Cover illustration
Front Cover Story (See: Yiwei Liu, Kaili Gu, Jinhua Zhang, Jinxiang Li, Jieshu Qian, Jinyou Shen, Xiaohong Guan 2024, 18(2): 14)
In this study, the interface of zerovalent iron (ZVI) was reconstructed by sulfidation and partial aging. It was illustrated that the subshell of iron sulfides could couple with the shell of iron (hydr)oxides to mediate the mass and electron transfer of ZVI to Cr(VI), thereby improving the reaction durability. This synergistic effect w
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● The historical development of free nitrous acid (FNA) technologies is reviewed. ● The roles of novel acid-tolerant ammonia oxidizers are highlighted. ● Acid-tolerant ammonia oxidizers can self-sustain high-level FNA production. ● The next-generation in situ FNA-based technologies are discussed.
The biocidal effects of free nitrous acid (FNA) have found applications in multiple units in an urban wastewater system, including sewer networks, wastewater treatment processes, and sludge treatment processes. However, these applications are associated with chemical costs as both nitrite and acid are needed to produce FNA at the required levels. The recent discovery of novel acid-tolerant ammonia oxidizers offers the possibility to produce FNA from domestic wastewater, enabling the development of next-generation FNA-based technologies capable of achieving self-sustaining FNA production. In this study, we focus on the concept of in situ FNA generation facilitated by acid-tolerant ammonia oxidizers and highlight the multiple benefits it creates, after a brief review of the historical development of FNA-based technologies. We will discuss how wastewater systems can be made more energy-efficient and sustainable by leveraging the potential of acid-tolerant ammonia oxidizers.
● A gentle series process is proposed to gradually leach valuable metals. ● Approximately 87% Li, 97.01% Co, 97.08% Ni and 99% Mn can be leached. ● The mechanism of LiNi x Co y Mn z O2 decomposition during reduction roasting is elucidated. ● Li2CO3, CoSO4, NiSO4 and MnSO4 are successfully recovered.
Substantial environmental and economic benefits can be achieved by recycling used lithium-ion batteries. Hydrometallurgy is often employed to recover waste LiNixCoyMnzO2 cathode materials. As Ni, Co and Mn are transition metals, they exhibit similar properties; therefore, separating them is difficult. Thus, most researchers have focused on leaching processes, while minimal attention has been devoted to the separation of valuable metals from waste LiNixCoyMnzO2 cathode materials. Herein, we propose an environment-friendly, gentle process involving the usage of pyrometallurgy and hydrometallurgy to gradually leach valuable metals and effectively separate them. Interestingly, Li is recovered through a reduction roasting and water leaching process using natural graphite powder, Ni and Co are recovered through ammonia leaching and extraction processes and Mn is recovered through acid leaching and evaporation–crystallization processes. Results show that ~87% Li, 97.01% Co, 97.08% Ni and 99% Mn can be leached using water, ammonia and acid leaching processes. The result obtained using the response surface methodology shows that the concentration of (NH4)2SO3 is a notable factor affecting the leaching of transition metals. Under optimal conditions, ~97.01% Co, 97.08% Ni and 0.64% Mn can be leached out. The decomposition of LiNixCoyMnzO2 is a two-step process. This study provides valuable insights to develop an environment-friendly, gentle leaching process for efficiently recycling valuable metals, which is vital for the lithium-ion battery recycling industry.
● Maldives’ unique natural and socioeconomic status cause waste management challenges. ● Context-specific solutions needed for sustainable waste management in Maldives. ● Waste management practices differ greatly between Male’ city and outer islands. ● Waste incineration in Male’ will double Maldives’ renewable energy supply. ● Decentralized anaerobic digestion proposed for outer islands to recover energy.
Effective waste management is a major challenge for Small Island Developing States (SIDS) like Maldives due to limited land availability. Maldives exemplifies these issues as one of the most geographically dispersed countries, with a population unevenly distributed across numerous islands varying greatly in size and population density. This study provides an in-depth analysis of the unique waste management practices across different regions of Maldives in relation to its natural and socioeconomic context. Data shows Maldives has one of the highest population density and per capita waste generation among SIDS, despite its small land area and medium GDP per capita. Large disparities exist between the densely populated capital Male’ with only 5.8 km2 area generating 63% of waste and the ~194 scattered outer islands with ad hoc waste management practices. Given Male’s dense population and high calorific waste, incineration could generate up to ~30 GW/a energy and even increase Maldives’ renewable energy supply by 200%. In contrast, decentralized anaerobic digestion presents an optimal solution for outer islands to reduce waste volume while providing over 40%–100% energy supply for daily cooking in local families. This timely study delivers valuable insights into designing context-specific waste-to-energy systems and integrated waste policies tailored to Maldives’ distinct regions. The framework presented can also guide other SIDS facing similar challenges as Maldives in establishing sustainable, ecologically sound waste management strategies.
● Double fluorescence peaks model is used to characterize membrane integrity. ● Tryptophan-like substances are used to detect membrane breakage. ● Double fluorescence peaks combination reduces the inner filter effect influence. ● The detection of the instrument is less affected by backwashing operation.
This study proposed the design, fabrication, and assembly of membrane integrity detection instruments in membrane bioreactors (MBR) based on fluorescence spectroscopy. Based on the PARAFAC model, we found that the peak at 280/335 nm strengthened after membrane breakage. The peak at 340/430 nm reflected the sludge concentration in the MBR and reduced the influence of internal filtration effects on detection. Therefore, we determined that the dual-LED light source excitation detection system can detect tryptophan-like substances at 280 nm (T-peak) and humic acid at 340 nm (C-peak). T-peak was identified as the core index indicating membrane integrity. Moreover, the C-peak is the reference indicator factor for a sensitive response to changes in the sludge concentration. The portable fluorescence instrument exhibited high sensitivity and good feedback accuracy compared to particle counting and turbidity detection, where the log reduction value was greater than 3.5. This overcomes the disadvantage of false alarms in particle counters and is not affected by the position of the pump system. This portable instrument provides a flexible and highly sensitive method for the assessment of industrial membrane integrity.
● Designing of flood passages toward inundation risk reduction was summarized. ● Resilience assessment and enhancement methods for flood passages were highlighted. ● Lifeline and emergency planning is vital for fulfilling flood-resilient passages. ● Special attention should be given to vulnerable groups during the design process.
Urban roads can be designated as surface flood passages to transport excess runoff during extreme storms, thereby preventing local flooding, which is known as the major drainage system. However, this practice poses significant risks, including human loss and property damage, due to the high flow rate and velocity carried by roads. Moreover, urban roads with low flood-resilience may significantly hamper the transportation function during severe storms, leading to dysfunction of the city. Therefore, there is an urgent need to transform risk-oriented flood passages into resilient urban road-based flood passages. This paper presents a systematic review of existing methodologies in designing a road network-based flood passage system, along with the discussion of new technologies to enhance system resilience. The study also addresses current knowledge gaps and future directions. The results indicate that flood management measures based on the urban road network should integrate accessibility assessment, lifeline and emergency planning to ensure human well-being outcomes. Furthermore, the special needs and features of vulnerable groups must be taken into serious consideration during the planning stage. In addition, a data-driven approach is recommended to facilitate real-time management and evaluate future works.
● Surface infiltration results in downward migration of PBDEs in soil core. ● Effluent BDE-209 concentration correlates well with colloid concentration. ● Colloidal and PBDE release from soil cores was promoted at lower ionic strength. ● Colloid-facilitated transport of PBDEs poses a risk to groundwater quality.
Polybrominated diphenyl ethers (PBDEs), a class of persistent organic pollutants, have been frequently detected in soil at e-waste recycling sites. However, the key factors controlling the transport of PBDEs from surface soil to the vadose zone and groundwater are unclear. Here, colloid-enhanced leaching of PBDEs from undisturbed soil cores collected at an e-waste recycling site in Tianjin, China, is reported. Spatially heterogeneous release of colloids and PBDEs was observed in all the tested soil cores under chemical and hydrodynamic perturbations, indicating the presence of preferential flow paths. Colloid concentration in the effluent significantly increased as ionic strength decreased (from 10 to 0.01 mmol/L), probably due to the stronger electrostatic repulsion between colloidal particles and the soil matrix at lower ionic strength. In contrast, colloid mobilization was not significantly affected by the changes in pH of the influent (from 4.0 to 10.0) and flow rate (from a Darcy velocity of 1.5 to 6.0 cm/h). The concentrations of 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether (BDE-209), the predominant PBDE congener at the site, detected in the leachate (ranging from 1.09 to 3.43 ng/L) were much lower than previously reported results from packed column leaching tests, and were positively correlated with colloid concentrations. This indicates that remobilization of colloids at e-waste recycling sites can promote the leaching and downward migration of PBDEs from surface soil. The findings highlight the potential risk of surface soil PBDE contamination to groundwater quality and call for further understanding of colloid-facilitated transport for predicting the fate of PBDEs at e-waste recycling sites.
● A hybrid model is proposed to overcome limitations of single model with time series. ● CNN and bidirectional NLSTM are combined to solve complex nonlinear monitoring issue. ● Attention mechanism is suitably introduced to hybrid model for better convergence. ● TPE is used to find the optimal parameter combination faster rather than manual.
The existing automated wastewater treatment control systems encounter challenges such as the utilization of specialized testing instruments, equipment repair complications, high operational costs, substantial operational errors, and low detection accuracy. An effective soft measure model offers a viable approach for real-time monitoring and the development of automated control in the wastewater treatment process. Consequently, a novel hybrid deep learning CNN-BNLSTM-Attention (CBNLSMA) model, which incorporates convolutional neural networks (CNN), bidirectional nested long and short-term memory neural networks (BNLSTM), attention mechanisms (AM), and Tree-structure Parzen Estimators (TPE), has been developed for monitoring effluent water quality during the wastewater treatment process. The CBNLSMA model is divided into four stages: the CNN module for feature extraction and data filtering to expedite operations; the BNLSTM module for temporal data’s temporal information extraction; the AM module for model weight reassignment; and the TPE optimization algorithm for the CBNLSMA model’s hyperparameter search optimization. In comparison with other models (TPE-CNN-BNLSTM, TPE-BNLSTM-AM, TPE-CNN-AM, PSO-CBNLSTMA), the CBNLSMA model reduced the RMSE for effluent COD prediction by 25.4%, decreased the MAPE by 32.9%, and enhanced the R2 by 14.9%. For the effluent SS prediction, the CBNLSMA model reduced the RMSE by 26.4%, the MAPE by 21.0%, and improved the R2 by 35.7% compared to other models. The simulation results demonstrate that the proposed CBNLSMA model holds significant potential for real-time effluent quality monitoring, indicating its high potential for automated control in wastewater treatment processes.
● The Cd(II) adsorption capacity followed the order of PA > PLA > PP. ● Oxygen groups played critical roles in Cd(II) adsorption by PLA MPs. ● Degradation of PLA MPs enhanced Cd(II) desorption in human digestive fluid. ● Cd(II) release was easier from PLA during human digestion than from PP or PA.
It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable MPs relative to those for conventional MPs remain poorly understood. In this study, cadmium (Cd(II)) adsorption and desorption characteristics of polylactic acid (PLA), a typical biodegradable MP, were investigated. Two conventional MPs, i.e., polypropylene (PP) and polyamide (PA) were used for comparison. The maximum Cd(II) adsorption capacities of the MPs studied in the adsorption experiments decreased in the order PA (0.96 ± 0.07 mg/g) > PLA (0.64 ± 0.04 mg/g) > PP (0.22 ± 0.03 mg/g). The Pseudo-second-order kinetic model and Freundlich isothermal model described the Cd(II) adsorption behaviors of PLA MPs well. X-ray photoelectron spectroscopy and two-dimensional Fourier transform infrared correlation spectroscopy analysis indicated that oxygen functional groups were the major and preferential binding sites of PLA MPs, which contributed to their high Cd(II) adsorption capacities. Simulated gastric and intestinal fluids both significantly enhanced the desorption capacities of the examined MPs. Notably, degradation of the PLA MPs during in vitro human digestion made the Cd(II) on the PLA MPs more bioaccessible (19% in the gastric phase and 62% in the intestinal phase) than Cd(II) on the PP and PA MPs. These results indicate the remarkable capacities of biodegradable MPs to accumulate Cd(II) and transfer it to the digestive system and show that biodegradable MPs might pose more severe threats to human health than conventional nonbiodegradable MPs.
● Most water samples had excellent quality and negligible or acceptable health risks. ● One summer sample’ quality was extremely poor due to the total bacterial count. ● Samples showed higher carcinogenic risk (7.63×10−5 ± 3.29×10−6) for children0–5. ● Arsenic was the major substance contributing to carcinogenic risk. ● Summer samples’ poor water quality and higher health risks deserve attention.
Secondary water supply systems (SWSSs) are important components of the water supply infrastructure that ensure residents’ drinking water safety. SWSSs are characterized by long detention time, warm temperature, and unreasonable management, which may trigger the deterioration of water quality and increase risks. In this study, drinking water quality index (DWQI) and health risk assessment (HRA) were selected and modified to quantitatively assess the water quality and health risks of SWSSs in residential neighborhoods. In total, 121 seasonal water samples were selected. It was observed that the water quality was excellent with the DWQI of 0.14 ± 0.04, excluding one sample, which was extremely poor owing to its excessive total bacterial count. The HRA results revealed that the health risks were low: negligible non-carcinogenic risk for any population; negligible and acceptable carcinogenic risk for children aged 6–17 and adults. However, samples revealed higher carcinogenic risk (7.63 × 10−5 ± 3.29 × 10−6) for children aged 0–5, and arsenic was the major substance. Summer samples had poor water quality and higher health risks, which called for attention. To further investigate the water quality and health risks of SWSSs, monthly sampling was conducted during summer. All 24 water samples were qualified in Chinese standard (GB 5749-2022) and characterized as excellent quality. Their HRA results were consistent with the seasonal samples’ and the health risks were mainly concentrated in May. Overall, our study provides a suitable framework for water quality security, advice for managers, and references for administrators in other cities.
● A machine learning approach was applied to predict free chlorine residuals. ● Annual data were obtained from chlorination unit at a 98 MGD water treatment plant. ● The last model iteration returned a high prediction value ( R 2 = 0.937). ● Non-intuitive parameters were found to be highly significant to predictions.
Chlorine-based disinfection is ubiquitous in conventional drinking water treatment (DWT) and serves to mitigate threats of acute microbial disease caused by pathogens that may be present in source water. An important index of disinfection efficiency is the free chlorine residual (FCR), a regulated disinfection parameter in the US that indirectly measures disinfectant power for prevention of microbial recontamination during DWT and distribution. This work demonstrates how machine learning (ML) can be implemented to improve FCR forecasting when supplied with water quality data from a real, full-scale chlorine disinfection system in Georgia, USA. More precisely, a gradient-boosting ML method (CatBoost) was developed from a full year of DWT plant-generated chlorine disinfection data, including water quality parameters (e.g., temperature, turbidity, pH) and operational process data (e.g., flowrates), to predict FCR. Four gradient-boosting models were implemented, with the highest performance achieving a coefficient of determination, R2, of 0.937. Values that provide explanations using Shapley’s additive method were used to interpret the model’s results, uncovering that standard DWT operating parameters, although non-intuitive and theoretically non-causal, vastly improved prediction performance. These results provide a base case for data-driven DWT disinfection supervision and suggest process monitoring methods to provide better information to plant operators for implementation of safe chlorine dosing to maintain optimum FCR.
● Sodium acetate significantly enriched the CGP synthetase-encoding gene. ● The highest CGP yield was obtained from activated sludge fed with sodium acetate. ● Biofilm is more conducive to CGP accumulation compared with floc sludge. ● Aggregation-induced luminescence of CGP was first reported.
In the sewage treatment process, facilitating the conversion of pollutants into value-added resources holds great potential for reducing the amount of greenhouse gas emissions and promoting economic circulation. Cyanophycin granule polypeptide (CGP), a recently discovered high value-added biopolymer present in activated sludge, has provided new avenues for the recovery of resources. However, the mechanisms that regulate CGP synthesis and the characteristics of this biopolymer in activated sludge remain unclear thus far. This study investigated the synthesis of CGP, polyhydroxyalkanoates (PHA), and alginate-like exopolysaccharides (ALE) in various microbial aggregates under different carbon sources feeding conditions. Our results showed that the CGP yields was superior that of PHA and ALE when subjected to identical carbon source feeding conditions. Furthermore, biofilm was more conducive to CGP accumulation than floc sludge. Compared with glucose and methanol, sodium acetate significantly enriched the CGP synthetase-encoding gene (cphAabundance = ~17419), resulting in the highest CGP yield (average 107.1 mg/g MLSS) in both biofilm and floc sludge. This study is the first to reported the characteristic fluorescence of CGP (Ex/Em = ~360/450 nm) caused by the aggregated luminescence of arginine on the side chains. Overall, this study highlights the potential application of CGP as a fluorescent material and offers insights into CGP recovery from activated sludge in wastewater treatment plants.
● A protocol is proposed for simultaneous oil/water separation and electricity generation. ● Oil/water separation efficiency achieves > 99% only out of solar energy. ● A derived extra electricity power of ~0.1 W/m2 is obtained under solar radiation. ● The protocol offers a prospect of solar-driven water treatment and resource recovery.
Oily wastewater from ocean oil spills endangers marine ecosystems and human health. Therefore, developing an effective and sustainable solution for separating oil-water mixtures is urgent. Interfacial solar photothermal evaporation is a promising approach for the complete separation of two-phase mixtures using only solar energy. Herein, we report a carbonized wood-based absorber with Janus structure of comprising a hydrophobic top-layer and an oleophobic bottom-layer for simultaneous solar-driven oil-water separation and electricity generation. Under sunlight irradiation, the rapid evaporation of seawater will induce a separation of oil-water mixtures, and cause a high salt concentration region underlying the interface, while the bottom “bulk water” maintains in a low salt concentration, thus forming a salinity gradient. Electricity can be generated by salinity gradient power. Therefore, oil-water separation efficiency of > 99% and derived extra electricity power of ~0.1 W/m2 is achieved under solar radiation, demonstrating the feasibility of oil-water separation and electricity production synchronously directly using solar energy. This work provides a green and cost-effective path for the separation of oil-water mixtures.
● Partial aging of SZVI can enhance its reactive durability toward Cr(VI). ● Partial aging can couple with sulfidation to reconstruct the interface of ZVI. ● Partial aging can retain the conductive FeS x in the subshell of SZVI. ● Iron (hydr)oxides and FeS x improve the mass and electron transfer of ZVI to Cr(VI).
Sulfated zero-valent iron (SZVI) has shown promising applications in wastewater treatment. However, the rapid decline in the reactivity of SZVI with time limits its real practice. To mediate this problem, partial aging was proposed to improve the reactive durability of SZVI. Taking Cr(VI) as the target contaminant, we found that the aged ZVI (AZVI) gradually lost reactivity as aging time increased from 0.5 to 2 d. Counter-intuitively, the partially aged SZVI (ASZVI) showed greater reactivity than SZVI when exposed to oxygenated water for a period ranging from 0.5 to 14 d. In addition, the ASZVI with 0.5 d of aging time (ASZVI-0.5) not only maintained reactivity in successive runs but also increased the Cr(VI) removal capacity from 9.1 mg/g by SZVI to 19.1 mg/g by ASZVI-0.5. Correlation analysis further revealed that the electron transfer from the Fe0 core to the shell was mediated by the conductive FeS and FeS2 in the subshell of ASZVI. Meanwhile, the lepidocrocite and magnetite on the surface of ASZVI facilitated Cr(VI) adsorption and subsequent electron transfer for Cr(VI) reduction. Moreover, the iron (hydr)oxide shell could retain the conductive FeS and FeS2 in the subshell, allowing ASZVI to reduce Cr(VI) efficiently and sustainably. In general, partial aging can enhance the reactive durability of ZVI when coupled with sulfidation and this synergistic effect will be beneficial to the application of SZVI-based technology for wastewater treatment.
