Abstract The present study investigates the hydrothermal carbonization of yard waste using box-Behnken design (BBD) to optimize key process parameters for enhanced fuel properties. The influence of temperature (180°C–240°C), residence time (240–480 min), and solids concentration (5%–15%) on the quality and yield of hydrochar was evaluated. Response surface methodology was employed to model and analyze the responses: mass yield, carbon content, higher heating value (HHV), and energy yield. Desirability function analysis was integrated to simultaneously maximize the HHV and carbon content while ensuring efficient conversion through optimal yield. The optimal conditions predicted were 220°C, 240 min, and 15% solids, yielding a desirability of 0.964 and energy yield of 62.98%. The analysis underscores the effectiveness of BBD in understanding parameter interactions with fewer experiments, enabling reliable and sustainable valorization of yard waste. By integrating desirability analysis with BBD and focusing on a heterogeneous urban biomass such as yard waste, the study offers a comprehensive process optimization framework that extends beyond conventional agricultural feedstocks and single-response approaches. The outcomes support an efficient and scalable pathway for converting lignocellulose yard residues into value-added hydrochar, aligning with sustainable waste-to-energy and circular bioeconomy strategies.
Abstract Separate anaerobic digestion of food waste often leads to system acidification and instability. Landfill leachate treatment is limited by ammonia inhibition and carbon deficiency. Conventional anaerobic processes struggle to maintain high treatment efficiency and operational stability under ultrahigh organic loading rates. The aim of this study was to construct a synergistic codigestion system for food waste and landfill leachate in an internal-circulation (IC) reactor in order to overcome this stability bottleneck and determine the underlying microbial mechanisms. A laboratory-scale IC reactor was operated continuously with substrates mixed at a volumetric ratio of 1 ∶ 1 . The organic loading rate (OLR) was increased progressively to 20.3 kg chemical oxygen demand ( COD ) / m 3 · day in order to evaluate pollutant removal, methane production, and key parameters, and high-throughput sequencing was employed to analyze the microbial community. The results showed that the system could operate stably at an ultrahigh OLR, achieving a maximum chemical oxygen demand removal efficiency of 88.3% and a volumetric methane production rate of 0.44 L CH 4 / L · day . The leachate provided crucial alkalinity and trace elements, which effectively neutralized acid accumulation and maintained a pH level of 6.9–7.6. Microbial analysis revealed a synergistic metabolic network in which the acetoclastic ( Methanothrix , 38.62%) and hydrogenotrophic ( Methanobacterium , 19.50%) methanogenesis pathways cooperated with the hydrolytic and syntrophic bacteria. In conclusion, integrating an IC reactor with a codigestion strategy successfully achieves a dual breakthrough in treatment performance and operational stability under ultrahigh organic loading. This offers a reliable technical solution for the efficient recovery of energy from complex organic waste.
Abstract The Gafsa-Metlaoui basin is responsible for over 90% of Tunisia’s phosphate production. It yields considerable sludge waste enriched with potentially toxic elements (Zn, Cr, Cu, Ni, and Cd). Despite well-documented total metal concentrations, insights into their precise geochemical fractionation and environmental mobility under arid conditions are notably lacking. In this study of the speciation, mobility, and ecological risk of these potentially toxic elements (PTEs), the Tessier sequential extraction procedure was applied to sludge samples from the region’s drainage network. Critically, this investigation presents the first comprehensive Tessier-based assessment of Metlaoui phosphate sludge and, uniquely, directly links PTE speciation to site-specific acidification processes induced by phosphogypsum leachates, a causal relationship previously overlooked. The selected sampling sites span major drainage sectors with differentiated industrial input signatures, ensuring robust spatial representation. Results indicated that although PTEs are predominantly associated with the stable residual fraction (44%), a substantial proportion (56%) is bound to more labile phases (exchangeable, carbonate, Fe/Mn oxides, and organic matter). Critically, the risk assessment code (RAC) identified Cd (43%) as posing a high risk and Ni (29%) a moderate risk due to their association with the most bioavailable fractions. The mobility index (MI) confirmed that Ni (50%) and Cd (45%) are highly mobile and susceptible to leaching. A key novelty of this research lies in the explicit demonstration, via principal component analysis (PCA), that pH is the master variable dictating PTE speciation. The strong negative correlations observed suggest that acidification (the acidity of phosphogypsum leachates) could significantly promote increased metal mobilization, a factor traditionally recognized as a source of contamination but which has never previously been quantified as the primary factor influencing the in situ mobility of PTE within the Metlaoui phosphate sludge deposits. By linking solid-phase speciation to site-specific geochemical triggers (e.g., acidification and redox changes), this study moves beyond total concentration surveys to provide a process-based risk assessment. The findings underscore the urgent need for engineered sludge management strategies, such as alkaline stabilization or phytoremediation, to mitigate the imminent threats to groundwater and ecosystem health in this vulnerable region, where shallow water tables and seasonal flooding create favorable conditions for contaminant transport.
Abstract This study systematically characterized volatile organic compound (VOC) compositions across cuisines in China, examined how edible oils affect VOC/polycyclic aromatic hydrocarbon (PAH) emissions, and evaluated associated health risks using both deterministic and Monte Carlo probabilistic models, from which a tiered health-risk early-warning classification was derived. Results showed distinct cuisine-specific VOC profiles: high-temperature frying cuisines [barbecue (BB) and western fast food (KFC)] were dominated by alkanes, whereas cooking-wine cuisines [Hunan cuisine (XC) and western cuisine (WC)] had high alcohols (13.2%–29.2% ethanol); Sichuan cuisine (CC) showed high VOC compositional similarity with the other cuisines ( similarity > 0.6 ). Rapeseed oil emitted the most particulate matter, soybean oil emitted the most nonmethane hydrocarbons, and both produced the highest PAHs, notably anthracene ( 276.88 μg m − 3 ) and benzo[a]pyrene. Noncarcinogenic risk arose mainly from acrolein, and the lifetime carcinogenic risk (LCR) exceeded 1.0 × 10 − 6 for all cuisines. VOCs contributed 86.3%–94.1% of total cancer risk and PAHs 5.9%–13.7%, the latter dominated by benzo[a]pyrene. Applying the proposed five-level early-warning scheme, high-oil, high-temperature methods (barbecue and Sichuan cuisine) reached the highest warning levels, and occupational workers were consistently classified one to two levels above nearby residents. The results highlight the need for targeted control of key pollutants (e.g., acrolein and 1,3-butadiene, benzo[a]pyrene) and for occupational protection in catering kitchens.
