Comparative study on electro-regeneration of antibiotic-laden activated carbons in reverse osmosis concentrate.

Electro-regeneration is emerging as a new technique to regenerate spent carbon adsorbents through an electrochemical process. In this study, sequential adsorption and electro-regeneration of ciprofloxacin (CIP)-laden carbon were investigated using both pristine and iron (Fe)-doped F400 activated carbon in distilled, deionized (DI) water and reverse osmosis (RO) concentrate water. The impact of reactor flow rate and sequential adsorption/electro-regeneration cycles on the regeneration efficiency were also evaluated. The results indicate that the breakthrough points for both adsorbents in DI water, where 100 % of the CIP molecules were adsorbed, occurred at around 7,800 bed volumes (BVs). Conversely, electro-regeneration for both adsorbents, where 94 % of the CIP molecules were desorbed, took place at 380 BVs. The main distinction between the two activated carbons lies in the initial range of BVs (<400 BVs).Fe doping on F400 appears to enhance its surface selectivity for CIP uptake, which can easily diffuse into the meso/macropore regions of Fe-doped F400. In contrast, pristine F400, being highly microporous, necessitated more contact time to fill its high-energy sites, resulting in a higher affinity for CIP adsorption. Over the four sequential adsorption/electro-regeneration cycles in DI water, a similar regeneration efficiency was observed at 190 BVs. As the flow rate increased from 2 to 6 mL/min, the CIP uptake on pristine F400 decreased in DI water, calculating 138, 74 and 57 mg/g for flow rates of 2, 4, and 6 mL/min, respectively. When the RO concentrate water was compared with DI water, the pristine F400 quickly reached saturation due to pore blockage caused by organic matter in RO concentrate. During electro-regeneration, up to 100 % of adsorbed CIP molecules were desorbed at around 120 BVs in RO concentrate, which is 3X faster than DI water. The effectiveness of this technology can be enhanced by implementing continuous flow systems, thereby improving the overall efficiency of CIP removal in RO concentrate.

Enhancing the selective ciprofloxacin adsorption in urine matrices through the metal-doping of carbon sorbents.

Pharmaceuticals excreted after administration can pollute water sources given their ineffective removal in conventional wastewater treatment plant. Among the techniques used during tertiary wastewater treatment, adsorption is an effective and cost-efficient method for removing antibiotics. This study aimed to investigate the adsorption of ciprofloxacin (CIP) on metal-doped granular activated carbon (GAC) and evaluate the impact of urine on CIP adsorption for pristine, pre-oxidized, and metal-doped GAC. The results showed that the uptake of CIP by iron (Fe)-doped GAC was higher than Ag-doped, pre-oxidized, and pristine GAC in single-solute isotherms (DI water). This higher uptake was attributed to the presence of Fe content (1.2%) on the carbon surface, which can strongly interact with zwitterionic CIP at a neutral pH. However, when synthetic human urine was introduced, the adsorption of CIP was negatively affected due to pore blockage and competition for available sorption sites on the GAC. Among the four types of GACs tested, the lowest reduction in CIP uptake in the urine solution was observed for Fe-doped GAC followed (%17) by pre-oxidized (64%), Ag-doped (%69), and pristine F400 (76%) carbon. These results suggested that the complexation between CIP and Fe-doped GAC in urine was stronger due to its higher functionalization compared to Ag-doped, pre-oxidized, and pristine GAC. As the equilibrium concentration of CIP increased, the competition between CIP and urine decreased on the surface of Fe-doped carbon, owing to the limited competition from urine for the available active sorption sites.

Opportunities for in situ electro-regeneration of organic contaminant-laden carbonaceous adsorbents.

Adsorptive separation technologies have proven to be effective on organic contaminant removal in aqueous water. However, the breakthrough of contaminants is inevitable and can be at relatively low bed volumes, which makes the regeneration of spent adsorbents an urgent need. Electrochemically induced regeneration processes are given special attention and may provide ease of operation through in situ regeneration avoiding (i) removal and transport adsorbents, and (ii) avoiding use of hazardous chemicals (i.e., organic solvents, acids, or bases). Therefore, this review article critically evaluates the fundamental aspects of in situ electro-regeneration for spent carbons, and later discusses specific examples related to the treatment of emerging contaminants (such as per- and polyfluoroalkyl substances or PFAS). The fundamental concepts of electrochemically driven processes are comprehensively defined and addressed in terms of (i) adsorbent characteristics, (ii) contaminant properties, (iii) adsorption/regeneration driving operational parameters and conditions, and (iv) the competitive effects of water matrices. Additionally, future research needs and challenges to enhance understanding of in situ electro-regeneration applications for organic contaminants (specifically PFAS)-laden adsorbents are identified and outlined as a future key perspective.

Emerging investigator series: microplastic sources, fate, toxicity, detection, and interactions with micropollutants in aquatic ecosystems - a review of reviews.

Hundreds of review studies have been published focusing on microplastics (MPs) and their environmental impacts. With the microbiota colonization of MPs being firmly established, MPs became an important carrier for contaminants to step inside the food web all the way up to humans. Thus, the continuous feed of MPs into the ecosystem has sparked a multitude of scientific concerns about their toxicity, characterization, and interactions with microorganisms and other contaminants. The reports of common subthemes have agreed about many findings and research gaps but also showed contradictions about others. To unravel these equivocal conflicts, we herein compile all the major findings and analyze the paramount discrepancies among these review papers. Furthermore, we systematically reviewed all the highlights, research gaps, concerns, and future needs. The covered focus areas of MPs' literature include the sources, occurrence, fate, existence, and removal in wastewater treatment plants (WWTPs), toxicity, interaction with microbiota, sampling, characterization, data quality, and interaction with other co-contaminants. This study reveals that many mechanisms of MPs' behavior in aquatic environments like degradation and interaction with microbiota are yet to be comprehended. Furthermore, we emphasize the critical need to standardize methods and parameters for MP characterization to improve the comparability and reproducibility of the incoming research.

Adsorption modeling of organic compounds (OCs) by carbon nanotubes (CNTs): role of OC and CNT properties on the linear solvation energy relationship.

This study evaluated a comprehensive database for the adsorption of polar and nonpolar organic compounds (OCs) by carbon nanotubes (CNTs) and to use the linear solvation energy relationship (LSER) technique for developing predictive adsorption models of OCs by multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs). The results showed that coefficient of determinations (R2) values for all compounds are higher variability in the 200 g/mol molecular weight cutoff (74-99%). When the molecular weight cutoff of all OCs is higher than 200 g/mol, the trend of their R2 values is decreased (less than 70%). Among all adsorbate descriptor coefficients, V and B terms are the most significant descriptors (p-values ≤ 0.05) in LSER equations for adsorption of low molecular weight polar and nonpolar OCs by both CNTs. Besides, KOW normalization of all Kd values did not have significant impact on the regression of the LSER model, indicating that hydrophobic interactions are not sole mechanism for the adsorption of OCs on CNTs. Lastly, SWCNTs exhibited higher polar OCs uptake than MWCNTs, which was attributed to more polar surface of SWCNTs as suggested by its high oxygen content (%10).

Predictive modeling of haloacetonitriles under uniform formation conditions.

The objective of this study was to develop models to predict the formation of HANs under uniform formation conditions (UFC) in chlorinated, choraminated, and perchlorinated/chloraminated waters of different origins. Model equations were developed using multiple linear regression analysis to predict the formation of dichloroacetonitrile (DCAN), HAN4 (trichloroacetonitrile [TCAN], DCAN, bromochloroacetonitrile [BCAN], and dibromoacetonitrile [DBAN]) and HAN6 (HAN4 plus monochloroacetonitrile, monobromoacetonitrile). The independent variables covered a wide range of values, and included ultraviolet absorbance,(UV254) dissolved organic carbon (DOC), dissolved organic nitrogen (DON), specific UV absorbance at 254 (SUVA254), bromide (Br-), pH, oxidant dose, contact time, and temperature. The regression coefficients (r2) of HAN4 and HAN6 models for natural organic matter (NOM), algal organic matter (AOM), and effluent organic matter (EfOM)  impacted waters were within the range of 60-88%, while the r2 values of HAN4 and DCAN models for both groundwater and distribution systems were lower, in the range of 41-66%. The r2 values for the DCAN model were mostly higher in the individual types as compared to the cumulative analysis of all source water data together. This was attributed to differences in HAN precursor characteristics. For chlorination, among all variables, pH was found to be the most significant descriptor in the model equations describing the formation of DCAN, HAN4, and HAN6, and it was negatively correlated with HAN formation in the distribution system, groundwater, AOM, and NOM samples, while it showed an inverse relationship with HAN6 formation in EfOM impacted waters. During chloramination, pH was the most influential model descriptor for DCAN formation in the NOM. Prechlorination dose was the most predominant parameter for prechlorination/chloramination, and it was positively correlated with HAN4 formation in AOM impacted waters.

Adsorption kinetics and aggregation for three classes of carbonaceous adsorbents in the presence of natural organic matter.

In this study, adsorption kinetics of phenanthrene (PNT) and trichloroethylene (TCE) by a graphene nanosheet (GNS), a graphene oxide nanosheet (GO), a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), and two coal based activated carbons (ACs) (F400 and HD3000) were examined in distilled and deionized water (DDW) and under natural organic matter (NOM) preloading conditions. The results showed the times needed for the adsorption of PNT and TCE to reach apparent equilibrium (i.e., ≤3% change per day) followed the order of GO ≥ MWCNT > GNS > SWCNT ∼ HD3000∼F400 and SWCNT > GNS ∼ HD3000 > F400 ∼ MWCNT > GO, respectively. The pseudo second order model successfully represented kinetics data for three classes of carbonaceous adsorbents. The Weber-Morris intraparticle diffusion model indicated three steps adsorption process for PNT and two step adsorption for TCE. In addition, the times needed to reach apparent equilibrium for the adsorption of PNT and TCE in the presence of hydrophobic (HPO) and hydrophilic (HPI) NOM solutions increased for all adsorbents (except for GO). In general, both NOM showed similar impacts on the adsorption rates of PNT and TCE. Aggregation of both GNS and CNTs rapidly occurred during initial couple hours of contact time during preloading, and spiking both PNT and TCE further increased their aggregation.

Predictive models for adsorption of organic compounds by Graphene nanosheets: comparison with carbon nanotubes.

The Linear Solvation Energy Relationships (LSER) technique was applied in the present study for predicting models of organic compounds (OCs) adsorption by Graphene and Graphene oxide (GO), and the results were compared with those of multi-walled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT). Adsorption database of 38 OCs (28 aromatic and 10 aliphatic) for Graphene and 69 OCs (59 aromatic and 10 aliphatic) for GO were collected from the literature and our laboratory. The r2 of the LSER models on the adsorption of aromatic OCs by Graphene and GO at three different equilibrium concentrations gradually increased up to OC molecular weight of 400 g/mol, after which a declining trend was observed for GO, while there was no visible change for Graphene. Among descriptors for all LSER models, V (molecular volume) and B (hydrogen bond accepting) for Graphene nanosheets (GNS) and carbon nanotubes (CNT) were the most significant descriptors (p values ≤ 0.05). B term had high value and was negatively correlated with adsorption of all OCs by Graphene (-1.24 to -9.45), GO (-0.55 to -9.31), SWCNT (-0.10 to -5.38) and MWCNT (-1.24 to -1.85). LSER successfully trained models for adsorption of OCs by GNS, and model coefficients were dependent on adsorbent type and OC properties.

Removal of intra- and extracellular microcystin by submerged ultrafiltration (UF) membrane combined with coagulation/flocculation and powdered activated carbon (PAC) adsorption.

In this study, we investigated the performance of conventional (coagulation/flocculation→powdered activated carbon [PAC] adsorption) and advanced treatment (coagulation/flocculation→PAC adsorption→submerged ultrafiltration [UF] membrane) processes separately and sequentially for the removal of total (intra- and extracellular) microcystin. Results of the conventional treatment process demonstrated that coagulation/flocculation alone was not effective (up to 70%) for the removal of total microcystin, while the uptake of total microcystin was achieved up to 84% by PAC adsorption (PAC dose of 20mg/L). In addition, the adsorption kinetic mechanism of PAC was also examined using several kinetic models. Results showed that the pseudo-second order (PSOM) and Weber-Morris intraparticle diffusion model (IPDM) are the most suitable models for this study (r2>0.98 and p-values ≤0.05). On the other hand, up to 94% of microcystin was effectively removed when the coagulation/flocculation and PAC systems were combined with UF membranes. Also, the permeate concentration was found to be 0.3mg/L, which is below the World Health Organization (WHO) guideline value of 1µg/L. Overall results indicated that higher removal of microcystin occurred using the advanced treatment process. Therefore, this combined system appears to be a promising treatment technique for the removal of total microcystin.

Adsorption of organic contaminants by graphene nanosheets: A review.

Graphene nanosheets (GNS) such as graphenes and graphene oxides (GOs) have been widely investigated as next-generation adsorbents in both water and wastewater treatment processes due to their unique physicochemical properties and their affinity towards different classes of organic contaminants (OCs). In the last five years, more than 40 articles investigating adsorption of different classes of OCs by graphene and GO were published in peer-reviewed journals. Adsorption mechanisms were controlled by molecular properties of OCs (e.g., aromatic vs aliphatic, molecular size and hydrophobicity), characteristics of adsorbents (e.g., surface area, pore size distribution, and surface functional groups), and background solution properties (e.g., pH, ionic strength, surfactants, NOM, and temperature). This literature survey includes: (i) a summary of adsorption of OCs by GNS, (ii) a comprehensive discussion of the mechanisms and factors controlling the adsorption of OCs by GNS and a comparison of their adsorption behaviors with those of CNT. This literature survey also identifies future research needs and challenges on the adsorption of OCs by GNS.

Linear solvation energy relationships (LSER) for adsorption of organic compounds by carbon nanotubes.

The objective of this paper was to create a comprehensive database for the adsorption of organic compounds by carbon nanotubes (CNTs) and to use the Linear Solvation Energy Relationship (LSER) technique for developing predictive adsorption models of organic compounds (OCs) by multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs). Adsorption data for 123 OCs by MWCNTs and 48 OCs by SWCNTs were compiled from the literature, including some experimental results obtained in our laboratory. The roles of selected OCs properties and CNT types were examined with LSER models. The results showed that the r(2) values of the LSER models displayed small variability for aromatic compounds smaller than 220 g/mol, after which a decreasing trend was observed. The data available for aliphatics was mainly for molecular weights smaller than 250 g/mol, which showed a similar trend to that of aromatics. The r(2) values for the LSER model on the adsorption of aromatic and aliphatic OCs by SWCNTs and MWCNTs were relatively similar indicating the linearity of LSER models did not depend on the CNT types. Among all LSER model descriptors, V term (molecular volume) for aromatic OCs and B term (basicity) for aliphatic OCs were the most predominant descriptors on both type of CNTs. The presence of R term (excess molar refractivity) in LSER model equations resulted in decreases for both V and P (polarizability) parameters without affecting the r(2) values. Overall, the results demonstrate that successful predictive models can be developed for the adsorption of OCs by MWCNTs and SWCNTs with LSER techniques.

Adsorption of organic contaminants by graphene nanosheets, carbon nanotubes and granular activated carbons under natural organic matter preloading conditions.

The effect of NOM preloading on the adsorption of phenanthrene (PNT) and trichloroethylene (TCE) by pristine graphene nanosheets (GNS) and graphene oxide nanosheet (GO) was investigated and compared with those of a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), and two coal based granular activated carbons (GACs). PNT uptake was higher than TCE by all adsorbents on both mass and surface area bases. This was attributed to the hydrophobicity of PNT. The adsorption capacities of PNT and TCE depend on the accessibility of the organic molecules to the inner regions of the adsorbent which was influenced from the molecular size of OCs. The adsorption capacities of all adsorbents decreased as a result of NOM preloading due to site competition and/or pore/interstice blockage. However, among all adsorbents, GO was generally effected least from the NOM preloading for PNT, whereas there was not observed any trend of NOM competition with a specific adsorbent for TCE. In addition, SWCNT was generally affected most from the NOM preloading for TCE and there was not any trend for PNT. The overall results indicated that the fate and transport of organic contaminants by GNSs and CNTs type of nanoadsorbents and GACs in different natural systems will be affected by water quality parameters, characteristics of adsorbent, and properties of adsorbate.