Constructed wetlands (CWs) are well-proven ecologically engineered systems that remove nutrients, pathogens, and other contaminants from wastewater. The inherent role of CWs as wastewater polishing systems makes them hotspots for microplastic accumulation. To investigate the transport and characteristics of microplastic pollution in full-scale surface flow municipal CWs, environmental microplastic samples were collected from the Se7en/Seven Wetlands in Lakeland (Florida), one of the largest wastewater CWs in the United States (650 hectares). Both water and sediment samples were collected at eight control stations in each of the seven wetland cells and at six locations in the influent distribution channel to investigate the linkage between water and sediments in microplastic fate and transport. This study found that the Se7en Wetlands has a near complete retention of microplastics greater than 300 μm. Concentrations at each sampling site in the CW ranged from 0 to 17 particles/m3 in water and 0–1217 particles/kg dry weight in sediment. The highest concentrations of particles were found in sediment samples, especially those found in locations of reduced flow, signaling settling occurring as water velocities decrease. Microplastics were also analyzed for size, shape indicators, and polymer type to inform how their properties change as they travel through the system. Particles were extracted visually and analyzed using ImageJ and Raman spectroscopy. Polyethylene and polypropylene were the most abundant polymer types with the highest proportion of particles being fragments between 1 and 5 mm in size. Shape indicators (particle area, circularity, and solidity) in water decreased through the treatment stream, whereas sediment samples saw no clear trend. Overall, this study finds that large CWs retain a vast amount of microplastics. It sheds light on how the dynamics of natural processes affect the fate and transport of microplastics as well as the importance of evaluating multimedia concentrations in CWs.

Antibiotic contamination has become a serious problem. As a category of catalysts, single-atom catalysts (SACs) exhibit efficient capabilities in antibiotic degradation. SACs can serve as catalysts to improve the efficiency of antibiotic degradation, thus reducing the efficacy of antibiotics. Among various SACs, nickel (Ni)- and copper (Cu)-based SACs present their unique advantages. The Ni-based SAC is characterized by good catalytic activity, high mechanical strength, and favorable thermal conductivity; the Cu-based SAC features a stable structure, high efficiency, environmental friendliness, and excellent thermal stability. These SACs (Ni/Cu-based SACs) and their complexes can fulfill functions in antibiotic degradation through the integration of their advantages. However, it is prone to generating more toxic intermediate products during the degradation of antibiotics, which may result in secondary pollution, thus blocking their industrial application. Therefore, developing new catalytic materials and modifying degradation pathways become important concerns. This article further predicts the application trend of SACs in the field of antibiotics and analyzes the problems in the degradation of antibiotics by SACs. These findings are expected to provide reference for the further degradation of antibiotics.

Propineb is a widely used protective fungicide in farmland. To investigate the effects of propineb on cadmium (Cd) accumulation and the physiological characteristics of wheat seedlings under Cd stress, we performed a hydroponic experiment with artificially added Cd. The results indicated that the application of propineb leads to a decrease in Cd accumulation in the shoots of wheat. During the low-Cd treatment experiment, propineb caused Cd to transfer from the soluble component to the cell wall. In terms of the chemical morphological distribution of Cd in wheat seedlings, propineb reduced the proportions of ethanol extracted state and deionized water extracted state, whereas the proportions of acetic acid extracted state and hydrochloric acid extracted state increased. The photosynthetic rate of wheat seedlings significantly increased, but there was no significant effect on the chlorophyll content. Foliar application of propineb increased the O2− clearance rate and hydrogen peroxide content in the wheat. However, the catalase content decreased. This study indicates that the application of propineb could decrease Cd accumulation in wheat seedlings and partially improve the physiological functions of plants. This study provides useful information for studying the effects of pesticides on Cd accumulation in crops and the physiological characteristics of Cd stress.

A calcium phosphate solid formed as an unintended consequence of a novel high-pH orthophosphate lead corrosion control strategy in Providence, RI, resulting in some consumer complaints and clogged plumbing. Investigations were carried out at pH levels of 8.9-10.4, at temperatures of 5-60°C, and with orthophosphate concentrations ranging from 0 to 4.0 μg/L as orthophosphate (PO4) to examine this phenomenon. During field testing, the calcium phosphate initially precipitated at orthophosphate doses above about 2 mg/L as PO4, and the extent of precipitation increased with water age and higher temperature. Laboratory-scale tests confirmed that doses above about 2 mg/L as PO4 were required to form the precipitate in the absence of preexisting calcium phosphate solids and that the solid formed quickly at 60°C (upper range for hot water heaters) and tended to dissolve at lower pH. Solubility studies and solids characterization indicate that the particles are a mixture of noncrystalline compounds containing calcium and phosphate. For water systems currently practicing a high pH/low alkalinity corrosion control strategy, orthophosphate dosing can enhance plumbosolvency control without the risk of pH reduction, but formation of this solid can place an upper limit on the maximum orthophosphate residual level in the distribution system.

The long-term maintenance of low concentration of dissolved oxygen (DO) is an important condition for the enrichment of anammox bacteria (AnAOB) in the electrochemical anammox system (EAS). In this study, a new method to control DO by the combination of sodium sulfite with nitrogen stripping was attempted, and the influence of sodium sulfite concentration on the nitrogen removal performance was studied. The results show that under the optimal conditions (i.e., sodium sulfite concentration = 200 mg/L, nitrogen stripping time = 40–60 min, nitrogen flow = 350 mL/min), the DO in the water was controlled below 0.3 mg/L, which saves more than half of the time required for removing DO compared with the nitrogen stripping method (120–140 min). However, the total nitrogen removal rate (NRR) at the optimal current density of 0.10 mA/cm2 decreased gradually, and the NRR was 0.0091, 0.0061, 0.0026, and 0.0006 g N/[L∙d] at the sodium sulfite concentration of 0, 200, 400, and 600 mg/L, respectively. Simultaneously the specific anammox activity decreased from 0.0077 g N/[g VSS∙d] to 0.0032 g N/[g VSS∙d]. It is concluded that when the current density was 0.10 mA/cm2 and the concentration of sodium sulfite was 200 mg/L, the optimal operating conditions were both anammox activity and deoxidation. Therefore, the combination of sodium sulfite with nitrogen stripping has great application potential to control DO in the EAS.

To alleviate the pollution problem of dye wastewater and the problem of resource utilization of red mud, a novel biochar-loaded red mud catalyst (RMbc) was synthesized using red mud and pomelo peel biochar by a low-cost coprecipitation method. Due to the high specific surface area and abundant oxygen-containing functional groups of RMbc, the synthesis process promoted the conversion of Fe2O3 to Fe3O4 and Fe0, which achieved higher catalytic activity. Moreover, the RMbc system showed better removal effects than raw red mud for methyl orange (MO) removal. Of the MO, 92.50% was removed within 60 min, and scanning electron microscope, X-ray powder diffractometer, fourier transform infrared spectrum, and X-ray photoelectron spectroscopy were applied to characterize the catalyst. The mechanism studies demonstrated that sodium persulfate was mainly activated by Fe0 and Fe(II) to produce reactive oxygen species O2•− and 1O2. The intermediate products of MO were identified, and a probable degradation pathway was proposed. Finally, the performance of RMbc for mixed dyes and coexisting pollutants was evaluated. The RMbc was low-cost and high catalytic activities, both showing good application prospects in experimental studies and further applications.

The biotransformation of atenolol, sotalol, and metoprolol by mixed culture denitrifying communities was examined as a function of carbon availability and pharmaceutical concentration to explore the possible roles of cometabolism and direct substrate utilization. Sotalol and metoprolol were not found to be transformed. A matrix of conditions explored the biotransformation of water resource recovery facility relevant (25 μg/L) and chemical oxygen demand (COD)-equivalent (10–100 mg/L) atenolol concentrations in batch reactors (1 L) containing 25 mg-N/L nitrate. Carbon (MicroC® 2000) conditions included Nonlimiting (COD:N ratio >10), Partially Limiting (COD:N ratio = 2–3), and Limiting (COD:N ratio <1). Reactors without atenolol served as denitrification control experiments. Results suggest that atenolol did not appreciably influence nitrate reduction. The extent of atenolol degradation was independent of carbon availability. In the experiments conducted in the μg/L range, 30–40% biotransformation was observed. Scant degradation at higher concentrations suggested that direct utilization of the pharmaceutical was either unlikely or occurring slowly and independent of the pharmaceutical concentration. Process-based modeling using the Activated Sludge Model framework assessed denitrification across carbon availability conditions and incorporated three individual pharmaceutical biotransformation modeling strategies: (1) direct metabolism model; (2) cometabolic model, and (3) biotransformation kinetic model. Results suggest that there was insufficient evidence to suspect direct metabolism meaningfully contributed to the reduction in atenolol concentration. The cometabolic process-based model, including both growth and nongrowth-linked rate coefficients offered the best model performance, although growth-linked cometabolism was limited and not readily apparent across all experiments (growth-linked transformation coefficient <0.4 g-atenolol·g-COD−1). Thus, the biotransformation kinetic model is favored for monitoring and forecasting biotransformation in larger-scale systems because use of the parsimonious model (rate coefficient of 7 mg-atenolol·g-COD−1·d−1) resulted in only modest performance reductions. The biotransformation model represents an improvement over pseudo first-order models as it is a mixed-order kinetic model that is linked to transient biomass conditions.

Permeable reactive barriers (PRBs) are being considered for treatment where the discharge of nitrate plumes contributes to eutrophication (e.g., Cape Cod, MA). PRBs enhance denitrification through the addition of carbon-based amendments such as the injection of emulsified vegetable oil (EVO). The use of EVO to stimulate denitrification foregrounds aspects of carbon utilization, dosing, longevity, and secondary effects in ways that differ from the application of EVO at hazardous waste sites. The overall objective of this study was to develop and evaluate a process-based modeling approach for simulating denitrification stimulated and supported by EVO. A series of one-dimensional column experiments assessed emulsion retention, production of soluble substrate, and utilization of carbon for nitrate reduction. Retention of 5.5 g dispersed phase emulsion resulted in sustained reduction of nitrate (∼43 mg/day) at ∼2 m/day porewater velocity. Biokinetic processes underlying the model are based on the two-step denitrification description of the Activated Sludge Model (ASM) No. 3. Biokinetic processes were integrated within the flow and transport simulator COMSOL to simulate the column experiment. The model capitalizes on the biokinetic parameters available in the ASM literature to limit the number of site-specific fits of model parameters. Simulation results demonstrate how this approach can result in reasonable predictions, although model performance was enhanced by fitting two parameters—yield coefficients for nitrate and nitrite. Comparisons with existing biokinetic transport models that were similarly fit to the column data suggest that the better overall descriptions of the column data using the process-based model stem from a more robust handling of spatial and temporal distribution of biomass. Sensitivity analyses highlight the importance of accurately describing the transformation of complex carbon into soluble substrate, and the subsequent utilization of that substrate. This research establishes a foundation for exploring implications of carbon processing on dosing, longevity, and effectiveness in denitrifying PRBs.