Abstract Microplastics (MPs) can be sheltered by bed grains, resulting in a higher threshold of mobilization compared with those moving on a smooth bed. Only one formula considering the sheltering effects has been proposed for the critical shear stress ( τc ) of MP mobilization by including the densities and sizes of MPs and bed grains, but it is inaccurate for MPs of certain materials such as PS and shows limitations in understanding the sheltering effects. Additionally, no method exists for the critical depth-averaged velocity ( Uc ). In this study, experiments were conducted measuring both τc and Uc of MPs (made of PA, PVC, and PET) deposited on rough beds of different roughnesses, with a focus on the sheltering effects. A power law relationship between τc and the density and size of MPs was found, and a new formula for estimating τc was proposed for MPs, which reduced the errors by approximately 40% compared with that of the previous formula (27.8%). To explicitly quantify the sheltering effects in MP mobilizations, hiddenness ( ΔZ ), exposure ( ΔH ), and longitudinal exposure ( ΔX ) were introduced, all of which were observed to follow a normal distribution. A semiempirical method for Uc was then proposed incorporating the new measures, which reduced the errors by around 70% compared to the methods developed for estimating the Uc values of sediments. https://doi.org/10.1021/acs.est.3c02500 Zijian Yu, Mark Loewen, Shuai Guo, Zhiyong Guo, and Wenming Zhang Environmental Science & Technology 2023 57 (30), 11259-11266 DOI: 10.1021/acs.est.3c02500

Abstract The ubiquitous distribution of microplastics (MPs) in aquatic environments is linked to their transport in rivers and streams. However, the specific mechanism of bedload microplastic (MP) transport, notably their stochastic behaviors, remains an underexplored area. To investigate this, particle tracking velocimetry was employed to examine the continuous near-bed movements of four types of MPs under nine setups with different experimental conditions in a laboratory flume, with an emphasis on their streamwise transport. It was found that the streamwise velocity of MPs follows a normal distribution, which can be characterized using the proposed equations to estimate the ensemble mean and standard deviation of MP streamwise velocity. The proposed equations show low relative errors of ∼5% when compared to experimental data. This study also revealed similarities in the continuous movement of MPs and sediments in the streamwise diffusion process. A superdiffusive regime was observed, with particle inertia identified as the primary source of this anomalous diffusion. These results indicate that adopting a probabilistic framework may provide a promising avenue for improving numerical models and enhancing the understanding of MP transport behavior. https://doi.org/10.1021/acs.est.4c13351 Zijian Yu, Mark Loewen, Yongchao Zhou, Zhiyong Guo, Abul Basar Baki, and Wenming Zhang, Environmental Science & Technology 2025 59 (3), 1835-1843

Abstract Climate change poses significant challenges to urban environments affecting both flood risks and stormwater pollutant loadings. However, studies on variations in stormwater runoff quantity and quality in cold regions, which are highly sensitive to climate change, are notably limited. Integrating climatic, hydrologic, and hydraulic modelling, the study assesses the potential impacts of climate change on stormwater runoff volume and pollutant dynamics in a Canadian urban watershed (Calgary). A two-year field program was conducted to support the calibration and validation of the Storm Water Management Model (SWMM). Intensity–duration–frequency curves were employed to evaluate the impacts of climate change on peak flow rate and flooding duration. In addition, typical dry, average, and wet years were applied to continuously simulate stormwater runoff quantity and quality during the 2050s and 2080s. The results suggest substantial increases in peak flow rates and flooding durations, particularly for the 5-year return period rainfall, with 1-h, 4-h, and 24-h peak inflow rates increasing by 74.3% (170.7%), 89.2% (158.4%), and 64.1% (102.8%) in the 2050s (2080s) Furthermore, the runoff quantity is projected to rise by 2.4–10.2% in the 2050s and 11.8–17.5% in the 2080s. Total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) loadings are anticipated to increase by 2.0–36.1%, 3.1–21.4%, and 4.1–20.7%, respectively. As a result, the current stormwater system could overload and stormwater quality is likely to deteriorate under the impact of climate change. The findings are beneficial for cold regions to develop adaptive strategies that enhance urban water security and environmental sustainability under climate change. https://doi.org/10.1016/j.scitotenv.2024.176439 Yang Yang, David Z. Zhu, Mark R. Loewen, Wenming Zhang, Bert van Duin, Khizar Mahmood, Impacts of climate change on urban stormwater runoff quantity and quality in a cold region, Science of The Total Environment, Volume 954, 2024, 176439, ISSN 0048-9697

Abstract The joint effect of mixed land uses and rainfall event types was studied using a two-year field monitoring program in four urban catchments in Calgary, Alberta, Canada. Event mean concentration (EMC) and event pollutant load (EPL) were employed to evaluate the total suspended sediment (TSS), nitrogen and phosphorus. The correlation analysis showed that most nitrogen and phosphorus components (except for NO2/NO3 and TDP) predominantly exist in particulate form in the study areas. The correlation for EPL was notably stronger than EMC, which can be attributed to varying rainfall characteristics. The differences in EMCs and EPLs of TSS, nitrogen and phosphorus across catchments indicated that the complexity and spatial distribution of mixed land use can influence the generation and transportation of pollutants in urban runoff. The impacts of rainfall characteristics on stormwater quality are integrated rather than driven by a single rainfall characteristic. Brief but intense events tended to elevate TSS, nitrogen and phosphorus concentrations, especially in complex land-use catchments. Events with long antecedent dry days and short duration also resulted in increased pollutant concentrations, while events with long duration and low intensity could result in higher EPLs. The effect of mixed land use on water quality can vary depending on rainfall event types. Seasonal variations were found in EMC and EPL of TSS, nitrogen and phosphorus, with higher values in the spring and summer than the fall. Seasonal variations are mainly influenced by rainfall conditions, temperature and anthropogenic activities (e.g. lawn fertilization and de-icing with sands). MLR considering rainfall characteristics is an effective method for predicting stormwater quality within a single catchment. Considering complexity and spatial distribution of mixed land use can improve the accuracy of the harmonized MLR model. This research provided insights into understanding the complexities introduced by mixed land use and rainfall event types in urban stormwater quality. https://doi.org/10.1016/j.scitotenv.2024.175124 Haibin Yan, David Z. Zhu, Mark R. Loewen, Wenming Zhang, Stacey Zhao, Bert van Duin, Lei Chen, Khizar Mahmood, Effects of mixed land use on urban stormwater quality under different rainfall event types, Science of The Total Environment, Volume 950, 2024,175124, ISSN 0048-9697.

Abstract Understanding the impact of rainfall characteristics on urban stormwater quality is important for stormwater management. Even though significant attempts have been undertaken to study the relationship between rainfall and urban stormwater quality, the knowledge developed may be difficult to apply in commercial stormwater management models. A data mining framework was proposed to study the impacts of rainfall characteristics on stormwater quality. A rainfall type-based calibration approach was developed to improve water quality model performance. Specifically, the relationship between rainfall characteristics and stormwater quality was studied using principal component analysis and correlation analysis. Rainfall events were classified using a K-means clustering method based on the selected rainfall characteristics. A rainfall type-based (RTB) model was independently calibrated for each rainfall type to obtain optimal parameter sets of stormwater quality models. The results revealed that antecedent dry days, average rainfall intensity, and rainfall duration were the most critical rainfall characteristics affecting the event mean concentrations (EMCs) of total suspended solids, total nitrogen, and total phosphorus, while total rainfall was found to be of negligible importance. The K-means method effectively clustered the rainfall events into four types that could represent the rainfall characteristics in the study areas. The rainfall type-based calibration approach can considerably improve water quality model accuracy. Compared to the traditional continuous simulation model, the relative error of the RTB model was reduced by 11.4 % to 16.4 % over the calibration period. The calibrated stormwater quality parameters can be transferred to adjacent catchments with similar characteristics. https://doi.org/10.1016/j.scitotenv.2022.160689 Haibin Yan, David Z. Zhu, Mark R. Loewen, Wenming Zhang, Shuntian Liang, Sherif Ahmed, Bert van Duin, Khizar Mahmood, Stacey Zhao, Impact of rainfall characteristics on urban stormwater quality using data mining framework, Science of The Total Environment, Volume 862, 2023, 160689, ISSN 0048-9697

Abstract The feasibility of enhancing quorum sensing (QS) in anode biofilm to improve the quantifications of commercial naphthenic acid concentrations (9.4–94 mg/L) in a microbial electrochemical cell (MXC) based biosensor was demonstrated in this study. First, three calibration methods were systematically compared, and the charging-discharging operation was selected for further experiments due to its 71–227 folds higher electrical signal outputs than the continuous closed-circuit operation and cyclic voltammetry modes. Then, the addition of acylase (5 μg/L) as an exogenous QS autoinducer (acylase) was investigated, which further improved the biosensor's electrical signal output by ∼70%, as compared to the control (without acylase). The addition of acylase increased the relative expression of QS-associated genes ( las R , las I , rhl R , rhl I , las A , and lux R) by 7–100%, along with increased abundances of known electroactive bacterial genera, such as Geobacter (from 42% to 47%) and Desulfovibrio (from 6% to 11%). Furthermore, toxicities of different NAs concentrations measured with the Microtox bioassay test were correlated with corresponding electrical signals, indicating that MXC-biosensor can provide a dual platform for rapid assessment of both NA concentrations and NA-associated toxicity. Chung, T. H., Zakaria, B. S., Meshref, M. N., & Dhar, B. R. (2022). Enhancing quorum sensing in biofilm anode to improve biosensing of naphthenic acids.  Biosensors and Bioelectronics ,  210 , 114275. https://www.sciencedirect.com/science/article/pii/S0956566322003153?casa_token=n-901-npzqIAAAAA:2xYl_PzI5gEIe89QgbPp34VcgryCCos8ZJdLhhrlURx1LE7TB1hAD7pWrexXE7rGZZStuojKINm9

Abstract Hydrogen peroxide (H2O2) production in microbial electrochemical systems (MESs) is an attractive option for enabling a circular economy in the water/wastewater sector. Here, a machine learning algorithm was developed, using a meta-learning approach, to predict the H2O2 production rates in MES based on the seven input variables, including various design and operating parameters. The developed models were trained and cross-validated using the experimental data collected from 25 published reports. The final ensemble meta-learner model (combining 60 models) demonstrated a high prediction accuracy with very high R2 (0.983) and low root-mean-square error (RMSE) (0.647 kg H2O2 m−3 d−1) values. The model identified the carbon felt anode, GDE cathode, and cathode-to-anode volume ratio as the top three most important input features. Further scale-up analysis for small-scale wastewater treatment plants indicated that proper design and operating conditions could increase the H2O2 production rate to as high as 9 kg m−3 d−1. Chung, T. H., Shahidi, M., Mezbahuddin, S., & Dhar, B. R. (2023). Ensemble machine learning approach for examining critical process parameters and scale-up opportunities of microbial electrochemical systems for hydrogen peroxide production.  Chemosphere ,  324 , 138313. https://www.sciencedirect.com/science/article/pii/S0048969722033083?casa_token=kuMRGZVvHlEAAAAA:wtB4RUUoF1D4UvUq89On72Ia8SnBSjOi0pIBXlKomb16QNQsJvpE2bE_wXWnRIKlA8JtnN0pQnyT

Abstract Phosphorus (P) recovery from wastewater is an essential component of the global P cycle. A contact precipitation process using chicken eggshells as a calcium (Ca) precursor was used to recover P from synthetic wastewater and real digested sludge centrate. Up to 96.4 % of P could be recovered from the digested sludge centrate after three repeated cycles of the contact precipitation process. In addition, 36.1 % of total chemical oxygen demand and 37.6 % of total ammonia nitrogen were removed from the centrate. Finally, most of the precipitates could be collected by a simple washing step. Scanning electron microscopy–energy dispersive spectroscopy and x-ray diffraction results indicated that the eggshells played three roles in this process: Ca source, precipitation substrate, and filter medium. Precipitates were mainly brushite. This research provides a new perspective on P recovery from wastewater using waste eggshells, and if further optimized, has a potential for practical future applications. Deng, L., Zakaria, B. S., Zhang, J., & Dhar, B. R. (2024). Utilizing waste eggshells as a calcium precursor for contact precipitation of phosphorus from digested sludge centrate.  Science of The Total Environment ,  919 , 170906. https://www.sciencedirect.com/science/article/pii/S0048969724010453

Abstract Nano/microplastics (NPs/MPs) in sewage sludge can induce oxidative stress to the anaerobic digestion (AD) and also proliferate antibiotic resistance genes (ARGs). Recently, granular activated carbon (GAC) has been used as an additive to enhance methane production in AD via direct interspecies electron transfer (DIET); however, its impact on AD exposed to NPs/MPs is yet to be studied. This study examined the effect of GAC (5 and 15 g/L) on sludge AD exposed to 150 µg/L of polystyrene nanoplastics (PsNPs). PsNPs decreased methane yield by 32.3% due to elevated levels of reactive oxygen species. However, GAC addition counteracted this adverse effect and improved methane production, attributed to the potential enrichment of DIET-active microbes and the adsorption of PsNPs by GAC. Moreover, GAC reduced the total abundance of ARGs, which was increased by PsNPs exposure. Thus, GAC can provide dual benefits in mitigating methanogenic inhibition caused by PsNPs and ARG spread. Azizi, S. M. M., Zakaria, B. S., Haffiez, N., & Dhar, B. R. (2023). Granular activated carbon remediates antibiotic resistance propagation and methanogenic inhibition induced by polystyrene nanoplastics in sludge anaerobic digestion.  Bioresource Technology ,  377 , 128938. https://www.sciencedirect.com/science/article/pii/S0960852423003644?casa_token=7f8e-AGfx50AAAAA:-q1J8-iCPrhiVkLG3-CAUoB3PvdwX1N_RCqqhg9fW0x120ph5Go8qRO49imyR-MgEWuwAMQRGP9q

Abstract Sewage sludge is a significant reservoir of nano/microplastics (NPs/MPs) and antibiotic resistance genes (ARGs). Research has revealed that NPs/MPs may exert an inhibitory effect on anaerobic digestion (AD) of sludge. Moreover, NPs/MPs can influence microbial community diversity and composition, potentially increasing ARGs dissemination. The morphological changes to NPs/MPs surface due to aging contribute to modifying hydrophobic properties. To date, there is limited comprehension regarding how various surface properties of NPs influence ARGs dissemination during AD. This study investigated the impact of primary aged/non-aged and secondary aged/non-aged polystyrene nanoplastics (PSNPs) on ARGs and mobile genetic elements (MGEs) propagation during AD. The findings indicated that the UV-aging process resulted in surface oxidation and distinct morphological characteristics in both primary and secondary PSNPs, while the surface oxidation effect was more pronounced in the secondary aged PSNPs. High concentrations (150 μg/L) of primary and secondary PSNPs inhibited methane production, with secondary PSNPs causing greater inhibition by 16 to 20 % compared to control. In contrast, low concentration (25 μg/L) had negligible or slightly positive effects on methane production. PSNPs at 150 μg/L reduced total VFA concentration, indicating an inhibitory effect on the fermentation step in the AD process. Primary and secondary PSNPs exhibited changes in EPS characteristics. ARGs abundance was enriched in reactors amended with PSNPs, with the highest abundance of 8.54 × 105 copies/g sludge observed in the secondary aged PSNPs (150 μg/L) reactor. Reactors exposed to aged PSNPs exhibited a relatively higher abundance of ARGs compared to reactors exposed to non-aged PSNPs. Exposure to PSNPs increased the microbial community diversity within the digesters and triggered the enrichment of Comamonadaceae and Syntrophaceae , belonging to Proteobacteria phylum. On the other hand, archaeal communities tended to shift towards hydrogenotrophic methanogens in PSNPs reactors. The correlation analysis showed that Comamonadaceae were positively correlated with the majority of ARGs and intl 1. A positive correlation was observed between MGEs and most ARGs, suggesting that the increased proliferation of ARGs under PSNPs exposure may be linked to the abundance of MGEs, which in turn promotes the growth of hosts carrying ARGs. These findings suggest that aged and non-aged NPs could substantially impact the spread of ARGs and MGEs, which also led to notable alterations in the composition of the microbial community. Overall, this study provides valuable insights into the multifaceted impacts of PSNPs with various characteristics on AD processes, microbial communities, and ARGs proliferation, highlighting the urgent need for comprehensive assessments of NPs pollutants in the environment. Haffiez, N., Kalantar, E., Zakaria, B. S., Azizi, S. M. M., Farner, J. M., & Dhar, B. R. (2024). Impact of aging of primary and secondary polystyrene nanoplastics on the transmission of antibiotic resistance genes in anaerobic digestion.  Science of The Total Environment ,  947 , 174213. https://www.sciencedirect.com/science/article/pii/S0048969724043614?casa_token=G4HAzViuyS0AAAAA:mCpZqfFCa9bifyr6QcRT_GpyPxZOXV6TRnldutF8tDuz5ozcVXvS7GcGExgzj6uVwPfrvLj5SRym

Abstract The increasing presence of nano and microplastics (NPs/MPs) in wastewater treatment plants and their inevitable accumulation in the sludge has raised serious concerns in recent years. This study investigated the effects of pristine and aged polyethylene microplastics (PEMPs), polystyrene nanoplastics (PsNPs), and their mixtures on the primary sludge fermentation process. Pristine MPs/NPs (150 μg/L and 2 g/L for PsNPs and PEMPs, respectively) underwent two weeks of weathering in the presence of humic and alginic acids. The results from a batch fermentation experiment (15 days, pH 10) revealed that the exposure to aged PEMPs/PsNPs experienced greater VFA production than pristine samples. Notably, the aged PEMPs/PsNPs mixture showed a 23.12% increase in VFA production over the pristine mixture. The relative abundance and total concentration of antibiotic resistance genes (ARGs) increased in all PEMPs/PsNPs batches compared to the control, with the most significant rise in total ARGs observed in the aged PEMPs sample. Aged PEMPs exhibited a 26.22-fold increase in tet A genes, while aged mix samples showed a 19.68-fold increase in tet M genes compared to their pristine counterparts. Both pristine and aged PEMPs/PsNPs, particularly the aged PEMPs adversely affected the microbial communities at the genus level and altered the microbial structure. Microbial richness and diversity were enhanced in samples exposed to pristine PEMPs/PsNPs and aged PsNPs but decreased in aged PEMPs and in the aged mixture group, suggesting a negative impact of aged polyethylene microplastics on microbial communities. Correlation analysis suggested that phyla Planctomycetes , Proteobacteria , and TM7 are potential hosts of ARGs. These findings manifest the substantial effects of aged nano/microplastics compared to their pristine forms, emphasizing the complex interplay between various forms of PEMPs/PsNPs and microbial dynamics in sludge fermentation processes. Saila, R., & Dhar, B. R. (2024). Effects of aging of polyethylene microplastics and polystyrene nanoplastics on antibiotic resistance gene transfer during primary sludge fermentation.  Science of the Total Environment ,  957 , 177589. https://www.sciencedirect.com/science/article/pii/S0048969724077465

Abstract A microbial electrolysis cell-assisted anaerobic digester (MEC-AD) was operated with vacuum toilet blackwater at different applied voltages (0–1.6 V) at room temperature (R20). A parallel MEC-AD was operated at 35 °C (R35) to provide a kinetics index at mesophilic temperature. Both reactors failed at 1.6 V due to the alkaline pH created by anodic corrosion. In R20, the best performance was observed at 1.2 V, with methane yield, COD removal, hydrolysis and acidogenesis efficiency increased by 59.9%, 27.0%, 52.0%, and 44.9%, respectively, compared to those of 0 V. Enrichment of hydrolytic and syntrophic bacteria (e.g., Clostridium , Bacteroidales , Sedimentibacter , Syntrophomonas ) and increased abundance of genes encoding complex organics (e.g., proteins, carbohydrates, lipids) metabolism in R20 at 1.2 V corresponded to the enhanced hydrolysis/acidogenesis processes. R20 at 1.2 V generated 1.16 times more net energy than R35 at the optimum voltage for methane yield (0.8 V), indicating ambient temperature operation of MEC-AD systems would be a more sustainable strategy. Huang, Q., Liu, Y., & Dhar, B. R. (2022). A multifaceted screening of applied voltages for electro-assisted anaerobic digestion of blackwater: Significance of temperature, hydrolysis/acidogenesis, electrode corrosion, and energy efficiencies.  Bioresource Technology ,  360 , 127533. https://www.sciencedirect.com/science/article/pii/S0960852422008628?casa_token=tEGoZQ8mNzYAAAAA:O-fITWO0tmRj7TwkEBwLHmcGlukoPd-40Z_CGfUDG_XE_MyEy6WG6wRDK57ObL1AXHbfvW1qMW-_