In 2018, the European Commission adopted the European Strategy for Plastics in a Circular Economy, which outlines key actions to reduce the negative impact of plastic pollution. The strategy aims to expand plastic recycling capacity and increase the proportion of recycled materials in plastic products and packaging. Using recycled plastic can save 50–60% energy compared to virgin plastic. Recycled PET can be used in the production of A-PET films, which are predominantly used in thermo-vacuum forming for food packaging. Storage conditions can influence the mechanical properties of polymer materials. This work presents changes in the mechanical properties of A-PET films after UV irradiation. An experimental investigation of the UV aging of A-PET films was conducted in a UV aging chamber. The specimens were exposed to a UV radiation dose rate of 2.45 W/m² for 1, 2, 4, 8, 16, 24, 32, and 40 h. UV measurements were also taken on a sunny day to compare the acceleration of UV irradiation in the UV aging chamber. Mechanical tensile tests were performed on two different three-layer A-PET films (100% virgin and 50% recycled). The tensile strength and relative elongation of the A-PET films were determined, and the work required to break the film was calculated. The total consumed work was divided into the work needed for elastic and plastic deformations. A study of the UV aging of A-PET films confirmed a significant effect on the films, including a loss of plasticity even after brief exposure to solar irradiance. The results of the puncture impact test further confirmed the deterioration of the mechanical properties of A-PET material due to exposure to UV radiation, with a greater effect observed for the recycled material.

Existing studies and methodologies do not offer designers clear guidelines for selecting optimal catamaran geometric parameters. Most focus on separate geometric characteristics or hull elements to minimize total resistance, providing only general trends that are not applicable when designing hull forms that differ from those in the mentioned studies. In this paper, a methodology is presented to evaluate the total resistance of a catamaran by determining its optimal geometric parameters. The approach involves selecting geometric parameters, defining variation limits to suit the design task, choosing appropriate evaluation methods and analyzing the results to identify the optimal catamaran geometric parameters. The application of the proposed methodology is achieved through the evaluation of different geometric parameters of an existing catamaran, such as its length, demihull separation, and hull symmetry. The CFD software Flow3D 2022 R1 is used to assess the influence of the selected geometric parameters on the total resistance of the catamaran, which is supported by experimental setup verification and validation using model tests. The results are analyzed using the system proposed in the developed methodology, enabling the selection of optimal geometric parameters for the considered catamaran design task. The research highlights the significance of optimizing catamaran hull forms by adjusting demihull spacing, symmetry, and length to achieve improved hydrodynamic performance and resistance reduction for applications during the vessel design stage.

The use of pyrolysis oil can be seen as an alternative fuel for maritime transport. However, pyrolysis oil from tires must be desulfurized for this. Recently, this can be done by hydrodynamic cavitation. This process does not require oxidation chemicals but only water, a cavitation generator, and a pump to drive it. In the literature, this concept has been successfully tested on model fuels. In this study, the cavitation generator for the desulfurization of waste tire pyrolysis oil was printed from polylactic acid-based on simulations of the optimal design, which allows for much cheaper production and easy replacement in case of wear or testing of alternative designs. After 60 min of treatment at 5 bar inlet pressure, a desulfurization of almost 33% was achieved. Furthermore, an interaction analysis showed that only from a pyrolysis oil content of 5.5 to 6% does hydrodynamic cavitation have an effective effect on desulfurization.

Growth kinetics, i.e. the relationship between specific growth rate and the concentration of a substrate, is one of the basic tools in the modelling of activated sludge community growth. The above‐described conventional growth kinetics derived from single‐substrate‐controlled laboratory experiments have invariably been used for describing both growth and substrate utilization in wastewater treatment. After technological processes various mineral substances, such as chlorides, get into water bodies. These substances are not removed from wastewater by the biological treatment method. The purpose of this study is to determine the concentrations of chlorides, investigate the influence of enzyme preparations upon wastewater treatment quality during biological process modelling. Kinetics of microbial growth was designed using the model of Monad. To analyse the chloride influence on the biooxidation process a series of laboratory tests was carried out: biochemical oxygen consumption (BOD), activated sludge concentration and other indexes. It is found experimentally that a 400 mg/l concentration of chlorides disarranges the activity of microorganisms and activated sludge is no longer suitable for biological treatment. Also, we investigated the effect of enzyme preparation on effluence on sewage treatment. As chloride concentrations are increased in a tank without an enzyme, bacterial spores contained in the enzyme preparation produce a renewing effect upon active sludge. Santrauka Mikroorganizmų augimo dinamika, t. y. priklausomybė tarp jų savitojo augimo spartos ir substrato koncentracijos, yra vienas iš svarbiausių veiksnių modeliuojant veikliojo dumblo kinetiką. Laboratorinėmis sąlygomis buvo atlikti eksperimentiniai nuotekų valymo tyrimai kompleksiškai įdėjus į substratą ir chloridų kaip papildomos užtaršos bei fermentinio preparato. Rezultatams palyginti buvo atlikti tyrimai ir be fermentinio preparato. Po įvairių technologinių procesų į valymo įrenginius patenka tokios mineralinės medžiagos kaip chloridai. Šios medžiagos biologiniu valymo būdu iš nuotekų nepašalinamos. Darbe nagrinėjama, kokios chloridų koncentracijos turi įtakos biologinio nuotekų valymo kokybei, veikliojo dumblo augimo dinamikai bei substrato biodegradacijai. Eksperimentų metu nustatytos tiriamų teršalų koncentracijos, turėjusios įtakos biologiniam valymo procesui: 400 mg Cl– /l ir didesnės sutrikdo mikroorganizmų veiklą, veiklusis dumblas biologiniam nuotekų valymui tampa netinkamas. Darbe modeliuojama veikliojo dumblo mikroorganizmų biocenozės dinamika, atliekant aerobinį nuotekų valymą. Nagrinėtas atvejis, kai nuotekų užtarša yra didesnė chloridų koncentracija. Veikliojo dumblo biocenozės dinamikai modeliuoti pasirinktas Monodo modelis. Atlikus eksperimentą nustatyti degradacijos koeficientai kd. Gautas Monodo diferencialinės lygties sprendinys, nusakantis veikliojo dumblo dinamiką. Skaitiniais metodais išspręsta veikliojo dumblo augimą bei substrato biodegradaciją nusakanti diferencialinių lygčių sistema. Įvertinus eksperimentų rezultatus nustatyti veikliojo dumblo sistemos degradacijos koeficientai įdėjus fermentinio preparato. Rezultatai parodė, kad fermentinis preparatas teigiamai veikia mikroorganizmų augimą t. y. veikliojo dumblo koncentracija mažėja lėčiau. Резюме Кинетика биомассы микроорганизмов, т. е. зависимость между концентрацией активного ила и концентрацией субстрата, один из важнейших аспектов в моделировании динамики активного ила. В лабораторных условиях были проведены экспериментальные исследования сточных вод в комплексе с добавлением в субстрат хлоридов как дополнительного загрязнения и ферментного препарата. Для сравнения результатов были проведены параллельные эксперименты без ферментного препарата. В результате технологических процессов в очистные сооружения попадают разные минеральные вещества, как, например, хлориды. Эти вещества методом биологической очистки не удаляются. В настоящей работе были исследованы концентрации хлоридов, влияющие на качество биологической очистки сточных вод, качество и кинетику активного ила и биодеградацию субстрата. Для определения влияния хлоридов на биологические процессы были проведены лабораторные исследования по определению биохимического потребления кислорода (БПК), концентрации активного ила и др. В результате эксперимента было установлено, что концентрация хлоридов, составляющая 400 мг/л и больше, поражает работу микроорганизмов, активный ил становится непригодным для биологической очистки cточных вод. Также исследовалось влияние ферментного препарата на качество очистки. Моделируя кинетику динамики активного ила, получено решение дифференциального уравнения, в котором идентифицированы коэффициенты деградации ила kd. В результате эксперимента определены коэффициенты деградации на систему активного ила в резервуаре с ферментным препаратом, т. е. концентрация активного ила уменьшается медленнее. Можно сделать вывод, что ферментный препарат эффективно влияет на концентрацию микроорганизмов. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: nuotekos, aerobinis valymas, veiklusis dumblas, chloridai, fermentai, matematinis modeliavimas. Ключевые слова: сточные воды, аэробная очистка, активный ил, хлориды, ферменты, математическое моделирование. Keyword : wastewater, aerobic treatment, activated sludge, chlorides, enzymes, mathematical modelling

The use of polymer materials in various fields has increased significantly due to their ease of thermoforming and relatively low production costs. The production volume of these materials is extremely high, and according to forecasts from global statistical centers, it is expected to continue rising in the future. However, the extensive use and easy availability of polymeric materials have caused significant ecological problems. The world faces large amounts of polymer waste and environmental pollution. Plastic recycling remains challenging due to issues related to sorting polymer waste and separating it according to polymer types. Recycling certain plastics requires only a quarter of the energy needed to produce new plastic. To address this, circular economy principles should be applied to 3D printing products made from polymeric materials. A particularly wide application of these technologies is found when polymeric materials are used due to their low cost, low melting temperatures, and other advantageous properties. This paper investigates the impact of plastic recycling on the quality of 3D-printed products. During the research, samples were 3D printed and tested using both virgin and recycled PLA, ABS, and PET-G materials. The samples underwent static and dynamic tests to determine their mechanical properties, such as tensile strength, elongation, and impact resistance. The research results showed that the properties of recycled polymer materials deteriorate, with relative elongation of recycled and 3D-printed materials decreased by 16–45%. Despite this, recycled polymer materials can still be used, but it is necessary to account for the reduction in plasticity when creating products that will be exposed to dynamic loads. The impact strength is reduced by 6% for PLA, 54% for ABS, and 58% for PET-G. Additionally, the research included tests on samples printed with 3D printing technology that were exposed to UV irradiation. The results indicated similar dependences, as UV exposure also affects the reduction of material plasticity. After 66 Wh/m² of UV radiation, the tensile strength of PET-G and PLA decreased by 17%, while ABS showed a reduction of about 5%.