● Urban water systems are challenged by climate change.

Urban water systems are facing various challenges against climate change, impacting cities’ security and their sustainable development. Specifically, there are three major challenges: submersion risk of coastal cities as glaciers melt and sea level rises, more and severe urban flooding caused by extreme weather like intensified storm surge and heavy precipitation, and regional water resource patterns challenged by alteration of spatial distribution of precipitation. Regarding this, two strategies including proactive adaptation and positive mitigation were proposed in this article to realize the reconstruction and optimization of urban water systems, to enhance their resilience, and eventually increase their adaptability and coping ability to climate change. The proactive adaptation strategy consists of 1) construction of sponge cities to accommodate the increased regular rainfall and to balance the alterations of spatial redistribution of precipitation; 2) reconstruction of excess stormwater discharge and detention system to increase capability for extreme precipitation events based on flood risk assessment under future climate change; 3) deployment of forward-looking, ecological, and integrated measures to improve coastal protection capability against inundation risks caused by climate change and sea level rise. The positive mitigation strategy is to employ the systematic concept in planning and design and to adopt advanced applicable energy-saving technologies, processes, and management practices, aiming at reduction in flux of urban water systems, reinforcement in energy conservation and carbon reduction in both water supply systems and wastewater treatment systems, and thus a reduction of greenhouse gas emission from urban water systems.

● Electrochemically exfoliated graphene (EEG) was prepared from pencil graphite rods.

Graphene materials have drawn tremendous attention in recent years. The formation of holes and pores on graphene sheets can provide transfer channels and facilitate the ion/electron transport kinetics. In this study, graphene nanosheets were prepared electrochemically, and then, they were used as the starting material for the preparation of holey graphene (HG) through the KOH activation process. The weight ratio of initial electrochemically exfoliated graphene (EEG) to KOH was optimized according to the morphological features, BET surface area examination, graphene number of layers calculated from XRD patterns, and the I_D/I_G ratio obtained from Raman analysis. Results showed that increasing the KOH amount led to the achievement of higher values of I_D/I_G and surface area and less re-stacking of graphene sheets which occurs because of the heat treatment process. The environmental burdens of the production routes for the preparation of EEG and HG were investigated by cradle-to-gate life cycle assessment (LCA). The LCA results of EEG production indicated that electricity with the contributions of 94%, 91%, 82%, and 75% of the total impact in four environmental categories, including fossil fuel depletion, ozone depletion, global warming, and smog was the main environmental weakness. In the pore generation process, KOH was recognized as the biggest contributor (about 51% to 83% of the total impact) in six impact categories, including ozone depletion, non-carcinogenics, smog, global warming, carcinogenics, and eutrophication which could be attributed to its high consumption amount (21.9 kg). This work offers environmental considerations for the development of sustainable graphene materials.

● Co-occurrence of SMX and Gd(III) enhances HGT of ARGs and MRGs.

With the increasing use of antibiotics and rare earth elements (REE) during the coronavirus disease (COVID-19) pandemic, the co-occurrence of sulfamethoxazole (SMX) and gadolinium (Gd) has increased in wastewater treatment plants (WWTPs). However, the effects of SMX and Gd exposure on the transmission of antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs) remain unknown. This study investigated the impacts of SMX and Gd on the fate of ARGs and MRGs in an activated sludge system. The diversity and relative abundance of ARGs, MRGs, and mobile genetic elements (MGEs) were detected by metagenomic sequencing. The results revealed an increased abundance of ARGs but a decreased abundance of MRGs under the joint effect of SMX and Gd. In addition, Gd alone exerted adverse effects on the proliferation and spread of ARGs and MRGs. However, SMX alone resulted in an increase in the diversity of ARGs and MRGs and promoted the growth of Pseudomonas, Thauera, and Streptomyces in the activated sludge system. Interestingly, a positive correlation was observed between most ARGs and MGEs. These findings provide comprehensive insights into the effects of co-occurring REEs and antibiotics on the fate of ARGs, MRGs, and MGEs, providing evidence to assist in controlling the spread and proliferation of ARGs and MRGs in activated sludge systems.

● Microplastics (MPs) decreased the protein/amino sugars and increased the lipids.

Chemodiversity of dissolved organic matter (DOM) is a crucial factor controlling soil nutrient availability, greenhouse gas emissions, and pollutant migration. Microplastics (MPs) are widespread pollutants in terrestrial ecosystems in many regions. However, the effects of MPs on DOM chemodiversity are not sufficiently understood, particularly under different types of polymers. Using UV–Vis spectroscopy, 3D fluorescence spectroscopy, and Fourier-transform ion cyclotron resonance mass spectrometry, the effects of three prevalent MPs [polyethylene, polystyrene, and polyvinyl chloride (PVC)] on the chemical properties and composition of soil DOM were investigated via a 310-d soil incubation experiment. The results showed that MPs reduced the aromatic and hydrophobic soil DOM components by more than 20%, with PVC MPs having the greatest effect. Furthermore, as MP contents increase, the humification level of soil DOM significantly decreases. MPs increased DOM molecules with no heteroatom by 8.3%–14.0%, but decreased DOM molecules with nitrogen content by 17.0%–47.8%. This may be because MPs cause positive “priming effect,” resulting in the breakdown of bioavailable components in soil DOM. This is also related to MPs changing microbial richness and diversity and enriching microbial communities involved in lignin compositions degradation. In the presence of MPs, soil DOM chemodiversity depended on soil pH, electrical conductivity, dissolved organic carbon, soil organic matter, bacterial Shannon, and fungal Chao index. Specifically, DOM in MP-contaminated soils featured more lipids and less condensed aromatics and proteins/amino sugars, thereby conferring a lower DOM aromaticity and higher lability.

● Online learning models accurately predict influent flow rate at wastewater plants.

Accurate influent flow rate prediction is important for operators and managers at wastewater treatment plants (WWTPs), as it is closely related to wastewater characteristics such as biochemical oxygen demand (BOD), total suspend solids (TSS), and pH. Previous studies have been conducted to predict influent flow rate, and it was proved that data-driven models are effective tools. However, most of these studies have focused on batch learning, which is inadequate for wastewater prediction in the era of COVID-19 as the influent pattern changed significantly. Online learning, which has distinct advantages of dealing with stream data, large data set, and changing data pattern, has a potential to address this issue. In this study, the performance of conventional batch learning models Random Forest (RF), K-Nearest Neighbors (KNN), and Multi-Layer Perceptron (MLP), and their respective online learning models Adaptive Random Forest (aRF), Adaptive K-Nearest Neighbors (aKNN), and Adaptive Multi-Layer Perceptron (aMLP), were compared for predicting influent flow rate at two Canadian WWTPs. Online learning models achieved the highest R², the lowest MAPE, and the lowest RMSE compared to conventional batch learning models in all scenarios. The R² values on testing data set for 24-h ahead prediction of the aRF, aKNN, and aMLP at Plant A were 0.90, 0.73, and 0.87, respectively; these values at Plant B were 0.75, 0.78, and 0.56, respectively. The proposed online learning models are effective in making reliable predictions under changing data patterns, and they are efficient in dealing with continuous and large influent data streams. They can be used to provide robust decision support for wastewater treatment and management in the changing era of COVID-19 and also under other unprecedented emergencies that could change influent patterns.

● Wetlands have been fragmented over the last century by environmental changes.

Mid and high latitude wetlands are becoming fragmented and losing ecosystem functions at a much faster rate than many other ecosystems. This is due in part to increasing human activities and climate change. In this study, we analyzed wetland distribution and spatial pattern changes for the Heilongjiang River Basin over the past 100 yr. We identified the driving factors and quantified the relative importance of each factor based on landscape pattern metrics and machine learning algorithms. Our results show that wetlands have been fragmented into smaller and regular patches with dominant factors that varied at different periods. Geographic features play the most important role in patterns of wetland change for the entire basin (with 50%–60% of relative importance). Human activities are more important than climate change at the century scale, but less important when magnified at the decadal scale. In the early 1900s, human activities were relatively low and localized and remained that way in the subsequent decades. Thus, the effect of human activities on wetland area of the entire basin is weaker when examined at the magnified decadal scale. The results also show that human activities are more important on the Chinese side of the Heilongjiang River Basin, in the Zeya-Bureya Plain on the Russian side, and at lower altitudes (0–100 m). Revealing the spatial and temporal processes and driving factors over the past 100 yr helps researchers and policymakers understand and anticipate wetland change and design effective conservation and restoration policies.

● Better packing density and higher early strength of SS-rich geopolymer.

Geopolymer is a material with high early strength. However, the insufficient durability properties, such as long-term strength, acid-base resistance, freeze–thaw resistance, leaching toxicity, thermal stability, sulfate resistance and carbonation resistance, restrain its practical application. Herein, a long-term stable geopolymer composite with high final strength (ASK1) was synthesized from shell coal gasification fly ash (SFA) and steel slag (SS). Additionally, a geopolymer composite with high early strength (ASK2) was also synthesized for comparison. The results showed that ASK1 exhibited better performance on freezing-thawing resistance, carbonization resistance and heavy metals stabilization compared to the ASK2 at long-term curing. Raising the curing temperature could accelerate the unconfined compressive strength (UCS) development at initial curing ages of 3 to 7 d. Both ASK1 and ASK2 exhibited excellent acid-base and sulfate corrosion resistance. An increase for UCS was seen under KOH solution and MgSO₄ solution corrosion for ASK1. All leaching concentrations of heavy metals out of the two geopolymers were below the standard threshold, even after 50 freezing-thawing cycles. Both ASK1 and ASK2 geopolymer concrete exhibited higher sustainability and economic efficiency than Portland cement concrete. The result of this study not only provides a suitable way for the utilization of industrial solid waste in civil and environmental engineering, but also opens a new approach to improve the long-term stabilities of the geopolymers.

● Up-to-date information on the preparation of zeolite from CFA were summarized.

The by-product of coal combustion, coal fly ash (CFA), has become one of the world’s most emitted solid wastes, and bulk utilization while achieving high value-added products is the focus of current research. Using CFA to prepare zeolite cannot only reduce environmental pressure, but also obtain high value-added products, which has a good market prospect. In this paper, the research progress of hydrothermal synthesis method of CFA zeolites is reviewed in detail and summarized several other synthetic methods of CFA zeolites. This review also presents an overview of CFA zeolites application in environmental applications like water treatment, gas adsorption and soil remediation. However, a considerable number of literature data have documented using CFA zeolites for water treatment, whereas research on CFA zeolites application to gas adsorption and soil remediation is still limited. In addition, the current status of basic research on the industrial production of CFA zeolites is briefly summarized, and the development trend of the synthetic zeolite of CFA is prospected. After the feasibility analysis of the industrial production of CFA zeolite, it is concluded that the only two methods with high feasibility for industrial application are two-step hydrothermal and alkali melting methods, and the industrial production technology still needs to be studied in depth.

● Screened 8862 metal-organic frameworks for I₂ capture via molecular simulation.

We performed large-scale molecular simulation to screen and identify metal-organic framework materials for gaseous iodine capture, as part of our ongoing effort in addressing management and handling issues of various radionuclides in the grand scheme of spent nuclear fuel reprocessing. Starting from the computation-ready experimental (CoRE) metal-organic frameworks (MOFs) database, grand canonical Monte Carlo simulation was employed to predict the iodine uptake values of the MOFs. A ranking list of MOFs based on their iodine uptake capabilities was generated, with the Top 10 candidates identified and their respective adsorption sites visualized. Subsequently, machine learning was used to establish structure-property relationships to correlate MOFs’ various structural and chemical features with their corresponding performances in iodine capture, yielding interpretable common features and design rules for viable MOF adsorbents. The research strategy and framework of the present study could aid the development of high-performing MOF adsorbents for capture and recovery of radioactive iodine, and moreover, other volatile environmentally hazardous species.

● H₂O₂ quenching rates by Cl/S-based chemicals were measured

Residual H₂O₂ from UV/H₂O₂ treatment can be quenched by thiosulfate, bisulfite, and chlorine, but the kinetics of these reactions have not been reported under the full range of practical conditions. In this study, the rates of H₂O₂ quenching by these compounds were compared in different water matrices, temperatures, pH, and when using different forms of bisulfite and chlorine. In general, it was confirmed that thiosulfate would be too slow to serve as a quenching agent in most practical scenarios. At pH 7–8.5, chlorine tends to quench H₂O₂ more than 20 times faster than bisulfite in the various conditions tested. An important observation was that in lightly-buffered water (e.g., alkalinity of 20 mg/L as CaCO₃), the form of chlorine can have a large impact on quenching rate, with gaseous chlorine slowing the reaction due to its lowering of the pH, and hypochlorite having the opposite effect. These impacts will become less significant when water buffer capacity (i.e., alkalinity) increases (e.g., to 80 mg/L as CaCO₃). In addition, water temperature should be considered as the time required to quench H₂O₂ by chlorine at 4 °C is up to 3 times longer than at 20 °C.

● A multi-scale model of catalytic ozonation in a packed-bed reactor was established.

Catalytic ozonation is regarded as a promising technology in the advanced treatment of refractory organic wastewater. Packed-bed reactors are widely used in practical applications due to simple structures, installation and operation. However, mass transfer of packed-bed reactors is relatively restrained and amplified deviations usually occurred in scale-up application. Herein, a multi-scale packed-bed model of catalytic ozonation was established to guide pilot tests. First, a laboratory-scale test was conducted to obtain kinetic parameters needed for modeling. Then, a multi-scale packed-bed model was developed to research the effects of water distribution structure, catalyst particle size, and hydraulic retention time (HRT) on catalytic ozonation. It was found that the performance of packed bed reactor was increased with evenly distributed water inlet, HRT of 60 min, and catalyst diameter of about 3–7 mm. Last, an optimized reactor was manufactured and a pilot-scale test was conducted to treat kitchen wastewater using catalytic ozonation process. In the pilot-scale test with an ozone dosage of 50 mg/L and HRT of 60 min, the packed-bed reactor filled with catalysts I was able to reduce chemical oxygen demand (COD) from 117 to 59 mg/L. The performance of the catalytic ozonation process in the packed-bed reactor for the advanced treatment of actual kitchen wastewater was investigated via both multi-scale simulation and pilot-scale tests in this study, which provided a practical method for optimizing the reactors of treating refractory organic wastewater.

● AOM input elevates water-soluble cysteine and labile DOM fractions in soil.

Algal-derived organic matter (AOM) regulates methylmercury (MeHg) fate in aquatic ecosystems, whereas its role in MeHg production and bioaccumulation in Hg-contaminated paddies is unclear. Pot and microcosm experiments were thus performed to understand the response characteristics of MeHg concentrations in soil and rice in different rice-growing periods to algal decomposition. Compared to the control, algal decomposition significantly increased soil water-soluble cysteine concentrations during the rice-tillering and grain-filling periods (P < 0.05). It also significantly lowered the molecular weight of soil-dissolved organic matter (SDOM) during the rice-tillering period (P < 0.05) and SDOM humification/aromaticity during the grain-filling period. Compared to the control, AOM input increased the abundance of potential Hg and non-Hg methylators in soil. Furthermore, it also greatly increased soil MeHg concentrations by 25.6%–80.2% and 12.6%–66.1% during the rice-tillering and grain-filling periods, with an average of 42.25% and 38.42%, respectively, which were significantly related to the elevated cysteine in soil and the decrease in SDOM molecular weight (P < 0.01). In the early stage (within 10 days of microcosm experiments), the MeHg concentrations in decayed algal particles showed a great decrease (P < 0.01), suggesting a potential MeHg source in soil. Ultimately, algal decomposition greatly increased the MeHg concentrations and bioaccumulation factors in rice grains, by 72.30% and 16.77%, respectively. Overall, algal decomposition in Hg-contaminated paddies is a non-negligible factor promoting MeHg accumulation in soil-rice systems.

● Structural and thermodynamical properties of semi-clathrate hydrate are summarized.

CO₂ is considered as the main contributor to global warming, and hydrate enclathration is an efficient way for carbon capture and separation (CCS). Semi-clathrate hydrate (SCH) is a type of clathrate hydrate capable of encaging CO₂ molecules under mild temperature and pressure conditions. SCH has numerous unique advantages, including high thermal stability, selective absorption of gas molecules with proper size and recyclable, making it a promising candidate for CCS. While SCH based CCS technology is in the developing stage and great efforts have to be conducted to improve the performance that is determined by their thermodynamical and structural properties. This review summarizes and compares the thermodynamic and structural properties of SCH and quaternary salt hydrates with gas mixtures to be captured and separated. Based on the description of the physical properties of SCH and hydrate of quaternary salts with gas mixture, the CO₂ capture and separation from fuel gas, flue gas and biogas with SCH are reviewed. The review focuses on the use of tetra-n-butyl ammonium halide and tetra-n-butyl phosphonium halide, which are the current application hotspots. This review aims to provide guidance for the future applications of SCH.