Review of trace organic chemicals in urban stormwater: Concentrations, distributions, risks, and drivers.

Urban stormwater, increasingly seen as a potential water resource for cities and towns, contains various trace organic chemicals (TrOCs). This study, conducted through a comprehensive literature review of 116 publications, provides a detailed report on the occurrence, concentration distribution, health, and ecological risks of TrOCs, as well as the impact of land use and rainfall characteristics on their concentrations. The review uncovers a total of 629 TrOCs detected at least once in urban stormwater, including 228 pesticides, 132 pharmaceutical and personal care products (PPCPs), 29 polycyclic aromatic hydrocarbons (PAHs), 30 per- and polyfluorinated substances (PFAS), 28 flame retardants, 24 plasticizers, 22 polychlorinated biphenyls (PCBs), nine corrosion inhibitors, and 127 other industrial chemicals/intermediates/solvents. Concentration distributions were explored, with the best fit being log-normal distribution. Risk assessment highlighted 82 TrOCs with high ecological risk quotients (ERQ > 1.0) and three with potential health risk quotients (HQ > 1.0). Notably, 14 TrOCs (including six PAHs, five pesticides, three flame-retardants, and one plasticizer) out of 68 analyzed were significantly influenced by land-use type. Relatively weak relationships were observed between rainfall characteristics and pollutant concentrations, warranting further investigation. This study provides essential information about the occurrence and risks of TrOCs in urban stormwater, offering valuable insights for managing these emerging chemicals of concern.

Soil carbon and nitrogen cycles driven by iron redox: A review.

Soil carbon and nitrogen cycles affect agricultural production, environmental quality, and global climate. Iron (Fe), regarded as the most abundant redox-active metal element in the Earth's crust, is involved in a biogeochemical cycle that includes Fe(III) reduction and Fe(II) oxidation. The redox reactions of Fe can be linked to the carbon and nitrogen cycles in soil in various ways. Investigating the transformation processes and mechanisms of soil carbon and nitrogen species driven by Fe redox can provide theoretical guidance for improving soil fertility, and addressing global environmental pollution as well as climate change. Although the widespread occurrence of these coupling processes in soils has been revealed, explorations of the effects of Fe redox on soil carbon and nitrogen cycles remain in the early stages, particularly when considering the broader context of global climate and environmental changes. The key functional microorganisms, mechanisms, and contributions of these coupling processes to soil carbon and nitrogen cycles have not been fully elucidated. Here, we present a systematic review of the research progress on soil carbon and nitrogen cycles mediated by Fe redox, including the underlying reaction processes, the key microorganisms involved, the influencing factors, and their environmental significance. Finally, some unresolved issues and future perspectives are addressed. This knowledge expands our understanding of the interconnected cycles of Fe, carbon and nitrogen in soils.

Photo-electrochemical oxidation flow system for stormwater herbicides removal: Operational conditions and energy consumption analysis.

Photoelectrochemical oxidation (PECO) is a promising advanced technology for treating micropollutants in stormwater. However, it is important to understand its operation prior to practical validation. In this study, we introduced a flow PECO system designed to evaluate its potential for full-scale applications in herbicides degradation, providing valuable insights for future large-scale implementations. The PECO flow reactor demonstrated the ability to treat a larger volume of stormwater (675 mL, approximately 10 times more than previous batch experiments) with effective removal rates of 92 % for diuron and 22 % for atrazine over 6 h of operation at 2 V. To address the large volume issue in stormwater treatment, a multiple module parallel application design is being considered to increase the treatment capacity of the PECO flow reactor. During the flow reactor operations, flow rate was found to have a notable impact on removal performance, particularly for diuron. At a flow rate of 610 mL min-1, approximately 90 % removal of diuron was achieved, while at 29 mL min-1, the removal efficiency decreased to 60 %. While light intensity had minimal effect on diuron degradation (all settings achieved over 90 % removal), it enhanced atrazine degradation from 9 % to 31 % with an increase in intensity from 63 mW cm-2 to 144 mW cm-2. Remarkably, the PECO flow system exhibited excellent removal performance (>90 % removal) for diuron even at extremely high initial pollutant concentrations (240 µg L-1), demonstrating its capacity to handle varying contaminant loads in stormwater. Energy consumption analysis revealed that flow rate as the primary factor influenced the specific energy consumption rate. Higher flow rate (e.g., 610 mL min-1) were preferable in flow reactor due to its well-balanced performance between removal and energy consumption. These findings confirm that the PECO flow system offers an efficient and promising approach for stormwater treatment applications.

Photo-electrochemical oxidation herbicides removal in stormwater: Degradation mechanism and pathway investigation.

Although advanced oxidation processes (AOPs) such as photoelectrochemical oxidation (PECO), electrochemical oxidation (ECO) and photocatalytic oxidation (PCO), have shown potential for wastewater treatment, their application in urban stormwater has rarely been studied. This paper explored their major degradation mechanisms and possible degradation pathways of herbicides for stormwater applications (with treatment difficulty compared with wastewater). PECO and ECO showed excellent removal performance for diuron (100 %) and moderate for atrazine (around 35 %) under a relatively low potential (2 V). Superoxide radical (·O2-) has been found to be the dominant reactive species. Besides, there is evidence to indicate that hydroxyl radical (·OH) and free chlorine (·Cl) also support the degradation reactions. Up to 11 possible intermediate products have been identified during both diuron and atrazine degradation processes under PECO operation. Based on the proposed possible degradation pathways, the intermediates presented during PECO are species with further oxidation. As evidenced by the undetected species of more oxidized intermediates for ECO and PCO, some further degradation steps are missing, which demonstrate their lower oxidation capacity leading to incomplete decomposition of stormwater herbicides. Thus, PECO has a great potential to be developed into a passive stormwater degradation system due to its strong oxidation potential.

Stormwater herbicides removal with a solar-driven advanced oxidation process: A feasibility investigation.

The solar driven advanced oxidation process (AOP) has the potential to be developed as a passive stormwater post-treatment method. Despite its widespread studies in wastewater treatment, the applicability of the process for micropollutant removal in stormwater (which has very different chemical properties from wastewater) is still unknown. This paper investigated the feasibility of three different AOP processes for the degradation of two herbicides (diuron and atrazine) in pre-treated stormwater: (i) photoelectrochemical oxidation (PECO), (ii) electrochemical oxidation (ECO), and (iii) photocatalytic oxidation (PCO). The durability of different anode materials, the effects of catalyst loading, and solar photo- and thermal impacts under different applied voltages were studied. Boron-doped diamond (BDD) was found to be the most durable anode material compared to carbon fiber and titanium foil for long-term operation. Due to the very low electroconductivity of stormwater, a high voltage was required, causing severe oxidation of the carbon fiber material. PECO achieved the best degradation results compared to ECO and PCO, with over 90% degradation of both herbicides in 2 h under 5 V, following a first-order decay process (with a half-life value of 0.40 h for diuron and 0.58 h for atrazine). The voltage increase had a positive impact on the oxidation processes, with 5 V found to be the optimal applied voltage, while catalyst loading had a negligible effect. Interestingly, the solar thermal effect plays a dominant role in enhancing the performance of the PECO process, which indicates the potential of integrating a photovoltaic chamber with a PECO system to harness both the light and heat of solar energy for stormwater treatment.