Efficiency of the bank filtration technique for diclofenac removal: A review

Fate of persistent and mobile chemicals in the water cycle: From municipal wastewater discharges to river bank filtrate

Persistent and mobile (PM) chemicals are considered detrimental for drinking water resources as they may pass through all barriers protecting these resources against pollution. However, knowledge on the occurrence of PM chemicals in the water cycle, that make their way into drinking water resources, is still limited. The effluents of six municipal wastewater treatment plants (WWTPs, n = 38), surface water of two rivers (n = 32) and bank filtrate of one site (n = 15) were analyzed for 127 suspected PM chemicals. In the rivers, median concentrations of 92 detected analytes ranged from 0.3 ng/L to 2.6 µg/L (tetrafluoroborate, BF4). Lower than average dilution from WWTP effluent to surface water of 43 PM chemicals suggests significant discharge from other sources. Many of these compounds were industrial chemicals, including cyanoguanidine, trifluoromethanesulfonic acid and BF4. River bank filtration (RBF) reduced the total concentration of 40 quantified compounds by 60 % from 19.5 µg/L in surface water to 8.4 µg/L in bank filtrate, on average. Of these, 20 compounds showed good removal (> 80 %), 14 intermediate (80 - 20 %) and 6 no removal (≤ 20 %), among them carbamazepine, hexafluorophosphate, and 2-pyrrolidone. 13 substances occurred at concentrations ≥ 0.1 µg/L in bank filtrate; for six of them toxicological data were insufficient for a health-based risk assessment. The regulatory definition of P and M chemicals, if used together with existing data on environmental half-lives (P) and Koc (M), showed little power to discriminate between chemicals well removed in RBF and those that were hardly removed. This comprehensive field study shows that RBF is a useful but incomplete barrier to retain PM chemicals from surface water. Thus, PM chemicals are, indeed, a challenge for a sustainable water supply.

Managed aquifer recharge as a potential pathway of contaminants of emerging concern into groundwater systems - A systematic review

Groundwater is an often-overlooked resource, while its declining quantity and quality is of global concern. To protect and ensure stable quantity and quality of groundwater systems used as drinking water supplies, a common method is to artificially recharge these groundwater supplies with surface water, a process called managed aquifer recharge (MAR), that has been used globally for decades. However, surface waters used for MAR often contain elevated concentrations of anthropogenic chemicals of emerging concern (CECs), such as plastics, pesticides, pharmaceuticals and personal care products (PPCPs), or per- and polyfluoroalkyl substances (PFAS). When infiltrating this surface water, MAR can thus act as a shortcut for CECs into groundwater systems and eventually drinking water supplies. Especially PFAS are an example of very persistent contaminants showing atypical transport patterns during MAR and thus posing a risk for ground- and drinking water contamination. This systematic review addresses the transport process of CECs through MAR systems by looking at (1) common CEC concentrations in surface waters, (2) factors affecting CEC transport and possible retention during MAR, such as sorption and other physio-chemical mechanisms of CECs, biological and chemical decomposition, or hydrogeological properties of the MAR system, and (3) key contaminants leaching through the MAR systems as well as possible treatment options to improve the retention of CECs during MAR. Since we are facing increasing needs for high quality drinking water, lower CEC drinking water guidelines as well as an increasing number of identified CECs in surface waters, we conclude with a series of recommendations and future research directions to address these issues. Those include the need for regular monitoring programs specifically addressing CECs and especially not yet regulated, (very) persistent and (very) mobile contaminants, such as PFAS, as well as redesigned MAR systems to ensure stable ground- and drinking water quantity and quality.

Efficiency of the bank filtration for removing organic priority substances and contaminants of emerging concern: A critical review

With growing concerns regarding the ecological and human risks of organic micropollutants (OMPs) in water, much effort has been devoted worldwide to establishing quality standards and compiling candidate and watch lists. Although bank filtration is recognized as an efficient natural water treatment in the removal of contaminants such as OMPs, the increase in exploitation requires continuous assessment of removal efficiency. This review aims to provide a critical overview of bank filtration (BF) reports on more than a hundred priority substances (PSs) and compounds of emerging concern (CECs) listed in the relevant European Union regulations. Field- and lab-scale studies analyzing the removal efficiency and its variance of individual OMPs and biological indicators using BF and the main influencing factors and their interactions, shortcomings, and future challenges are discussed in this review. The removal efficiency of EU-relevant contaminants by BF has been comprehensively investigated for only a few pollutants listed in the environmental EU regulations: pharmaceutically active compounds, (e.g., the anti-inflammatory drug diclofenac, some antibiotics (e.g., sulfamethoxazole and trimethoprim)), a few pesticides (e.g., atrazine), and faecal indicators such as Escherichia coli. In many cases, the measured concentrations of PSs and CECs have not been published numerically, which hinders comprehensive statistical analysis. Although BF is one of the most cost-effective and efficient water treatments, present field and lab studies have demonstrated the diversity of site-specific factors affecting its efficiency. Even in the case of substances known to be removed by BF, the efficiency rates can vary with environmental and anthropogenic factors (e.g., hydrogeological parameters and the contamination level of infiltrating water) and abstraction well parameters (e.g., the depth, distance, and pumping volume). The published removal rate variations and influencing factors often reflect the research design (field or lab-scale), which can lead to ambiguities.

Fates of potentially persistent and mobile organic substances in embedded outdoor columns for artificial groundwater recharge simulation

Persistent and mobile organic micropollutants (OMP) are ubiquitously found in the aquatic environment and have a high propensity to distribute in water resources and are difficult to remediate. Managed aquifer recharge systems such as artificial groundwater recharge, produce high-quality drinking water by removing numerous OMP from the source water. In this study, the fates of selected emerging and potentially persistent and mobile OMP were investigated in outdoor columns for artificial groundwater recharge simulation. Breakthrough curves of OMP were modeled to differentiate between sorption and bio-transformation. The study showed that selected OMP were persistent in the surface water and no photo-degradation was observed, except for diclofenac. The trends of dissolved organic carbon concentrations and UV light absorption at 254 nm wavelength suggest elevated biological activity in the first 0.3 m of the columns. The study revealed that the bio-transformation of cyanoguanidine, valsartan acid and diclofenac correlated with the biological activity in the sand columns. Benzyltrimethylammonium, n-(3-(dimethylamino)-propyl)methacrylamide, 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine and melamine were completely eliminated within the first 0.3 m, likely due to sorption. Less mobile compounds such as carbamazepine and adamantan-1-amine also showed sorption. Sorption was also observed for diclofenac, likely due to decreased pH along the column depth. Retardation factors of several OMP were higher in the first 0.3 m of the columns, likely due to higher organic carbon contents compared to the remaining depth. Six organic substances (for example 2-acrylamido-2-methylpropane sulfonate and dimethylbenzene sulfonate) were persistent and mobile throughout the experiment. Overall, this study reveals the vital role of pH and sand organic carbon for sorption and residence time and biological activity for OMP elimination.

Green Synthesis of Hydrogel-Based Adsorbent Material for the Effective Removal of Diclofenac Sodium from Wastewater

The removal of pharmaceutical contaminants from wastewater has gained considerable attention in recent years, particularly in the advancements of hydrogel-based adsorbents as a green solution for their ease of use, ease of modification, biodegradability, non-toxicity, environmental friendliness, and cost-effectiveness. This study focuses on the design of an efficient adsorbent hydrogel based on 1% chitosan, 40% polyethylene glycol 4000 (PEG4000), and 4% xanthan gum (referred to as CPX) for the removal of diclofenac sodium (DCF) from water. The interaction between positively charged chitosan and negatively charged xanthan gum and PEG4000 leads to strengthening of the hydrogel structure. The obtained CPX hydrogel, prepared by a green, simple, easy, low-cost, and ecological method, has a higher viscosity due to the three-dimensional polymer network and mechanical stability. The physical, chemical, rheological, and pharmacotechnical parameters of the synthesized hydrogel were determined. Swelling analysis demonstrated that the new synthetized hydrogel is not pH-dependent. The obtained adsorbent hydrogel reached the adsorption capacity (172.41 mg/g) at the highest adsorbent amount (200 mg) after 350 min. In addition, the adsorption kinetics were calculated using a pseudo first-order model and Langmuir and Freundlich isotherm parameters. The results demonstrate that CPX hydrogel can be used as an efficient option to remove DCF as a pharmaceutical contaminant from wastewater.

Effective adsorption of diclofenac sodium from aqueous solution using cationic surfactant modified Cuminum cyminum agri-waste: kinetic, equilibrium, and thermodynamic studies

The occurrence of pharmaceutical pollutants in aqueous media has increased where significant research is being conducted to eliminate these toxic compounds. In the present study, Tetradecyltrimethylammonium bromide (TTAB) modified Cuminum cyminum agri-waste (CCW) was prepared to investigate the removal of diclofenac sodium (DCF) from aqueous solution in the batch process for the first time. Physical and chemical characterizations of as-prepared adsorbent were conducted using field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, N₂ adsorption-desorption, and point of zero charge analysis. Besides, the effect of the main parameters that affect the adsorption process, i.e., adsorbent dosage (0.25-6 g/L), contact time (0-300 min), initial DCF concentration (10-500 mg/L), and pH of the solution, were investigated. Furthermore, the resulted data were analyzed using various kinetic and isotherm models. The Pseudo-second-order model with R² = 0.9981 showed the highest agreement with kinetic behavior. Also, the maximum adsorption capacity of DCF is 93.65 mg/g, according to the Langmuir isotherm. In acidic media, the adsorption capacity reached the highest value (44.69 mg/g). As a result, this study revealed that the agri-waste material could be modified and, as a low-cost adsorbent, have promising adsorption potential to remove pharmaceutical contaminants from the aqueous solution.