Acesulfame as a suitable sewer tracer on groundwater pollution: A case study before and after the 2016 Mw 7.0 Kumamoto earthquakes

Acesulfame allows the tracing of multiple sources of wastewater and riverbank filtration

Aquifers providing drinking water are increasingly threatened by emerging contaminants due to wastewater inputs from multiple sources. These inputs have to be identified, differentiated, and characterized to allow an accurate risk assessment and thus ensure the safety of drinking water through appropriate management. We hypothesize, that in climates with seasonal temperature variations, the sweetener acesulfame potassium (ACE) provides new pathways to study wastewater inputs to aquifers. Specifically, this study investigates the temperature-driven seasonal oscillation of ACE to assess multiple sources of wastewater inputs at a riverbank filtration site. ACE concentrations in the river water varied from 0.2 to 1 μg L^-1 in the cold season (T < 10 °C) to 0-0.1 μg L^-1 in the warm season (T > 10 °C), due to temperature-dependent biodegradation during wastewater treatment. This oscillating signal could be traced throughout the aquifer over distances up to 3250 m from two different infiltration sources. A transient numerical model of groundwater flow and ACE transport was calibrated over hydraulic heads and ACE concentrations, allowing the accurate calculation of mixing ratios, travel times, and flow-path directions for each of the two infiltration sources. The calculated travel time from the distant infiltration source was of 67 days, while that from the near source was of 20 days. The difference in travel times leads to different potential degradation of contaminants flowing into the aquifer from the river, thus demonstrating the importance of individually assessing the locations of riverbank infiltration. The calibrated ACE transport model allowed calculating transient mixing ratios, which confirmed the impact of river stage and groundwater levels on the mixing ratio of the original groundwater and the bank filtrate. Therefore, continuous monitoring of ACE concentrations can help to optimize the management of the water works with the aim to avoid collection of water with very short travel times, which has important regulative aspects. Our findings demonstrate the suitability of ACE as a transient tracer for identifying multiple sources of wastewater, including riverbank filtration sites affected by wastewater treatment plant effluents. ACE seasonal oscillation tracking thus provides a new tool to be used in climates with pronounced seasonal temperature variations to assess the origins of contamination in aquifers, with time and cost advantages over multi-tracer approaches.

Seasonal biodegradation of the artificial sweetener acesulfame enhances its use as a transient wastewater tracer

The persistence of the artificial sweetener acesulfame potassium (ACE) during wastewater treatment and subsequently in the aquatic environment has made it a widely used tracer of wastewater inputs to both surface water and groundwater. However, the recently observed biodegradation of ACE during wastewater treatment has questioned the validity of this application. In this study, we assessed the use of ACE not only as a marker of wastewater, but also as a transient wastewater tracer that allows both the calculation of mixing ratios and travel times through the aquifer as well as the calibration of transient groundwater flow and mass transport models. Our analysis was based on data obtained in a nearly 8-year river water and groundwater sampling campaign along a confirmed wastewater-receiving riverbank filtration site located close to a drinking water supply system. We provide evidence that temperature controls ACE concentration and thus its seasonal oscillation. River water data showed that ACE loads decreased from 1.5-4 mg·s^-1 in the cold season (December to June; T<10 °C) to 0-0.5 mg·s^-1 in the warm season (July to November; T>10 °C). This seasonal variability of >600% was detectable in the aquifer and preserved >3 km, with ACE concentrations oscillating between <LOQ in the warm season up to 1 μg·L^-1 in the cold season. The large seasonal variation in ACE concentrations during wastewater treatment, compared to the other sweeteners (sucralose, cyclamate, and saccharin) and chloride enables its use as a transient tracer of wastewater inflows and riverbank filtration. In addition, the arrival time of the ACE concentration peak can be used to estimate groundwater flow velocity and mixing ratios, thereby demonstrating its potential in the calibration of groundwater numerical models.

Self-organizing map improves understanding on the hydrochemical processes in aquifer systems

The holistic understanding of hydrochemical features is a crucial task for management and protection of water resources. However, it is challenging for a complex region, where multiple factors can cause hydrochemical changes in studied catchment. We collected 208 groundwater samples from such region in Kumamoto, southern Japan to explicitly characterize these processes by applying machine learning technique. The analyzed groundwater chemistry data like major cations and anions were fed to the self-organizing map (SOM) and the results were compared with classical classification approaches like Stiff diagram, standalone cluster analysis and score plots of principal component analysis (PCA). The SOM with integrated application of clustering divided the data into 11 clusters in this complex region. We confirmed that the results provide much greater details for the associated hydrochemical and contamination processes than the traditional approaches, which show quite good correspondence with the recent high resolution hydrological simulation model and aspects from geochemical modeling. However, the careful application of the SOM is necessary for obtaining accurate results. This study tested different normalization approaches for selecting the best SOM map and found that the topographic error (TE) was more important over the quantization error (QE). For instance, the lower QE obtained from min-max and log normalizations showed problems after clustering the SOM map, since the QE did not confirm the topological preservation. In contrast, the lowest TE obtained from Z-transformation data showed better spatial matching of the clusters with relevant hydrochemical characteristics. The results from this study clearly demonstrated that the SOM is a helpful approach for explicit understanding of the hydrochemical processes on reginal scale that may capably facilitate better groundwater resource management.

Enabling Sustainable Chemistry with Ionic Liquids and Deep Eutectic Solvents: A Fad or the Future?

Ionic liquids (ILs) and deep eutectic solvents (DESs) debuted with a promise of a superior sustainability footprint due to their low vapor pressure. However, their toxicity and high cost compromise this footprint, impeding their real-world applications. Fortunately, their property tunability through a rational selection of precursors, including bioderived ones, provides a strategy to ameliorate toxicity, lower cost, and endow new functions. This Review discusses whether ILs and DESs are sustainable solvents and how they contribute to sustainable chemical processes.

Persulfate-based strategy for promoted acesulfame removal during sludge anaerobic fermentation: Combined chemical and biological effects

The acesulfame (ACE) degradation in waste activated sludge (WAS) via direct anaerobic fermentation is difficult and the efficient elimination techniques are imperative for the ultimate safe WAS disposal. Persulfate (PS)-based approach was developed to promote the ACE removal during WAS anaerobic fermentation. Results demonstrated the effectiveness of PS-based treatments on ACE degradation, and the ACE removal efficiency was respectively 48.2% and 96.2% in the PS and PS/Fe-treated reactors while it was only 6.0% in the control reactor. Mechanism explorations revealed that the active free radicals (i.e. OH• and SO₄^•-) generated in the PS-based reactors were the key oxidative species for the ACE degradation. However, such effects were interfered by the released soluble substrates (i.e. protein, carbohydrate and inorganic ions) during anaerobic fermentation by competing and/or quenching free radicals, which caused the deceleration of the ACE removal efficiency. Moreover, the PS-based treatment facilitated the enrichment of functional microorganisms (i.e. Phyllobacteriaceae and Bradyrhizobiaceae) and upregulated the critical genes (i.e. pncB and nadE) involved in the ACE degradation. Based on the density functional theory (DFT) and metabolic intermediates analysis, the hydroxylation and oxidative ring-opening were the two main proposed metabolic pathways for ACE degradation. Overall, the combined chemical and biological metabolism effects collectively contributed to the efficient ACE degradation, and it provided a novel and effective strategy for refractory pollutants removal during WAS anaerobic fermentation.

Aquifer heterogeneity controls to quality monitoring network performance for the protection of groundwater production wells

A groundwater monitoring network surrounding a pumping well (such as a public water supply) allows for early contaminant detection and mitigation where possible contaminant source locations are often unknown. This numerical study investigates how the contaminant detection probability of a hypothetical sentinel-well monitoring network consisting of one to four monitoring wells is affected by aquifer spatial heterogeneity and dispersion characteristics, where the contaminant source location is randomized. This is achieved through a stochastic framework using a Monte Carlo approach. A single production well is considered that results in converging non-uniform flow close to the well. Optimal network arrangements are obtained by maximizing a weighted risk function that considers true and false positive detection rates, sampling frequency, early detection, and contaminant travel time uncertainty. Aquifer dispersivity is found to be the dominant parameter for the quantification of network performance. For the range of parameters considered, a single monitoring well screening the full aquifer thickness is expected to correctly and timely identify at least 12% of all incidents resulting in contaminants reaching the production well. This proportion increases to a global maximum of 96% for a network consisting of four wells and very dispersive transport conditions. Irrespective of network size and sampling frequency, more dispersive transport conditions result in higher detection rates. Increasing aquifer heterogeneity and decreasing aquifer spatial continuity also lead to higher detection rates, though these effects are diminished for networks of 3 or more wells. Statistical anisotropy has no effect on the network performance. Earlier detection, which is critical for remedial action and supply safety, comes with a significant cost in terms of detection rate, and should be carefully considered when a monitoring network is being designed.

Occurrence, source apportionment and potential risks of selected PPCPs in groundwater used as a source of drinking water from key urban-rural settings of Pakistan

BACKGROUND

Pharmaceuticals and personal care products (PPCPs) are emerging contaminants that have been extensively used in present time to improve the living standards. Their persistence in water resources due to various anthropogenic sources such as wastewater treatment plants, pharmaceutical industries, and runoff from agricultural and livestock farms has not only threaten aquatic life but their occurrence in groundwater has also raised concerns related to humans' wellbeing.

METHODS

Considering this as a neglected area of research in Pakistan, a systematic monitoring study was designed to investigate their occurrence, sources, and potential environmental and human health risks in groundwater from urban-rural areas of six cities. Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS) was used to analyze the collected samples preceded by solid-phase extraction.

RESULTS

Overall, 8 out of 11 selected PPCPs were detected in groundwater samples with detection frequency ranging from 5.5-65%. Their concentrations ranged from below limit of detection (<LOD) to 1961 ng/L. The overall mean concentrations of detected PPCPs were found below 100 ng/L. The highest mean concentration was reported for Ibuprofen (154 ng/L) in Rawalpindi/Islamabad. Results of PCA-MLR revealed that domestic wastewater discharge (76.4%) was the dominant source contributing to PPCPs contamination in groundwater. Followed by mixed source (pharmaceutical & hospital waste) 17.8%, and rural discharge/animal husbandry 5.8%. No appreciable risk to human health upon exposure to detected PPCPs via drinking water was anticipated. However, environmental risk assessment indicated moderate risk posed to P. subcapitata (RQ = 0.98) and D. magna (RQ = 0.2) by ibuprofen.

CONCLUSION

The current study reports the first evidence of PPCPs occurrence in groundwater in Pakistan. Reporting their occurrence in groundwater is a fundamental initial step to inform public-health decisions concerning sewage systems and drinking water quality. Hence, comprehensive monitoring programs are required to further investigate contamination of emerging contaminants in groundwater and their associated risks.

Anthropogenic activities and seasonal properties jointly drive the assemblage of bacterial communities in subtropical river basins

Anthropogenic activities have inevitably impacted riverine ecosystems, yet their overall contribution to the assemblage of bacterial communities at a large river basin scale remains unclear. In this study, 16S amplicon sequencing was implemented to investigate the bacterial ecosystems in paired water and sediment of North River and West River basins in South China., which contains various anthropogenic environments (e.g., rural/urban area, mining area and livestock area). Subsequently, the links between bacterial community and various types of emerging pollutants in river water were analyzed. The results show that the bacterial assemblage of water and sediment had their own properties that the bacterial community of sediment were mainly affected by seasonal properties, while the bacterial community of water were affected by both seasons and anthropogenic activities. Therein, the aquatic bacterial compositions and abundances were driven by changes in temperature, dissolved oxygen and the emerging pollutants. The dominant phyla Proteobacteria and Firmicutes exhibited adaptability to the mining-affected regions, therein many clades (e.g., Beijerinckiaceae, Acetobacteraceae and Mycobacteriaceae) were also prevalent in the livestock-affected and densely-populated regions. In addition, these two phyla presented associations to the antibiotic resistance in water. The levels of antibiotics, relative antibiotic resistance gens (ARGs) and non-antibiotic pharmaceuticals (NAPs) were closely related to bacterial community composition, diversity and functional diversity, indicating their drive in shifting bacterial communities. Collectively, this work provides a basis for understanding the contribution of anthropogenic activities in shifting bacterial community at a large river basin scale. Further, the results provide new insights for expansion of ecological assessment.

Estimation of Groundwater Recharge in Kumamoto Area, Japan in 2016 by Mapping Land Cover Using GIS Data and SPOT 6/7 Satellite Images

Agricultural fields, grasslands, and forests are very important areas for groundwater recharge. However, these types of land cover in the Kumamoto area, Japan, were damaged by the Kumamoto earthquake and heavy rains in 2016. In this region, where groundwater provides almost 100% of the domestic water supply for a population of about 1 million, quantitative evaluation of changes in groundwater recharge due to land cover changes induced by natural disasters is important for the sustainable use of groundwater in the future. The objective of this study was to create a land cover map and estimate the groundwater recharge in 2016. Geographic information system (GIS) data and SPOT 6/7 satellite images were used to classify the Kumamoto area into nine categories. The maximum likelihood classifier of supervised classification was applied in ENVI 5.6. Eventually, the map was cleaned up with a 21 × 21 kernel filter, which is larger than the common size of 3 × 3. The created land cover map showed good performance of the larger filter size and sufficient validity, with overall accuracy of 91.7% and a kappa coefficient of 0.88. The estimated total groundwater recharge amount reached 757.56 million m3. However, if areas of paddy field, grassland, and forest had not been reduced due to the natural disasters, it is estimated that the total groundwater recharge amount would have been 759.86 million m3, meaning a decrease of 2.30 million m3 in total. The decrease of 2.13 million m3 in the paddy fields is temporary, because the paddy fields and irrigation channels have been improved and the recharge amount will recover. On the other hand, since the topsoil on the landslide scars will not recover easily in natural conditions, it is expected to take at least 100 years for the groundwater recharge to return to its original state. The recharge amount was estimated to decrease by 0.17 million m3 due to landslides. This amount is quite small compared to the total recharge amount. However, since the reduced recharge amount accounts for the annual water consumption for 1362 people, and 12.1% of the recharge decrease of 1.41 million m3 each year to fiscal year 2024 is expected by municipalities, we conclude that efforts should be made to compensate for the reduced amount due to the disasters.

Evaluating sewer exfiltration in groundwater by pharmaceutical tracers after the 2016 Kumamoto earthquakes, Japan

In April 2016, a series of earthquakes (M 7.3 on the Japan Meteorological Agency scale) occurred in Kumamoto, Japan causing serious damage to underground sewerage networks. In this study, we evaluated sewer exfiltration in groundwater in the Kumamoto area after the earthquakes by using multiple tracers. We used 14 pharmaceuticals, including carbamazepine and crotamiton, and anthropogenic Gd as tracers, and we measured concentrations of these tracers from September 2016 to November 2017 seasonally. The detection frequency of caffeine, carbamazepine, crotamiton, ibuprofen, and anthropogenic Gd ranged from 29% to 45%, and the concentrations of the pharmaceuticals in the groundwater were lower than those in previous studies. The median of all pharmaceutical concentrations did not decrease, whereas the median of the sum of crotamiton and carbamazepine concentrations, which are quantitative sewage markers, decreased with time. The sewer exfiltration rates in September 2016 estimated using carbamazepine, crotamiton, and anthropogenic Gd were 0.59 ± 0.27%, 0.66 ± 0.47%, and 0.11 ± 0.18% of sewage dry weather flow, respectively, indicating that the effect of the earthquakes on sewer exfiltration was small, probably because the damaged sewers were quickly repaired. This study demonstrated that a multiple-tracer approach is useful for evaluating sewer exfiltration after major earthquakes.