Selection of priority emerging contaminants in surface waters of India, Pakistan, Bangladesh, and Sri Lanka

Electrochemical oxidation for the rapid degradation of emerging contaminants: Insights into electrolytes and process parameters for phytotoxicity reduction

Atrazine (ATZ), carbamazepine (CBZ), and sulfamethoxazole (SMX) are contaminants of emerging concern (CECs) commonly detected in water sources, posing a risk to health, sanitation, and the ecosystems. This study evaluates the degradation, mineralization, and phytotoxicity reduction of a solution containing these three CECs using an electrochemical advanced oxidation process (EAOP). Key operational parameters - pH, flow rate (Q), current density (j), and type and concentration of supporting electrolytes (NaCl and Na2SO4) - were systematically investigated. The results showed that pH had minimal impact on the process. Higher flow rates (250 L h-1) improved mineralization due to enhanced mass transfer to •OH on the anode surface. However, the flow rate had less effect on degradation, as the dominant degradation mechanisms involved chlorine- or sulfate-based oxidants. Current densities of 1 and 10 mA cm-2 produced the most favorable results, leading to efficient degradation and mineralization, along with satisfactory mineralization current efficiency (up to 47 %) and energy consumption values (91,76-3142,88 kW h kg-1). When NaCl was used as supporting electrolyte, the degradation of CECs was twice as fast as with Na2SO4, achieving over 88 % degradation in 5 min and 40 % mineralization within 60 min. While chlorinated and sulfate species enhance process efficiency, excessive electrolyte concentration should be avoided to prevent scaling and •OH scavenging. Phytotoxicity tests with Allium cepa revealed an unexpected reduction in toxicity in samples treated with NaCl, suggesting that Na2SO4 may be more phytotoxic under the tested conditions.

Microplastics in municipal solid waste landfill leachate and their removal in treatment units: A perspective of controlled and uncontrolled landfills

Leachate produced from municipal solid waste landfill serves as a potential pathway for microplastics (MPs) release into the environment with a high potential for soil, surface water, and groundwater contamination. These MPs not only persist for longer duration of time in the landfill but also interact with toxic chemical contaminants. These interactions arise from the hydrophobic characteristics and minuscule size of MPs, which absorb a variety of emerging toxic contaminants present in these systems thereby amplifying the risk to surrounding environment. This study was performed to investigate the abundance, characteristics, and pollution risk of MPs in leachate from two contrasting landfill systems in the cities of Chandannagar and Baidyabati, India. A total of 8 leachate samples from an uncontrolled landfill (UCL), i.e., open dump, and 24 samples from different leachate treatment units (LTUs) of a controlled landfill (CL) were evaluated. Particle sizes of 1-5 mm (41.9%) in UCL and 0.025-0.5 mm (46.2%) in CL were predominant. Seven different types of polymers were identified in untreated leachate samples from UCL having concentration 53.4 ± 6.69 p/L (mean ± standard deviation) and in CL 34.7 ± 4.73 p/L. The predominant shapes were films, fragments, and fibers in UCL, whereas fragments and fibers dominated in CL. Polyethylene and polypropylene were the most frequent types of polymers observed in both sites. In CL, collection well, aeration lagoon, and sedimentation pond were used for LTUs, in which overall 83.3% MPs removal was achieved. High removal in LTUs highlights the importance of engineered systems for leachate management. However, optimization of these units is needed for enhanced removal of particles <0.5 mm. For UCL the findings suggest urgent need for implementing basic containment and treatment systems, particularly given their higher pollution risk indices. Varying landfill designs, waste compositions, and weather conditions of specific locations restrict generalisation of the findings to other regions. Therefore, long-term monitoring studies across different geographical and climatic conditions are recommended to develop more comprehensive management strategies.

Toxicological and environmental risks of enalapril and their possible transformation products generated under phototransformation reactions

Pharmaceutical active compounds (PACs) in the concentration range of hundreds of ng/L to μg/L have been identified in urban surface water, groundwater, and agricultural land where they cause various health risks. These pollutants are classified as emerging and cannot be efficiently removed by conventional wastewater treatment processes. The use of nano-enabled photocatalysts in the removal of pharmaceuticals in aquatic systems has recently received research attention owing to their enhanced properties and effectiveness. In the current study, toxicological and environmental risks of enalapril (ENL) and their possible transformation products (TPs) generated under phototransformation processes (e.g., photolysis and photocatalysis reactions) were assessed. In photolysis reaction, removal of ENL was incomplete (< 16 %), while mineralization degree was negligible. In contrast, total removal of ENL was achieved through the photocatalytic process and its maximum mineralization ratio was 66 % by using natural radiation. Proposed transformation pathways during the phototransformation of ENL include hydroxylation and fragmentation reactions generating transformation products (TPs) such as hydroxylated TPs (m/z 393) and enalaprilat (m/z 349). Potential environmental risks for aquatic organisms were not observed in the concentrations of both ENL and enalaprilat contained in surface water. However, the acute and chronic toxicities prediction of TPs such as m/z 409, 363, and 345 showed toxic effects on aquatic organisms. Thus, more studies regarding TPs monitoring for both ENL and PhACs with the highest occurrence worldwide are necessary for the creation of a database of the concentrations contained in surface water and groundwater for the assessment of the potential environmental risk for aquatic organisms.

Biofilm formation and microbial interactions in moving bed-biofilm reactors treating wastewater containing pharmaceuticals and personal care products: A review

The risk of pharmaceuticals and personal care products (PPCPs) has been paid more attention after the outbreak of COVID-19, threatening the ecology and human health resulted from the massive use of drugs and disinfectants. Wastewater treatment plants are considered the final stop to restrict PPCPs from wide spreading into the environment, but the performance of conventional treatment is limited due to their concentrations and characteristics. Previous studies have shown the unreplaceable capability of moving bed-biofilm reactor (MBBR) as a cost-effective method with layered microbial structure for treating wastewater even with toxic compounds. The biofilm community and microbial interactions are essential for the MBBR process in completely degrading or converting types of PPCPs to secondary metabolites, which still need further investigation. This review starts with discussing the initiation of MBBR formation and its influencing parameters according to the research on MBBRs in the recent years. Then the efficiency of MBBRs and the response of biofilm after exposure to PPCPs are further addressed, followed by the bottlenecks proposed in this field. Some critical approaches are also recommended for mitigating the deficiencies of MBBRs based on the recently published publications to reduce the environmental risk of PPCPs. Finally, this review provides fundamental information on PPCPs removal by MBBRs with the main focus on microbial interactions, promoting the MBBRs to practical application in the real world of wastewater treatment.

Priority list of pharmaceutical active compounds in aquatic environments of Mexico considering their occurrence, environmental and human health risks

Pharmaceutical active compounds (PhACs) are detected pollutants in aquatic environments worldwide at concentrations ranging from ng L-1 to µg L-1. Currently, PhAC monitoring is poorly realized in Mexico. This study proposes a priority list of PhACs in Mexican aquatic environments, considering their occurrence and environmental and human health risks. Ecological risks were assessed as Risk Quotients (RQ) values using the PhAC concentrations detected in surface water, obtaining high risks (RQ > 1) against aquatic organisms, especially of naproxen, ibuprofen, diclofenac, acetaminophen, 17β-estradiol, carbamazepine, ketoprofen, caffeine. In contrast, potential human health risks (RQH) were assessed on the Mexican population using the concentrations quantified in groundwater, demonstrating potential risks (RQH > 0.2) on the population, particularly of DCF and CBZ. Thus, a priority list of PhACs can be used as a reference for environmental monitoring in Mexican water supplies as well as PhACs monitoring in countries of the Caribbean region and Central America.

Are we underestimating stormwater? Stormwater as a significant source of microplastics in surface waters

Stormwater represent a critical pathway for transporting microplastics (MPs) to surface waters. Due to complex dynamics of MPs in stormwater, its dispersion, weathering, risk, and transport are poorly understood. This review bridges those gaps by summarizing the latest findings on sources, abundance, characteristics, and dynamics involved in stormwater MP pollution. Weathering starts before or after MPs enter stormwater and is more pronounced on land due to continuous heat and mechanical stress. Land use patterns, rainfall intensity, MPs size and density, and drainage characteristics influence the transport of MPs in stormwater. Tire and road wear particles (TRWPs), littering, and road dust are major sources of MPs in stormwater. The concentrations of MPs varies from 0.38-197,000 particles/L globally. Further MP concentrations showed regional variations, highlighting the importance of local monitoring efforts needed to understand local pollution sources. We observed unique signatures associated with the shape and color of MPs. Fibers and fragments were widely reported, with transparent and black being the predominant colors. We conclude that the contribution of stormwater to MP pollution in surface waters is significantly greater than wastewater treatment plant effluents and demands immediate attention. Field and lab scale studies are needed to understand its behavior in stormwater and the risk posed to the downstream water bodies.