The evaluation of energy efficiency in wastewater treatment plants (WWTPs) is essential for improving operational management, reducing energy consumption, and mitigating emissions. In this study, the energy efficiency of WWTPs in Jiangsu Province, China, was assessed using three-stage data envelopment analysis (DEA), and the results were compared with those from other provinces. Tobit regression analysis was also performed to explore the key factors affecting energy efficiency. The results revealed that energy efficiency in Jiangsu’s WWTPs was generally at a low level (< 0.26), with only two plants achieving an efficiency score of 1. Scale efficiency was at a relatively high level (> 0.69), but technical efficiency was at a lower level (> 0.33), contributing to the low level of overall efficiency. Compared with the other provinces, Jiangsu (0.241) exhibited moderate performance, with Zhejiang (0.403) and Shanghai (0.387) ranking higher, while Yunnan had the lowest (0.208). Factors influencing efficiency included technology type, treatment volume, plant age, and pollutant removal rate. Anaerobic–anoxic–oxic technology had a moderate level of efficiency but was less effective than were rotating biological contactors and anaerobic–oxic technologies. Energy efficiency levels decreased with increasing treatment scale and plant age but improved with increasing pollutant removal rates in plants meeting the Class I-B standard. This study provides a novel application of three-stage DEA in evaluating the energy efficiency of WWTPs and offers valuable insights to support more energy-efficient operational and management practices.
Anaerobic digestion (AD) is widely considered an effective approach for the treatment of food waste (FW). However, the diversity of antibiotic resistance genes (ARGs) in FW, together with ARG dynamics and their interactions with prokaryotes and DNA viruses during AD, remain insufficiently explored. This study performed metagenomic analyses of FW and digestate samples collected from 9 centralized biogas plants. The results showed that FW served as an important reservoir of ARGs. Although the distribution patterns of ARGs in FW and digestate differed, MLS, multidrug, tetracycline, aminoglycoside, and bacitracin were the five most abundant ARG types in both FW and digestate. While AD reduced the overall quantity of ARGs, its capacity to markedly decrease ARG abundance was limited. Procrustes analysis revealed associations between ARGs and prokaryotes and DNA viruses. Among the reconstructed prokaryotic metagenome-assembled genomes (180), 130 were identified as carrying ARGs. DNA viruses showed close associations with antibiotic-resistant bacteria (ARB), with viral-host relationships detected between 181 DNA viruses and 77 ARBs. Most of these viruses were temperate DNA viruses, which may indirectly influence ARG distribution by regulating ARB populations. Nevertheless, the contribution of DNA viruses to ARG dissemination appeared limited, given the small number of detected ARG-carrying viruses and the lack of high-risk ARGs.
Achieving carbon peak at the city level is crucial for China in the context of its carbon peaking and carbon neutrality goals. Here we established a framework based on MRIO and SDA to investigate the stages, pathways, and key driving factors associated with carbon peaking processes in four Chinese megacities from 2007 to 2017. Our result reveals three-stage evolutionary pathways for urban carbon peaking. In the early stage, declining energy intensity is the main driver of emission reductions, while energy structure changes have limited effects. From 2012 to 2017, lower energy intensity cut emissions by 35.2 Mt in Beijing, 89.4 Mt in Tianjin, 97.5 Mt in Shanghai, and 72.9 Mt in Chongqing. As efficiency gains diminished, accelerating energy structure adjustment toward cleaner energy became crucial, further reducing emissions by 8.2 Mt in Beijing, 5.3 Mt in Tianjin, and 2.9 Mt in Chongqing. The second stage is characterized by industrial transfer, revealing three interregional transfer patterns: emissions-only shifts, simultaneous shifts of emissions and economic benefits, and limited outsourcing. However, this spatial redistribution alone fails to address carbon challenges fundamentally. Consequently, transferring regions must pursue industrial upgrading, marking the third stage, which is dominated by the structural transformation of industries. The transition from traditional manufacturing to strategic emerging manufacturing and services not only reduces total carbon emissions but also enhances economic benefits and job opportunities. The three-stage pathway identified in this study provides valuable guidance for achieving carbon peak at both city and national levels in China.
As a vital atmospheric halogen, gaseous hydrochloric acid (HCl) exerts a key influence on various physicochemical processes, particularly in coastal regions. Sea-Land Breeze (SLB) is a common local mesoscale circulation in coastal area that alters local weather conditions and further affects the diffusion and transport of air pollutants. However, the fate of HCl under SLB circulation remains poorly understood, which hinders a comprehensive understanding of coastal halogen chemistry and its associated atmospheric impacts. Here, a measurement campaign conducted in Xiamen, China, during winter 2023 revealed substantial levels of gaseous HCl, with concentrations ranging from 3.9 ppt to 290.4 ppt. Average HCl concentrations were 102.2 ppt and 71.4 ppt under SLB and non-SLB (NSLB) conditions, respectively. The integration of field observations and machine learning methods indicated that gas-particle partitioning could be a key driver of elevated HCl levels. In addition, high RH and abundant particulate nitrate concentrations on SLB days were the dominant factors affecting the HCl formation and reactions between HCl and OH radicals generated atomic chlorine at significant rates, up to 3.6×103 molecules/(cm3·s). The potential adverse health effects from chlorine-containing oxygenated organic molecules (Cl-OOMs) were greater under SLB conditions than on NSLB days. The observed elevation in HCl concentrations through sea-land air exchange can indicate an important chlorine cycling pathway in the coastal urban environment, further explaining the potential influence of chlorine chemistry on atmospheric oxidizing capacity and health effects in coastal cities.
Small marine trash fish are widely consumed and used in aquaculture feed in Bangladesh. However, microplastic (MP) contamination in these species remains poorly quantified, limiting understanding of risks to food safety and aquaculture sustainability. This study aimed to quantify MPs in 10 prevalent trash fish from the eastern coast of Bangladesh, assess exposure risks to human health, and infer their potential role in transferring MPs to aquaculture via fishmeal. In this study, MP abundance was highest in Cynoglossus arel (muscle: 2.00 ± 0.25 MPs/g; gastrointestinal tract (GIT): 5.00 ± 0.29 MPs/g) and lowest in Escualosa thoracata (muscle: 0.33 ± 0.14 MPs/g; GIT: 0.20 ± 0.06 MPs/g). Fibers dominated across all species, accounting for 76.91%–100% in muscle and 100% in several GIT samples, with most particles < 0.5 mm. The predominant polymers were PE (32%), PET (24%), and PP (18%), largely originating from textiles, packaging, and fishing gear, with species-specific patterns. Risk assessment using the Contamination Factor (CF), Pollution Load Index (PLI), and Polymer Hazard Index (PHI) indicated moderate environmental contamination (PLI: 1.32–1.84). Polymer-associated risks were moderate to high (PHI: 122.6–187.3; Potential Risk Index: 268.5–402.1), with the highest PHI recorded in species dominated by PET and polystyrene. Notably, Eupleurogrammus muticus and Otolithoides pama present considerable ecological and health risks to humans. Direct consumption of these fishes or use in fishmeal production may facilitate the transfer of MP into seafood chain. Dietary exposure estimates were highest for children (3.12 items/kg bw/day) versus adults (1.08 items/kg bw/day), highlighting increased vulnerability in younger populations.
Biochar amendment has been proposed to enhance thermophilic anaerobic digestion (AD), yet the influence of biochar physicochemical properties on co-digestion performance and microbial restructuring remains unknown. In this study, three biochars derived from bamboo, hog manure, and hickory shell were evaluated during thermophilic (55 °C) co-digestion of food waste and waste activated sludge. Compared with the control (310.5 ± 7.6 mL CH4 /g volatile solids), biochar supplementation significantly increased cumulative methane yield, with hickory shell biochar achieving the highest production (393.4 ± 9.8 mL CH4 /g volatile solids), corresponding to a 26.7% increase. Kinetic analysis showed that biochar increased the maximum methane production rate by up to 34.6% and shortened the lag phase by approximately one-third. Propionate accumulation was suppressed with hickory shell biochar, accompanied by enhanced soluble chemical oxygen demand removal and improved pH buffering. Biochar particle-size variation at the millimeter scale had a negligible effect. Microbial analysis revealed enrichment of hydrolytic Clostridium_sensu_stricto_1 and versatile methanogens such as Methanosarcina and Methanoculleus in biochar-amended systems. Functional prediction indicated an increase in carbohydrate metabolism, acetate conversion (ackA, pta), and methanogenesis genes (mcrA/B/G). Overall, biochar enhanced thermophilic AD through coordinated improvements in hydrolysis, syntrophic metabolism, and methanogenic activity.