Search Results (435)

The high-rate biological contactor (HRBC) is an enhanced-primary, biosorption-based, carbon-diversion wastewater treatment process with short hydraulic retention time (HRT), short solids retention time (SRT), low dissolved oxygen (DO), and high food-to-microorganism ratio (F/M). This paper presents modifications to a commercial full-plant wastewater biodegradation model using extracellular polymeric substances (EPS) in waste activated sludge (WAS) to simulate pilot test biosorption data. Bench-scale HRBC tests found that each mg of EPS as COD (COD_EPS) biosorbed 1.02 mg sCOD contained in raw wastewater. The fraction of AS organics identified as EPS in terms of COD was 37% in a conventional AS (CAS), 33% in a trickling filter-solids contact (TF/SC), and 18% in a membrane bioreactor (MBR). The modeling process used stoichiometry equations to convert EPS from its constituent concentrations (carbohydrates, proteins, humic acids, uronic acids) into COD. The conversion did not alter the finding that the normalized total EPS showed a positive relationship with soluble chemical oxygen demand sCOD biosorption with a 0.91 coefficient of determination. The modified commercial biodegradation model gave a maximum error of −12.6% when simulating pilot-scale results, and 80% of all data points were less than ±10% error. The modified model predicted 16% sCOD biosorption by EPS using the design data for a full-scale HRBC facility currently under construction. Full article

Volatile organic compounds (VOCs) are major contributors to air pollution and pose significant risks to both environmental quality and human health. Biochar-based adsorption technology is an efficient and sustainable approach to VOCs removal. Herein, hybrid biochar was prepared from corn stover and municipal sewage sludge using the water vapor activation method, and its physicochemical characteristics and adsorption mechanisms for typical volatile organic compounds commonly produced during biomass-derived energy generation—such as methylbenzene, isopentane, and ethylene—were systematically investigated. The results show that hybrid biochar significantly outperformed single-source biochar, with its ability to adsorb methylbenzene, isopentane, and ethylene exceeding that of pure sludge biochar by 112.21%, 74.53%, and 66.72%, respectively, and surpassing pure corn stover biochar by 74.25%, 62.98%, and 55.25%, respectively. Competitive adsorption analysis indicated that the interaction strength between VOC molecules and the steam-treated hybrid carbon material was associated with their boiling points; compounds with higher boiling points tended to exhibit stronger affinity. This work provides an integrated waste utilization and pollution control strategy for VOCs removal. Full article

Blast furnace sludge is a micro- and nano-dispersed metallurgical waste rich in iron and zinc, yet its accumulation poses a serious environmental challenge. Here we demonstrate its potential as a source of iron and zinc for sugar beet (Beta vulgaris L.), a crop with high micronutrient demand and economic importance. At application rates of 0.5–2 t ha⁻¹ in alluvial-meadow soils with neutral pH, the sludge increased root yield by up to 1.5-fold and sugar content by up to 1.4-fold compared to untreated controls. The optimal dose (0.1 g kg⁻¹ in greenhouse) significantly reduced the activity of oxidative stress markers—polyphenol oxidase (PPO) by 7.5-fold and peroxidase (POD) by 8-fold—indicating alleviation of cellular stress. The sludge also exhibited phytoprotective properties, reducing leaf necrosis under field conditions. A single application at these rates posed no food safety risks: lead and cadmium levels in beetroots and soil remained below international regulatory limits, and zinc accumulation in beetroots (≤10 mg kg⁻¹) was an order of magnitude below the FAO/WHO guideline. However, repeated annual applications would gradually increase soil zinc; preliminary screening suggests that applying 2 t ha⁻¹ annually could approach the soil MPC within 4–5 years under a linear accumulation scenario, necessitating long-term monitoring. Full article

This study assessed the long-term energy self-sufficiency and operational dynamics of a full-scale wastewater treatment plant over the period 2015–2023, with particular emphasis on biogas-driven energy recovery and time-dependent process interactions. The relationship between biogas production and electricity and heat generation was evaluated alongside the influence of different sludge streams on system performance using cross-correlation analysis. The results demonstrated a high level of energy recovery, with biogas-derived electricity covering, on average, 60% of the plant’s demand and reaching a maximum of 74% annually. A very strong correlation was observed between annual biogas production and electricity generation (r = 0.94), confirming the direct energetic coupling of both processes. Monthly analyses further indicated strong consistency between biogas yield and both electricity and heat production (r = 0.55–0.91 and r = 0.86, respectively). Cross-correlation analysis identified Thickened Waste Activated Sludge and Primary Sludge as important process drivers, with statistically significant delayed effects at 10–20 days. In contrast, recirculation-related streams exhibited negligible influence on system dynamics. Statistical analysis revealed that most heavy metals, including Cd, Cr, Ni, and Hg, exhibited high variability (Coefficient Variability > 40%), which can directly impact the stability of methane production. These results indicate that wastewater treatment plants’ energy performance is governed by delayed process responses linked to sludge residence time, highlighting the need for predictive models incorporating at least two weeks of historical operational data. In addition, physicochemical analysis of sewage sludge confirmed generally stable nutrient content, despite variability in biological parameters and heavy metal concentrations. Overall, the study demonstrates that integrating long-term operational datasets with time-lag analysis provides valuable insights for optimizing energy recovery and supporting circular economy strategies in wastewater treatment plants. Full article

In the present study, Fe₃O₄@hydrothermal carbon was prepared successfully using rice straw waste. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis confirmed that the material had rich and strong redox-active centers on its surface, indicating that it has potential to be used as a redox mediator for electron transfer. Fe₃O₄@hydrothermal carbon was added into the anaerobic sludge treatment system for the collaboration of dye decolorization. The results showed that azo dye decolorization efficiency reached the maximum value (98.3%) with the presence of Fe₃O₄@hydrothermal carbon, which was 16.6% higher than control reactor (without Fe₃O₄@hydrothermal carbon added). In addition, Fe₃O₄@hydrothermal carbon exhibits good reusability and the dye decolorization rates in the “anaerobic sludge–material” combining system were significantly higher than that in the “sludge-alone” system during the semi-continuous wastewater treatment process. Mechanistic investigations revealed that the enhanced decolorization is driven by a synergistically constructed interspecies electron transfer pathway. Specifically, the addition of Fe₃O₄@hydrothermal carbon improved the formation of the extracellular polymeric substance (EPS), which had positive effects on sludge stability and its interaction with the material. CV and electron transport system (ETS) activity analysis showed that the sludge exhibited high electrochemical activities with the support of the material, which led to a high electron transfer efficiency between the electron-donating and accepting microbial pairs in the treatment system. The high-throughput sequencing analysis showed that the structure of the microbial community changed during the semi-continuous treatment process; Megasphaera and Clostridium accounted for more than 87.5% of the total abundance of the bacterial community in the anaerobic sludge with material addition. Driven by the material-mediated process, these enriched functional taxa exhibited a high electron transfer efficiency between electron-donating and accepting pairs, accelerating the catalytic cleavage of azo bonds and ultimately improving the overall anaerobic treatment performance. Full article

Mining and industrial activities generate large volumes of waste, up to 99% of the extracted material, forming a major global residue source. In this context, the valorization of mining sludge for sustainable construction materials gains relevance. This study examines the fabrication of ceramic bricks incorporating mining sludge from the Panasqueira mine, evaluating sludge incorporation levels and sintering temperatures to optimize resource use and reduce environmental impacts. Bricks were produced by blending residual clays from Víznar (Granada, Spain) with Panasqueira sludge at substitution rates of 10, 25 and 50%, and fired at 800, 950 and 1100 °C. Granulometry was determined for the Víznar clay and mining sludge, while bulk density was measured for the fired bricks. The raw materials were analyzed by XRF and XRD, whereas the ceramic samples were characterized by water absorption, porosimetry, ultrasound pulse velocity, compressive strength testing, ESEM, leaching and colorimetry, to assess their chemical, physical and mechanical behaviour. Both clays and sludge are rich in SiO₂ and Al₂O₃, suitable for ceramic processing, while fluxing oxides promote vitrification and densification. Incorporating 25 and 50% sludge reduces porosity, increases ultrasonic velocity and improves mechanical strength, achieving optimal performance at 1100 °C. Moreover, firing immobilizes toxic metals and allows controlled colour development, confirming their technical performance and suggesting their potential suitability from an environmental perspective. Their microstructure and stability depend on sludge content and firing temperature, essential factors for sustainable construction and architectural rehabilitation. Full article

Mining activities generate large volumes of waste that pose both environmental liabilities and potential secondary resource value. A significant fraction of these materials still contains recoverable copper, making leaching a promising strategy for reprocessing and valorization, given the natural decline in ore grade. This study presents a PRISMA-based systematic review of recent literature on leaching technologies applied to mining waste, with emphasis on technical performance, environmental implications, and economic feasibility. The reviewed residues include tailings, slags, copper smelter dusts, sludges, waste rock, leaching residues, and other secondary mining and metallurgical wastes. The main leaching routes identified were acidic, biological, alkaline, and hybrid systems, including conventional H₂SO₄ leaching, pressure oxidative leaching, chloride-based systems, glycine- and ammonia-based alkaline media, organic acids, deep eutectic solvents, and biologically mediated processes. Reported Cu recoveries ranged from low values in refractory systems to near-complete extraction under optimized conditions. Overall, copper recovery was controlled primarily by the mineralogical occurrence of Cu rather than by leaching category alone. In contrast, the highest recoveries were generally associated with intensified conditions capable of overcoming sulfide- and silicate-related constraints. Environmental and circular economy benefits were frequently claimed but less often demonstrated through direct evidence, while economic assessment remained limited. Future research should better integrate mineralogical interpretation, environmental verification, and economic feasibility. Full article

The separation of copper and arsenic from spent copper electrolyte plays a pivotal role in electrolyte recirculation and arsenic-bearing solid hazardous waste minimization. In this study, the deep copper removal process in high arsenic and low copper spent copper electrolyte by gas–liquid sulfidation is studied. Thermodynamic analysis indicates that under strongly acidic conditions, regulating the oxidation-reduction potential enables the selective precipitation of Cu²⁺ as CuS while inhibiting the formation of As₂S₃. The influence of hydrogen sulfide excess coefficient and gas–liquid sulfidation temperature on copper and arsenic co-precipitation behavior is investigated. Under the optimal gas–liquid sulfidation conditions with the sulfide excess coefficient of 47 and gas–liquid sulfidation for 60 min at 328.15 K, the copper concentration can be reduced from 0.312 g/L to 1.25 mg/L, while arsenic co-precipitation can be effectively suppressed. The copper gas–liquid sulfidation process is chemical reaction and diffusion mix controlled with an activation energy of 33.47 kJ/mol, while arsenic sulfidation is chemical reaction controlled with an activation energy of 51.22 kJ/mol. The copper–arsenic co-precipitated sludge predominantly consists of As₂S₃, CuS, and Cu₂S. Arsenic precipitation involves a multi-step process: As(V) is first reduced to As(III) and subsequently sulfurized. However, the majority of cupric ions are directly precipitated as sulfides, whereas a minor fraction is firstly reduced by hydrogen sulfide and subsequently precipitated. The present study clarifies the intrinsic mechanism and external regulatory factors for the gas–liquid sulfidation deep copper removal process, providing a theoretical basis for optimizing sulfidation processes to synergistically achieve valuable metal recovery and arsenic pollution control. Full article

Beauty salon wastewater is an emerging commercial greywater characterized by high chemical oxygen demand (COD), intense color, and low biodegradability due to the presence of surfactants and oxidative dye precursors. This study evaluated a solar-assisted photo-Fenton process using waste-derived iron sludge as a heterogeneous catalyst for treating real beauty salon effluent. Operational parameters, including pH, H₂O₂ concentration, iron sludge dosage, reaction time, and temperature, were optimized based on dye removal and COD reduction. Under optimal conditions (pH = 3, H₂O₂ = 400 mg L⁻¹, iron sludge = 40 mg L⁻¹), the system achieved approximately 98% dye removal and 95% COD reduction within 50 min of irradiation. Additionally, maximum performance was observed at 40 °C, while higher temperatures reduced efficiency due to non-productive H₂O₂ decomposition. Kinetic analysis was performed, and the results indicated predominant second-order behavior. Thermodynamic evaluation confirmed an endothermic process with moderate activation energy (Eₐ = 21.8 kJ mol⁻¹). Response surface methodology confirmed strong parameter interactions and high predictive accuracy. The integration of solar irradiation with iron sludge valorization provides a sustainable and decentralized solution for treating dye-loaded beauty salon wastewater. Full article

Anaerobic digestion (AD) of thickened waste-activated sludge (TWAS) is widely applied for sludge stabilization and renewable energy recovery; however, hydrolysis of complex organics often limits fermentation performance. This study evaluated the effects of multiple pretreatment strategies on solubilization, volatile fatty acids (VFAs) production, and extracellular polymeric substances (EPS) during 80 h mesophilic batch fermentation. Pretreatments included hydrothermal treatment (HTP; 70, 90, and 170 °C), ultrasonication (US; 3000, 5000, and 10,000 KJ/kg TS), chemical pretreatment (acidic pH 4 and alkaline pH 10), and biological augmentation using YDRO Process^® (YDRO^®; 5%, 10%, 15% v/v). Across feedstock pretreatments, HTP generated the greatest improvements in solubilization, increasing SCOD by 56–113-fold and producing substantial acetate levels, particularly at 70 °C, alongside substantial phosphorus release. Ultrasonication resulted in moderate solubilization (28–56-fold) and elevated soluble phosphorus and ammonia. Acidic pretreatment maximized soluble phosphorus, but showed limited VFAs production, whereas alkaline pretreatment rapidly increased soluble EPS due to pH-induced cell disruption. Bioaugmentation achieved the highest total COD but yielded comparatively low soluble fractions. Following fermentation, HTP 170 °C consistently outperformed other treatments, maintaining elevated soluble COD and producing the highest acetate concentration. EPS analysis revealed extensive protein and polysaccharide degradation in thermal and bioaugmented systems, indicating active utilization during fermentation. Overall, the results demonstrate that targeted pretreatment strategies significantly enhance organic solubilization, EPS disruption, and VFAs yields, with thermal pretreatment showing the greatest potential to accelerate hydrolysis and acidogenesis. These findings provide valuable insights for optimizing the pre-methanogenic stages of AD and improving the efficiency of sludge treatment and resource recovery. Full article

Sustainable phosphorus (P) management in agriculture requires a circular economy approach through the use of so-called bio-based fertilizers (BBFs). The properties of BBFs vary widely depending on raw materials and production processes. However, it is still unknown how these properties, and particularly the dominant P compounds determine not only the efficiency of BBFs in supplying P to crops, but also their effects on soil functioning and crop quality. This study aimed to evaluate the efficiency of a representative set of BBFs, and relate this efficiency to their composition and dominant P compounds. To this end, 14 BBFs were studied: four from water purification (struvite, vivianite, and sewage sludge with and without composting), four composts (municipal solid waste (MSW), vineyard residues, and two using olive husks), three vermicomposts (two homemade and one commercial), fish meal, digestate, and a commercial organic fertilizer. Phosphorus forms in BBFs were determined using ³¹P nuclear magnetic resonance spectroscopy (P-NMR). The BBFs were compared to a single superphosphate (SSP) in a pot experiment growing wheat in two different alkaline soils, one rich in iron (Fe) oxides and one rich in carbonates. The effects on critical elements in grain [magnesium, Fe, zinc (Zn), manganese, and copper] and enzyme activities related to soil functioning and P cycling were also assessed. The dominant P compound in the BBFs was orthophosphate (73.8–89.5% of the total P in the NaOH–EDTA extracts). The MSW had the highest polyphosphate content (4.1%), a complex inorganic P compound. The organic P content ranged from 9.2% (fish meal) to 25.5% (Moge). Sewage sludge and composted sludge contributed high levels of phosphonates (4.1 and 5.6% of extracted P). The most abundant organic P compound class was inositol hexakisphosphates (IHPs), and myo-IHP (phytate) was the dominant IHP stereoisomer (1.2–6.4%) followed by D-chiro-IHP and scyllo-IHP. Plant dry matter and grain yield with most BBFs were not significantly different from that of SSP in both soils, likely due to the high concentrations of phosphate in relatively soluble forms in most of the BBFs. Vivianite and sewage sludge resulted in significantly higher grain yield than SSP (43% and 40%, respectively) in the carbonate-rich soil, likely due to progressive phosphate dissolution, which decreased the precipitation rate of insoluble calcium (Ca) phosphates. The highest P recoveries were obtained with horse manure vermicompost (65% and 15% higher than SSP in the Fe oxide-rich and in the carbonate-rich soil, respectively), partially attributed to the decreased precipitation rate of insoluble Ca phosphates with the added organic matter. Some BBFs increased micronutrient concentrations in grains and most decreased the P-to-Zn ratio relative to SSP. Overall, phosphatase and β-glucosidase activities increased with carbon-rich BBFs. Most of the studied BBFs could effectively replace fertilizers from non-renewable sources, in some cases with better crop P recoveries. Furthermore, some BBFs could provide additional benefits to grain quality, in terms of micronutrient supply for humans, and soil functioning. Full article

To mitigate the effects of climate change, the world must significantly reduce its reliance on fossil fuels to lower greenhouse gas emissions. The nuclear power and renewable energy sources, such as solar, wind, water, waste, and geothermal energy, emit minimal to no greenhouse gases or pollutants during operation. These sources are considered crucial for combating climate change and supporting sustainable development. However, the production of electricity, like most industries, generates waste. Comparisons show clear differences: fossil fuel plants produce the largest total waste mass (primarily combustion ash, flue gas desulfurization residues, and wastewater sludge), while nuclear facilities generate a minimal volume but high-activity spent fuel and long-lived radioactive materials. Solar PV systems generate significant end-of-life electronic waste and glass encapsulant, and wind turbines yield moderate composite blade residues. Hydropower sediment management and geothermal scaling contribute unique waste streams of local concern. Regardless of the energy source, responsible waste management is critical to minimize environmental impacts. This article explores the sustainability of low-carbon energy sources, specifically focusing on waste management with the aim of highlighting the need of implementing targeted strategies such as advanced recycling and material substitution in order to minimize environmental impacts and enhance the circularity of low-carbon energy systems. Full article

Caproic acid (CA) production through ethanol-driven chain elongation (CE) is a promising pathway to valorize organic wastes. However, the effect of pH and inoculum source on substrate conversion properties and microbial communities was not fully explored. In this study, performance of caproic acid production with anaerobic methanogenic sludge (AMS), aerobic sludge (AS) and chain elongation sludge (CES) at different pH conditions (uncontrolled (UN), 5, 6, and 7) were investigated. It was found that microorganisms in all inocula could degrade ethanol, but the consumption rate was different. The AS mainly used substrate for biogas production, without CA accumulation, while AMS and CES could synthesize butyrate and caproate with ethanol and acetate as substrates. At pH UN and 5, excessive ethanol oxidation (EEO) was activated and transformed ethanol into acetate resulting in low CA yield. Increasing pH to 7, the AMS produced more caproate and achieved a higher CA yield (0.36 g-COD/g-COD) than that of CES (0.33 g-COD/g-COD). Microbial communities in raw inocula were different, which led to distinct substrate conversion pathways. After fermentation, Anaerolineaceae was the dominate family in AMS, while Corynebacteriaceae and Dysgonomonadaceae dominated in the reactor with CES, explaining the distinct caproate yield in both reactors. The results of this study provided useful information for constructing ethanol-driven CE processes from organic wastes. Full article

The accelerating generation of waste streams is observed globally. Spanning lignocellulosic biomass, plastic waste, sewage sludge, and industrial residues, this review presents both an urgent management challenge and a compelling materials opportunity. Carbon materials derived from these waste streams offer a sustainable route to functional carbons applicable in electrochemical energy storage, adsorption, heterogeneous catalysis, and high-temperature applications. Yet their rational design remains constrained by incomplete understanding of the relationships between feedstock composition, processing pathway, structural characteristics, and functional performance. This review provides an integrated analysis of waste-derived carbon materials from processing pathways to structure–property–function relationships. The principal feedstock categories are examined for their compositional characteristics and implications for carbon yield and structure. Five primary processing routes are assessed. The five routes examined are pyrolysis, hydrothermal carbonisation, physical and chemical activation, and microwave-assisted processing. They are assessed comparatively with emphasis on structural outcomes and governing parameters. The resulting structural characteristics are discussed. These are morphology, hierarchical pore architecture, surface chemistry, heteroatom doping, and crystallinity. They are discussed alongside their characterisation methods and known limitations as performance predictors. Structure–property relationships are examined quantitatively. Heteroatom-doped hierarchical porous carbons achieve 612 F/g specific capacitance. Turbostratic hard carbons deliver 450 mAh/g sodium storage with over 90% retention. Hierarchical porous carbons demonstrate CO₂ uptake of 5.0 mmol/g and dye adsorption exceeding 9000 mg/g under optimised laboratory conditions; these values reflect individual studies and are not directly comparable across systems. Biomass-derived sulfonated carbon catalysts sustain biodiesel yields above 90% over multiple cycles. Challenges of feedstock variability, process scalability, environmental compliance, and economic feasibility are addressed, and machine learning-guided design, standardised characterisation methodology, and circular economy policy frameworks are identified as key enablers for translating laboratory performance into industrial reality. Full article

The high-rate contact stabilization (HiCS) process is a potential technology for recovering energy from organic matter in wastewater; however, further performance improvement is required. This study proposes a biologically enhanced HiCS (BE-HiCS) process that introduces waste-activated sludge (WAS) from a separate conventional activated sludge (CAS) train within a wastewater treatment plant (WWTP) into the HiCS stabilization tank. The performance of the proposed process was verified using a pilot-scale plant. In a scenario combining the CAS and BE-HiCS processes, which is considered feasible for practical WWTP implementation due to the ready availability of WAS, a recovery of 0.24 ± 0.03 g-COD/g-COD of the influent COD mass was projected. This value was statistically significantly higher than that achieved by either the CAS process alone or the HiCS process alone. In this scenario, WAS was added to the BE-HiCS process at a ratio of 0.15 ± 0.03 g-COD/g-COD, resulting in a net recovery rate of 0.33 ± 0.04 g-COD/g-COD, after subtracting the COD contribution of the added WAS. The superior organic matter recovery of the BE-HiCS process was attributed to its enhanced ability to convert non-particulate organic matter into sludge through absorption and adsorption, while maintaining adequate sludge settleability for effective solid–liquid separation. Full article