Waste, Volume 4, Issue 3 (September 2026) – 9 articles

Fermented fish residue (FFR) is a byproduct generated from the fermented fish industry and presents a significant opportunity for waste valorization into liquid organic fertilizer (OF). This study aimed to determine the chemical properties of FFR and its derived OF, along with the effects of OF application on soil chemical properties, nutrient use efficiency, and leafy vegetable growth. A field experiment was conducted in randomized complete block design with five treatments, including the application of inorganic fertilizer (IF) as the control and four OF to water dilution ratios (1:100, 1:200, 1:500, and 1:1000). Both FFR and OF were acidic with elevated amounts of nitrogen (N), electrical conductivity, and sodium (Na), but low levels of phosphorus (P), potassium (K), and toxic elements. Compared with the IF treatment, the OF application increases available iron (36–62 mg kg⁻¹) and the exchangeable sodium percentage to 3.2% in the 1:100 treatment, while lowering soil pH (5.8–5.9), exchangeable calcium (1.1–1.9 cmol kg⁻¹), and magnesium (0.28–0.39 cmol kg⁻¹). Plant Na concentration also increased from 4159 to 17,666 mg kg⁻¹ under OF treatments, with the highest concentration in the 1:100 treatment. The OF applied at higher dilution ratios (>500) significantly improved the partial fertilizer productivity (PFP) of N (7.2 t ka⁻¹), P (18.6 t kg⁻¹), and K (2.4 t kg⁻¹). Fresh biomass was approximately 88% lower under OF treatments than under IF. This indicates an enhanced nutrient use efficiency under lower nutrient input conditions. This improvement in nutrient use efficiency is accompanied by reduced fresh biomass and increased Na accumulation in plants, together with changes in soil Na-related properties, highlighting a trade-off between nutrient supply and potential salinity risk. These findings, therefore, suggest that FFR-derived OF when applied at 1:500 or greater has potential as a low-input fertilizer option. Full article

This study investigates the flow and economic valuation of recyclable materials across fifteen Secondary Transfer Stations (STSs) in Dhaka North City Corporation (DNCC), Bangladesh, with the aim of understanding how market dynamics influence material recovery and circular economy potential. Primary data were collected through field surveys, structured questionnaires administered to 50 waste workers, five waste dealers and five local traders. Recovered materials were classified into six major categories, paper, plastic, metal, glass, electronic waste (e-waste), and other materials with further sub-categorization, to capture price variations and material characteristics. The results reveal a highly differentiated recycling market, with prices varying by more than an order of magnitude across materials. High-value materials, including copper wire, scrap aluminum, scrap metal, and electrical wire, are consistently recovered, whereas medium-value materials such as HDPE, PET, polypropylene, PVC, LDPE, Styrofoam, plastic crates, and mixed plastics are recovered selectively depending on market demand. In contrast, low-value materials, including packaging cartons, white paper, glass items, mixed LDPE, damaged LED lights, and mixed wastepaper, are frequently discarded due to weak economic incentives. Despite spatial and socioeconomic differences across STSs, price variability remains relatively low, indicating an integrated city-wide recycling market driven by active trader networks and broader commodity trends. To the best of our knowledge, this is one of the first studies to integrate recyclable material flow with economic valuation across multiple STSs in Dhaka. The findings highlight that recovery efficiency is strongly governed by economic value and informal practices, with limited segregation efficiency and inadequate occupational safety conditions. Enhancing source segregation, improving storage infrastructure, and introducing targeted market and policy interventions for low-value materials are critical for advancing Dhaka’s transition toward a circular and resource-efficient urban waste management system. Full article

Fish scales are collagen-rich processing by-products with considerable potential as a sustainable source of non-mammalian gelatin. This study aimed to extract gelatin from Rohu (Labeo rohita) fish scales and comprehensively characterize its physicochemical, thermal, structural, rheological, textural and functional properties for potential food and industrial applications. Gelatin was extracted by acid demineralization followed by hot-water extraction and characterized using physicochemical analyses, Fourier transform infrared spectroscopy (FTIR), sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), texture profile analysis (TPA) and functional property measurements. The extracted gelatin exhibited a yield of 21.86%, a protein content of 88.37%, an ash content of 1.5%, a gel strength of 182.82 g, a viscosity of 6.56 cP, a solubility of 87.49%, a melting temperature of 23.38 °C, a setting temperature of 20.4 °C and a setting time of 660 s. FTIR and SDS–PAGE confirmed the characteristic structural features of type I collagen-derived gelatin with well-preserved α₁, α₂ and β chains. The gelatin also demonstrated favorable water-holding capacity (169.70%), fat-binding capacity (188.50%), foaming capacity (193.33%) and foaming stability (77.65%), while emulsion capacity and stability increased with gelatin concentration, reaching 44.11% and 42.15%, respectively, at a gelatin concentration of 2.0%. These findings demonstrate the potential of Rohu fish scale gelatin as a sustainable, value-added non-mammalian biomaterial for food, packaging, pharmaceutical and related industrial applications while promoting the valorization of fish-processing waste. Full article

São Paulo is the largest city in Brazil and the second in Latin America. Its domestic waste production reached 3,515,678.96 tons in 2024. Historically, the city has a low recycling rate, and several laws and policies have been implemented to reverse this situation. The objective of this study was to investigate whether there have been advances in the recycling of household solid waste in São Paulo 15 years after the National Solid Waste Policy, from municipal and intra-urban perspectives. The extended period studied and segregated data by regional administration represent the innovative approach of this manuscript. The methodology consisted of a case study with an analysis of the legislation, official data research and evaluation of goals, and socio-spatial distribution. The separate collection rate grew from 0.69% in 2006 to 2.85% in 2024, but this volume represents less than 10% of the target originally projected for the period. A socio-spatial inequality was found as well as a lack of dedicated collection for the organic fraction. It can be concluded that progress is incremental, but limited by structural barriers and urban inequities. Results indicate for São Paulo and for other large cities, mainly in low and middle-income countries, recycling success cannot depend on legislation as it is also correlated with demographic factors, such as educational level, and to the need of targeted policies for a progressive increase in source-separated recycling. Full article

Urban development increases impervious surfaces and stormwater runoff, while the construction sector generates large volumes of construction and demolition waste (CDW). Pervious concrete can mitigate runoff through infiltration and may also valorize CDW, yet its production and testing procedures remain heterogeneous, particularly with recycled aggregates. This study experimentally screens practical processing parameters for pervious concrete produced with basalt and CDW coarse aggregates. The influence of chemical admixture, consolidation method, and end-surface preparation was first assessed to define suitable production conditions: adequate cohesion without admixture required raising the water-to-cement ratio from 0.30 to 0.65; high-energy Proctor compaction crushed the CDW aggregates, favoring standard tamping-rod consolidation; and end-surface preparation had only a minor effect on compressive strength. The selected procedures were then applied to an ACI 522R-based basalt mixture designed for a target void content of 25%, which achieved a fresh density of 1985 kg/m³, a void ratio of 16.88%, and a mean permeability coefficient of 12.18 × 10⁻³ m/s, about twelve times the minimum required by ABNT NBR 16416. Its 28-day compressive strength (12.75 MPa) remained below the 20 MPa pavement-surfacing requirements, although within the typical range reported by ACI 522R for pervious concrete (2.8 to 28 MPa). Overall, aggregate gradation, compaction procedure, and admixture-enabled paste cohesion emerged as the dominant factors governing the strength–porosity–permeability trade-off, guiding subsequent mix optimization. Full article

Automotive paint sludge (APS) is a hazardous industrial waste generated during automotive coating operations and is characterized by high moisture content, variable organic and inorganic composition, volatile organic compounds, pigments and heavy metals. Conventional disposal methods, including landfilling and direct incineration, present increasing environmental and regulatory challenges, thereby motivating interest in thermochemical conversion technologies for APS valorization and energy recovery. This review evaluates the current state of research on APS thermochemical conversion through incineration, pyrolysis and gasification pathways. The review compares the major operational characteristics of thermochemical pathways, including reactor conditions, temperature ranges, product yields, energy recovery potential, pollutant formation and downstream cleanup requirements. Also, techno-economic considerations such as drying energy demand and scale-up limitations are discussed. According to the current literature, incineration is the most industrially mature route for APS destruction, whereas pyrolysis offers more flexibility for fuel and material recovery. Gasification shows potential for syngas and hydrogen production but remains insufficiently studied for APS applications. Despite growing interest in APS valorization, a lot of research gaps remain regarding standardized feedstock classification, pilot-scale validation, process integration, environmental risk assessment and techno-economic optimization. Conclusively, future approaches towards managing APS would need to incorporate process optimization for specific APS types, incorporation of co-processing techniques, as well as an overall assessment for both environmental and economic feasibility. Full article

Conventional thermal disposal of chlorinated hydrocarbon (CHC) waste poses high risks of dioxin, furan, chlorine, and phosgene formation, while plasma destruction remains energy-intensive. This work determines the optimal thermodynamic conditions for the allothermal, non-catalytic steam—carbon dioxide gasification of various CHCs utilizing high-temperature detonation gases (2450–2850 K) expanded to atmospheric pressure to achieve non-toxic, valuable syngas and commercial-grade hydrochloric acid. Thermodynamic modeling ensures complete soot- and hydrocarbon-free conversion with 100% carbon conversion efficiency, dry syngas yield up to 5.7 Nm³/kg, and cold gas efficiency reaching 138%. For highly chlorinated (above 70 wt.% chlorine) or unsaturated feedstocks, a co-feeding method using external hydrocarbons (C₄H₈O₂ as an example) was validated to suppress the formation of major ecotoxicants like Cl₂, COCl₂, and C₂Cl₂. As for other chlorine-containing ecotoxicants, including highly toxic dioxins, their concentrations in the equilibrium gasification products remain negligibly small, even in the absence of dilution. Importantly, a solvent mass fraction of no more than 0.33 in the initial blend is sufficient to entirely achieve this toxic species suppression. For all considered CHCs (undiluted or diluted with C₄H₈O₂), chlorine is shown to bind exclusively to hydrogen chloride (HCl), with all hazardous emissions remaining below the conditional 1 ppm safety limit. To achieve this, a chlorine capture algorithm was substantiated based on the dissolution of generated HCl within the residual steam condensate or externally delivered water upon cooling the gasification products to 293 K. The proposed technology offers an efficient and environmentally safe alternative to expensive plasma methods for toxic organic waste disposal. Full article

Household food waste remains a huge challenge for solid waste management in municipalities worldwide, especially in the Global South. Existing studies that measure food waste (FW) in cities are scarce, have limited geographic scope, and have limited timeframes. In that direction, the current investigation provides data on the FW composition of nine regions of the municipality of Rio de Janeiro (Brazil), based on a three-year sampling across 155 neighborhoods. Waste samples were collected from 2021 to 2023. In total, about 24,038 kg (fresh weight) was analyzed. Results showed that FW accounts for an average of 47.7 ± 1.9% of household waste in the study period. The FW composition in the city of Rio de Janeiro ranged from 60.3–76.5% for fruits, vegetables, and salads, 15.0–25.1% for fine aggregate (small-sized food residues < 2.54 cm, like rice, beans, grains, and fragmented food particles), and 3.2–5.8% for proteins (discarded animal-based protein foods like chicken and meat). The chi-square goodness-of-fit test was applied to evaluate whether the FW composition in each of the nine regions differed from the mean FW composition of the Rio de Janeiro municipality. The findings revealed statistically significant differences (p-value < 0.05) in the average FW fractions in specific regions and years compared with the city’s average composition. Thus, one of the key takeaways of this investigation was that the percentages of discharged food waste fractions vary over time and across locations, even within the same municipality. The present research took a first step toward understanding the food waste problem in Rio de Janeiro (Brazil) and underscores the importance of monitoring food waste data to guide the development of locally specific strategies for sustainable urban food systems, including waste prevention, recycling, and food recovery. Full article

Brackish-water aquaculture provides important livelihoods for many coastal regions worldwide, but it also generates nutrient-rich wastewater that may cause eutrophication if untreated. The use of plants to absorb dissolved nutrients and convert them into harvestable biomass has become an important research direction in aquaculture wastewater management. This study evaluated the performance of Sesuvium portulacastrum L. grown on floating rafts placed directly on the water surface of 0.5 m³ plastic tanks used for Litopenaeus vannamei culture under controlled salinity conditions ranging from 5 to 25‰. During the 28-day experiment, plant growth, shrimp growth performance, plant nutrient accumulation, and nitrogen/phosphorus mass-balance partitioning were assessed. The results showed that S. portulacastrum grew well under brackish conditions, with stronger biomass production at salinities below 15‰, while shrimp growth performance was most favorable at 10–15‰. Nutrient analysis of harvested S. portulacastrum biomass showed that the plant accumulated 19,735–29,433 mg N kg⁻¹ DW and 1099–1912 mg P kg⁻¹ DW, indicating its capacity to recover inorganic N and P through harvestable biomass. At 10‰ salinity, the integrated system reached the highest apparent total nitrogen removal/recovery efficiency of 46.98%, calculated from system-level mass-balance partitioning rather than water-concentration reduction alone. The areal nitrogen recovery rate in harvested S. portulacastrum biomass reached 383 mg N m⁻² day⁻¹. Although S. portulacastrum is a salt-tolerant plant, higher salinity levels (≥20‰) reduced plant biomass production and nutrient recovery efficiency. These findings indicate that integrating floating-raft S. portulacastrum into brackish shrimp-culture systems at moderate salinity, particularly 5–15‰, is a feasible strategy for converting dissolved nutrients into harvestable plant biomass. Full article