How aromatic dissolved organic matter differs in competitiveness against organic micropollutant adsorption.

Activated carbon is employed for the adsorption of organic micropollutants (OMPs) from water, typically present in concentrations ranging from ng L-1 to µg L-1. However, the efficacy of OMP removal is considerably deteriorated due to competitive adsorption from background dissolved organic matter (DOM), present at substantially higher concentrations in mg L-1. Interpreting the characteristics of competitive DOM is crucial in predicting OMP adsorption efficiencies across diverse natural waters. Molecular weight (MW), aromaticity, and polarity influence DOM competitiveness. Although the aromaticity-related metrics, such as UV254, of low MW DOM were proposed to correlate with DOM competitiveness, the method suffers from limitations in understanding the interplay of polarity and aromaticity in determining DOM competitiveness. Here, we elucidate the intricate influence of aromaticity and polarity in low MW DOM competition, spanning from a fraction level to a compound level, by employing direct sample injection liquid chromatography coupled with ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry. Anion exchange resin pre-treatment eliminated 93% of UV254-active DOM, predominantly aromatic and polar DOM, and only minimally alleviated DOM competition. Molecular characterization revealed that nonpolar molecular formulas (constituting 26% PAC-adsorbable DOM) with medium aromaticity contributed more to the DOM competitiveness. Isomer-level analysis indicated that the competitiveness of highly aromatic LMW DOM compounds was strongly counterbalanced by increased polarity. Strong aromaticity-derived π-π interaction cannot facilitate the competitive adsorption of hydrophilic DOM compounds. Our results underscore the constraints of depending solely on aromaticity-based approaches as the exclusive interpretive measure for DOM competitiveness. In a broader context, this study demonstrates an effect-oriented DOM analysis, elucidating counterbalancing interactions of DOM molecular properties from fraction to compound level.

SARS-CoV-2 infection dynamics revealed by wastewater sequencing analysis and deconvolution.

The use of RNA sequencing from wastewater samples is a valuable way for estimating infection dynamics and circulating lineages of SARS-CoV-2. This approach is independent from testing individuals and can therefore become the key tool to monitor this and potentially other viruses. However, it is equally important to develop easily accessible and scalable tools which can highlight critical changes in infection rates and dynamics over time across different locations given sequencing data from wastewater. Here, we provide an analysis of lineage dynamics in Berlin and New York City using wastewater sequencing and present PiGx SARS-CoV-2, a highly reproducible computational analysis pipeline with comprehensive reports. This end-to-end pipeline includes all steps from raw data to shareable reports, additional taxonomic analysis, deconvolution and geospatial time series analyses. Using simulated datasets (in silico generated and spiked-in samples) we could demonstrate the accuracy of our pipeline calculating proportions of Variants of Concern (VOC) from environmental as well as pre-mixed samples (spiked-in). By applying our pipeline on a dataset of wastewater samples from Berlin between February 2021 and January 2022, we could reconstruct the emergence of B.1.1.7(alpha) in February/March 2021 and the replacement dynamics from B.1.617.2 (delta) to BA.1 and BA.2 (omicron) during the winter of 2021/2022. Using data from very-short-reads generated in an industrial scale setting, we could see even higher accuracy in our deconvolution. Lastly, using a targeted sequencing dataset from New York City (receptor-binding-domain (RBD) only), we could reproduce the results recovering the proportions of the so-called cryptic lineages shown in the original study. Overall our study provides an in-depth analysis reconstructing virus lineage dynamics from wastewater. While applying our tool on a wide range of different datasets (from different types of wastewater sample locations and sequenced with different methods), we show that PiGx SARS-CoV-2 can be used to identify new mutations and detect any emerging new lineages in a highly automated and scalable way. Our approach can support efforts to establish continuous monitoring and early-warning projects for detecting SARS-CoV-2 or any other pathogen.

Intra aquifer variations in pesticide sorption during a field injection experiment.

A field injection experiment was performed in an anoxic sandy aquifer over 6 days to assess sorption characteristics of 7 commonly applied pesticides in agriculture and 2 frequently detected metabolites. Pesticide use changed considerably in the last decades, and there is insufficient knowledge of the fate of currently used pesticides in aquifers. Injected water arrival was monitored at 6 depth intervals of 1 m ranging from 11.4 to 32.2 m-below surface level with varying organic carbon contents (0.057-0.91%d.w.) to examine intra-aquifer variations in sorption. Observed pesticide concentrations were fit using a non-linear least squares routine to an advection-dispersion equation, from which retardation factors (R) were obtained. Pesticide degradation did not significantly influence the simulated R during the experiment. We observed that bentazon and cycloxydim were most mobile with R < 1.1 at all depths. Desphenyl chloridazon, methyl desphenyl chloridazon, and imidacloprid were, on average, less mobile, with maximum R of 1.5. Boscalid, chloridazon, fluopyram, and flutolanil showed a larger range of R, and R > 2.0 were observed in the shallowest part of the aquifer. Largest R were observed at the top of the aquifer and decreased with depth. Koc values varied similarly, which indicates that sorption is not only influenced by sedimentary organic matter (SOM) content but also by its sorption reactivity. Obtained sorption parameters were substantially lower than reported in a widely used pesticide sorption database, which suggests that sorption parameters are influenced by methodological differences and variations in the sorption reactivity of SOM. The large intra-aquifer variations in pesticide sorption highlights that aquifer heterogeneity should be considered in groundwater risk assessments.

How properties of low molecular weight model competitors impact organic micropollutant adsorption onto activated carbon at realistically asymmetric concentrations.

Low molecular weight (LMW) dissolved organic matter (DOM) is the predominant competitor for adsorption sites against organic micropollutants (OMPs) in activated carbon adsorption. However, top-down approaches using highly complex mixtures of real water DOM do not allow to concisely examine the impacts of specific LMW DOM molecular properties on competitive adsorption. Therefore, we followed a bottom-up approach using fifteen model compounds (mDOM) to elucidate how important DOM characteristics, including hydrophobicity and unsaturated structures (ring, double/triple bond), impact competitiveness. Large concentration asymmetry (~500 µg DOC/µg OMP) made mDOM compounds, which were overall less preferentially adsorbed than OMPs, become competitive against OMPs and inhibit OMP adsorption kinetics by pre-occupation of adsorption sites. Our results revealed that both hydrophobicity interactions and π-interactions increased mDOM competitiveness, while π-interactions outweighed hydrophobic interactions. However, π-interactions could not be satisfactorily evaluated with a parameter such as specific ultraviolet absorbance (SUVA) due to interferences of carboxyl groups in aromatic mDOMs. Instead, mDOM adsorbability, described by mDOM adsorption capacity, proved to be a comprehensive indicator for mDOM competitiveness. To our knowledge, this is the first study that systematically clarifies the impacts of intricately interacting molecular properties on DOM adsorption and the related competition against OMP adsorption. DOM adsorbability may inspire a new fractionation, and assist the further isolation, identification and detailed characterization of LMW DOM competitors in real DOM-containing waters.

Projecting competition between 2-methylisoborneol and natural organic matter in adsorption onto activated carbon from ozonated source waters.

Though the ozone-activated carbon process has been widely applied for drinking water purification, little is known about how ozone-modified natural organic matter (NOM) competes with micropollutants in activated carbon adsorption. In this study, three natural waters and one synthetic water (standard humics solution) with highly heterogeneous NOM compositions were employed to investigate the interference of ozonated NOM with the adsorption of 2-methylisoborneol (MIB). Analysis using liquid chromatography with online carbon and UV254 detection (LC-OCD-UVD) revealed that ozonation led to various disintegration patterns of macromolecules in NOM, and UV absorbance was reduced markedly for nearly all NOM fractions. Powdered activated carbon (PAC) adsorption experiments showed that increasing ozone consumption coincided with reducing NOM competition against MIB in the three natural waters, as expressed by the fitted initial concentrations of the equivalent background compound (c0,EBC). In the synthetic water, in contrast, competition increased under low/moderate specific ozone consumptions and then decreased with further elevation of ozone consumptions. Regarding the significance on affecting ozonated NOM interference, aromaticity reduction outweighed formation of low molecular weight (LMW) organics in most cases, enhancing MIB adsorption capacity. However, disintegration of the humics fraction with larger molecular weight (1,103 g/mol, as compared to 546-697 g/mol in three natural waters) into smaller, more competitive fractions caused the observed initial deteriorated MIB adsorption in synthetic water. A superior correlation between c0,EBC and the UV absorbance of LMW organics (R2 = 0.93) over concentrations of LMW organics underlined the importance of the aromatic properties in competitive adsorption projection for ozone pretreated natural waters. Furthermore, the change of relative concentration of UV absorbing compounds during ozonation could help estimate the decrease of c0,EBC, which could be a promising tool for waterworks to adjust PAC doses for MIB removal in ozonated waters.

Fluoride removal by Ca-Al-CO3 layered double hydroxides at environmentally-relevant concentrations.

In this study, F- removal by Ca-Al-CO3 layered double hydroxides (LDHs) was investigated at environmentally-relevant concentration ranges (2-12 mg/L) to below the WHO guideline, with an emphasis on the effect of LDHs' modification, as well as the effects of initial F- concentration, adsorbent dose, pH, temperature and co-existing ions. Ca-Al-CO3 LDHs, either untreated, calcined or microwave treated, showed affinity for the removal of F- from synthetic groundwater with capacities of 6.7-8.4 mg F-/g LDHs at groundwater-relevant pH, with a higher F- removal capacity at lower pH (<8) and lower temperature (12 °C, as compared to 25 °C & 35 °C). Since calcination and microwave treatment resulted in only marginal defluorination improvements, using untreated LDHs appears the practically most feasible option. For the untreated LDHs, competition with Cl- and NO3- was not observed, whereas at higher HCO3- and SO42- concentrations (>250 mg/L) a slight reduction in F- removal was observed. This study indicates the potential of Ca-Al-CO3 LDHs as a cost-effective F- removal technology, particularly when locally sourced and in combination with low-cost pH correction.

Organic micropollutant desorption in various water matrices - Activated carbon pore characteristics determine the reversibility of adsorption.

The adsorption of organic micropollutants (OMP) onto activated carbon (AC) in real waters is strongly affected by dissolved organic matter (DOM). This study examines the impact of DOM quantity and composition in terms of OMP desorption from different AC, by using four different water samples. In batch tests, an OMP concentration drop in the influent of an AC treatment system was simulated. These tests were conducted with six AC products with different internal pore structures. The tests were evaluated with respect to the extent of OMP desorption by interpreting corresponding OMP adsorption and desorption isotherms. For each tested AC and each evaluated OMP the isotherms in the different water samples were qualitatively very similar. Thus, despite different DOM composition very similar OMP desorption extents can be expected in different waters. Among the AC products a clear trend can be seen in all waters, namely that increasing pore size results in increasing desorption. The OMP desorption extent was quantified by a simple Freundlich equation-based approach, expressing the relative position of corresponding adsorption and desorption isotherms via the ratio KF, Des/KF, Ads. Plotting KF, Des/KF, Ads of any given substance for the different tested AC in one water over the average AC pore size shows a linear correlation. This confirms that the OMP desorption extent in real waters is strongly impacted by the AC pore structure. Furthermore, it indicates that the average AC pore size might be a good tool to assess the vulnerability of treatment systems towards desorption.

Impact of different DOM size fractions on the desorption of organic micropollutants from activated carbon.

Whereas the adsorption of organic micropollutants (OMP) onto activated carbon (AC) is relatively well studied, little is known about potential OMP desorption effects, especially in real waters. In this study, the impact of different fractions of drinking water DOM on OMP desorption from AC was examined. By different pre-treatments of a raw drinking water, a high molecular weight (hmw) and a low molecular weight (lmw) DOM solution were prepared. These solutions were used as background matrix in AC adsorption/desorption batch tests, simulating a drop of the OMP inflow concentration to a fixed-bed adsorber. The tests were conducted in parallel with three AC of different pore structures (microporous, mesoporous/balanced, macroporous). The tests were evaluated with respect to the extent of OMP adsorption and its reversibility, which represents the potential extent of OMP desorption. In terms of OMP adsorption, the lmw-DOM fraction induced a higher competitive effect on OMP adsorption in comparison to the hmw-DOM fraction. In terms of their impact on OMP desorption extent, both fractions led to very similar results. In case of the macroporous AC, both DOM fractions induce an enhanced OMP desorption that can be attributed to displacement effects in both cases. For the microporous AC, an increased irreversibility of OMP adsorption was found in both cases, which shows that DOM adsorption prevents OMP desorption, independently of the size of the adsorbed DOM compounds. Whereas results from this study as well as from former studies indicate that this effect might be induced by permanent pore blockages by adsorbed DOM, further results show that there could be more complex DOM interactions that lead to the decreased desorption in case of microporous AC. Nonetheless, the very similar impact of the different DOM fractions on the reversibility of OMP adsorption indicates that the potential extent of desorption is similar in different waters (with different DOM composition) and primarily depending on the pore structure of the used AC.

Competition in chromate adsorption onto micro-sized granular ferric hydroxide.

Hexavalent chromium is highly toxic and elaborate technology is necessary for ensured removal during drinking water production. The present study aimed at estimating the potential of a micro-sized iron hydroxide (µGFH] adsorbent for chromate removal in competition to ions presents in drinking water. Freundlich and Langmuir models were applied to describe the adsorption behaviour. The results show a high dependency on the pH value with increasing adsorption for decreasing pH values. The adsorption capacity in deionized water (DI) at pH 7 was 5.8 mg/g Cr(VI) while it decreased to 1.9 mg/g Cr(VI) in Berlin drinking water (DW) at initial concentrations of 1.2 mg/L. Desorption experiments showed reversible adsorption indicating ion exchange and outer sphere complexes as main removal mechanisms. Competing ions present in DW were tested for interfering effects on chromate adsorption. Bicarbonate was identified as main inhibitor of chromate adsorption. Sulfate, silicate and phosphate also decreased chromate loadings, while calcium enhanced chromate adsorption. Adsorption kinetics were highly dependent on particle size and adsorbent dose. Adsorption equilibrium was reached after 60 min for particles smaller than 63 µm, while 240 min were required for particles from 125 µm to 300 µm. Adsorption kinetics in single solute systems could be modelled using the homogeneous surface diffusion model (HSDM) with a surface diffusion coefficient of 4∙10 -14 m2/s. Competitive adsorption could be modelled using simple equations dependent on time, adsorption capacity and concentrations only.

Fast empirical lab method for performance projections of large-scale powdered activated carbon re-circulation plants.

Powdered activated carbon (PAC) for organic micro-pollutant (OMP) removal can be applied effectively on wastewater treatment plant (WWTP) effluents by using re-circulation schemes, accumulating the PAC in the system. This technique is complex because several factors are unknown: (i) the PAC concentration in the system, (ii) specific and average contact times of PAC particles, and (iii) PAC particle loadings with target compounds/competing water constituents. Thus, performance projections (e.g. in the lab) are very challenging. We sampled large-scale PAC plants with PAC sludge re-circulation on eight different WWTPs. The PAC plant-induced OMP removals were notably different, even when considering PAC concentrations in proportion to background organic sum parameters. The variability is likely caused by differing PAC products, varying water composition, differently effective plant/re-circulation operation, and variable biodegradation. Plant PAC samples and parts of the PAC plant influent samples were used in laboratory tests, applying multiples (0.5, 1, 2, 4) of the respective large-scale "fresh" PAC doses, and several fixed contact times (0.5, 1, 2, 4, 48 h). The aim was to empirically identify suitable combinations of lab PAC dose (as multiples of the plant PAC dose) and contact time, which represent the PAC plant performances in removing OMPs (for specific OMPs at single locations, and for averages of different OMPs at all locations). E.g., for five well adsorbing, little biodegradable OMPs, plant performances can be projected by using a lab PAC dose of twice the respective full-scale PAC dose and 4 h lab contact time (standard deviation of 13 %-points).

Quantification and isotherm modelling of competitive phosphate and silicate adsorption onto micro-sized granular ferric hydroxide.

Adsorption onto ferric hydroxide is a known method to reach very low residual phosphate concentrations. Silicate is omnipresent in surface and industrial waters and reduces the adsorption capacity of ferric hydroxides. The present article focusses on the influences of silicate concentration and contact time on the adsorption of phosphate to a micro-sized iron hydroxide adsorbent (µGFH) and fits adsorption data to multi-component adsorption isotherms. In Berlin drinking water (DOC of approx. 4 mg L-1) at pH 7.0, loadings of 24 mg g-1 P (with 3 mg L-1 initial PO4 3--P) and 17 mg L-1 Si (with 9 mg L-1 initial Si) were reached. In deionized water, phosphate shows a high percentage of reversible bonds to µGFH while silicate adsorption is not reversible probably due to polymerization. Depending on the initial silicate concentration, phosphate loadings are reduced by 27, 33 and 47% (for equilibrium concentrations of 1.5 mg L-1) for 9, 14 and 22 mg L-1 Si respectively. Out of eight tested multi-component adsorption models, the Extended Freundlich Model Isotherm (EFMI) describes the simultaneous adsorption of phosphate and silicate best. Thus, providing the means to predict and control phosphate removal. Longer contact times of the adsorbent with silicate prior to addition of phosphate reduce phosphate adsorption significantly. Compared to 7 days of contact with silicate (c 0 = 10 mg L-1) prior to phosphate (c 0 = 3 mg L-1) addition, 28 and 56 days reduce the µGFH capacity for phosphate by 21 and 43%, respectively.

Simulating Effluent Organic Matter Competition in Micropollutant Adsorption onto Activated Carbon Using a Surrogate Competitor.

Adsorption onto activated carbon is a promising option for removing organic micropollutants (OMPs) from wastewater treatment plant (WWTP) effluents. The heterogeneity of activated carbons and adsorption competition between OMPs and adsorbable compounds of the effluent organic matter (EfOM) complicate the prediction of OMP removals. Thus, reliable and simple test systems are desirable. For this study, batch experiments with powdered activated carbon (PAC) were carried out to examine methyl orange (MO) as a selected surrogate competitor to simulate EfOM adsorption competition. MO solutions were spiked with carbamazepine (CBZ) as an indicator substance for well-adsorbing OMPs. On the basis of CBZ adsorption isotherms in WWTP effluents, MO concentrations for batch test solutions with identical adsorption competition toward CBZ were calculated. The calculations were performed according to an empirical model of CBZ adsorption in the presence of MO, since predictions employing the ideal adsorbed solution theory (IAST) proved to be inaccurate. Comparative batch tests with five different PACs were conducted with WWTP effluent and respective MO batch test solutions. Except for one PAC, the achieved CBZ removals were very similar in WWTP effluent and the test solution. Additionally, a universal correlation between MO and CBZ removals was found for four PACs.

Influence of dissolved organic matter and activated carbon pore characteristics on organic micropollutant desorption.

By simulating decreasing inflow concentrations, the extent of desorption of organic micropollutants (OMP) from three activated carbons (AC) was examined in laboratory batch tests. The tested AC showed strong differences in pore size distribution and could therefore be characterized as typical micro-, meso- and macroporous AC, respectively. Adsorption and desorption conditions were varied by using drinking water (containing dissolved organic matter (DOM)) and DOM-free pure water as background solutions to examine the influence of DOM on OMP desorption for the different AC. Under ideal conditions (adsorption and desorption in pure water) adsorption of the tested OMP was found to be highly up to completely reversible for all tested AC. Under real conditions (adsorption and desorption in drinking water) additional DOM adsorption affects desorption in different ways depending on the AC pore structure. For the micro- and mesoporous AC, an increased irreversibility of OMP adsorption was found, which shows that DOM adsorption prevents OMP desorption. This could be referred to pore blockage effects that occur during the parallel adsorption of DOM and OMP. For the macroporous AC, DOM adsorption led to an enhanced OMP desorption which could be attributed to displacement processes. These results show that smaller pores tend to be blocked by DOM which hinders OMP from desorption. The overall larger pores of the macroporous AC do not get blocked which could allow (i) OMP to desorb and (ii) DOM to enter and displace OMP.

Comparing and modeling organic micro-pollutant adsorption onto powdered activated carbon in different drinking waters and WWTP effluents.

The adsorption of organic micro-pollutants (OMP) onto powdered activated carbon (PAC) was compared between regionally different waters within two groups, namely five drinking waters and seven wastewater treatment plant (WWTP) effluents. In all waters, OMP were spiked to adjust similar ratios of the initial OMP and DOC concentrations (c0,OMP/c0,DOC). PAC was dosed specific to the respective DOC (e.g. 2 mg PAC/per mg DOC). Liquid chromatography with online carbon detection shows differences of the background organic matter (BOM) compositions. The OMP removals at given DOC-specific PAC doses vary by ±15% (drinking waters) and ±10% (WWTP effluents). Similar BOM-induced adsorption competition in the waters of the respective group results in overall relationships between the PAC loadings and the liquid phase concentrations of each OMP (in the case of strong adsorbates). Weaker adsorbates show no overall relationships because of the strong BOM-induced adsorption competition near the initial OMP concentration. Correlations between OMP removals and UV254 removals were independent of the water (within the respective group). The equivalent background compound (EBC) model was applied to the experimental data. Using global EBC Freundlich coefficients, the initial EBC concentration correlates with the DOC (both water groups separately) and the low molecular weight (LMW) organics concentrations (all waters combined). With these correlations, the EBC could be initialized by using the DOC or the LMW organics concentration of additional drinking water, WWTP effluent, and surface water samples.

Granular activated carbon adsorption of organic micro-pollutants in drinking water and treated wastewater--Aligning breakthrough curves and capacities.

Small-scale granular activated carbon (GAC) tests for the adsorption of organic micro-pollutants (OMP) were conducted with drinking water and wastewater treatment plant (WWTP) effluent. In both waters, three influent OMP concentration levels were tested. As long as the influent OMP concentrations are below certain thresholds, the relative breakthrough behavior is not impacted in the respective water. Accordingly, the GAC capacity for OMP is directly proportional to the influent OMP concentration in the corresponding water. The differences between the OMP breakthrough curves in drinking water and WWTP effluent can be attributed to the concentrations of the low molecular weight acid and neutral (LMW) organics of the waters. Presenting the relative OMP concentrations (c/c0) over the specific throughput of the LMW organics (mg LMW organics/g GAC), the OMP breakthrough curves in drinking water and WWTP effluent superimpose each other. This superimposition can be further increased if the UV absorbance at 254 nm (UV254) of the LMW organics is considered. In contrast, using the specific throughput of the dissolved organic carbon (DOC) did not suffice to obtain superimposed breakthrough curves. Thus, the LMW organics are the major water constituent impacting OMP adsorption onto GAC. The results demonstrate that knowing the influent OMP and LMW organics concentrations (and UV254) of different waters, the OMP breakthroughs and GAC capacities corresponding to any water can be applied to all other waters.

Impacts of coagulation on the adsorption of organic micropollutants onto powdered activated carbon in treated domestic wastewater.

The application of powdered activated carbon (PAC) as an advanced wastewater treatment step for the removal of organic micropollutants (OMP) necessitates complete separation of the PAC particles, e.g. by coagulation. In this study, potential positive or negative indirect or direct effects of coagulation on the adsorption of OMPs onto PAC in treated wastewater were investigated. Although the concentration of dissolved organic matter (DOM) was significantly reduced by coagulation, the selective removal of mainly larger DOM components such as biopolymers and humic substances did not improve subsequent OMP adsorption onto PAC, demonstrating that coagulation has minor effects on DOM constituents that are relevant for direct competition or pore blocking. The combination of coagulation and adsorption yielded the sum of the individual removals, as adsorption predominantly affected smaller compounds. While the formation of flocs led to visible incorporation of PAC particles, no significant mass transfer limitations impeded the OMP adsorption. As a result, the dosing sequence of coagulant and PAC is not critical for efficient adsorption of OMPs onto PAC. The relationships between adsorptive OMP removal and corresponding reduction of UV absorption at 254 nm (UVA254) as a promising surrogate correlation for the real-time monitoring and PAC adjustment were affected by coagulation, leading to individual correlations depending on the water composition. Correcting for UVA254 reduction by coagulation produces adsorptive UVA254 removal, which correlates highly with OMP removal for different WWTP effluents and varying coagulant doses and can be applied in combined adsorption/coagulation processes to predict OMP removal and control PAC dosing.

Impact of EfOM size on competition in activated carbon adsorption of organic micro-pollutants from treated wastewater.

The competitive impacts of different fractions of wastewater treatment plant effluent organic matter (EfOM) on organic micro-pollutant (OMP) adsorption were investigated. The fractionation was accomplished using separation by nanofiltration (NF). The waters resulting from NF were additionally treated to obtain the same dissolved organic carbon (DOC) concentrations as the initial water. Using size exclusion chromatography (LC-OCD) it could be shown that the NF treatment resulted in an EfOM separation by size. Adsorption tests showed different competitive effects of the EfOM fractions with the OMP. While large EfOM compounds that were retained in NF demonstrated a reduced competition as compared to the raw water, the NF-permeating EfOM compounds showed an increased competition with the majority of the measured OMP. The effects of small size EfOM are particularly negative for OMP which are weak/moderate adsorbates. Adsorption analysis was carried out for the differently fractionized waters. The small sized EfOM contain better adsorbable compounds than the raw water while the large EfOM are less adsorbable. This explains the observed differences in the EfOM competitiveness. The equivalent background compound (EBC) model was applied to model competitive adsorption between OMP and EfOM and showed that the negative impacts of EfOM on OMP adsorption increase with decreasing size of the EfOM fractions. The results suggest that direct competition for adsorption sites on the internal surface of the activated carbon is more substantial than indirect competition due to pore access restriction by blockage. Another explication for reduced competition by large EfOM compounds could be the inability to enter and block the pores due to size exclusion.

Estimating organic micro-pollutant removal potential of activated carbons using UV absorption and carbon characteristics.

Eight commercially available powdered activated carbons (PAC) were examined regarding organic micro-pollutant (OMP) removal efficiencies in wastewater treatment plant (WWTP) effluent. PAC characteristic numbers such as B.E.T. surface, iodine number and nitrobenzene number were checked for their potential to predict the OMP removal of the PAC products. Furthermore, the PAC-induced removal of UV254 nm absorption (UVA254) in WWTP effluent was determined and also correlated with OMP removal. None of the PAC characteristic numbers can satisfactorily describe OMP removal and accordingly, these characteristics have little informative value on the reduction of OMP concentrations in WWTP effluent. In contrast, UVA254 removal and OMP removal correlate well for carbamazepine, diclofenac, and several iodinated x-ray contrast media. Also, UVA254 removal can roughly describe the average OMP removal of all measured OMP, and can accordingly predict PAC performance in OMP removal. We therefore suggest UVA254 as a handy indicator for the approximation of OMP removal in practical applications where direct OMP concentration quantification is not always available. In continuous operation of large-scale plants, this approach allows for the efficient adjustment of PAC dosing to UVA254, in order to ensure reliable OMP removal whilst minimizing PAC consumption.

Direct comparison of ozonation and adsorption onto powdered activated carbon for micropollutant removal in advanced wastewater treatment.

Organic micropollutants (OMPs) may occur ubiquitously in the aquatic environment. In order to protect the ecosystem and drinking water sources from potentially toxic effects, discharges of an increasing number of OMPs are being regulated. OMP removal from wastewater treatment plant (WWTP) effluents as a point source is a preferred option with removal by adsorption onto powdered activated carbon (PAC) and OMP transformation to presumably harmless compounds by ozonation as the most promising techniques. In this study, effluents of four WWTPs were treated with PAC and ozone in bench-scale experiments to compare the removal efficiencies of seven relevant OMPs. Concentrations of carbamazepine and diclofenac were reduced by more than 90% with 20 mg/L PAC or 5-7 mg/L ozone (0.5 mg O3 per mg dissolved organic carbon (DOC)). Comparing typical doses for practical applications ozonation proved to be more efficient for abatement of sulfamethoxazole, while removal of benzotriazole and iomeprol was comparatively more efficient with activated carbon. While well known for ozonation, DOC-normalized doses were also applied to PAC and correlated better to relative OMP removal than volume proportional PAC addition. Furthermore, OMP removal efficiencies corresponded well with the reduction of ultraviolet light absorption at 254 nm for both treatment options.