Lab-scale engineered hydrochar production and techno-economic scaling-up analysis.

Despite the extensive use of engineered hydrochar (EHC) for contaminants adsorption in water, little is known about the scaling-up of EHC production which has kept the technology at a low readiness level (TRL). Full-scale EHC production was simulated to help bridge this knowledge gap. A systematic analysis was performed where EHC was produced from rice straw using hydrothermal carbonization (HTC) at 200 °C with iron addition. A techno-economic evaluation model was employed to simulate the production process and to estimate energy requirements, configuration, and cost scenarios for the HTC process. The minimum selling price (MSP) analysis of the engineered hydrochar was found to be almost half compared to the market price for other similar sorbents ($ 76/t vs. $136/t) suggesting that EHC production is feasible for scaling up. Finally, as a trial, the resulting material was tested for its efficacy in the adsorption of an anionic organic contaminant (e.g., Congo Red, C32H22N6Na2O6S2) in water to identify its potential for water treatment. Experimental results showed that EHC adsorbed > 95% CR suggesting significant adsorption capability and feasibility for production scale-up.

Effect of varying hydrologic regime on seasonal total maximum daily loads (TDML) in an agricultural watershed.

Rising hypoxia due to the eutrophication of riverine ecosystems is primarily caused by the transport of nutrients. The majority of existing TMDL models cannot be efficienty applied to represent nutrient concentrations in riverine ecosystems having varying flow regimes due to seasonal differences. Accurate TMDL assessment requires nutrient loads and suspended matter estimation under varying flow regimes with minimal uncertainty. Though a large database can enhance accuracy, it can be resource intensive. This study presents the design of an innovative modeling strategy to optimize the use of existing datasets to effectively represent streamflow-load dynamics while minimizing uncertainty. The study developed an approach to assess TMDLs using six different flux models and kriging techniques (i) to enhance the accuracy of nutrient load estimation under different hydrologic regimes (flow stratifications) and (ii) to derive an optimal modeling strategy and sampling scheme for minimizing uncertainty. The flux models account for uncertainty in load prediction across varying flow strata, and the deployment of multiple load calculation procedures. Further, the proposed flux approach allows the determination of load exceedance under different TMDL scenarios aimed at minimizing uncertainty to achieve reliable load predictions. The study employed a 10-year dataset (2009-2018) consisting of daily flow data (m3/sec) and weekly data (mg/L) for nitrogen (N), phosphorus (P) and total suspended solids (TSS) concentrations in three distinct agricultural sites in+ the Minnesota River Watershed. The outcomes were analyzed geospatially in a Geographic Information System (GIS) environment using the kriging interpolation technique. The study recommends (i) triple stratification of flows to obtain accurate load estimates, and (ii) an optimal sampling scheme for nitrogen and phosphorous with 30.6 % and 49.8 % datapoints from high flow strata. The study outcomes are expected to contribute to the planning of economically and technically sound combinations of best management practices (BMPs) required for achieving total maximum daily loads (TMDL) in a watershed.

Influence of landscape patterns on nitrate and particulate organic nitrogen inputs to urban stormwater runoff.

This study investigated the effect of the landscape pattern of permeable/impermeable patches on NO3--N and particulate organic nitrogen (PON) concentrations during stormwater runoff transport and their source contributions. Six landscape pattern indices, namely, mean proximity index (MPI), largest patch index (LPI), mean shape index (MSI), landscape shape index (LSI), connect index (CONNECT), and splitting index (SPLIT), were selected to reflect the fragmentation, complexity, and connectivity of permeable patches in urban catchments. The results show that lower fragmentation, higher complexity, and greater connectivity can reduce NO3--N concentrations in road runoff and drainage flow (i.e., the flow in the stormwater drainage network), as well as PON concentrations in road runoff. Further, the above landscape pattern is effective for mitigating the contributions of NO3--N and PON from road runoff. Low impact development (LID) can be incorporated with the landscape pattern of permeable/impermeable patches to mitigate nitrogen pollution in urban stormwater at the catchment scale by optimizing the spatial arrangement.

Understanding the role of land use for urban stormwater management in coastal waterways.

A holistic understanding of the quality and quantity of stormwater in the context of catchment land use plays a crucial role in stormwater management. This study investigated the quality and quantity of stormwater from forested, residential, industrial, and mixed land use areas. Water samples were collected from seven sites over two years at different stages of the runoff hydrograph using fixed sampling stations. Analysis of physicochemical and hydrological variables showed different patterns across the four land use types at various flow conditions highlighting the complex nature of stormwater quality influenced by catchment and rainfall characteristics. Mean concentrations of dissolved organic and oxidised nitrogen (DON and NOx-N) and dissolved organic and filterable reactive phosphorus (DOP and FRP) in stormwater from industrial, mixed-use and residential catchment types were statistically different from stormwater originating from a forested catchment. On average, residential, mixed-use and industrial catchments transported over 50 times more NOx-N to the receiving waters compared to forested catchments. Under high flow conditions, total phosphorus, FRP and total suspended solids (TSS) were mobilised, indicating that phosphorous export is directly related to sediment export regardless of the land use. The study outcomes contribute to the formulation of more effective stormwater management strategies to deal with the drivers of nutrients and TSS inputs resulting from modified land use types to minimise the urbanisation impacts on aquatic biota. In particular, the elevated dissolved nitrogen fractions from all the catchment types other than the forested catchment is a concern for receiving waters, as these can potentially impair water quality and impact the ecosystem health of downstream water bodies such as Intermittently Closed and Open Lakes or Lagoons (ICOLL). The stochastic nature of hydrology and corresponding nutrient loads should be prioritised in stormwater management action plans. However, as space limitations hinder the expansion of vegetation cover and retrofitting stormwater management devices, a paradigm shift in stormwater management is required to achieve the desired outcomes. The study outcomes further indicate that a one-size-fits-all approach to stormwater management may not deliver the desired outcomes, and a suite of tailor-made approaches targeting various flow conditions and catchment surface types is needed.

Occurrence and risk associated with urban road-deposited microplastics.

An in-depth understanding of urban road-deposited MPs is important for the accurate prediction of the risk posed by MPs in different exposure scenarios. This study provides new insights into the intrinsic/extrinsic factors in terms of the variability of concentration and species in urban road-deposited MPs. The study results confirmed that a considerable abundance of road-deposited MPs can be identified with the average concentration ranging from 0.33 to 3.64 g m-2. Land use types and sediment particle size are the important factors that contribute to MPs abundance. The majority of detected MPs including polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) are mainly derived from anthropogenic activities in commercial and residential land uses while rubber MP particles in urban road surfaces are mainly derived from tyre wear. The significant correlation (p < 0.05) between MPs and fine dust particles (< 150 µm) indicated the high affinity of small dust particles for MPs. The risk scores from MPs varied greatly from 10 to 11,000 among the study sites, which indicated the significant spatial variation of potential environmental risks posed by road-deposited MPs. The hotspots of risks posed by MPs were in areas with a high fraction of industrial, commercial and residential land uses. Specifically, the highest risk from MPs was found in mixed industrial and residential areas.

Characterizing molecular transformation of dissolved organic matter during high-solid anaerobic digestion of dewatered sludge using ESI FT-ICR MS.

In this study, the effects of anaerobic digestion (AD) on molecular characteristics of dissolved organic matter (DOM) in the dewatered sludge has been described by advanced electrospray ionization combined with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) technology. With the progress of AD, molecular amounts in DOM samples increased with the lowering in the carbon atom number of average molecular formula and average double bond equivalent (DBE). CHON and CHONS groups are the two main organic substances in sludge with their relative DOM proportions of 29.64% and 32.56%, respectively. The resistants (i.e., refractory organic matter) mainly consist of the proteins regions of CHO groups as well as the proteins/lignin regions of CHON groups. The contrasting temporal trends in protein contents (e.g., decrease (CHO and CHON) vs. increase (CHONS)) may imply differences in their degradation characteristics. Likewise, the multi-N (N3, N4) and S2 organic groups in the sludge are converted to N2 and S1 molecules, while the relative abundance of O atoms (in Ox molecules) tends to increase. In addition, the resistants in sludge DOM contain high oxidizing C and low unsaturation. The overall results of this research are expected to provide the theoretical basis for further optimization of the sludge AD process.

Distribution and variation of metals in urban river sediments in response to microplastics presence, catchment characteristics and sediment properties.

Despite well documented studies on metal pollutants in aquatic ecosystems, knowledge on the combined effects of catchment characteristics, sediment properties, and emerging pollutants, such as microplastics (MPs) on the presence of metals in urban river sediments is still limited. In this study, the synergistic influence of MPs type and hazard indices, catchment characteristics and sediment properties on the variability of metals present in sediments was investigated based on a typical urban river, Brisbane River, Australia. It was noted that the mean concentrations of metals in Brisbane River decreases in the order of Al (94,142 ± 12,194 µg/g) > Fe (62,970 ± 8104 µg/g) > Mn (746 ± 258 µg/g) > Zn (196 ± 29 µg/g) > Cu (50 ± 19 µg/g) > Pb (47 ± 25 µg/g) > Ni (25 ± 3 µg/g) while the variability of metals decreases in the order of Pb > Cu > Mn > Al > Ni > Zn > Fe along the river. According to enrichment factor (Ef) contamination categories, Mn, Cu and Zn exert a moderate level of contamination (Ef > 2), while Fe, Ni, and Zn show slight sediment pollution (1 3) was found at sampling locations having a high urbanisation level and traffic related activities. Crustal metal elements (namely, Al, Fe, Mn) were found to be statistically significantly correlated with sediment properties (P < 0.05). Anthropogenic source metals (namely, Cu, Ni, Pb, Zn) were observed to be highly correlated with catchment characteristics. Additionally, the presence of metals in sediments were positively correlated with MPs concentration, and negatively correlated with MPs hazard indices. The outcomes of this study provide new insights for understanding the relationships among metals and various influential factors in the context of urban river sediment pollution, which will benefit the formulation of risk assessment and regulatory measures for protecting urban waterways.

Understanding nutrient dynamics for effective stormwater treatment design.

Current stormwater quality modelling tools lack robust mathematical replication of nutrient entrainment in runoff. This makes it challenging to design effective stormwater treatment systems such as nature based solutions with adequate resilience to future changes in nutrient inputs in urban environments. Consequently, poorly treated stormwater can be discharged into receiving waters, leading to nutrient enrichment and in turn, environmental and human health impacts. This study integrated empirically based with statistical modelling techniques to incorporate nutrient dynamics into commonly used Intensity-Frequency-Duration (IFD) distributions of design rainfall. Field based nutrient wash-off experiments were conducted to understand nutrient behaviour during a runoff event. New mathematical formulations were derived to describe the decay (wash-off) of nutrients. Rainfall intensity, duration and initially accumulated pollutant load exert positive influence on the decay of nitrogen and phosphorous, while organic carbon has a negative impact on phosphorus decay. It was also evident that nitrogen species would decay at a similar rate, while phosphorus species may decay at different rates. Compared to nitrogen species, phosphorous species were found more likely to be washed-off during a rainfall event. Using the mathematical formulations developed, wash-off of nitrogen and phosphorous was simulated for 435 very frequent and frequent/infrequent design rainfall events leading to the creation of Intensity-Frequency-Duration-Wash-off (IFDW) curves. Analysis of uncertainty associated with IFDW indicated that total phosphorous could be completely washed-off during most of the design rainfall events, while total nitrogen would only be completely washed-off by very few events that are rarer than 10 % AEP (annual exceedance probability). IFDW can act as a tool for supporting effective stormwater treatment design in order to promote sustainable stormwater management and reuse.

Inherent and external factors influencing the distribution of PAHs, hydroxy-PAHs, carbonyl-PAHs and nitro-PAHs in urban road dust.

The distribution and fate of hazardous polycyclic aromatic hydrocarbons (PAHs) and their associated transformed PAHs products (TPPs) notably carbonyl-PAHs (CPAHs), hydroxy-PAHs (HoPAHs), and nitro-PAHs (NPAHs) on urban road surfaces are influenced by diverse factors to varying extent. The pollutants are eventually transported to urban receiving waters via stormwater runoff posing risks to human and ecosystem health. In order to formulate an effective mitigation strategy, it is essential to comprehensively examine the role of both inherent and external factors in the distribution and fate of these hazardous pollutants, and thus, the need for this study. The research study showed that commercial land use has the highest cumulative concentration of PAHs and TPPs. Antecedent dry days (ADDs) has an inverse influence on the distribution of the total concentrations of low-molecular weight PAHs (LMW-PAHs), PAHs, and (PAHs + TPPs) irrespective of the type of land use, whilst there was no major influence on the total concentrations of high molecular weight PAHs (HMW-PAHs), and TPPs. The high volatility of LMW-PAHs compared to HMW-PAHs is considered to account for the decreasing concentration of LMW-PAH with increasing ADD. Particle size range has significant inverse influence on the cumulative concentration of pollutants across all land uses, since smaller particles are characteristically associated with larger surface area leading to the higher sorption of pollutants. Multivariate analysis of the influential factors indicated that two particle size ranges (0.45-150 µm and 150-425 µm) constitute the major influential factors on the distribution and fate of PAHs and TPPs in urban road dust. Greater quantum of pollutants are sorbed to the 0.45-150 µm particles due to the relatively higher specific surface area (SSA), concentration of total organic carbon (TOC) and total suspended solids (TSS) concentration. Therefore, it is critical to effectively remove finer particles from road surfaces in order to reduce exposure to hazardous pollutants.

Risk associated with microplastics in urban aquatic environments: A critical review.

The presence of microplastics (MPs) has been recognized as a significant environmental threat due to adverse effects spanning from molecular level, organism health, ecosystem services to human health and well-being. MPs are complex environmental contaminants as they bind to a wide range of other contaminants. MPs associated contaminants include toxic chemical substances that are used as additives during the plastic manufacturing process and adsorbed contaminants that co-exist with MPs in aquatic environments. With the transfer between the water column and sediments, and the migration within aquatic systems, such contaminants associated MPs potentially pose high risk to aquatic systems. However, only limited research has been undertaken currently to link the environmental risk associated with MPs occurrence and movement behaviour in aquatic systems. Given the significant environmental risk and current knowledge gaps, this review focuses on the role played by the abundance of different MP species in water and sediment compartments as well as provides the context for assessing and quantifying the multiple risks associated with the occurrence and movement behaviour of different MP types. Based on the review of past literature, it is found that the physicochemical properties of MPs influence the release/sorption of other contaminants and current MPs transport modelling studies have primarily focused on virgin plastics rather than aged plastics. Additionally, risk assessment of contaminants-associated MPs needs significantly more research. This paper consolidates the current state-of-the art knowledge on the source to sink movement behaviour of MPs and methodologies for assessing the risk of different MP species. Moreover, knowledge gaps and emerging trends in the field are also identified for future research endeavours.

Hydro-conditioning: Advanced approaches for cost-effective water quality management in agricultural watersheds.

Accurate simulation of landscape hydrological connectivity is pivotal for planning practices required for treating agricultural farm pollution. This study assesses the role of an advanced geospatial approach, namely, 'hydro-conditioning' employed for modifying Digital Elevation Models, termed hDEMs to replicate landscape hydrology by simulating continuous downslope flow through drainage structures such as bridges and culverts. The capabilities of manual and automated hDEMs in delineating optimal locations and water treatment potential of Best Management Practices (BMPs) in a typical agricultural watershed were evaluated. Parallel processing of both hDEMs revealed that 'ground truthing' plays a critical role in the accurate placement of breach lines for allowing water movement through digitally elevated surfaces. Outcomes guide the practitioners in selecting appropriate hDEM (manual or automated) depending on the complexity of modeled hydrological pathways, which is essential for planning BMPs in a cost-effective manner at different spatial scales. Modeling results show that hDEMs greatly influence hydrological connectivity, catchment boundaries, BMP locations, treatment capacities, and related costs. The accuracy of hDEMs was verified using a robust sub-basin scale validation approach. The study recommends a hybrid approach for utilizing the strengths of both, automated and manual hDEMs for efficient agricultural farm pollution in an economical manner.

Biosorption of heavy metals: Transferability between batch and column studies.

The design of an industrial water treatment system using sorption is based on laboratory column tests. To verify the applicability of a column sorption system at industrial scale, it is necessary to determine the system's breakthrough time (BT) in a laboratory setting. In a laboratory column set-up, BT is referred to as the time taken by the adsorbate to appear at column outlet for the first time. This is when the mass transfer zone (MTZ), where the equilibrium sorption occurs, reaches the end of the sorbent bed. However, such laboratory set-up requires significant resources including laboratory space, time and multiple trials, which is the opposite to the batch experimental approach that is commonly used to assess efficiency of sorbents. This study identified batch sorption parameters that can be used to determine BT for a column sorption setting for three toxic heavy metals commonly found in industrial wastewater, namely, Pb2+, Cd2+ and Cu2+. The study conducted a comprehensive evaluation of the relationships between column BT and its key influential factors, namely, equilibrium sorption capacity (qe), pseudo second-order kinetic rate constant (k2) and initial sorption rate (h). The results revealed that BT can be better estimated using h compared to qe and k2. As such, a batch experiment which is more resource efficient could be undertaken for an initial estimation of the experimental BT of a column system. Moreover, a simulation model developed to replicate column sorption could demonstrate the behaviour of the breakthrough curve, which is a key to the selection and assessment of the performance of a sorbent in an adsorbent column. The estimation errors in qe and k2 were found to influence the simulation outcomes. Hence, it is necessary to further investigate the other factors that can potentially influence sorption behaviour.

Influence of land use class and configuration on water-sediment partitioning of heavy metals.

Influence of land use and population characteristics on solid-liquid partitioning of heavy metals in aquatic ecosystems is little understood. This study hypothesised that the partitioning of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) between water and sediments is influenced by different land use classes, their configuration patterns including patch density, Shannon's diversity index, largest patch index, and splitting index and population density. Relationships between variables were investigated from different distances to the stream network (sub-catchment and riparian scales) and considering land use patterns within individual land use classes and individual sub-catchments as a whole (class and landscape levels, respectively). The study outcomes confirmed that the influence of land use and configuration on metals partitioning is scale independent. However, population density increases metal bioavailability at the riparian scale compared to the sub-catchment scale. Agricultural lands discharge the highest fractions of dissolved metals at both spatial scales (eigenvectors = 0.409 - sub-catchment, and -0.533 - riparian, whilst metals have opposite loadings). Positive relationships between splitting index and metal partitioning confirmed that the division of anthropogenic land uses into smaller patches reduces water pollution. However, high fragmentation of forested areas increases the fraction of soluble metals. Further, high patch density and patch diversity are beneficial for controlling the solubility of some metals. Configuration metrics at the landscape level fundamentally reproduce the patterns of the largest land use type and are not effective for assessing metal partitioning. Therefore, analyses at the class level are preferred. This research investigation contributes essential knowledge to improve land use management strategies and, thereby, help safeguard urban waterways.

Adsorption-desorption behavior of heavy metals in aquatic environments: Influence of sediment, water and metal ionic properties.

Limited knowledge of the combined effects of water and sediment properties and metal ionic characteristics on the solid-liquid partitioning of heavy metals constrains the effective management of urban waterways. This study investigated the synergistic influence of key water, sediment and ionic properties on the adsorption-desorption behavior of weakly-bound heavy metals. Field study results indicated that clay minerals are unlikely to adsorb heavy metals in the weakly-bound fraction of sediments (e.g., r = -0.37, kaolinite vs. Cd), whilst dissociation of metal-phosphates can increase metal solubility (e.g., r = 0.61, dissolved phosphorus vs. Zn). High salinity favors solubility of weakly-bound metals due to cation exchange (e.g., r = 0.60, conductivity vs. Cr). Dissolved organic matter does not favor metal solubility (e.g., r = -0.002, DOC vs. Pb) due to salt-induced flocculation. Laboratory study revealed that water pH and salinity dictate metal partitioning due to ionic properties of Ca2+ and H+. Selectivity for particulate phase increased in the order Cu>Pb>Ni>Zn, generally following the softness (2.89, 3.58, 2.82, 2.34, respectively) of the metal ions. Desorption followed the order Ni>Zn>Pb>Cu, which was attributed to decreased hydrolysis constant (pK1 = 9.4, 9.6, 7.8, 7.5, respectively). The study outcomes provide fundamental knowledge for understanding the mobility and potential ecotoxicological impacts of heavy metals in aquatic ecosystems.

Integrating Tank Model and adsorption/desorption characteristics of filter media to simulate outflow water quantity and quality of a bioretention basin: A case study of biochar-based bioretention basin.

Reliable approaches for accurately assessing the performance of stormwater treatment systems is essential for their effective design, including filter media selection which can be a significant constituent in stormwater treatment systems. This study presents an innovative modelling approach integrating the Tank Model with the adsorption-desorption characteristics of the filter media. The resulting modelling approach was applied to simulate a field-scale bioretention basin where biochar was used as filter media with over ten years of rainfall records. The resulting outflow and overflow volumes were compared with observed data for calibration. The Stormwater Treatment Tank Model (STTM) was validated using the Leave-One-Out-Cross-Validation (LOOCV) method. The simulation outcomes include water outflow and overflow (quantity) from the bioretention basin as well as outflow water quality represented by three heavy metals (Pb, Cu, and Zn). The modelling approach developed was found to be capable of accurately simulating outflow and overflow volumes, with outlet water quantity being significantly influenced by the total rainfall depth. The modeling results also suggested that a sole treatment system would not be adequate, particularly for large rainfall events (>100 mm) and a treatment train would be more effective. Simulating long-term (over ten years) pollutant removal performance in the bioretention basin indicated that heavy metals outflow event mean concentration (EMCs) values calculated using simulated results of 30% biochar application rate generated the best pollutant removal with consistent values (2.7 µg/L, 3.0 µg/L, 17.2 µg/L for Pb, Cu, and Zn, respectively). These results confirm that the modelling approach is reliable for assessing long-term treatment performance, as well as a robust tool able to contribute to more effective treatment system design, particularly filter media selection and evaluation.

Emerging materials and technologies for landfill leachate treatment: A critical review.

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Water-sediment interactions and mobility of heavy metals in aquatic environments.

The adsorption-desorption behaviour of heavy metals in aquatic environments is complex and the processes are regulated by the continuous interactions between water and sediments. This study provides a quantitative understanding of the effects of nutrients and key water and sediment properties on the adsorption-desorption behaviour of heavy metals in riverine and estuarine environments. The influence levels of the environmental factors were determined as conditional regression coefficients. The research outcomes indicate that the mineralogical composition of sediments, which influence other sediment properties, such as specific surface area and cation exchange capacity, play the most important role in the adsorption and desorption of heavy metals. It was found that particulate organic matter is the most influential nutrient in heavy metals adsorption in the riverine environment, while particulate phosphorus is more important under estuarine conditions. Dissolved nutrients do not exert a significant positive effect on the release of heavy metals in the riverine area, whilst dissolved phosphorus increases the transfer of specific metals from sediments to the overlying water under estuarine conditions. Furthermore, the positive interdependencies between marine-related ions and the release of most heavy metals in the riverine and estuarine environments indicate an increase in the mobility of heavy metals as a result of cation exchange reactions.

A Bayesian approach to model the trends and variability in urban stormwater quality associated with catchment and hydrologic parameters.

Stormwater runoff pollution has become a key environmental issue in urban areas. Reliable estimation of stormwater pollutant discharge is important for implementing robust water quality management strategies. Even though significant attempts have been undertaken to develop water quality models, deterministic approaches have proven inappropriate as they do not address the variability in stormwater quality. Due to the random nature of rainfall characteristics and the differences in catchment characteristics, it is difficult to generate the runoff pollutographs to a desired level of certainty. Bayesian hierarchical modelling is an effective tool for developing complex models with a large number of sources of variability. A Bayesian model does not look for a single value of the model parameters, but rather determines a distribution of the model parameters from which all inference is drawn. This study introduces a Bayesian hierarchical linear regression model to describe a catchment specific runoff pollutograph incorporating the associated uncertainties in the model parameters. The model incorporates catchment and rainfall characteristics including the effective impervious area, time of concentration, rain duration, average rainfall intensity and the antecedent dry period as the contributors to random effects.

Dispersal and transport of microplastics in river sediments.

Rivers are viewed as major pathways of microplastic transport from terrestrial areas to marine ecosystems. However, there is paucity of knowledge on the dispersal pattern and transport of microplastics in river sediments. In this study, a three dimensional hydrodynamic and particle transport modelling framework was created to investigate the dispersal and transport processes of microplastic particles commonly present in the environment, namely, polyethylene (PE), polypropylene (PP), polyamide (PA), and polyethylene terephthalate (PET) in river sediments. The study outcomes confirmed that sedimental microplastics with lower density would have higher mobility. PE and PP are likely to be transported for a relatively longer distance, while PA and PET would likely accumulate close to source points. High water flow would transport more microplastics from source points, and high flow velocity in bottom water layer are suggested to facilitate the transport of sedimental microplastics. Considering the limited dispersal and transport, the study outcomes indicated that river sediments would act as a sink for microplastic pollutants instead of being a transport pathway. The patchiness associated with the hotspots of different plastic types is expected to provide valuable information for microplastic source tracking.

Impacts of COVID-19 pandemic on the wastewater pathway into surface water: A review.

With global number of cases 106 million and death toll surpassing 2.3 million as of mid-February 2021, the COVID-19 pandemic is certainly one of the major threats that humankind have faced in modern history. As the scientific community navigates through the overwhelming avalanche of information on the multiple health impacts caused by the pandemic, new reports start to emerge on significant ancillary effects associated with the treatment of the virus. Besides the evident health impacts, other emerging impacts related to the COVID-19 pandemic, such as water-related impacts, merits in-depth investigation. This includes strategies for the identification of these impacts and technologies to mitigate them, and to prevent further impacts not only in water ecosystems, but also in relation to human health. This paper has critically reviewed currently available knowledge on the most significant potential impacts of the COVID-19 pandemic on the wastewater pathway into surface water, as well as technologies that may serve to counteract the major threats posed, key perspectives and challenges. Additionally, current knowledge gaps and potential directions for further research and development are identified. While the COVID-19 pandemic is an ongoing and rapidly evolving situation, compiling current knowledge of potential links between wastewater and surface water pathways as related to environmental impacts and relevant associated technologies, as presented in this review, is a critical step to guide future research in this area.