Groundwater Pollution Research Articles

Long-term spatiotemporal changes in nitrate contamination of municipal groundwater resources after sewerage network construction in the Hungarian Great Plain.

Over the last decades, as a consequence of wastewater discharges and other anthropogenic sources, severe nitrate (NO3-) pollution has developed in municipal environment causing global concern. Thus, eliminating the potential sources of pollution is one of the major challenges of the twenty-first century, whereby sanitation services are essential for ensuring public health and environmental protection. In the present study, long-term monitoring (2011-2022) of shallow groundwater NO3- contamination in municipal environment was carried following the construction of the sewerage network (2014) in the light of the pre-sewerage situation. Our primary aim was to assess the long-term effects of sewerage on nitrate NO3- levels in the shallow groundwater and evaluate the efficiency of these sanitation measures over time. Based on the results, significant pollution of the shallow groundwater in the municipality was identified. During the pre-sewer period, NO3- concentrations exceeded the 50mg/L limit in the majority of monitoring wells significantly, upper quartile values ranged between 341 and 623mg/L respectively. Using Nitrate Pollution Index (NPI) and interpolated NO3- pollution maps, marked spatial north-south differences were detected. In order to verify the presence of wastewater discharges in the monitoring wells, the isotopic ratio shifts (δ) for 18O and D(2H) were determined, confirming municipal wastewater effluent. Variations in NO3-/Cl- molar ratios suggest also contamination from anthropogenic sources, including septic tank effluent from households and the extensive use of manure. Data series of 7years (2015-2022) after the investment indicate marked positive changes by the appearance of decreasing trends in NO3- values confirmed by Wilcoxon signed rank test and ANOVA. By comparing the pre- and post-sewerage conditions, the mean NO3- value decreased from 289.7 to 175.6mg/L, with an increasing number of monitoring wells with concentrations below the limit. Our results emphasise the critical role of sanitation investments, while also indicating that the decontamination processes occur at a notably slow pace. Detailed, long-term monitoring is therefore essential to ensure accurate follow-up of the ongoing changes. The results can provide information for local citizens and authorities to improve groundwater management tools in the region.

Co-tracing of groundwater emerging and conventional contaminants in karst area of Southwest China: Distribution, source, and source-specific health risks

Groundwater pollution, especially the co-contamination of emerging contaminants (ECs) and conventional contaminants, is increasingly recognized as a critical global concern. Karst aquifers are found throughout the world, providing critical water sources and sustaining rivers and ecosystems, and are particularly vulnerable to pollution. In this study, the characteristics of the contamination, potential sources, and source-specific health risks related to ECs and trace elements (TEs) in groundwater were investigated in Guiyang (a typical karst city in southwest China). The distribution of TEs followed a descending pattern from urban to suburban to rural areas. Interestingly, the median concentrations (217 ng/L) of Caffeine (CAF) in rural areas surpassed those in urban areas (145 ng/L) and even exceeded these in densely populated areas. Additionally, ECs and TEs in groundwater are significantly influenced by population density and land use types within a 1000-meter buffer zone around the sampling sites. Hierarchical cluster analysis and positive matrix factorization suggested that five principal sources of contamination were identified: domestic wastewater (29.7 %), industrial production (25.2 %), agricultural activities (16.3 %), natural and industrial sources (14.9 %), and pharmaceuticals (13.9 %). Monte Carlo simulations revealed that the non-carcinogenic risks to children in urban areas are significant, with 30.0 % of these risks exceeding the safety threshold. Source-specific health risk assessments indicated that industrial production is the primary source of risk. Furthermore, this study introduces a co-tracing method to trace the sources of groundwater contamination in karst systems. The co-tracing method based on the ECs and TEs allows for a deeper understanding of contaminant transfer and its fate in karst groundwater.

Evaluation of Effects of Cotton Growing on the Environment and the Population in the Koutiala Circle

Since 1960, cotton cultivation has experienced considerable expansion in the Koutiala district of Mali. This expansion has not been without consequences on people’s health and natural resources in terms of soil, water and natural vegetation. Based on the analysis of satellite images and a socio-economic survey of production unit chiefs, this study highlights the degradation of soils, biological diversity, population health, and pollution of groundwater and surface water. To reduce these effects, the adoption of good agroecological practices, the organic cotton farming, the reduction of the use of chemicals, and the sustainable management of water and soil are becoming a necessity to ensure sustainable management of environmental resources and the preservation of the livelihoods of local producers.

Assessing Groundwater Vulnerability to Pollution in a Rapidly Urbanizing River Basin Using a Modified DRASTIC Land Use–Lineament Density Method

ABSTRACTGroundwater quality assessment is crucial for ensuring safe drinking water, protecting public health, and maintaining sustainable water resources for agricultural and industrial uses. The Awash River basin faces significant groundwater quality challenges due to rapid population growth, high urbanization, large‐scale irrigation, and industrial pollution. The main objective of this study is to evaluate the intrinsic vulnerability of aquifers to pollution in the Awash Basin and identify hotspots requiring urgent intervention using a modified DRASTIC overlay analysis method. In addition to the seven parameters considered in the generic DRASTIC overlay analysis (depth to the water table, recharge, aquifer media, slope, soil media, vadose zone, and hydraulic conductivity), we incorporated land use/land‐cover (LULC) and lineament density (LD) distributions (DRASTIC‐LU‐LD). This modification allowed us to produce more realistic groundwater vulnerability maps for the basin. To identify the most influential parameters in the overlay, sensitivity analysis was conducted using Map Removal Sensitivity Analysis (MRSA) and Single Parameter Sensitivity Analysis (SPSA). Initially, the generic DRASTIC index in the area ranges from 69 to 181, categorizing the area into four vulnerability zones: very low (21%), low (51%), medium (27%), and high (1%). After incorporating LU and LD, the index values ranged from 90 to 240. Based on the percentage of the total area studied, the inclusion of LU decreased the very low and low vulnerability zones from 72% to 44% and the inclusion of LD increased the high‐ and very‐high‐vulnerability zones from 14% to 27%. The areas most vulnerable to groundwater pollution are in the western (upper Awash), middle Awash, and northwestern regions, particularly in city centers where groundwater abstraction is significant. These high‐vulnerability zones coincide with municipal, industrial, and agricultural pollution sources. The vadose zone parameter has the highest impact in both MRSA and SPSA, with a variation index value of 3.08% and a mean effective weight of 27.93%, respectively. By identifying areas vulnerable to groundwater pollution, this study provides a valuable basis for informed decision‐making and the development of effective strategies for protecting groundwater from urban, industrial, and agricultural pollution sources.

Evaluation of human and ecological health risks associated with the potentially toxic heavy metals in groundwater of Vellore city, Tamil Nadu, India

Groundwater pollution by heavy metals is a significant and alarming threat globally, through its chronic effect on human health and ecosystem. The current study evaluated the identification and risk assessment of heavy metals in groundwater of the Vellore city, Tamilnadu, India. Groundwater samples were collected from 32 locations over a continuous period of 2022–2023 for every three months on seasonal basis. The samples were analysed for pH, Total Dissolved Solids (TDS), Hardness and heavy metals (Al, As, Ba, Cd, Cu, Pb, Al and Zn). The analysed mean concentrations of these heavy metals were found in the order: As > Cd > Pb > Ba >Zn >Al> Cu. Elevated concentrations of heavy metals were observed in 2022, likely influenced by rainfall and land use patterns. Heavy metals such as Al, As, Pb, and Cd exceeded the BIS limits and whereas Ba, Cu, and Zn concentrations remain within desirable limits. Groundwater Quality Index (GWQI) classified 41% as 'unfit for drinking'. Ecological risk indices (ERI) indicate significant contamination in 34% of samples, with Al and Pb being primary contributors. Non-carcinogenic health risk assessments reveal, chronic hazards, where children facing higher risks followed by men and women groups. Carcinogenic risk assessments indices such as Heavy metal pollution Index (HPI) shown 25% of samples in critical quality, Heavy metal Evaluation Index (HEI) evaluated all samples were in low contamination and Contamination Index (CI) shown 72% samples under high contamination posing high risk to humans. Probable Cancer Risk (PCR) values for As, Pb, and Cd exceed acceptable ranges across all demographic groups posing cancer risk to humans particularly children. The present study highlights the need for groundwater treatment and regulatory interventions to mitigate health and ecological risks due to the contamination of heavy metals in Vellore city.

Groundwater quality assessment for drinking and irrigation purposes in arid to semiarid region of Indus Basin of South Punjab, Pakistan

<p><a name="_Hlk173243332"><span style="background-color:white;color:black;font-family:"Times New Roman",serif;font-size:12.0pt;line-height:150%;">As the groundwater pollution is increasing, it is crucial to assess groundwater quality and characterize hydrogeochemistry accurately for long term water supply. </span></a><span style="background-color:white;color:black;font-family:"Times New Roman",serif;font-size:12.0pt;line-height:150%;">In this study groundwater samples were collected from 120 locations from Bahawalpur district and analyzed for electrical conductivity (EC), pH, total dissolved solids (TDS), sodium (Na<sup>+</sup>), potassium (K<sup>+</sup>), calcium (Ca<sup>2+</sup>), magnesium (Mg<sup>2+</sup>), carbonate (CO<sub>3</sub><sup>-</sup>), bicarbonate (HCO<sub>3</sub><sup>-</sup>), sulfate (SO<sub>4</sub><sup>2-</sup>), chloride (Cl<sup>-</sup>), nitrate (NO<sub>3</sub><sup>-</sup>), fluoride (F<sup>-</sup>) and heavy metals. The results obtained from the analysis of samples showed that the SAR of nearly 65% of samples collected from Bahawalpur district were in acceptable limit (<6 meq L<sup>-1</sup>), while 12% found to be unfit for irrigation (>10 meq L<sup>-1</sup>). Similarly, the RSC values depicted that 8% samples were unfit while 64% samples were falling in the category of fit irrigation water. Most of the water samples were predominantly Ca<sup>2+</sup>-HCO<sub>3</sub><sup>-</sup> and Na<sup>+</sup>-HCO<sub>3</sub><sup>-</sup> type, that were controlled by various processes of cation exchange, water-rock interaction, dissolution and evaporation. Some samples fall in the middle of diamond and lower triangles of Piper diagram are showing no dominant type of water (mixed water type) due to the complex influence of rock-water interactions as well as anthropogenic activities. The Water Quality Index (WQI) showed that out of total 120 sampling sites in Bahawalpur the number of excellent water samples were only 2% while 18% water samples were characterized as hazardous. Moreover, the number of samples falling in the categories of good, poor and very poor quality water were 36%, 29% and 13% respectively.</span></p>

Nitrate source analysis of underground drinking water sources in Zhangjiakou main urban area and its health risk assessment

<p style="line-height:200%;text-align:justify;text-justify:inter-ideograph;"><span lang="EN-US">In order to investigate the main pollution factors of underground drinking water sources in semi-arid agricultural areas in China, and to reveal the threatening influence of pollutants on the normal water security of local society. Single-factor evaluation index, principal component analysis, basic data statistics are used to clarify the main pollution indicators of underground drinking water sources in Zhangjiakou main city and discuss the main influencing factors of the change of their pollution concentration, and evaluate the degree of health threat of its pollution to the drinking water of local residents. The results show that: the water sources of Taobeiying and Gushi are deeply affected by human activities, and nitrate, as the only exceeding substance under drinking water standards, is the most important indicator of groundwater pollution; and the nitrate con-centration of groundwater is higher in the pasture and nearby agricultural activities; nitrate contamination levels in groundwater are within the health acceptability range for the vast majority of the population, with only newborns in the Taobeiying drinking water source being exposed to a non-carcinogenic risk of nitrate. The results of the study will help to maintain a stable groundwater environment.</span></p>

Differences in Nitrogen Sources and Contributions in Shallow Groundwater in Plateau Lake Area with Different Climate Types

Clarifying the concentration, major sources, and contribution differences of nitrogen in shallow groundwater in plateau lake areas with different climate types can provide a novel direction for the control of nitrate （NO3-） pollution in regional groundwater. Taking the shallow groundwater around Erhai Lake in the subtropical monsoon climate zone and Chenghai Lake in the dry-hot valley area of the Jinsha River as the research objects, using hydrochemical indexes and multi-isotope techniques （δ15N-NO3-, δ18O-NO3-, δ18O-H2O, and δ2H-H2O） combined with the stable isotope （SIAR） model； the differences in nitrogen concentration in shallow groundwater around Erhai Lake and Chenghai Lake were analyzed, the sources of NO3- were identified, and the contribution rates of each pollution source were calculated. The results showed that water quality of more than 33% and 5% of shallow groundwater sampling points around Erhai Lake and Chenghai Lake was worse than the groundwater Class Ⅲ quality requirements （GB/T 14848） of 20 mg·L-1 for nitrate nitrogen （NO3--N）, respectively. The δ18O-H2O and δ2H-H2O in shallow groundwater around Erhai Lake and Chenghai Lake were parallel to the global and Chinese atmospheric precipitation lines, and a large intercept was present, indicating that atmospheric precipitation was not the major recharge source of groundwater in the two regions. The contribution rate of different NO3- sources in shallow groundwater around Erhai Lake was the highest for soil organic nitrogen （53.77%）, followed by nitrogen fertilizer （21.75%） and manure and sewage （21.55%）, and atmospheric deposition nitrogen （2.93%） was the lowest. Denitrification occurred in the transformation process of nitrogen in groundwater. The contribution rate of different NO3- sources in shallow groundwater around Chenghai Lake was manure and sewage （44.88%） > soil organic nitrogen （37.03%） > nitrogen fertilizer （16.17%） > atmospheric deposition nitrogen （1.92%）, and nitrification occurred in the transformation process of nitrogen in groundwater. The climate type significantly affected the shallow groundwater level, altering the migration and transformation process of nitrogen, thereby affecting the nitrogen concentration in groundwater and the contribution of NO3- as the chief source. However, the major source of NO3- was not affected by the climate type； however was more affected by land use, agricultural activities, and manure treatment methods.

Effect of nitrogen fertilizer on growth, yield and quality parameters of three sugarcane (<em>Saccharum Officinarum</em> L.) varieties

This study examines the effects of nitrogen on the growth, yield and quality of three sugarcane varieties under irrigated conditions in the low country dry zone of Sri Lanka. Three sugarcane varieties (SL96-128, SL04-624 and SL8306) were tested at four nitrogen fertilizer levels (0, 100, 200, 300 kg/ha) in a split plot design with four replicates. Selected growth, yield and quality parameters were studied in this field experiment. The results of the study demonstrated that application of 100kg/ha or 300kg/ha N fertilizer has shown highest girth of stem (cm), partitioning biomass to millable stalk (PBMS), brix and pol percentage in all three varieties, SL04-624, SL8306 and SL96-128. In addition, variety SL04-624 have shown highest total above ground biomass production (dry matter) (41987.8kg/ha), partitioning biomass to millable stalk (PBMS) (74.5%), brix (19.4%), pol (17.1%) and pure obtainable cane sugar (POCS) (12.3%). Therefore 100k/ha (N2) could be concluded as the best rate of N fertilizer application for the varieties tested in this study considering the cost of production, environmental and groundwater pollution. SL04-624 could be recommended as the most suitable variety for low country wet zone of Sri Lanka responding to 100kg/ha N fertilizer.

Electrocatalytic Nitrate Reduction for Brackish Groundwater Treatment: From Engineering Aspects to Implementation

In recent years, nitrate has emerged as a significant groundwater pollutant due to its potential ecotoxicity. In particular, nitrate contamination of brackish groundwater poses a serious threat to both ecosystems and human health and remains difficult to treat. A promising, sustainable, and environmentally friendly solution when biological treatments are not applicable is the conversion of nitrate to harmless nitrogen (N2) or ammonia (NH3) as a nutrient by electrocatalytic nitrate reduction (eNO3R) using solar photovoltaic energy. This review provides a comprehensive overview of the current advances in eNO3R for the production of nitrogen and ammonia. The discussion begins with fundamental concepts, including a detailed examination of the mechanisms and pathways involved, supported by Density Functional Theory (DFT) to elucidate specific aspects of ammonium and nitrogen formation during the process. Furthermore, the integration of artificial intelligence (AI) and machine learning (ML) offers promising advancements in enhancing the predictive power of DFT, accelerating the discovery and optimization of novel catalysts. In this review, we also explore various electrode preparation methods and emphasize the importance of in situ characterization techniques to investigate surface phenomena during the reaction process. The review highlights numerous examples of copper-based catalysts and analyses their feasibility and effectiveness in ammonia production. It also explores strategies for the conversion of nitrate to N2, focusing on nanoscale zerovalent iron as a selective material and the subsequent oxidation of the produced ammonia. Finally, this review addresses the implementation of the eNO3R process for the treatment of brackish groundwater, discussing various challenges and providing reasonable opinions on how to overcome these obstacles. By synthesizing current research and practical examples, this review highlights the potential of eNO3R as a viable solution to mitigate nitrate pollution and improve water quality.

Assessing drinking water quality in Eloued, south-East Algeria, using the groundwater pollution index (GPI) and the synthetic pollution index (SPI) model.

Groundwater quality degradation is a significant environmental issue worldwide, with potentially severe economic consequences and harm to ecosystems and biodiversity. This can directly affect human health, particularly in developing countries where rapid and uncontrolled urbanization is on the rise. Groundwater is the primary resource for meeting the water needs of the Eloued region, located in southeastern Algeria. Water is considered unfit for human consumption if its physico-chemical elements exceed national or international standards or guidelines. We used the GPI and SPI indices to evaluate the quality of groundwater suited for drinking. Groundwater samples were obtained from 22 wells at depths of more than 250m. Standard analytical procedures were used to determine the physicochemical characteristics of the collected samples, which included pH, EC, TDS, Na+, Ca+2, Mg+2, K+, Cl-, HCO3-, SO4-2, NO3-, NO2-, NH4+ and PO4-3. Multivariate statistical analysis and GIS techniques were used to process the results. The results of the selected physicochemical parameters were compared with World Health Organization (WHO) guidelines to determine the quality of drinking water. The findings indicate that the waters of the terminal complex aquifer are salty and contain medium to high quantities of main ions that surpass the established drinking water limits. The primary ions' relative abundance is Cl- > SO4-2 > HCO3- > NO3 for anions and Na+ > Ca+2 > Mg+2 > K+ for cations. Groundwater chemical types were dominated by Na+, Ca+2, Cl-, and SO4-2. Principal Component Analysis (PCA) showed that alteration and dissolution of carbonates, evaporates, salts, partly silicates, and evaporation, are the main reasons affecting the chemical composition of water in Eloued. The GPI results show that 18.18%, 54.54%, and 27.27% of the water samples were classed as lightly polluted, moderately polluted, or substantially polluted for drinking purposes, respectively. According to the SPI study, 9.09%, 36.36%, 36.36%, and 18.18% were considered drinkable, mildly contaminated, moderately polluted, and seriously polluted for drinking purposes, respectively. According to the GPI and SPI models' geographical distribution maps, potable water is generally scarce and concentrated in the northeastern section of the research area, near the town of Ourmes.

Groundwater geochemistry using modified integrated water quality index (IWQI) and health indices with special emphasis on nitrates and heavy metals in southern parts of Tirupati, South India.

Groundwater is particularly vulnerable to pollution in places with a high population density and extensive human usage of the land, especially in southern parts of Tirupati, India. To assess this, 60 bore-well samples were obtained and assessed for physical specifications, ion chemistry, and heavy metals during the pre- and post-monsoon seasons 2022. The current investigation employed a modified integrated water quality index (IWQI), conventional graphical and human health risk assessment (HHRA) of nitrates and heavy metals to know the groundwater chemistry and its detrimental health effects on humans. The major ions were analyzed using American public health association (APHA)standards, whereas heavy metals were analyzed using inductively coupled plasma optical emission spectrometry(ICP-OES). Additionally, pH Redox Equilibrium and C (PHREEQC),a geochemical model written in C programming language was employed to determine the saturation indices of mineral facies and ArcGIS 10.3.1 was used for spatial distribution patterns of IWQI. Then, the HHRA of nitrates and heavy metals was performed using United States environmental protection agency (USEPA)guidelines. The noteworthy outcomes include elevated levels of Ca2+, Mg2+, Cl-, NO3-, Cu,Fe, Mn, and Pb, demonstrating rock-water interaction, silicate weathering, Ca-Mg-HCO3 followed by mixed water facies, dissolution/precipitation, reverse exchange, and anthropogenic contamination are the major controlling processes in groundwater of southern Tirupati, India. The modified IWQI reveals that most groundwater samples (38%) fall under the bad quality class, with (47%) in the poor quality class and only (15%) classified as medium qualityclass in pre- and post-monsoon seasons. Elevated IWQI were observed in all directions except in the east, which is suitable for drinking. Moreover, the major hazard quotient (HQ) and hazard index (HI)for nitrates (NO3-) and heavy metals like copper(Cu), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn) are above the critical value of 1, revealing potential risk to humans, especially infants, followed by children and adults, entailing the instantaneous implementation of proper remedial measures and stringent policies to reduce the risk associated with groundwater pollution in the southern parts of Tirupati.

Groundwater contamination forecast using numerical modeling (on example of Qibray site of Chirchiq watershed)

The article presents a forecast of groundwater pollution on the example of the Kibray site of the Chirchik field. Models were developed to predict the entry of pollution into groundwater and to identify flow and transport processes. With the help of these models, the relationship between the quality of groundwater and surface water was established and it was revealed that the formation of operational reserves of the Chirchik field occurs due to artificial resources and attracted resources (surface water from the Chirchik riverbed).

Spatial variability, source identification, and partitioning of groundwater constituents in a typical lakeside plain on Yungui Plateau

The fragile ecological balance of lakeside plains on plateau makes groundwater hydrochemical composition highly susceptible to human disturbances. This research investigates a typical plain on Yunnan Plateau to quantitatively identify the potential sources of groundwater pollution in lakeside plains on plateau by combining receptor models with risk assessment models. Receptor models show there are three potential pollution sources for groundwater including water-rock interactions, agricultural pollution, and domestic sewage/manure discharge. Groundwater hydrochemical composition is predominantly shaped by natural water-rock interactions, accounting for an average of 50.12 % of the influence. This is followed by agricultural non-point source pollution, which contributes 10.79 %, and the discharge of domestic sewage and manure, which accounts for 10.61 %. Groundwater in the current plain could pose a minor non-carcinogenic risk for long-term drinking, with the total hazard index (THI) for adults varying between 0.015 and 1.089, and for children between 0.024 and 1.737. Notably, 4.35 % of groundwater samples have a THI exceeding the safe threshold of 1. NO3- (72 %) is the primary contributor to non-carcinogenic risks, accounting for 72 %, trailed by Mn (13 %), NH4+ (9 %), Fe (6 %) and NO2- (1 %). The non-carcinogenic risks are predominantly attributed to agricultural non-point source pollution (71.6 %) and the discharge of domestic sewage and manure (26.9 %). A conceptual model has been developed to encapsulate the dynamics of groundwater quality formation in lakeside plains on plateau. This research will aid residents in safeguarding against groundwater contamination and enhancing agricultural practices in present plain and similar lakeside plain worldwide.

Electrocatalytic arsenic removal: Unveiling selective capturing and conversion with a redox-active silica-lignosulfonate hybrid framework

Addressing the global challenge of arsenic groundwater pollution to ensure a safe water supply is crucial. Thus, we developed a versatile ferrocene (Fc) incorporated silica-lignosulphonate nano framework (Fc–Si–LS). This framework was precisely designed to target and transform the toxic arsenite (As+3) into a controllable form of arsenic (As+5). Results revealed that the unique Fc–Si–LS framework had significantly targeted As+3 and showed an impressive selective conversion (84 %) performance even at high concentrations (1 mM). Additionally, in real water application (As = 150 μg/L), the As+3 conversion rate remained effective (∼81.6 %). Remarkably, the synergy between Fc and Si–LS resulted in an exceptional adsorption capacity (106 mg/g) at 1.2 V, attaining a low energy consumption of only 0.072 kWh/m3. DFT simulations established a phenomenon that simultaneous selective capturing and conversion of arsenic requires a redox moiety integration on the catalyst surface to accept electrons from the selectively trapped As+3 to the electrode. Hence, this study highlighted the potential of precisely persuading Si–LS based redox-active nano frameworks in evolving energy effective solutions for arsenic removal from drinking water, thereby offering significant implications for sustainable water treatment technologies.

Unraveling the synergistic interplay of sulfur and wheat straw in heterotrophic-autotrophic denitrification for sustainable groundwater nitrate remediation

Nitrate pollution in groundwater is a global environmental issue that poses significant threats to human health and ecological security. This study focuses on elucidating the mechanisms of heterotrophic-autotrophic cooperative denitrification (HAD) by employing wheat straw and elemental sulfur as electron donors in varying proportions. The research initially underscores that heterotrophic denitrification (HD) accelerates the denitrification process due to its high-energy metabolism. However, as readily degradable organic matter diminished, reliance on more complex substrates such as lignocellulose posed a challenge to HD. This marks a pivotal transition towards autotrophic denitrification (AD), which, despite a slower initial rate, exhibits a more sustained denitrification performance. A low proportion of heterotrophic denitrification layer (e.g., 3:1) at the bottom facilitating efficient and sustainable denitrification. HD is capable of simultaneous removal of nitrates and nitrites, whereas AD demonstrates a higher affinity for nitrates, with nitrite accumulation reaching 100% at high influent nitrate concentrations (100 mg/L). HD not only provides the necessary alkaline environment for AD but also reduces sulfate production, whereas AD utilizes the residual organic carbon and ammonia produced by HD. The heterotrophic layer is characterized by a diverse community, whereas the autotrophic layer is predominantly composed of Thiobacillus. By delineating the interactive mechanisms and characteristics of HAD, this study highlights the importance of balancing heterotrophic and autotrophic activities for the effective remediation of groundwater nitrates.

Study on the carbon sequestration performance and barrier mechanism of biochar cement-based vertical cutoff walls for phenol pollution in groundwater

Study on the carbon sequestration performance and barrier mechanism of biochar cement-based vertical cutoff walls for phenol pollution in groundwater

Ecologically friendly remediation of groundwater sulfamethoxazole contamination: Biologically synergistic degradation by thermally modified activated carbon-activated peracetic acid in porous media

This study examines the efficacy and environmental impact of peracetic acid (PAA) activated by thermally modified activated carbon (AC600) for degrading antibiotics in actual groundwater. Laboratory-scale experiments evaluated the system's effects on contaminant degradation, ecological balance, and substance cycling in the hyporheic zone. Our findings demonstrated the effectiveness of the AC600/PAA system in removing sulfamethoxazole (SMX) from groundwater porous media. Additionally, the AC600/PAA system synergistically interacted with the in-situ microbiota of the hyporheic zone, producing more fragmented degradation products without increasing mixed toxicity. Bacterial abundance increased post-reaction, with notable alterations in the bacterial community and enhanced bacterial metabolism. Key genera such as Lysobacter thrived in the treated environment, playing critical roles in microbiota modification and SMX degradation. The pH remained stable before and after the reaction, while dissolved organic carbon content increased. Overall, our results highlight the promising potential of PAA activation by carbonaceous materials as a low-impact, ecologically friendly technology for in-situ remediation of organic pollutants in groundwater, characterized by high compatibility and biosynthesis.

How Pharmaceutical Residues Occur, Behave, and Affect the Soil Environment.

Many pharmaceuticals (PhMs), compounds for the treatment or prevention of diseases in humans and animals, have been identified as pollutants of emerging concern (PECs) due to their wide environmental distribution and potential adverse impact on nontarget organisms and populations. They are often found at significant levels in soils due to the continuous release of effluent and sludge from wastewater treatment plants (WWTPs), the release of which occurs much faster than the removal of PhMs. Although they are generally present at low environmental concentrations, conventional wastewater treatment cannot successfully remove PhMs from influent streams or biosolids. In addition, the soil application of animal manure can result in the pollution of soil, surface water, and groundwater with PhMs through surface runoff and leaching. In arid and semiarid regions, irrigation with reclaimed wastewater and the soil application of biosolids are usual agricultural practices, resulting in the distribution of a wide number of PhMs in agricultural soils. The ability to accurately study the fate of PhMs in soils is critical for careful risk evaluation associated with wastewater reuse or biosolid return to the environment. The behavior and fate of PhMs in soils are determined by a number of processes, including adsorption/desorption (accumulation) to soil colloids, biotic (biodegradation) and abiotic (chemical and photochemical degradation) degradation, and transfer (movement) through the soil profile. The sorption/desorption of PhMs in soils is the main determinant of the amount of organic chemicals taken up by plant roots. The magnitude of this process depends on several factors, such as crop type, the physicochemical properties of the compound, environmental properties, and soil-plant characteristics. PhMs are assumed to be readily bioavailable in soil solutions for uptake by plants, and such solutions act as carriers to transport PhMs into plants. Determining microbial responses under exposure conditions can assist in elucidating the impact of PhMs on soil microbial activity and community size. For all of the above reasons, soil remediation is critical when soil pollutants threaten the environment.

Ozone Plasma Nanobubble (OPN) Reactor Combined with Coagulation-Flocculation Process: A Promising Technology for Leachate Treatment

According to World Bank data, approximately 2.01 billion tons of urban waste is produced annually, with approximately 33% of waste being improperly managed, leading to concentrated and toxic leachate. This poses a global challenge due to its varied characteristics influenced by climate, landfill age, and waste composition, resulting in groundwater and surface water pollution with severe impacts on human health, ecosystems, and biodiversity, necessitating stringent treatment measures. To address this, a study integrated coagulation-flocculation and advanced oxidation processes (AOPs) using a dielectric barrier discharge (DBD) ozone plasma nanobubble (OPN) reactor to degrade leachate. Gas flow rate, plasma voltage, and gas sources are variated. This research uses O2 or air as a gas source that produces plasma. The leachate is fed into the DBD reactor, so the bubble will burst and produce further ROS. Optimal results were observed after 60 min, with oxygen gas feed reducing total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD) by 100, 93.93, and 74.12%, respectively, alongside a decrease in pH. This study indicates the promising potential of this technology for leachate treatment and demonstrates the potential for nitrate production using both types of gas feed.