A QSAR-like analysis of the adsorption of endocrine disrupting compounds, pharmaceuticals, and personal care products on modified activated carbons

Rapid small-scale column tests (RSSCTs) examined the removal of 29 endocrine disrupting compounds (EDCs) and pharmaceutical/personal care products (PPCPs). The RSSCTs employed three lignite variants: HYDRODARCO 4000 (HD4000), steam-modified HD4000, and methane/steam-modified HD4000. RSSCTs used native Lake Mead, NV water spiked with 100–200 ppt each of 29 EDCs/PPCPs. For the steam and methane/steam variants, breakthrough occurred at 14,000–92,000 bed volumes (BV); and this was 3–4 times more bed volumes than for HD4000. Most EDC/PPCP bed life data were describable by a normalized quantitative structure–activity relationship (i.e. QSAR-like model) of the form:

where TPV is the pore volume, ρ_mc is the apparent density, CV is the molecular volume, C_o is the concentration, ⁸χ_p depicts the molecule's compactness, and FOSA is the molecule's hydrophobic surface area.     

Adsorption of anionic and cationic dyes on activated carbons with different surface chemistries

The influence of the surface chemical groups of an activated carbon on the removal of different classes of dyes is evaluated. Starting from the same material (NORIT GAC 1240 PLUS), the following treatments were carried out in order to produce a series of samples with different surface chemical properties but with no major differences in their textural properties: oxidation in the liquid phase with 6M HNO(3) and 10 M H(2)O(2) (acid materials) and heat treatment at 700 degrees C in H(2) or N(2) flow (basic materials). The specific micropores volume and mesopores surface area of the materials were obtained from N(2) adsorption equilibrium isotherms at 77K. The surface chemistry was characterised by temperature programmed desorption, by the determination of the point of zero charge (pH(pzc)) and by the evaluation of the acidity/basicity of the samples. Elemental and proximate analyses were also carried out. Equilibrium isotherms of selected dyes (an acid, a basic and a reactive dye) on the mentioned samples were obtained and the results discussed in relation to their surface chemistry. In general, the Langmuir model provided the best fit for the adsorption data. It is shown that the surface chemistry of the activated carbon plays a key role in dye adsorption performance. The basic sample obtained by thermal treatment under H(2) flow at 700 degrees C is the best material for the adsorption of all the tested dyes.     

Suspended biofilm carrier and activated sludge removal of acidic pharmaceuticals

Removal of seven active pharmaceutical substances (ibuprofen, ketoprofen, naproxen, diclofenac, clofibric acid, mefenamic acid, and gemfibrozil) was assessed by batch experiments, with suspended biofilm carriers and activated sludge from several full-scale wastewater treatment plants. A distinct difference between nitrifying activated sludge and suspended biofilm carrier removal of several pharmaceuticals was demonstrated. Biofilm carriers from full-scale nitrifying wastewater treatment plants, demonstrated considerably higher removal rates per unit biomass (i.e. suspended solids for the sludges and attached solids for the carriers) of diclofenac, ketoprofen, gemfibrozil, clofibric acid and mefenamic acid compared to the sludges. Among the target pharmaceuticals, only ibuprofen and naproxen showed similar removal rates per unit biomass for the sludges and biofilm carriers. In contrast to the pharmaceutical removal, the nitrification capacity per unit biomass was lower for the carriers than the sludges, which suggests that neither the nitrite nor the ammonia oxidizing bacteria are primarily responsible for the observed differences in pharmaceutical removal. The low ability of ammonia oxidizing bacteria to degrade or transform the target pharmaceuticals was further demonstrated by the limited pharmaceutical removal in an experiment with continuous nitritation and biofilm carriers from a partial nitritation/anammox sludge liquor treatment process.     

Regeneration of acid orange 7-exhausted granular activated carbons with microwave irradiation

An investigation was performed for the regeneration of three granular activated carbons (GACs) exhausted with acid orange 7 (AO7). The three GACs were made from different materials, i.e. coconut shells, almond nucleus and coal. The AO7 adsorption process was carried out in a continuous-flow adsorption column. After adsorption, the AO7-saturated GAC was dried at 120 °C, then regenerated in a quartz reactor by 2450 MHz microwave (MW) irradiation at 850 W for 5 min. The efficacy of this procedure was analyzed by determining the rates and amounts of AO7 adsorbed in successive adsorption–MW regeneration cycles. Effects of this regeneration on the structural properties, surface chemistry and the AO7 adsorption capacities of GAC samples were examined. It was found that after several adsorption–MW regeneration cycles, the adsorption rates and capacities of GACs could maintain relatively high levels, even higher than those of virgin GACs, as indicated by AO7 breakthrough curves and adsorption isotherms. The improvement of GAC adsorption properties resulted from the modification of pore size distribution and surface chemistry by MW irradiation.     

Chemical regeneration of exhausted activated carbon—II

This paper represents the second of a series of reports on the chemical regeneration of exhausted activated carbon following experimental research studies carried out at the University of Birmingham, U.K.

A wide range of regenerants, inorganic and organic, was evaluated in the treatment of carbon samples exhausted with 2-naphthol, 2-methoxyphenol, 2-chlorophenol, o-cresol and 2-nitrophenol, in order to compare the effects of the introduction of a second benzene ring (i.e. in effect the addition of C₄H₄, OCH₃, Cl, CH₃ and NO₂ groups to phenol on susceptibility to desorption.

There was a marked correlation between decreasing molecular weight of adsorbate and decreasing value of regeneration efficiency; the smaller the adsorbate, the further it could penetrate into the micropores of the carbon thereby resisting displacement by the regenerant. Furthermore, it was observed that, in general, the smaller the organic regenerant the further it could penetrate into the micropores of the carbon and displace the adsorbate. These complementary observations indicate that where chemical reactions are unlikely between organic regenerant and adsorbate, the success of the regeneration process is governed by the mechanism of physical displacement of the adsorbate molecule by the organic solvent molecule. The importance of the molecular weights and sizes of the adsorbate and the solvent is thus confirmed.     

Regeneration of ortho-chlorophenol-exhausted activated carbons with liquid water at high pressure and temperature

A study was undertaken of the regeneration of three activated carbons exhausted with ortho-chlorophenol. The regeneration process was carried out using liquid water at 623 K and 150 atm in the absence of oxygen. The efficiency of this procedure was analyzed by determining the rate and amount of ortho-chlorophenol adsorbed in successive adsorption-regeneration cycles. The present procedure showed a much greater efficiency than that reported for chemical and/or thermal regeneration. Effects of this regeneration on the adsorption kinetics, adsorption capacity and textural characteristics of the carbon were investigated. The increase in adsorption capacity of the regenerated carbon compared with that of the original carbon seems mainly due to the opening of porosity during the regeneration treatment.     

Removal of naphthalene from aqueous solution on chemically modified activated carbons

The aim of this work was to correlate the textural and chemical features of carbonaceous adsorbents with the adsorption capacity of naphthalene from aqueous phase, at the concentration in which this compound is usually found in wastewater from coke ovens. The study reveals that the adsorption capacity in different carbon materials depends not only on the textural characteristics of the material but also on the functionalities of the activated carbons. The micropores of the adsorbents, particularly those of narrower diameter, were found to be active sites for the retention of naphthalene. In contrast, the modification of the surface chemistry of the carbon materials led to a decrease in the adsorption capacities. Dispersive forces play an important role, and adsorbents with a higher non-polar character have proven to be more efficient for the naphthalene adsorption. This behaviour has been linked to the presence of specific interactions between the basal planes and the polyaromatic structure of the naphthalene molecule.     

Electrochemical regeneration of field spent GAC from two water treatment plants

The effectiveness of on-site thermal regeneration of field-spent granular activated carbon (GAC) from two municipal drinking water facilities was compared with bench-scale electrochemical regeneration, a novel regeneration technology. The regeneration method was evaluated using aqueous natural organic material (NOM) adsorption, iodine number analysis, and surface area analysis. In contrast to the large electrochemical regeneration efficiencies reported in the literature for GAC loaded with phenolics and other individual organic compounds, the electrochemical reactor tested was only able to regenerate 8-15% of the NOM adsorption capacity of the field spent GAC. In contrast, thermal reactivation achieved up to 103% regeneration efficiency. To more accurately assess the efficiency of regeneration processes for water treatment applications, GAC should be loaded in continuous-flow columns and not batch rectors. The iodine number analysis yielded higher efficiency values, however it did not give an accurate estimate of the regeneration efficiency. The small changes in GAC pore size distribution were consistent with the low electrochemical regeneration efficiencies. These low efficiencies appear to be related to the low reversibility of NOM adsorption and to pH-induced adsorbate desorption being the primary mechanism for this type of electrochemical regeneration system.     

Occurrence, partition and removal of pharmaceuticals in sewage water and sludge during wastewater treatment

During 8 sampling campaigns carried out over a period of two years, 72 samples, including influent and effluent wastewater, and sludge samples from three conventional wastewater treatment plants (WWTPs), were analyzed to assess the occurrence and fate of 43 pharmaceutical compounds. The selected pharmaceuticals belong to different therapeutic classes, i.e. non-steroidal anti-inflammatory drugs, lipid modifying agents (fibrates and statins), psychiatric drugs (benzodiazepine derivative drugs and antiepileptics), histamine H2-receptor antagonists, antibacterials for systemic use, beta blocking agents, beta-agonists, diuretics, angiotensin converting enzyme (ACE) inhibitors and anti-diabetics. The obtained results showed the presence of 32 target compounds in wastewater influent and 29 in effluent, in concentrations ranging from low ng/L to a few μg/L (e.g. NSAIDs). The analysis of sludge samples showed that 21 pharmaceuticals accumulated in sewage sludge from all three WWTPs in concentrations up to 100 ng/g. This indicates that even good removal rates obtained in aqueous phase (i.e. comparison of influent and effluent wastewater concentrations) do not imply degradation to the same extent. For this reason, the overall removal was estimated as a sum of all the losses of a parent compound produces by different mechanisms of chemical and physical transformation, biodegradation and sorption to solid matter. The target compounds showed very different removal rates and no logical pattern in behaviour even if they belong to the same therapeutic groups. What is clear is that the elimination of most of the substances is incomplete and improvements of the wastewater treatment and subsequent treatments of the produced sludge are required to prevent the introduction of these micro-pollutants in the environment.     

Occurrence and removal of pharmaceuticals and personal care products (PPCPs) in an advanced wastewater reclamation plant

The occurrence of nineteen pharmaceutically active compounds and personal care products was followed monthly for 12 months after various stages of treatment in an advanced wastewater reclamation plant in Gwinnett County, GA, U.S.A. Twenty-four hour composite samples were collected after primary clarification, activated sludge biological treatment, membrane filtration, granular media filtration, granular activated carbon (GAC) adsorption, and ozonation in the wastewater reclamation plant. Compounds were identified and quantified using high performance liquid chromatography/tandem mass spectrometry (LC-MS/MS) and gas chromatography/mass spectrometry (GC-MS) after solid-phase extraction. Standard addition methods were employed to compensate for matrix effects. Sixteen of the targeted compounds were detected in the primary effluent; sulfadimethoxine, doxycycline, and iopromide were not found. Caffeine and acetaminophen were found at the highest concentrations (∼10⁵ ng/L), followed by ibuprofen (∼10⁴ ng/L), sulfamethoxazole and DEET (∼10³ ng/L). Most of the other compounds were found at concentrations on the order of hundreds of ng/L. After activated sludge treatment and membrane filtration, the concentrations of caffeine, acetaminophen, ibuprofen, DEET, tetracycline, and 17α-ethynylestradiol (EE2) had decreased by more than 90%. Erythromycin and carbamazepine, which were resistant to biological treatment, were eliminated by 74 and 88%, on average, by GAC. Primidone, DEET, and caffeine were not amenable to adsorption by GAC. Ozonation oxidized most of the remaining compounds by >60%, except for primidone and DEET. Of the initial 16 compounds identified in the primary effluent, only sulfamethoxazole, primidone, caffeine and DEET were frequently detected in the final effluent, but at concentrations on the order of 10-100 ng/L. Removal of the different agents by the various treatment processes was related to the physical-chemical properties of the compounds.     

Parameters from a new kinetic equation to evaluate activated carbons efficiency for water treatment

The fractal dimension of some commercial activated carbon (AC) was determined in the micro-, meso- and macropore range using mercury porosimetry and N(2) adsorption data. We studied the kinetic of adsorption of phenol, tannic acid and melanoidin on those ACs. The typical concentration-time profiles obtained here could be very well fitted by a general fractal kinetics equation q(n,alpha)(t)=q(e)[1-(1+(n-1)(t/tau(n,alpha))(alpha))(-1/(n-1))] deduced from recently new methods of analysis of reaction kinetics and relaxation. The parameter n is the reaction order, alpha is a fractional time index, q(e) measures the maximal quantity of solute adsorbed, and a "half-reaction time", tau(1/2), can be calculated, which is the time necessary to reach half of the equilibrium. The adsorption process on AC is clearly a heterogeneous process, taking place at the liquid-solid boundary, and the diffusion process occurs in a complex matrix with a fractal architecture as demonstrated here. In fact, these systems belong to what has been called "complex systems" and the fractal kinetic, which has been extensively applied to biophysics, can be a useful theoretical tool for study adsorption processes.     

Fenton-driven chemical regeneration of MTBE-spent GAC

Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was chemically regenerated utilizing the Fenton mechanism. Two successive GAC regeneration cycles were performed involving iterative adsorption and oxidation processes: MTBE was adsorbed to the GAC, oxidized, re-adsorbed, oxidized, and finally re-adsorbed. Oxidant solutions comprised of hydrogen peroxide (H2O2) (1.7-2.0%) and FeSO4 x 7H2O (3 g/L) (pH 2.5), were recirculated through the GAC column (30% bed expansion). The regeneration efficiency after two full cycles of treatment was calculated to be 91%. The cost of H2O2 was 0.59 dollars/kg GAC (0.27 dollars/lb) per regeneration cycle. There was no loss of sorptive capacity. Small reductions in carbon surface area and pore volume were measured. The lack of carbon deterioration under aggressive oxidative conditions was attributed to the oxidation of the target contaminants relative to the oxidation of carbon surfaces. The reaction byproducts from MTBE oxidation, tertiary butanol and acetone, were also degraded and did not accumulate significantly on the GAC. Excessive accumulation of Fe on the GAC and consequent interference with MTBE sorption and carbon regeneration was controlled by monitoring and adjusting Fe in the oxidative solution.     

The repeated exhaustion and chemical regeneration of activated carbon

Following experimental research studies carried out at the University of Birmingham, U.K., this paper presents data on the repeated application of the cycle of exhaustion, chemical regeneration and re-exhaustion of activated carbon. The adsorbates studied were nitrobenzene (a small organic molecule of mol. wt approx. 123), Rhodamine B (a much larger adsorbate of mol. wt approx. 480) and humic acid (an ill-defined substance consisting of macromolecules of molecular weight predominantly in the range 20,000–50,000). The regenerants used were all organic with solubilising powers to encourage the physical displacement of the adsorbate molecule by the regenerant molecule. As a general conclusion, it may be stated that chemical regenerants could be used to regenerate granular activated carbon repeatedly with little loss of adsorption capacity. Earlier studies which considered the effect of water on the powers of the carboxylic acid regenerants were confirmed in the results reported here. Bonding between the acids and water hindered the regeneration process.     

Adsorption studies of recalcitrant compounds of molasses spentwash on activated carbons

Due to high levels of residual chemical oxygen demand (COD) in the effluent of molasses spentwash (MSW) after anaerobic treatment, acceptable COD levels for discharge cannot be achieved without some form of post-treatment. In this study, the particulate composition of molasses spentwash after anaerobic digestion (MSWD), is characterised as to its particle size distribution, using micro- and ultrafiltration and three activated carbons are characterised as to their ability to reduce significantly the COD of MSWD effluent. The activated carbons tested as adsorbent, were characterised by XPS spectroscopy, elemental analysis, surface area, pore size distribution, and acid-base titration using the Boehm's method. Adsorption of phenol, used here as a reference compound, and of some organic compounds contained in MSWD (gallic acid, tannic acid, and melanoidin, respectively), was studied. It was clearly demonstrated that an activated carbon with a significant distribution of both micropores and mesopores and a significant amount of macropores that are assumed to act as conduits providing access to micro- and mesopores, have a good adsorption efficiency for compounds such as tannic acid and melanoidins. It is a good adsorbent for melanoidin and coloured compounds of MSWD, which represents a large source of the aqueous pollution in sugar cane industries.     

电化学法再生活性炭试验研究

采用电化学法再生吸附重金属离子的饱和活性炭,得出不同反应条件对活性炭再生效果的影响,并考察了电解时间、电解质投加量、搅拌状态、再生位置及辅助药剂等因素对活性炭再生率的影响。结果表明,再生液中硝酸的加入和饱和炭的再生位置对活性炭再生效果影响显著。电解时间为4h,NaCl投加量为5g,间歇搅拌,电解液中硝酸体积分数为0．5％时,电化学法再生活性炭可取得最佳效果。     

Mineralisation of coloured aqueous solutions by ozonation in the presence of activated carbon

The degradation of organic matter in coloured solutions of different classes of dyes by ozonation in the presence of activated carbon is investigated. The kinetics of the decolourisation and mineralisation of three different dyes solutions (CI Acid Blue 113, CI Reactive Red 241 and CI Basic Red 14) were studied in a laboratory scale reactor by three different processes: adsorption on activated carbon, oxidation with ozone and ozonation in the presence of activated carbon. The mineralisation of the solutions was followed by measuring the total organic carbon (TOC). Under the experimental conditions used in this work, activated carbon was not capable of completely removing the colour of the solutions in reasonable time. On the other hand, ozonation quickly decolourised all the solutions, but satisfactory removal of TOC was never achieved by this process. The combination of activated carbon with ozone enhanced the decolourisation of the solutions and especially the mineralisation of the organic matter. Activated carbon acts both as an adsorbent and as a catalyst in the reaction of ozonation. The surface chemistry of the activated carbon is an important parameter; it was observed that basic samples improve TOC removal. The main conclusions of this work were validated by treating a real textile effluent collected after the conventional biological treatment.     

Wet air regeneration of PAC: Comparison of carbons with different surface oxygen characteristics

Surface oxygen has an important effect on the wet air regeneration (WAR) of powdered activated carbons (PAC) and on the adsorption properties of the regenerated PAC. Virgin and phenanthrene-loaded PACs were regenerated in a bench-scale reactor, and then analyzed to determine surface oxygen content, adsorption capacity, and extent of phenanthrene oxidation.Even though the virgin wood-base (WB) and lignite-base (LB) PACs had about the same oxygen content, the oxygen content of the WB PAC increased more than twice as much as the LB PAC during regeneration. The difference was caused by the larger amount of CO₂-evolving oxides that formed on the WB PAC. WAR reduces the capacity of PAC for p-nitrophenol (PNP). Removing the surface oxides had varying effects on the carbon's capacity for PNP. Also, adsorbed phenanthrene was more easily oxidized on the WB PAC than on the LB PAC during regeneration.     

Fate and distribution of pharmaceuticals in wastewater and sewage sludge of the conventional activated sludge (CAS) and advanced membrane bioreactor (MBR) treatment

In this paper we report on the performances of full-scale conventional activated sludge (CAS) treatment and two pilot-scale membrane bioreactors (MBRs) in eliminating various pharmaceutically active compounds (PhACs) belonging to different therapeutic groups and with diverse physico-chemical properties. Both aqueous and solid phases were analysed for the presence of 31 pharmaceuticals included in the analytical method. The most ubiquitous contaminants in the sewage water were analgesics and anti-inflammatory drugs ibuprofen (14.6-31.3 μg/L) and acetaminophen (7.1-11.4 μg/L), antibiotic ofloxacin (0.89-31.7 μg/L), lipid regulators gemfibrozil (2.0-5.9 μg/L) and bezafibrate (1.9-29.8 μg/L), β-blocker atenolol (0.84-2.8 μg/L), hypoglycaemic agent glibenclamide (0.12-15.9 μg/L) and a diuretic hydrochlorothiazide (2.3-4.8 μg/L). Also, several pharmaceuticals such as ibuprofen, ketoprofen, diclofenac, ofloxacin and azithromycin were detected in sewage sludge at concentrations up to 741.1, 336.3, 380.7, 454.7 and 299.6 ng/g dry weight. Two pilot-scale MBRs exhibited enhanced elimination of several pharmaceutical residues poorly removed by the CAS treatment (e.g., mefenamic acid, indomethacin, diclofenac, propyphenazone, pravastatin, gemfibrozil), whereas in some cases more stable operation of one of the MBR reactors at prolonged SRT proved to be detrimental for the elimination of some compounds (e.g., β-blockers, ranitidine, famotidine, erythromycin). Moreover, the anti-epileptic drug carbamazepine and diuretic hydrochlorothiazide by-passed all three treatments investigated.Furthermore, sorption to sewage sludge in the MBRs as well as in the entire treatment line of a full-scale WWTP is discussed for the encountered analytes. Among the pharmaceuticals encountered in sewage sludge, sorption to sludge could be a relevant removal pathway only for several compounds (i.e., mefenamic acid, propranolol, and loratidine). Especially in the case of loratidine the experimentally determined sorption coefficients (K_ds) were in the range 2214-3321 L/kg (mean). The results obtained for the solid phase indicated that MBR wastewater treatment yielding higher biodegradation rate could reduce the load of pollutants in the sludge. Also, the overall output load in the aqueous and solid phase of the investigated WWTP was calculated, indicating that none of the residual pharmaceuticals initially detected in the sewage sludge were degraded during the anaerobic digestion. Out of the 26 pharmaceutical residues passing through the WWTP, 20 were ultimately detected in the treated sludge that is further applied on farmland.     

Sorption of perfluorooctane sulfonate and perfluorooctanoate on activated carbons and resin: Kinetic and isotherm study

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) have increasingly attracted global concerns in recent years due to their global distribution, persistence, strong bioaccumulation and potential toxicity. The feasibility of using powder activated carbon (PAC), granular activated carbon (GAC) and anion-exchange resin (AI400) to remove PFOS and PFOA from water was investigated with regard to their sorption kinetics and isotherms. Sorption kinetic results show that the adsorbent size influenced greatly the sorption velocity, and both the GAC and AI400 required over 168 h to achieve the equilibrium, much longer than 4 h for the PAC. Two kinetic models were adopted to describe the experimental data, and the pseudo-second-order model well described the sorption of PFOS and PFOA on the three adsorbents. The sorption isotherms show that the GAC had the lowest sorption capacity both for PFOS and PFOA among the three adsorbents, while the PAC and AI400 possessed the highest sorption capacity of 1.04 mmol g⁻¹ for PFOS and 2.92 mmol g⁻¹ for PFOA according to the Langmuir fitting. Based on the sorption behaviors and the characteristics of the adsorbents and adsorbates, ion exchange and electrostatic interaction as well as hydrophobic interaction were deduced to be involved in the sorption, and some hemi-micelles and micelles possibly formed in the intraparticle pores.     

17alpha-Ethinylestradiol sorption to activated sludge biomass: thermodynamic properties and reaction mechanisms

Sorption is an important mechanism for removal of 17alpha-ethinylestradiol (EE(2)) in biological wastewater treatment. In an effort to deepen our understanding of this process, this work investigated the underlying thermodynamic parameters. Biomass was harvested from a membrane bioreactor (MBR) and a sequencing batch reactor (SBR), and sorption experiments were conducted over a range of temperatures. Sorption of EE(2) to activated sludge was spontaneous (DeltaG values were between -16 and -11 KJ/mol), enthalpy-driven (DeltaH values were -37 KJ/mol (MBR) and -48 KJ/mol (SBR)), and entropy-retarded (DeltaS values were -74 (MBR) and -119 J/mol/K (SBR)). Although EE(2) is nonpolar, hydrophobic interactions were not dominant driving forces. The thermodynamic data also suggested that EE(2) sorption to biomass was primarily physisorption, but it also included low-level chemisorption. The FT-IR results suggested that chemical reactions were not significant enough to shift the detectable chemical bonding characteristics of the biomass functional groups.