Environmental Science: Water Research & Technology最新文献

To maximize energy recovery in municipal wastewater treatment plants, the high-rate contact stabilization and activated sludge (HiCS–AS) process—consisting of a two-stage sequencing batch reactor—represents a promising technology for the efficient recovery of organic matter from wastewater as sludge that can be readily converted to methane. The HiCS–AS process was studied under practical conditions using actual wastewater to determine the effect of seasonal water temperature fluctuations (15.9–26.5 °C) in the reaction tank on the methane gas production of sludge recovered from the entire system, compared with the simple activated sludge (SAS) process. The methane recovery rates were in the ranges of 0.13–0.17 g COD CH₄ per g COD (produced methane as g COD per g COD of influent) for the HiCS–AS process and 0.08–0.15 g COD CH₄ per g COD for the SAS process across all periods, with the HiCS–AS process consistently having higher methane recovery rates. Methane production from HiCS sludge ranged from 0.41 to 0.45 NL CH₄ per g volatile solid (VS), surpassing the range of 0.27–0.28 NL CH₄ per g VS for the SAS sludge across all periods. Furthermore, the quality of the effluent was verified, and the concentration of residual organic matter in the effluent of the HiCS–AS process was equivalent to that of the SAS process.

Two photo-sequencing batch reactors (PSBR) fed with real wastewater were evaluated to understand the elimination and particle association of fecal indicator bacteria (FIB) and coliphages. The average log₁₀ removal of E. coli and Enterococcus spp. were 3.2 and 2.9, respectively, for the PSBR with a low airflow rate of 0.2 LPM (PSBR-L), and 2.8 and 2.7, respectively, for the PSBR with a high airflow rate of 0.5 LPM (PSBR-H). The average log₁₀ removals of F-specific and somatic coliphages were 2.9 and 3.2, respectively, for the PSBR-L reactor, and 2.5 and 3.1, respectively, for the PSBR-H reactor. FIB had a maximum association on the 20–0.45 μm particles (46.1–63.3%), while the coliphages had the highest association on the 0.45–0.03 μm particles (44.7–51.2%). The dynamic adaptations in the microbial community structure (16S rRNA gene) were also investigated during the operation period. Genera involved in nutrient removal, such as Thauer spp., and Nitrospira spp., were detected across samples. The outcomes reveal the efficiency of photobioreactors in removing pathogen indicators from real wastewater.

While per- and polyfluoroalkyl substances (PFAS) are not actually generated at water resource recovery facilities (WRRFs), utilities are being forced to consider PFAS in biosolids management plans due to mounting political pressure and pending regulations. Emerging thermal technologies including pyrolysis, gasification, and super critical water oxidation have garnered recent attention for PFAS destruction. Drying, however, is a conventional technology that might also be a tool for utilities to manage PFAS in biosolids, but research on the impacts of drying on PFAS in biosolids is scarce. The objective of this research was to determine how drying affected the fate of PFAS in biosolids. Full-scale sampling was paired with lab-scale oven drying experiments to understand the impact of drying on measurable PFAS in biosolids. Overall, drying substantially reduced the total PFAS concentration in biosolids. PFAS removal during a full-scale facility's drying process matched the removal achieved when solids were taken from that facility and dried in a lab-scale oven instead, with average PFAS removal being approximately 80%. Precursors to perfluoroalkyl acids (PFAAs), primarily 5 : 3 fluorotelomer carboxylic acid (FTCA) and 6 : 2 FTCA, as well as perfluorooctane sulfonic acid (PFOS) were substantially reduced between pre-drying and post-drying triplicate samples. Additional lab-scale oven drying experiments corroborated that measurable PFAS were removed from biosolids collected from three different utilities. Drying experiments at 30 °C and 105 °C revealed that the PFAS profiles were similar, but PFAS concentrations were lower in the 105 °C samples compared to 30 °C samples. While more research is necessary to determine and validate the removal mechanism, drying could be a viable technology to reduce measurable PFAS levels in biosolids to concentrations below guidelines for land application.

The generative ability of abundant reactive species ensures peroxymonosulfate (PMS) pre-oxidation coupled with subsequent Fe-based coagulation (PPFeC) a promising drinking water treatment process, whereas these abundant reactive species can also oxidize chloride in water matrices to form reactive chlorine species (RCS). These RCS can further oxidize organic compounds, resulting in the unexpected cytotoxic and genotoxic disinfection by-product (DBP) formation. Thus, this study investigated the effect of PMS pre-oxidation coupled with subsequent Fe-based coagulation on the mitigation of organic matter and DBP. Here, results showed that the PPFeC process presented better dissolved organic carbon (DOC) removal performance than PMS pre-oxidation and Fe-based coagulation. Compared to Fe³⁺-based coagulation, Fe²⁺-based coagulation resulted in higher DOC removal performance (increased by 63.5% in natural water), higher DBP concentration and water toxicity (increased by 31.3% for the cytotoxicity index and 18.5% for the genotoxicity index in natural water) during the PPFeC process. DBP concentration and toxicity decreased with the increase of the pre-oxidation time, and increased with the increase of PMS concentration. Furthermore, concentration of DBP and toxicity of water initially increased and then decreased with the increase of sedimentation time and coagulant concentration. In addition, compared to SO₄˙⁻ and PMS, HO· played a more significant role in the DBP formation and toxicity during the PPFeC process. Therefore, Fe³⁺-based coagulants were reliable to ensure drinking water safety as PMS was applied as the pre-oxidant.

Heavy metal pollution is extremely deleterious and has emerged as a major environmental concern, posing a hazardous threat to humans and aquatic organisms. It is increasing at an alarming rate owing to significant contributions from natural and anthropogenic activities, which include mining operations, spraying pesticides, land filling, rock abrasion, volcanic eruptions, and fossil fuel combustion. Heavy metals are potentially toxic even at low concentrations and can induce hepatotoxicity, nephrotoxicity, neurotoxicity, carcinogenicity, genotoxicity, and cardiovascular toxicity. Thus, the removal of heavy metals is critical from an environmental perspective. Recently, various efficient adsorbents have been developed for the treatment of heavy metal contaminants, among which LDHs have received great interest owing to their outstanding features such as structural flexibility, biocompatibility, reusability, simple synthesis, low cost, high adsorption efficiency as well as rheological and swelling properties. This review presents an extensive summary of LDH-based adsorbents reported in the literature in the last ten years for heavy metal remediation. Herein, we systematically explore the recent advancements in aspects such as sources of heavy metals, toxicological effects, functionalization strategies, application of LDH-based hybrids in metal detoxification, influencing factors, and machine learning approaches. Moreover, this review highlights pivotal parameters such as isotherms, kinetics, thermodynamics, adsorption capacity, adsorption mechanisms, and optimised experimental values. Finally, we discuss the future perspectives in this promising field. This work will provide valuable insights to new researchers for further exploring the potential of LDH-based adsorbents in heavy metal remediation.

Nitrates (measured as nitrate-nitrogen) in drinking water exceeding the maximum contaminant level (MCL) of 10 mg L⁻¹ can cause significant health risks, such as methemoglobinemia. Even long-term exposure to concentrations below the MCL can also increase the risks of cancer. Iowa, a major agricultural producer, has grappled with decades-long nitrate pollution in its water systems due to intensive farming practices and animal feeding operations. To help in developing interventions and policies to protect public health, this study delves into long-term nitrate levels in 871 Iowa public water systems (PWSs) between 2012 and 2022 and examines sociodemographic disparities in potential nitrate exposure in drinking water. Average nitrate concentration in Iowa's PWSs increased between 2012 and 2016, reaching an average peak of 3 mg L⁻¹ in 2016. 2.5% of 871 PWSs are classified as ‘high-risk’, with nitrate concentrations consistently exceeding 5 mg L⁻¹ over the study period, primarily in eastern and western Iowa, where animal feeding operations are concentrated. The absence of nitrate removal processes at these PWSs contributes to the sustained elevated levels. On average, 7.4% of the state's population served by PWSs has been exposed to nitrate levels consistently exceeding 5 mg L⁻¹ in the past decade. Disparities exist among various sociodemographic groups, with statistically significant higher exposure rates (10.1%, 9.6%, 9.2%, and 8.7%) observed for people whose incomes are below the federal poverty threshold ($26 496/year), older adults (65 years and above), people of colour, and children (5 years and younger). These disparities are particularly concerning as these populations often lack the resources to address the consequences of water contamination. Our study highlights inequities in Iowa's PWSs concerning potential nitrate exposures and underscores a need for nitrate remediation in specific areas. Addressing these disparities is crucial to safeguarding the health of vulnerable populations and promoting environmental justice in water management.

Membrane biofilm reactors (MBfRs), which efficiently remove pollutants and reduce carbon emissions, hold great promise for wastewater treatment. However, the lack of a cheap local supply of hydrogen, uncontrolled substrate competition, and other issues pose challenges on the long-term stability of these reactors. At the same time, membrane bioreactors have strong bonding capabilities and can be coupled with a variety of processes. Therefore, these reactors are coupled with metal catalysts, electrochemistry, or anaerobic ammonia oxidation (anammox) technology to overcome these challenges. Metal catalysts reduces the replacement cycle and improves the operation stability of MBfRs, while electrochemistry removes pollutants in situ along with providing sufficient hydrogen. When coupled with anammox, the performance of the reactor improves and the energy consumption reduces. In this review, coupling of the hydrogen-based membrane biofilm reactor with the above technologies is discussed in view of their practical applications. Furthermore, their working principles, carbon emission reduction and applications are analyzed. Based on these, practical application and carbon emission reduction of membrane biofilm reactors are discussed along with providing ideas on overcoming their limitations.

Emerging contaminants, particularly pesticides and microplastics (MPs), pose a substantial risk to both human beings and ecosystems. While atrazine (ATZ) and MPs have been found to coexist in environmental media, limited studies have investigated their combined interaction and removal. Moreover, the application of electrocoagulation (EC) for simultaneously addressing these contaminants remains unexplored. This study was conducted with ATZ concentration (3–20 mg L⁻¹), where the effects of electrode materials, current density, pH, and supporting electrolyte concentration were analysed. In general, the removal kinetics for ATZ were best described by the first-order model for both Al and Cu electrodes. The ATZ removal efficiencies were evaluated in real water matrices and found to be 79.85 ± 1.03, 75.92 ± 1.25, 70.58 ± 1.49, 68.09 ± 1.10, and 64.42 ± 2.25% in distilled deionized water, ground, lake, river, and wastewater, respectively using Cu electrodes. Removal of ATZ was higher (84.52 ± 1.04%) in the presence of microplastics as they served as coagulant aids. The effect of polarity reversal was examined to reduce anode fouling during electrolysis and longer intervals of 10 min yielded higher removal efficiencies than intervals of 5 min or no polarity reversal. This research found that EC is an economical and sustainable solution to pesticide and MP pollution in aquatic ecosystems. This study advances Sustainable Development Goals (SDG) by enhancing clean water access (SDG 6), promoting health through pollutant removal (SDG 3), and using solar power as an energy source to run the reactor is aligned with SDG 7.

More and more halogenating agents have been identified in disinfection systems; however, quantifying their reactivity remains challenging. In this study, 18 electrophiles, including 11 halogenating agents (H), 4 halogenated amines (HA), and 3 sulfonylating/acylating (S/A) agents, as well as 12 substrates containing 5 C-reactive compounds (C-), 6 N-reactive amines (N-), and 1 O-reactive alcohol (O-) were chosen to explore their reactivity in electrophilic substitution reactions using the DFT method. The results indicated that the reactivity of electrophiles was highly sensitive to the hardness (energy gap E_LUMO–HOMO as a descriptor) of the substrate. Among the electrophiles, HA generally exhibited the lowest reactivity, except for NH₂Br with some substrates. For the soft C-substrates, the reactivity of H was higher than that of S/A; however, as the hardness of substrates increased, the reactivity of S/A surpassed that of some/all H for hard N- and O-substrates. Interestingly, alcohol, the hardest substrate tested in this study, shared the same reactivity order as phenolate, the softest substrate, in reactions with H, which was X–X′/OX′/OX >/≈ X–X > X–OH and HOI > HOBr > HOCl, but the rate constant k_est was lower by 7–17 orders of magnitude. However, the order was Cl- > Br- > I-agents for the medium aliphatic amine-N substrates. This explains the experimentally observed differences in halogenated product generation from various electrophiles. The results provide valuable insights into the reactivity of various electrophiles and substrates, providing a theoretical reference for choosing appropriate disinfectants based on the types of substrates present in water.

The excessive release of biocidal agents and their consecutive impact are critical issues that can lead to secondary toxicity, and decreased longevity of the water disinfection process. Various antimicrobial agents, such as chlorine, biocidal salts, nanoparticles, etc., have been used for water purification. However, ensuring the longevity and stability of the material becomes a vital concern when dealing with long-term disinfection. This review explores diverse approaches to mitigate excessive biocide release, offering applications in point-of-use disinfection treatment with a controlled release phenomenon. Comprehensive literature is highlighted, emphasizing the use of biocides in various forms, including filters, resins, membranes, hydrogels, antimicrobial films, tablets, etc. Techniques such as carrier-modulated and stimuli-responsive methods, which aim to modify the biocide's inherent structural and chemical properties, are focused on enhancing selectivity and functionality for a prolonged effect with minimal leaching. The controlled-release action phenomena on reduced disinfection by-products are also highlighted, and a perspective toward reduced secondary toxicity is provided. Additionally, a strength, weakness, opportunity, and threat (SWOT) analysis is conducted to evaluate the potential of these systems for real-world applications. Such systems can pave a roadmap for long-term disinfection operations and potentially enhance the shelf-life of materials.