Laboratory tests on the impact of superabsorbent polymers on transformation and sorption of xenobiotics in soil taking 14C-imazalil as an example

Due to water scarcity, the agricultural production in arid areas is dependent on a sustainable irrigation management. In order to optimize irrigation systems, the application of superabsorbent polymers (SAP) as soil amendments, frequently studied within the last years, may be an appropriate measure to enhance the water holding capacity and the plant-available water in poor arable soils. These persistent polymers are also able to reduce heavy metal and salt stress to crops by accumulating those inorganic compounds. However, the impact of SAP on fate and behavior of organic xenobiotics in soil is unknown. Therefore, transformation and sorption of the model substance ¹⁴C-imazalil were monitored without and with SAP amendment in silty sand and sand soil under laboratory conditions.Within the 100-d incubation period, the transformation of ¹⁴C-imazalil was not substantially affected by the SAP amendment even though the microbial activity increased considerably. In the silty sand soil, extractable residues dropped from 90% to 45% without and from 96% to 46% with SAP amendment. Non-extractable residues continuously increased up to 49% and 35% while mineralization reached 6% and 5%, respectively. In the sand soil, characterized by its lower microbial activity and lower organic carbon content, extractable residues merely dropped from 99% to 81% and from 100% to 85% while non-extractable residues increased from 2% to 14% and 1% to 10%, respectively. Mineralization was lower than 2%. The increased microbial activity, usually promoting transformation processes of xenobiotics, was compensated by the enhanced sorption in the amended soils revealed by the increase of soil/water distribution coefficients (K_d) of 26 to 42 L kg^− 1 for the silty sand and 6 to 25 L kg^− 1 for the sand, respectively.     

Ultrafiltration of natural organic matter and black carbon: Factors influencing aggregation and membrane fouling

There are concerns about black carbon (BC), due to its potential for sorption of toxic pollutants and inevitably entering drinking water sources. This study aimed to evaluate factors affecting BC aggregation and membrane fouling in the ultrafiltration of river water. Hydrophilic carbon black (CB) was selected as a surrogate of submicron BC in natural waters. Calcium, pH, and natural organic matter (NOM) were found to influence CB aggregation. Calcium induced interparticle interactions in a pH range of 4.3-7.7. In river water at 0.3 mM Ca²⁺, CB remained as fine aggregates (<300 nm) that caused substantial filtration resistance. At 1.3 mM Ca²⁺, CB size increased to 2.2-3.3 μm and membrane fouling was reduced. Interactions between particles and NOM enhanced organic rejection and eliminated irreversible membrane fouling. BC in water resources is a noxious substance, but it was easily aggregated in hard waters and could enhance NOM removal in the ultrafiltration process.     

Sorption of ionized and neutral emerging trace organic compounds onto activated sludge from different wastewater treatment configurations

The objective of this study was to examine sorption of a suite of 19 trace organic contaminants (TOrCs) to activated sludge. Compounds examined in this study included neutral, nonionized TOrCs as well as acidic TOrCs which may carry a negative charge and basic TOrCs which may carry a positive charge at the pH of wastewater. These TOrCs were evaluated to examine how sorptive behavior might differ for TOrCs in different states of charge. Additionally, multiple sludges from geographically and operationally different wastewater treatment plants were studied to elicit how solid-phase characteristics influence TOrC sorption. Characterization of sludge solids from 6 full scale treatment facilities and 3 bench-scale reactors showed no significant difference in fraction organic carbon (f_oc) and cation exchange capacity (CEC). Sorption experiments demonstrated that sorption of TOrCs also exhibits little variation between these different sludges. Organic carbon normalized partition coefficients (log K_oc) were determined as a measure of sorption, and were found to correlate well with octanol-water partition coefficients (log K_ow) for nonionized TOrCs, and log D_ow for anionic TOrCs where log D_ow is greater than 2. These data were used to construct a linear free energy relationship (LFER), which was comparable to existing LFERs for sorption onto sludge. No trend in sorption was apparent for the remaining anionic TOrCs or for the cationic TOrCs. These data suggest that predicting sorption to activated sludge based on K_ow values is a reasonable approach for neutral TOrCs using existing LFERs, but electrostatic (and likely other) interactions may govern the sorptive behavior of the charged organic chemicals to sludge.     

Investigation of timber harvesting impacts on herbaceous cover,forest floor and surface soil properties on skid road in an oak (Quercus petrea L.) stand

In this study, we investigated the timber harvesting effects on some soil properties (sand, silt, clay, pH, electrical conductivity, fine soil <2 mm, coarse soil >2 mm, root mass, organic carbon, moisture equivalent, total porosity, bulk density, moisture and compaction) at soil depths (0–5 and 5–10 cm), herbaceous cover and forest floor (unit mass, organic matter and moisture) on skid road of an oak (Quercus petrea L.) stand in Istanbul Belgrad Forest of Turkey.     

Effect of sunlight irradiation on photocatalytic pyrene degradation in contaminated soils by micro-nano size TiO2

The enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils by micro-nano size TiO₂ in the presence and absence of sunlight was investigated. The results showed that the synergistic effect of sunlight irradiation and TiO₂ was more efficient on pyrene degradation in quartz sand and red and alluvial soils than the corresponding reaction system without sunlight irradiation. In the presence of sunlight irradiation, the photooxidation (without TiO₂) of pyrene was very pronounced in alluvial and red soils and especially in quartz sand. However, in the absence of sunlight irradiation, the catalytic pyrene degradation by TiO₂ and the photooxidation (without TiO₂) of pyrene were almost nil. This implicates that ultra-violet (UV) wavelength range of sunlight plays an important role in TiO₂-enhanced photocatalytic pyrene degradation and in photooxidation (without TiO₂) of pyrene. The percentages of photocatalytic pyrene degradation by TiO₂ in quartz sand, alluvial and red soils under sunlight irradiation were 78.3, 23.4, and 31.8%, respectively, at 5 h reaction period with a 5% (w/w) dose of the amended catalyst. The sequence of TiO₂-enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils was quartz sand > red soil > alluvial soil, due to different texture and total organic carbon (TOC) contents of the quartz sand and other two soils. The differential Fourier transform infrared (FT-IR) spectra of degraded pyrene in alluvial soil corroborate that TiO₂-enhanced photocatalytic degradation rate of degraded pyrene was much greater than photooxidation (without TiO₂) rate of degraded pyrene. Based on the data obtained, the importance for the application of TiO₂-enhanced photocatalytic pyrene degradation and associated organic contaminants in contaminated soils was elucidated.     

Effect of Fenton's oxidation on the particle size distribution of organic carbon in olive mill wastewater

The study evaluated the effect of Fenton's oxidation on the particle size distribution (PSD) of significant parameters reflecting the organic carbon content of olive oil mill wastewater (OMW). The organic carbon content of the studied OMW was characterized by a COD level of around 40,000 mg/L, with 13,500 mg/L of TOC and 1670 mg/L of total phenols. The corresponding antioxidant activity (AOA) was determined as 33,400 mg/L. PSD of the selected organic carbon parameters was investigated using a sequential filtration/ultrafiltration procedure. COD fractionation based on PSD revealed two major components, a soluble fraction below 2 nm and a particulate fraction above 1600 nm representing 49% and 20% of the total COD, respectively. The remaining COD was distributed in the colloidal and supracolloidal zones. The PSD of TOC, total phenols and AOA exhibited similar profiles with peaks at the two ends of the studied size range. Overall COD removals achieved via Fenton's oxidation both at pH = 3.0 and pH = 4.6 (the original pH of the OMW) remained in the range of 40-50%. As anticipated, the effect of Fenton's treatment was more pronounced in the soluble size range. Fenton's oxidation at pH = 3.0 resulted in 46% and 63% removals for total phenols and AOA, respectively. The results obtained indicated that Fenton's process could only be useful as an alternative preliminary treatment option of the required full treatment scheme that could involve a sequence of filtration, oxidation and/or biological treatment steps.     

Oxidative degradation of pyrene in contaminated soils by δ-MnO2 with or without sunlight irradiation

The enhanced oxidative degradation of pyrene in quartz sand and alluvial and red soils by micro-nano size birnessite (δ-MnO₂) in the presence and absence of sunlight was investigated. The degradation of pyrene by δ-MnO₂ in quartz sand showed very little synergistic effect of sunlight irradiation on δ-MnO₂ oxidizing power. However, pyrene degradation by δ-MnO₂ in alluvial and red soils was greater under solar irradiation than the combination of photooxidation of pyrene and oxidation of pyrene by δ-MnO₂. The oxidative degradation percentages of pyrene by δ-MnO₂ under sunlight irradiation are 94.8, 97.7, and 100% for alluvial soil, red soil, and quartz sand, respectively. Oxidative degradation percentages of pyrene by δ-MnO₂ in alluvial and red soils with irradiation of sunlight almost attained a maximum at 1 h with a 5% (w/w) dose of the amended oxidant. Due to their different total organic carbon (TOC) contents, the sequence of enhanced oxidative degradation of pyrene by δ-MnO₂ in quartz sand and alluvial and red soils was quartz sand > red soil > alluvial soil. Further, this study revealed that δ-MnO₂-enhanced oxidative degradation of pyrene is very pronounced in contaminated soils in situ even at deep soil layers where irradiation by sunlight is very limited.     

Biodegradability enhancement of a pesticide-containing bio-treated wastewater using a solar photo-Fenton treatment step followed by a biological oxidation process

This work proposes an efficient combined treatment for the decontamination of a pesticide-containing wastewater resulting from phytopharmaceutical plastic containers washing, presenting a moderate organic load (COD = 1662-1960 mg O₂ L⁻¹; DOC = 513-696 mg C L⁻¹), with a high biodegradable organic carbon fraction (81%; BOD₅ = 1350-1600 mg O₂ L⁻¹) and a remaining recalcitrant organic carbon mainly due to pesticides. Nineteen pesticides were quantified by LC-MS/MS at concentrations between 0.02 and 45 mg L⁻¹ (14-19% of DOC). The decontamination strategy involved a sequential three-step treatment: (a) biological oxidation process, leading to almost complete removal of the biodegradable organic carbon fraction; (b) solar photo-Fenton process using CPCs, enhancing the bio-treated wastewater biodegradability, mainly due to pesticides degradation into low-molecular-weight carboxylate anions; (c) and a final polishing step to remove the residual biodegradable organic carbon, using a biological oxidation process. Treatment performance was evaluated in terms of mineralization degree (DOC), pesticides content (LC-MS/MS), inorganic ions and low-molecular-weight carboxylate anions (IC) concentrations. The estimated phototreatment energy necessary to reach a biodegradable wastewater, considering pesticides and low-molecular-weight carboxylate anions concentrations, Zahn-Wellens test and BOD₅/COD ratio, was only 2.3 kJ_UV L⁻¹ (45 min of photo-Fenton at a constant solar UV power of 30 W m⁻²), consuming 16 mM of H₂O₂, which pointed to 52% mineralization and an abatement higher than 86% for 18 pesticides. The biological oxidation/solar photo-Fenton/biological oxidation treatment system achieved pesticide removals below the respective detection limits and 79% mineralization, leading to a COD value lower than 150 mg O₂ L⁻¹, which is in agreement with Portuguese discharge limits regarding water bodies.     

Sorption of emerging trace organic compounds onto wastewater sludge solids

This work examined the sorption potential to wastewater primary- and activated-sludge solids for 34 emerging trace organic chemicals at environmentally relevant concentrations. These compounds represent a diverse range of physical and chemical properties, such as hydrophobicity and charge state, and a diverse range of classes, including steroidal hormones, pharmaceutically-active compounds, personal care products, and household chemicals. Solid-water partitioning coefficients (K_d) were measured where 19 chemicals did not have previously reported values. Sludge solids were inactivated by a nonchemical lyophilization and dry-heat technique, which provided similar sorption behavior for recalcitrant compounds as compared to fresh activated-sludge. Sorption behavior was similar between primary- and activated-sludge solids from the same plant and between activated-sludge solids from two nitrified processes from different wastewater treatment systems. Positively-charged pharmaceutically-active compounds, amitriptyline, clozapine, verapamil, risperidone, and hydroxyzine, had the highest sorption potential, log K_d = 2.8-3.8 as compared to the neutral and negatively-charged chemicals. Sorption potentials correlated with a compound’s hydrophobicity, however the higher sorption potentials observed for positively-charged compounds for a given log D_ow indicate additional sorption mechanisms, such as electrostatic interactions, are important for these compounds. Previously published soil-based one-parameter models for predicting sorption from hydrophobicity (log K_ow > 2) can be used to predict sorption for emerging nonionic compounds to wastewater sludge solids.     

Measuring the saturation limit of low-volatility organic compounds in soils: implications for estimates of dermal absorption

Estimating dermal absorption from contaminated soils typically requires extrapolations from measurements obtained on soils artificially contaminated at much larger concentrations. Such extrapolations should be constrained by the fact that maximum absorption will occur for the largest possible concentration of chemical on the soil without neat chemical being present; i.e., at the soil saturation limit (S_soil). Saturation limits of two low-volatility model compounds (4-cyanophenol and methyl paraben) were determined on the 38-63 μm sieve fraction of four soils with different fractions of organic carbon (f_oc = 0.015-0.45) and specific surface areas (σ_soil = 4-34 m² g^− 1) using two methods: equilibrium uptake into silicone rubber membranes and differential scanning calorimetry. Except for Pahokee peat, which had the largest f_oc, a model assuming contributions from both surface adsorption and organic carbon absorption provided excellent predictions of S_soil. In all soils, the surface saturation concentration of both chemicals was estimated at 2.2 mg m^− 2. The saturation concentration of 4-cyanophenol in the soil organic carbon was 1.7-fold higher than methyl paraben, which is consistent with the estimated solubility limits of these two chemicals in octanol.     

Measurements and modeling of pesticide persistence in soil at the catchment scale

Degradation of pesticides in soils is both spatially variable and also one of the most sensitive factors determining losses to surface water and groundwater. To date, no general guidance is available on suitable approaches for dealing with spatial variation in pesticide degradation in catchment or regional scale modeling applications. The purpose of the study was therefore to study the influence of various soil physical, chemical and microbiological characteristics on pesticide persistence in the contrasting cultivated soils found in a small (13 km²) agricultural catchment in Sweden and to develop and test a simple model approach that could support catchment scale modeling. Persistence of bentazone, glyphosate and isoproturon was investigated in laboratory incubation experiments. Degradation rate constants were highly variable with coefficients of variation ranging between 42 and 64% for the three herbicides. Multiple linear regression analysis and Mallows Cp statistic were employed to select the best set of independent parameters accounting for the variation in degradation. Soil pH and the proportion of active microorganisms (r) together explained 69% of the variation in the bentazone degradation rate constant; the Freundlich sorption co-efficient (K_f) and soil laccase activity together explained 88% of the variation in degradation rate of glyphosate, while soil pH was a significant predictor (p < 0.05) for isoproturon persistence. However, correlations between many potential predictor variables made clear interpretations of the statistical analysis difficult. Multiplicative models based on two predictors chosen ‘a priori’, one accounting for microbial activity (e.g. microbial respiration, laccase activity or the surrogate variable soil organic carbon, SOC) and one accounting for the effects of sorption on bioavailability, showed promise to support predictions of degradation for large-scale modeling applications, explaining up to 50% of the variation in herbicide persistence.     

Characterization of soil phosphorus in a fire-affected forest Cambisol by chemical extractions and P-NMR spectroscopy analysis

This study was conducted to investigate the long-term effects of fire on soil phosphorus (P) and to determine the efficiency of different procedures in extracting soil P forms. Different P forms were determined: labile forms (Olsen-P, Bray-P, and P extracted by anion exchange membranes: AEM-P); moderately labile inorganic and organic P, obtained by NaOH-EDTA extraction after removing the AEM-P fraction; and total organic and inorganic soil P. ³¹P-NMR spectroscopy was used to characterize the structure of alkali-soluble P forms (orthophosphate, monoester, pyrophosphate, and DNA). The studied area was a Pinus pinaster forest located at Arenas de San Pedro (southern Avila, Spain). The soils were Dystric Cambisols over granites. Soil samples were collected at 0-2 cm, 2-5 cm, and 10-15 cm depths, two years after a fire in the burned area and in an adjacent unburned forest area. Fire increased the total N, organic C, total P, and organic and inorganic P content in the surface soil layer. In burned soil, the P extracted by the sequential procedure (AEM and NaOH + EDTA) was about 95% of the total P. Bray extraction revealed a fire-induced increase in the sorption surfaces. Analysis by chemical methods overestimated the organic P fraction in the EDTA-NaOH extract in comparison with the determination by ignition procedure. This overestimation was more important in the burned than unburned soil samples, probably due to humification promoted by burning, which increased P sorption by soil particles. The fire-induced changes on the structure of alkali-soluble P were an increase in orthophosphate-P and a decrease in monoester-P and DNA-P.     

Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar

Lead sorption capacity and mechanisms by sludge-derived biochar (SDBC) were investigated to determine if treatment of acid mine drainage (AMD) containing metals with SDBC is feasible. It was found that the biochar derived from pyrolysis treatment of sewage sludge could effectively remove Pb²⁺ from acidic solution with the capacities of 16.11, 20.11, 24.80, and 30.88 mg g⁻¹ at initial pH 2, 3, 4 and 5, respectively. Lead sorption processes were pseudo-second order kinetic and faster at a higher pH. Furthermore, the relative contribution of both inorganic mineral composition and organic functional groups of SDBC for Pb²⁺ removal mechanisms, was quantitatively studied at pH 2-5. The results showed that Pb sorption primarily involved the coordination with organic hydroxyl and carboxyl functional groups, which was 38.2-42.3% of the total sorbed Pb varying with pH, as well as the coprecipitation or complex on mineral surfaces, which accounted for 57.7-61.8% and led to a bulk of Ca²⁺ and Mg²⁺ release during sorption process. A new precipitate was solely observed on Pb-loaded SDBC as 5PbO·P₂O₅·SiO₂(lead phosphate silicate) at initial pH 5, confirmed by XRD and SEM-EDX. The coordination of Pb²⁺ with carboxyl and hydroxyl functional groups was demonstrated by FT-IR, and the contribution of free carboxyl was significant, ranging from 26.1% to 35.5%. Results from this study may suggest that the application of SDBC is a feasible strategy for removing metal contaminants from acid solutions.     

Selective removal of perfluorooctane sulfonate from aqueous solution using chitosan-based molecularly imprinted polymer adsorbents

Perfluorooctane sulfonate (PFOS) pollution in aqueous environment is a problem of global concern. A novel chitosan-based molecularly imprinted polymer (MIP) was prepared by crosslinking with epichlorohydrin (ECH) in the presence of PFOS as the template. During the preparation of the MIP adsorbents, the template amount and crosslinking agents significantly affected the imprinting effect. The optimized MIP adsorbents had a sorption amount of 560 μmol g⁻¹ for PFOS, while the sorption amount of the non-imprinted polymer (NIP) was only 258 μmol g⁻¹. The sorption behaviors of the MIP adsorbents including sorption kinetics, isotherms, effect of pH, ionic strength and selective sorption were investigated in detail. Sorption experimental results showed that the MIP adsorbents had good selectivity for PFOS, while other anionic contaminants with different structure had little influence on the sorption of the target PFOS. It was found that the electrostatic interaction played an important role in recognizing the target compound in the sorption process. Additionally, the MIP adsorbents could be used at least five times without any loss in sorption capacity. The chitosan-based MIP adsorbents may find potential application in water or wastewater treatment for the selective removal of PFOS.     

Oxidation of organics in retentates from reverse osmosis wastewater reuse facilities

The use of membrane processes for wastewater treatment and reuse is rapidly expanding. Organic, inorganic, and biological constituents are effectively removed by reverse osmosis (RO) membrane processes, but concentrate in membrane retentates Disposal of membrane concentrates is a growing concern. Applying advanced oxidation processes (AOPs) to RO retentate is logical because extensive treatment and energy inputs were expended to concentrate the organics, and it is cheaper to treat smaller flowstreams. AOPs (e.g., UV irradiation in the presence of titanium dioxide; UV/TiO₂) can remove a high percentage of organic matter from RO retentates. The combination of AOPs and a simple biological system (e.g., sand filter) can remove higher levels of organic matter at lower UV dosages because AOPs produce biologically degradable material (e.g., organic acids) that have low hydroxyl radical rate constants, meaning that their oxidation, rather than that of the primary organic matter in the RO retentate, dictates the required UV energy inputs. At the highest applied UV dose (10 kWh m⁻3), the dissolved organic carbon (DOC) in the RO retentate decreased from ∼40 to 8 mg L⁻1, of which approximately 6 mg L⁻1 were readily biologically degradable. Therefore, after combined UV treatment and biodegradation, the final DOC concentration was 2 mg L⁻1, representing a 91% removal. These results suggest that UV/TiO₂ plus biodegradation of RO retentates is feasible and would significantly reduce the organic pollutant loading into the environment from wastewater reuse facilities.     

Effects of altered groundwater chemistry upon the pH-dependency and magnitude of bacterial attachment during transport within an organically contaminated sandy aquifer

The effects of a dilute (ionic strength = 5 × 10⁻³ M) plume of treated sewage, with elevated levels (3.9 mg/L) of dissolved organic carbon (DOC), upon the pH-dependency and magnitude of bacterial transport through an iron-laden, quartz sand aquifer (Cape Cod, MA) were evaluated using sets of replicate, static minicolumns. Compared with uncontaminated groundwater, the plume chemistry diminished bacterial attachment under mildly acidic (pH 5.0-6.5) in-situ conditions, in spite of the 5-fold increase in ionic strength and substantively enhanced attachment under more alkaline conditions. The effects of the hydrophobic neutral and total fractions of the plume DOC; modest concentrations of fulvic and humic acids (1.5 mg/L); linear alkyl benzene sulfonate (LAS) (25 mg/L); Imbentin (200 μg/L), a model nonionic surfactant; sulfate (28 mg/L); and calcium (20 mg/L) varied sharply in response to relatively small changes in pH, although the plume constituents collectively decreased the pH-dependency of bacterial attachment. LAS and other hydrophobic neutrals (collectively representing only ∼3% of the plume DOC) had a disproportionately large effect upon bacterial attachment, as did the elevated concentrations of sulfate within the plume. The findings further suggest that the roles of organic plume constituents in transport or bacteria through acidic aquifer sediments can be very different than would be predicted from column studies performed at circumneutral pH and that the inorganic constituents within the plume cannot be ignored.     

Improved retention of imidacloprid (Confidor) in soils by adding vermicompost from spent grape marc

Batch sorption experiments of the insecticide imidacloprid by ten widely different Spanish soils were carried out. The sorption was studied for the active ingredient and its registered formulation Confidor. The temperature effect was studied at 15 degrees C and 25 degrees C. The addition of a vermicompost from spent grape marc (natural and ground), containing 344 g kg(-1) organic carbon, on the sorption of imidacloprid by two selected soils, a sandy loam and a silty clay loam, having organic carbon content of 3.6 g kg(-1) and 9.3 g kg(-1), respectively, was evaluated. Prior to the addition of this vermicompost, desorption isotherms with both selected soils, were also performed. The apparent hysteresis index (AHI) parameter was used to quantify sorption-desorption hysteresis. Sorption coefficients, K(d) and K(f), for the active ingredient and Confidor(R) in the different soils were similar. Sorption decreased with increasing temperature, this fact has special interest in greenhouse systems. A significant correlation (R(2)=0.965; P<0.01) between K(f) values and the organic carbon (OC) content was found, but some soils showed higher sorption coefficients than that expected from their OC values. The normalized sorption coefficients with the soil organic carbon content (K(oc)) were dispersed and low, implying that other characteristics of soils could contribute to the retention capacity as well. The spent grape marc vermicompost was an effective sorbent of this insecticide (K(f)=149). The sorption of imidacloprid increased significantly in soils amended with this vermicompost. The most pronounced effect was found in the sandy loam soil with low OC content, where the addition of 5% and 10% of vermicompost increased K(f) values by 8- and 15-fold, respectively. Soil desorption of imidacloprid was slower for the soil with the higher OC and clay content.     

Occurrence and removal of pharmaceuticals, caffeine and DEET in wastewater treatment plants of Beijing, China

The occurrence and removal of 13 pharmaceuticals and 2 consumer products, including antibiotic, antilipidemic, anti-inflammatory, anti-hypertensive, anticonvulsant, stimulant, insect repellent and antipsychotic, were investigated in four wastewater treatment plants (WWTPs) of Beijing, China. The compounds were extracted from wastewater samples by solid-phase extraction (SPE) and analyzed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Most of the target compounds were detected, with the concentrations of 4.4 ng L⁻¹-6.6 μg L⁻¹ and 2.2-320 ng L⁻¹ in the influents and secondary effluents, respectively. These concentrations were consistent with their consumptions in China, and much lower than those reported in the USA and Europe. Most compounds were hardly removed in the primary treatment, while their removal rates ranging from −12% to 100% were achieved during the secondary treatment. In the tertiary treatment, different processes showed discrepant performances. The target compounds could not be eliminated by sand filtration, but the ozonation and microfiltration/reverse osmosis (MF/RO) processes employed in two WWTPs were very effective to remove them, showing their main contributions to the removal of such micro-pollutants in wastewater treatment.     

Similarities in effluent organic matter characteristics from Connecticut wastewater treatment plants

Effluent organic matter (EfOM) from five Connecticut (USA) municipal wastewater treatment plants was isolated with DAX8 (hydrophobic fraction) and XAD4 (transphilic fraction) resins. Isolate recoveries ranged from 18 to 42% of the total organic carbon for DAX8 resin and from 6 to 12% for XAD4 resin. Isolated EfOM was characterized by traditional organic geochemistry techniques. Weight-averaged molecular weights of extracted EfOM by size exclusion chromatography were 450-670 Da with higher weights observed for the hydrophobic fractions than the transphilic fractions. Fluorescence characterization showed both humic- and fulvic-like fluorescence, as well as tryptophan- and tyrosine-like fluorescence, the latter not commonly observed for terrestrial organic matter. Fluorescence indices were between 1.5 and 1.9 with lower values observed for hydrophobic EfOM fractions than for transphilic fractions. Specific ultraviolet absorbance was measured between 0.8 and 3.0 L mg⁻¹ m⁻¹ with higher values for the hydrophobic EfOM fractions. Together these results indicated that isolated EfOM is similar in characteristics to microbially derived organic matter from natural aquatic systems. Little variation in EfOM characteristics was observed between the five wastewater treatment plants, suggesting that the characteristics of EfOM are similar, regardless of treatment plant design.     

Sorption of phosphate from acidic wastewater into three Tunisian type clay soils

The removal of phosphates from acidic wastewater using three types of soil minerals (Soil 1, Soil 2, and Soil 3) with a high content of paligorskite, smectite, and illite, respectively, is studied. The effect of the medium pH value, contact duration, and solid-liquid ratio is considered. The smectite-containing soil possesses the highest sorption capacity with respect to phosphate. The isotherms of phosphate sorption by soils are processed in the Freundlich and Langmuir equation coordinates. It is shown that the fitting of isotherms in the Freundlich equation coordinates results in better correspondence with experimental data. In addition, the adsorption selectivity of ions (PO₄ ^3?, F^?, Cl^?) existing in the waste solution by these soils was studied, and the fluoride is more selective in the acid pH region.