Harnessing Fly Ash and Foundry Sand Waste Potentials for Sustainable Concrete Towards Building a Greener Future: A Case of South Africa

Opeoluwa R. DADA*^a, Fitz M. YEMBA^a, Bolanle D. IKOTUN^a, Makungu M. MADIRISHA^ba, Patrick K. GEVERA^a

^a Department of Civil and Environmental Engineering and Building Science, College of Science, Engineering and Technology, University of South Africa, Florida, 1709, Johannesburg, South Africa, e-mail: dadaopeoluwa@gmail.com & dadaor@unisa.ac.za
^b Chemistry Department, College of Natural and Applied Sciences, University of Dar es Salaam, P.O Box 35061, Dar es Salaam, Tanzania.

The effective reuse of waste resources across sectors has contributed to sustainable solid waste management, the development of new products, and advances in materials science. This study investigated the feasibility and effectiveness of incorporating industrial waste streams, specifically Type F Fly Ash (FA) and Foundry Sand Waste (FSW), into concrete mixes to promote sustainability in the African construction sector. The research assessed the effects of these secondary materials on the mechanical properties of concrete and evaluated their potential for practical use in infrastructure projects. A comprehensive characterization approach, including determination of the Fineness Modulus, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and X-ray Fluorescence (XRF) analyses, was employed to characterise the physical and chemical properties of FSW. Concrete samples were prepared with FSW replacement levels of 25% and 50%, while maintaining a constant 30% FA substitution, and were tested for compressive strength, split tensile strength, and water absorption at 7, 14, and 28 days of curing. The results showed that as more FSW was added, concrete strength decreased, but it remained within acceptable standards and was suitable for use on lightly trafficked roads and low-load-bearing structures.

Keywords: Circular Economy, Concrete, Fly Ash, Foundry Sand Waste, Sustainable Construction

Bioconversion of Lettuce, Potato and Pasta by Black Soldier Fly Larvae (Hermetia illucens) into high value insect biomass

Filip TAKÁCS, Igor BODÍK
Department of Environmental Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, Bratislava, 812 37, Slovakia, e-mail: filip.takacs@stuba.sk

The growing demand for sustainable alternative protein sources and effective food waste management highlights the potential of Black Soldier Fly Larvae (BSFL, Hermetia illucens). This study investigates the growth and bioconversion efficiency of BSFL reared on three substrates - lettuce, potatoes, and pasta. These substrates were subjected to pre-treatment methods such as slicing, blending and boiling. Larval performance was evaluated through wet and dry weight, length, and bioconversion rate (BCR). Pasta supported the highest insect biomass yield, with blending increasing larval weight to 77.6 mg and BCR to 14.8%, compared to 48.6 mg and 8.9% for whole pasta. Potatoes resulted in moderate growth, with boiling enhancing BCR from 7.4% to 9.2%. Lettuce, characterized by low nutrient content and high moisture, produced the poorest results, and blending slightly negatively affected BCR. The findings underline that both nutrient composition and pre-treatment of substrates are critical factors for maximizing BSFL growth and bioconversion outcomes.

Keywords: BSFL; food waste; substrate pre-treatment; bioconversion; Hermetia illucens

Evaluation of the impact of recycled automotive waste in particleboard on water quality

Helena HYBSKÁ^a, Dagmar SAMEŠOVÁ^a, Iveta ČABALOVÁ^b, Jozef KRILEK^c, Lýdia SOBOTOVÁ^d, Alexandra VIERGOVÁ^a

^aDepartment of Environmental Engineering, Faculty of Ecology and Environmental Sciences; Technical University in Zvolen, Študentská 26, 96001 Zvolen, Slovakia, e-mail: hybska@tuzvo.sk
^bDepartment of Chemistry and Chemical Technologies, Faculty of Wood Sciences and Technology, Technical University in Zvolen, T. G. Masaryka 24, 96001 Zvolen, Slovakia
^cDepartment of Environmental and Forestry Machinery, Faculty of Technology, Technical University in Zvolen, Študentská 26, 96001 Zvolen, Slovakia
^dInstitute of special engineering processes, Faculty of Mechanical Engineering,  Technical University in Košice, Letná 9, 042 00 Košice, Slovakia

This article assesses the environmental impacts of three-layer wood-based composites containing automotive industry waste (incorporated into the core layer) on aquatic environments. Water leachates from the composite samples were evaluated using ecotoxicological biotests with the test organisms Lemna minor, Sinapis alba, and Daphnia magna. Physicochemical parameters, specifically pH and chemical oxygen demand (COD), were determined to represent the total amount of organic substances leached into the water. A particleboard without automotive waste served as the control sample. The results indicate that incorporating automotive waste into wood-based materials is a viable recycling method, and the use of bioassays proves to be an effective tool for evaluating their environmental safety. The findings suggest the need to optimize the quantity of waste in production to minimize inhibitory effects on test organisms in aquatic environments while maintaining the required physical and mechanical properties of the composites.   

Keywords: waste, plastic, water leachate, automotive industry, chipboard, ecotoxicity

The Importance of the Layered Structure in the Application of Recycled Automotive Plastics into Particleboards

Iveta ČABALOVÁ, Jozef KRILEK, Anna DARABOŠOVÁ, Vladimír MANCEL

Faculty of Wood Sciences and Technology, Faculty of Technology, Technical University in Zvolen, T.G. Masaryka 24, 96001 Zvolen.

This paper deals with the analysis of the behavior of particleboards containing recycled plastics from the automotive industry depending on their structural arrangement. Single- and threelayer boards are compared in terms of their mechanical strength and physical properties related to the ifluence of moisture. The results point to a different distribution of stresses in the material and the importance of the layered structure in optimizing the properties of wood-plastic composites. The work contributes to the expansion of knowledge about the use of secondary raw materials in the production of agglomerated materials.

Keywords: particleboard, layered structure, recycled plastics, mechanical properties, physical properties.

Mechanical and Thermo-Mechanical Recycling of Polyurethane Waste Generated during CNC Machining of Tooling Boards

Filip HAVLÍČEK^a, Islam GIMADIEV^a, Petr MOHYLA^b, Marek HAROK^a, Marek BESEDA^a, Jan RYGEL^a, Pavel KLAUS^a, Michal WEISZ^a

^aVSB – Technical University of Ostrava, Faculty of Materials Science and Technology, Ostrava, Czech Republic, e-mail: filip.havlicek@vsb.cz
^bVSB – Technical University of Ostrava, Faculty of Mechanical Engineering, Ostrava, Czech Republic
Polyurethane (PU) tooling boards generate clean pre-consumer waste during CNC machining, but crosslinked PU cannot be remelted like thermoplastics. This preliminary proof-of-concept study evaluates two simple recycling routes for chips from rigid SB-0140 and SB-0600 boards: thermo-mechanical hot pressing without binder and cold pressing with binder followed by optional epoxy sealing. The exploratory matrix was not statistically replicated; therefore, the results are reported as qualitative observations of compactness, apparent porosity, machinability and surface integrity. Hot pressing gave the most coherent blocks, while cold pressing was feasible mainly at higher nominal pressure and with crushed feedstock. Epoxy sealing improved the surface of cold-pressed blocks. The results indicate possible internal recovery of clean PU tooling-board waste as non-structural semi-finished blocks, but not certified material-property data. Further work should quantify density, porosity, mechanical properties, dimensional stability and surface durability on replicated specimens.

Keywords: polyurethane waste; tooling boards; mechanical recycling; compression moulding; epoxy sealing

Transformation of hazardous asbestos-cement waste into safe functional products

Theodor STANĚK^a, Martin NGUYEN^a, Michaela KREJČÍ KOTLÁNOVÁ^a, Jiří HOLUB^b, Zdeněk KREJZA^a
aVýzkumný ústav stavebních hmot, a.s., Czech Republic, e-mail: stanek@vush.cz
 ^bLB Cemix, s.r.o., Czech Republic

Asbestos-cement materials are among the most widespread forms of hazardous waste containing asbestos. Their disposal is usually carried out in the form of landfilling. However, in the current circular economy, they can advantageously serve as a raw material for the production of building materials. By burning them in a shaft furnace without prior treatment and grinding after thermal inertization, it is possible to obtain a hydraulic binder. In addition, the binder is carbonatable and can be used to produce prefabricated parts in CO₂ chambers. The resulting product could thus contribute to the very current goal of today, which is the reduction of greenhouse gas emissions. In the first case, it is possible to obtain a hydraulic binder of the strongly hydraulic lime type with a compressive strength after 28 days of over 5 MPa. Using accelerated carbonation, the compressive strength after 2 days increases 6times. The research used methods of X-ray fluorescence analysis, X-ray diffraction, optical and electron microscopy and technological tests according to the EN 196 series standards.

Keywords: Hazardous waste, asbestos cement, hydraulic lime, carbonatable binder.

Influence of fly ash fouling properties on boiler furnace design for low-grade fuels based on waste and biomass

Jan ZABLOUDIL^a, Zdeněk JEGLA^a, Petr SKÁLA^b

^a Institute of Process Engineering, Faculty of Mechanical Engineering, Brno University of Technology; Technická 2; 616 69, Brno; Czech Republic, e-mail: 191771@vutbr.cz (Jan Zabloudil)
^b EVECO Brno, s.r.o., Hudcova 660/76d, Brno; Czech Republic

The article addresses the need to update empirical parameters used in boiler furnace design due to the transition from high-quality coal to lower-grade fuels such as combustible wastes and biomass. It focuses on the influence of three empirical parameters related to fly ash properties and fouling behaviour within the Gurvich furnace calculation method. A basic sensitivity study was performed on a real reference boiler by comparing calculated results with measured furnace outlet gas temperatures under several steady operating conditions. The results showed that adjusting the empirical furnace wall fouling parameter (ξ) can significantly reduce discrepancies between calculated and measured values. The paper also presents a newly developed experimental device for evaluating fly ash fouling effects on convective heat exchanger surfaces, which has been tested with biomass fuels.

Keywords: waste-to-energy plant, grate waste incineration, grate firing of biomass, furnace design, furnace exit gas temperature, solid waste fuels, fly ash and particulate fouling

Comparative Life Cycle Assessment of Detergent Packaging Systems: Analysis of the Environmental Impact of Six Commercial Formats on the European Market

Roman KOVÁŘ^a, Vladimír KOČÍ^a,b

^a České vysoké učení technické v Praze, Fakulta architektury, Thákurova 9, 166 34 Praha 6 – Dejvice, Czech Republic, e-mail: kovarro2@cvut.cz
^b Ústav udržitelnosti a produktové ekologie, VŠCHT Praha, Jankovcova 23, 170 00 Praha 7, Czech Republic, e-mail: vlad.koci@vscht.cz

This study presents a comparative Life Cycle Assessment (LCA) of six commercially available laundry detergent packaging formats on the European market, focusing specifically on the environmental impacts associated with packaging systems. The assessed formats included: laundry powder in cardboard packaging, liquid detergent in an HDPE bottle, concentrated liquid detergent in an LDPE/PET refill pouch, detergent capsules in PP packaging, detergent capsules in cardboard packaging, and laundry detergent sheets in LDPE packaging. The study was conducted in accordance with ISO 14040 and ISO 14044 standards using the Ecoinvent 3.10 database and the ReCiPe 2016 midpoint (H) method. The functional unit was defined as one standard washing cycle for 4 – 5 kg of laundry.

The results revealed substantial differences among the evaluated packaging formats in terms of material consumption and environmental impacts. Laundry detergent sheets demonstrated the lowest environmental burden, achieving a climate change impact of 1.967 g CO₂ eq. per washing dose, representing a 73.6% reduction compared to liquid detergent in an HDPE bottle. Low environmental impacts were also observed for cardboard-based capsule packaging and concentrated refill systems. In contrast, liquid detergents packaged in rigid plastic bottles showed the highest impacts across most categories. The life cycle analysis confirmed that raw material extraction and packaging material production represented the dominant contributors to environmental impacts, while high recycling rates of cardboard packaging significantly reduced the final environmental burden.

The study confirms that packaging dematerialisation, product concentration, and the use of recyclable materials are effective strategies for reducing the environmental impacts of detergent packaging systems. The findings further indicate that emerging formats, particularly laundry detergent sheets, may contribute significantly to the objectives of European circular economy policies and packaging waste reduction strategies

Keywords: LCA, packaging, detergents, laundry detergent powder, laundry detergent concentrate, laundry detergent capsules, laundry detergent sheets

Evaluation of the state of recycling of photovoltaic panels and batteries in the context of the circular economy in five European countries

Vilém GABRHEL^a, Lenka WIMMEROVÁ^a, Olga ŠOLCOVÁ^b

^a Czech University of Life Sciences Prague, Faculty of Environmental Sciences, Kamýcká 129, 165 00 Praha - Suchdol, Czech Republic, e-mail: gabrhel@fzp.czu.cz; wimmerova@fzp.czu.cz;
^b Institute of Chemical Process Fundamentals of the CAS, Rozvojová 135, 165 02 Praha, Czech Republic, e-mail: solcova@icpf.cas.cz

The aim of the study was to evaluate the status and development of recycling performance in selected European countries with a focus on photovoltaic panels (PV) and batteries within the context of the circular economy. The analysis is based on Eurostat data for five European countries: Belgium, the Czech Republic, the Netherlands, Germany, and Poland. The most comprehensive data tracking for photovoltaic panels and batteries focused on the recent five-year span from 2019 to 2023, while patents and investments in circular economy sectors were analysed based on data from 2017 to 2021. Monitoring was conducted on the recycling rates of electrical and electronic waste, material flows, processing capacities for PV panels and batteries, as well as socio-economic factors such as employment within the circular economy sectors. In the field of PV panels and batteries for the monitored variables, Germany was the dominant country in terms of the reported amount of waste. Only limited information regarding the processing capacities of batteries and PV panels was typically available, and this data was often specific to individual companies. Employment in circular economy sectors in the EU has been growing for a long time, with the Czech Republic and Poland accounting for the highest share of total employment, while Belgium and the Netherlands showed lower shares.

Keywords: circular economy, photovoltaic panels, batteries, recycling, employment, Eurostat