derived from the first imaginary constant of the same acid. That is, the researchers experimentally determined the proposed constant based on the results of pH value, CO₂ and HCO₃^- concentrations, but calculated the imaginary constant from these values. The pH increase observed following filtration on the cationic resin in Na⁺ form is attributed to the weakened HCO₃^- decomposition via the H-mechanism, resulting in decreased H⁺ and CO₃^2- concentrations. A significant decrease in Ca²⁺ concentration (from 5.0 to 0.05 mmol/dm³) is the main reason for the observed phenomenon, as it leads to a decrease in the driving force of calcium carbonate formation. The mechanism of bicarbonate ions decomposition based on two reactions has been confirmed experimentally. An increase in the pH of the mixture of CaCl₂ and NaHCO₃ solutions (both with the same pH and concentration) indicates the H-mechanism, while a decrease in the pH indicates the OH-mechanism decomposition of bicarbonate ions. The pH value at which the pH does not change indicates a change in the decomposition mechanism. The change in the HCO₃^- dissociation mechanism depends on hardness and alkalinity, and the pH of this change decreases from softened water (pH 8.30) to seawater (pH 7.5).

MATERIALS AND METHODS FOR CERAMIC MEMBRANE SYNTHESIS. SHORT REVIEW

Svitlana Kyrii — Mon, 03 Jul 2023 00:00:00 +0300

This article briefly overviews the main types of raw materials used to synthesise ceramic membranes. Traditional materials such as aluminium oxide, silicon dioxide, titanium dioxide, zirconium dioxide, zeolites, and cost-effective materials like various clays and industrial waste are highlighted. Modern methods for producing high-performance ceramic membranes are discussed, including slip casting, tape casting, pressing, extrusion, solid state method etc. The general scheme for preparing a selective layer on a ceramic membrane using various methods for synthesising it is also examined. Furthermore, the cost of commercial ceramic membranes and influencing factors are analysed. Based on contemporary literature, ceramic membranes exhibit distinct advantages over polymer membranes with their potential for application under high temperature, high pressure, and aggressive environments. Additionally, their energy efficiency, compactness, and versatility make them a viable alternative for water purification, replacing more expensive methods like coagulation and adsorption. Ceramic membranes have become a competitive alternative to polymer membranes, showcasing unique material properties and excellent characteristics. Using cost-effective materials for ceramic membrane fabrication allows for utilisation in economically sensitive sectors. Such membranes demonstrate excellent mechanical properties and high permeability, while inexpensive materials can reduce costs. Current scientific research and developments focus on utilising various clays and waste materials to produce ceramic membranes, aiming to create new generations of ceramic membranes for environmentally friendly applications.

THE EFFECT OF THE TYPE AND CONTENT OF CARBONATES ON THE CHARACTERISTICS OF POROSITY OF CERAMIC MEMBRANES

Olena Yanushevska — Mon, 03 Jul 2023 00:00:00 +0300

The main issue considered in the work is the creation of a matrix for ceramic membranes, which would be distinguished by low cost and high porosity. In order to reduce the cost of ceramic membranes, a widespread approach was chosen, which is powerfully used by many researchers, namely the use of natural minerals - kaolin and saponite - as the main components of the matrix. Carbonates were used as pore generating agents to achieve the required porosity value. Three series of ceramic membranes (CM) differing in chemical composition were synthesized in the work: KP1, KP2, and KP3 series. The main composition of CM includes: kaolin, saponite, sodium silicate and carbonates. The effect of the type and amount of carbonates (CaCO₃, NH₄HCO₃, (NH₄)₂CO₃) as pore generating agents on the formation of the porous structure of the samples was studied. The type and content of carbonates varied in different samples from 8 wt% up to 40 wt%. The dry pressing method using pressure equivalent to 8 tons and 15 tons was used to form ceramic membranes. The main parameters by which the properties of ceramic membranes were evaluated: water absorption, total and open porosity. Standard methods were used to determine these parameters for synthesized samples. The chemical composition of the dry mixture of the ceramic membrane, for which the porosity is the maximum in the series of manufactured samples, was established. It was established that the addition of calcium carbonate components to the dry mixture increases the porosity of ceramic membranes and water absorption. The chemical composition of a ceramic membrane sample with the best indicators of total and open porosity in the KP2 series is given. The chemical and phase composition of samples of the KP2 series, as well as their structural and adsorption characteristics, were investigated by X-ray fluorescence and diffraction methods of analysis and low-temperature nitrogen adsorption-desorption. The effect of the addition of silicon carbide on the characteristics of the porosity of the samples was determined.

RATIONAL CONDITIONS OF PRODUCING THE ACTIVATED CARBON WITH WELL-DEVELOPED NANOPOROUS STRUCTURE FOR THE TREATMENT OF NATURAL AND WASTE WATERS

Nataliia Klymenko, Liudmyla Savchina , Iryna Kosogina, Tetiana Vrubel — Mon, 03 Jul 2023 00:00:00 +0300

Rational conditions for the activation of coal of a high stage of metamorphism (anthracite) have been determined, which allow the development of a nanoporous structure. Obtained activate carbon with nanoporous structure can be use for the treatment of natural and waste waters have been carried out. The structurally sorptive characteristics and granulometric size composition of obtained samples were determined. It was established that in order to obtain a sorbent with specified properties, it is necessary to introduce oxygen into the reacting mixture at the second stage of anthracite activation and control the activation time. The activation in the first stage was carried out with steam at a temperature of 750–800 °C, and in the second stage – with steam in the presence of air oxygen at 280–300 °C. The rational content of oxygen in the activating mixture is in the range of 2.7–4.4 %, while the specific surface area of activated carbon increases, which corresponds to nano-sized pores and, accordingly, the volume of the adsorption space of coal. The process led to the development of mesoporosity ~ 0.2–0.3 cm³/g, after which the microporous sample of activated carbon was impregnated with a surfactant solution. Thus, the rational conditions of activation are the duration of the process of 1.5 hours in the presence of 4.4 % oxygen in the activating mixture. It is shown that the largest values of the total specific surface area and the specific surface area of mesopores are achieved when using ionic surfactants with alkyl chain length n = 10–16 as modifiers. In particular, the use of sodium dodecyl sulfate СН₃(СН₂)₁₁SO₃Na as a modifier allows to obtain the largest value of the total surface S_tot 1030 m²/g and the surface of mesopores S_mе 334 m²/g. It was established that the activation of modified samples of activated carbon leads to a decrease in the size of granules.The content of fractions with a size of 1.0–2.0 mm and 0.5–1.0 mm is 80–85 %, which are rational for use for water purification from organic compounds.