Biological nitrogen removal in wastewater treatment has long been described as a two-step process, in which ammonia is oxidized aerobically to nitrate and nitrate is reduced anoxically to dinitrogen gas. Over the past 2 decades, this picture has been extended by the recognition of (1) complete ammonia oxidation (comammox), (2) anaerobic ammonium oxidation (anammox), (3) heterotrophic nitrification–aerobic denitrification (HNAD), and (4) dissimilatory nitrate reduction to ammonium (DNRA). Earlier reviews have mostly treated these pathways one at a time. Three questions have received less attention: how the pathways interact within a shared community, how operating conditions shift nitrogen among them, and how the contribution of each pathway can be demonstrated in a working reactor. This review addresses all three. Organizing the pathways by nitrogen oxidation state shows that ammonium, nitrite, and nitrate are the points where they compete and exchange intermediates. Cooperative and competitive relationships are examined together with the spatial structure of flocs, biofilms, and granules. These include the nitrite handoff in partial nitritation–anammox, the dual role of DNRA, which competes with anammox for nitrite but can also return ammonium to it, and the division of denitrification steps among different organisms. Dissolved oxygen and organic carbon are then used to define a conceptual niche space for the main guilds. Its boundaries shift with pH, temperature, solids retention time, reactor configuration, and salinity, so no single threshold, such as a fixed carbon-to-nitrate ratio, reliably predicts which pathway will dominate. A guild-level summary links each group to its preferred operating conditions, main limitations, and optimization strategies. The review also sets out four levels of evidence for a pathway: metabolic potential (genes), expression (transcripts and proteins), pathway-specific flux, and contribution to reactor-scale nitrogen fate. Most molecular methods remain correlative, and attributing removal to a pathway requires isotope tracing, gaseous-product measurement, and nitrogen mass balances, ideally linked to the responsible organisms. Remaining priorities include measuring pathway-specific rates in operating reactors, explaining when an operating condition redirects nitrogen from one pathway to another, and understanding how microbial interactions withstand and recover from disturbance.
Microplastics (MPs) have emerged as ubiquitous pollutants in marine, freshwater, and terrestrial environments. Their amorphous structure, high surface area, and hydrophobicity enable the strong adsorption of environmental contaminants. At the same time, embedded additives such as phthalates, bisphenols, ultraviolet (UV) stabilizers, and polycyclic aromatic hydrocarbons (PAHs) leach into ecosystems during degradation. This review synthesizes current findings on the chemical diversity of MPs’ leachates, highlighting major sources, including tire wear, textile fibers, landfills, and wastewater treatment plants (WWTPs). Environmental drivers, such as UV radiation, temperature fluctuations, mechanical stress, salinity, and microbial colonization, accelerate additive release, while polymer-additive interactions dictate diffusion dynamics. Toxicological evidence demonstrates endocrine disruption, oxidative stress, reproductive toxicity, and ecosystem-level impacts in aquatic organisms. The persistence of these compounds in landfill leachates, wastewater sludge, and marine debris underscores their resilience and long-term ecological risk. Collectively, MPs act not only as physical pollutants but as dynamic chemical carriers, necessitating integrated risk assessment frameworks and stricter regulatory policies to mitigate their latent toxicity in the environment.
IntroductionThe presence of lead ions in water bodies represents a persistent environmental problem due to their toxicity, mobility, and bioaccumulation capacity, which demands the development of efficient and sustainable treatment alternatives. In this context, the present study aimed to evaluate the adsorption of lead ions in aqueous solutions using magnetite nanoparticles through factorial optimization of operating conditions and isotherm analysis.Methodswas developed under a quantitative experimental approach, employing a full factorial 23 design that considered solution pH, contact time, and adsorbent dosage as independent variables. The experiments were conducted in batch systems, and the obtained data were analyzed using descriptive and inferential statistics, including analysis of variance and regression models, supported by the SPSS and Orange software. Likewise, Langmuir and Freundlich isotherms were fitted to describe the adsorption equilibrium.Resultsshowed that magnetite dosage is the factor with the greatest influence on removal efficiency, followed by pH and contact time, achieving high adsorption percentages under moderately alkaline conditions, short contact times, and higher amounts of adsorbent. The satisfactory fit to both isotherm models indicated the coexistence of monolayer mechanisms and surface heterogeneity.Conclusionmagnetite nanoparticles exhibit outstanding adsorptive performance for Pb(II) removal in aqueous solutions, demonstrating high efficiencies under controlled operational conditions. The results confirm that the process is strongly dependent on adsorbent dosage and system pH, while contact time contributes to the stabilization of adsorption equilibrium.
Water is essential for human physiological and socio-economic activities; however, increasing dependence on hand-dug wells (HDWs) for domestic water supply in the Oghara-Sub-Saharan Ecozone raises concerns regarding water integrity, ecological quality, and potential human health risks. This study assessed the physicochemical characteristics, heavy metal contamination, pollution status, and associated health risks of groundwater from HDWs in Oghara, Ethiope West Local Government Area, Delta State, Nigeria. Groundwater samples were collected from nine HDWs used for domestic purposes over 3 months using standard procedures. Water quality variables analysed included pH, dissolved oxygen, biochemical oxygen demand (BOD5), total dissolved solids, total suspended solids, phosphate, nitrate, chloride, sulphate, zinc, iron, manganese, lead, bicarbonate, and sodium. Heavy metal contamination and groundwater quality were evaluated using the Water Quality Index (WQI), Modified Water Quality Index (MWQI), Pollution Index of Groundwater (PIG), Nemerow Integrated Pollution Index (NIPI), Quantification of Contamination (QoC), Contamination Degree (CD), and Contamination Factor (CF). Human health risks associated with heavy metal exposure were also assessed. All physicochemical parameters differed significantly among sampling stations (P < 0.05). WQI values were high at Stations 1 and 4–9, exceeding recommended standards. The PIG identified Station 1 as being strongly influenced by Zn, Fe, and Pb contamination, whereas elevated NIPI values at Stations 4, 5, 6, and 9 were mainly associated with Mn. Contamination levels fluctuated considerably among stations, with CF indicating high contamination at Stations 2–9 and low contamination at Station 1. QoC results suggested that heavy metals originated from both geogenic and anthropogenic sources. Non-carcinogenic risk estimates were below acceptable thresholds, indicating no significant non-carcinogenic health risk. However, the carcinogenic risk associated with Pb suggested potential health concerns from prolonged consumption. Overall, groundwater quality varied substantially across the study area. Improved control of anthropogenic activities, particularly indiscriminate agricultural chemical use, and further microbiological investigations are recommended to safeguard public health.
Membranes are widely applied in water and wastewater treatment in the removal of a wide range of organic, inorganic, and biological pollutants. Despite their application, polyethersulfone (PES)‐based membranes are limited due to their hydrophobic nature; the inherent hydrophobicity restricts water transport, promotes membrane fouling, and reduces the effective removal of hydrophilic organic contaminants. This study systematically investigated the impact of hydrophilic additives (polyethylene glycol, glycerol and starch) on the structural properties, permeability, contaminant rejection, and antifouling and antimicrobial behavior of polyethersulfone (PES)‐based membranes. The additives produced distinct changes in membrane morphology, hydrophilicity, permeability, contaminant rejection, and fouling behaviour. Starch modification provided the highest rejection of ciprofloxacin (CIP), rhodamine B (RhB), and natural organic matter (NOM) (21.5%, 22.9%, and 67%, respectively), whereas glycerol provided the best antifouling performance (flux recovery ratio, FRR = 62.2%). PEG produced a highly porous membrane (94.95%) with a small estimated mean pore radius (2.2 nm), while the PEG/glycerol membrane exhibited the highest water permeability (1238 LMH). The ternary PEG/glycerol/starch formulation did not simultaneously improve membrane performance. Real water experiments further showed that NOM fouling affected contaminant rejection differently, with RhB rejection increasing whereas CIP rejection generally decreased after fouling. This study demonstrates that hydrophilic additive modification of PES membranes is an effective strategy for tuning membrane structure and performance, but the choice of additive and the decision to combine additives must be strategically aligned with the target application.
