Sequential Chemical Extraction Research Articles

Assessment of Heavy Metal Pollution and Potential Ecological Risk in Sewage Sludge from Municipal Wastewater Treatment Plant Located in the Most Industrialized Region in Poland-Case Study.

This study aimed to assess the pollution and potential ecological risk of seven heavy metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in the sewage sludge collected from a wastewater treatment plant (WWTP), located in the most industrialized region of Poland (Silesian Voivodeship). The concentrations of heavy metals were determined using inductively coupled plasma optical spectrometry (ICP-OES) and cold vapor atomic absorption spectrometry (CVAAS). The chemical forms (chemical speciation) of heavy metals were determined using the three-step chemical sequential extraction procedure, developed by the Community Bureau of Reference (BCR). To assess the pollution level and potential ecological risk, the following indices were used: Geoaccumulation Index (Igeo), Potential Ecological Risk Factor (ER), Individual Contamination Factor (ICF), Risk Assessment Code (RAC), and Ecological Risk Factor (ERF)—the author’s index. Sludge samples were collected at successive stages of processing. The results revealed that the activated sludge process and sludge thickening have a significant impact on heavy metal distribution, while anaerobic digestion and dehydration decrease their mobility. The most dominant metals in the sludge samples were Zn and Cu. However, the content of heavy metals in sewage sludge did not exceed the permissible standards for agricultural purposes. The concentrations of heavy metals bound to the immobile fractions exhibited higher concentrations, compared to those bound to mobile fractions (except Zn). The values of the total indices indicated that sludge samples were moderately to highly contaminated with Zn, Hg, Cd, Cu, and Pb, of which only Hg, Cd, and Cu posed a potential ecological risk, while according to the speciation indices, sludge samples were moderately to very highly polluted with Zn, Cu, Cd, Cr, and Ni, of which Zn, Ni, and Cd were environmentally hazardous. The obtained results proved that assessment of the pollution level and potential ecological risk of heavy metals in sewage sludge requires knowledge on both their total concentrations and their chemical forms. Such an approach will help prevent secondary pollution of soils with heavy metals, which may influence the reduction of health risks associated with the consumption of plants characterized by a high metal content.

Effect of occurrence mode of heavy metal elements in a low rank coal on volatility during pyrolysis

The harmful trace elements will be released during coal utilization, which can cause environment pollution and further endangering human health, especially for heavy metal elements. Compared to combustion, the release of heavy metal elements during coal pyrolysis process, as a critical initial reaction stage of combustion, has not received sufficient attention. In the present paper, a low rank coal, from Xinjiang province in China, was pyrolyzed in a fixed bed reactor from room temperature, at atmospheric pressure, with the heating rate of 10 °C/min, and the final pyrolysis temperature was from 400 to 800 °C with the interval of 100 °C. The volatility of heavy metal elements (including As, Hg, Cd and Pb) during pyrolysis process was investigated. The results showed the volatility of all heavy metal elements increased obviously with increasing temperature, and followed the sequence as Hg > Cd > As > Pb, which was mainly caused by their thermodynamic property and occurrence modes in coal. The occurrence modes of heavy metals were studied by sink-and-float test and sequential chemical extraction procedure, and it can be found that the heavy metal elements were mainly in the organic and residual states (clay minerals) in the raw coal. And most of the organic heavy metals escaped during the pyrolysis process, the remaining elements were mainly in the residual state, and the elements in Fe–Mn state also tended to remain in the char.

Organic wastes as alternative sources of phosphorus for plant nutrition in a calcareous soil

Recycled organic wastes (OW) can be a valuable P source; however, their P-fertilising capacity is still poorly known. In this study, we selected three anaerobic digestates [wastewater sludge (D1), winery sludge (D2), and bovine-slurry/energy crops (BD)] and two animal effluents [bovine slurry (BS) and swine slurry (SS)] to test their P-release and P-fertilising capacities via sequential chemical extraction (SCE), X-ray diffraction (XRD), and 31P-nuclear magnetic resonance (31P NMR). Subsequently, the three digestates (30 mg P kg−1 of soil) were compared for the release of Olsen-P during a soil incubation and for plant-P apparent recovery (ARF) in a pot experiment using ryegrass (112 days) in a soil with poorly available-P (Olsen-P < 5 mg kg−1), under a non-limiting N environment. The amount of labile-P (H2O + NaHCO3), as determined from SCE, related well to the Olsen-P following OW addition to the soil. It was shown via 31P NMR spectroscopy that orthophosphate was the leading P-form in highly P-releasing OW. The amount of labile-P, however, was affected by soil adsorption, thereby reducing plant-P uptake. The plant-P ARF (%) showed that the recycled P-sources were clustered in highly (BD and SS: ≈20%), intermediately (D1 and BS: ≈15%), and poorly performing OWs (D2: ≈10%) vs. chemical P-source (P-chem: 20%). Therefore, only BD and SS were effective alternatives to P-chem; however, the other OW can be efficient P-sources in soils with higher Olsen-P. Thus, crop fertilisation can be tailored on a P-basis by SCE as a function of soil adsorption capacity and on an N-basis according to the demand.

Relationship of the mobile forms of calcium and strontium in soils with their accumulation in meadow plants in the area of Kashin-Beck endemia.

This study was aimed at assessment of strontium and calcium mobility in soils and their accumulation with plants in the areas endemic for Kashin-Beck disease in Eastern Transbaikalia. The strontium and calcium mobility levels were determined using the method of sequential chemical extraction for 7 samples of meadow soils collected from the endemic region and 7 soil samples taken from conditionally control sites. To measure the Ca and Sr levels in the soil and plant samples, XRF analysis and AAS were used. The increased strontium level in the meadow soils of the endemic areas is accompanied by the element's higher mobility. The highest strontium yield was observed in the course of soil extraction using 1 M ammonium acetate, while the soils taken from the control sites gave lower amounts of the trace element. Furthermore, there is a positive correlation between the amount of the strontium extracted and its content in plants (r = + 0.86 - 0.98). At the sequential chemical extraction of calcium from the soils using the above method, the calcium yield was maximal in the ammonium acetate fraction (background sites) and in ammonium acetate and 6M HCl fractions (endemic areas). The correlation between the amount of the calcium extracted in 1M ammonium acetate and the macroelement levels found in plants was + 0.968. In addition, a peculiarly high accumulation of strontium in various willow species as compared to other meadow plants was revealed for the first time ever. Thus, the work introduces new data into the trace element biogeochemistry and environmental monitoring.

Pretreatment method for the analysis of phosphate oxygen isotope (δ18OP) of different phosphorus fractions in freshwater sediments

Accurate measurement of the oxygen isotopic composition of dissolved phosphate (δ18OP) of different phosphorus (P) fractions in lacustrine sediments is very difficult because of the influence of large amounts of impurities. In this study, we developed a five-step method for obtaining high purity Ag3PO4 sample for the analysis of δ18OP of different P fractions in freshwater sediments. Sedimentary P was divided into NaHCO3-P, NaOH-P and HCl-P by chemical sequential extraction. Pretreatment procedures for different sedimentary P fractions were improved in the following respects: 1) abandonment of the magnesium-induced coprecipitation method to avoid the introduction of impurity ions, such as Mg2+ and Cl−, and reduce the loss of P; 2) use of a small amount of non-phosphate activated carbon powder to efficiently remove organic matter in extracts of NaHCO3-P and NaOH-P, and reduce the loss of P; 3) adjustment of the HCl-P extract pH to 4 in order to form Fe(OH)3-PO43− coprecipitate, thereby removing most of metals and Cl−. This method reduces the pretreatment steps, simplifies the operation and increases the recovery of phosphate (90.98%–96.69%). The high purity Ag3PO4 sample can be obtained and the repeatability and accuracy of measured δ18OP is better than 0.3‰, demonstrating high reliability and accuracy. This new method was used to analyze the δ18OP of different P fractions in sediments of a eutrophic lake in southwestern China. The preliminary results indicated that the δ18OP in the sediments can be used to identify different P sources, and provide new insights into sedimentary P cycling. The method established in this study provides a powerful tool for investigating the sources and biogeochemical cycle of P in freshwater sediments.

Determination of mercury occurrence and thermal stability in high ash bituminous coal based on sink-float and sequential chemical extraction method

The high-ash coals have gradually become essential energy resources due to their availability, and the occurrence of Hg in coals and its thermal stability could be significantly influenced by ash-forming minerals. In this work, a high-ash bituminous coal was divided into 4 density fractions using sink-float procedure. The sequential chemical extraction procedures, temperature-programmed pyrolysis and TG/DTG experiments were carried to investigate the Hg occurrence and thermal stability in different samples. The results showed that the Hg contents in samples has a positive relation with the ash, sulfate and sulfide contents, and the correlation coefficients were 0.868, 0.535 and 0.924, respectively. However, the negative value with correlation coefficient of 0.751 between the Hg and organic sulfur content was obtained. The Hg species in different samples were quite distinct, the organic matrix-bound Hg was the dominate form in SG1 with the content of 76.14%, the SG2 and SG3 were mainly composed of HCl soluble Hg and Hg(NO3)2·xH2O, and the Hg species occurred in SG4 were mainly HCl soluble Hg and pyrite-bound Hg. In the process of pyrolysis, the matrix-bound Hg, HCl soluble Hg, HgS and Hg(NO3)2·xH2O were thermally unstable and could be released into gas in the drying and desorption stage of 30–400 °C, while the pyrite-bound Hg mainly released with the decomposition of pyrite in the temperature range of 400–600 °C. There was only little Hg released in the temperature range of 600–850 °C, indicating the negligible relationship of Hg with carbonate and silicate minerals.

Phosphorus Fractionation in Soils Fertilized with Recycled Phosphorus Products

Phosphorus (P) will be exhausted, and its recovery and cycling will play a pivotal role in agricultural systems. Different technologies have been developed to recover P from waste materials, such as mono-incineration, acid digestion, and coprecipitation of P from wastewaters. The aim of this study was to assess the plant availability of P from different recycled P products by using a sequential chemical P fractionation of soil P and to study the fate of P applied to the soil. We evaluated the plant P availability in soils fertilized with eight recycled P products in comparison with two commercial fertilizers (triple superphosphate [TSP] and rock phosphate [Rock-P]) by means of a sequential chemical extraction of soil P and combined this data with previously published information for soil isotopically exchangeable P (IEP) and P uptake by plants (PU). We sequentially extracted inorganic P with alkaline extractants and an acid solution and analyzed the increase in P fractions caused by the application of different fertilizers. P extracted by alkali solutions was positively correlated with the IEP and with PU, whereas P extracted by the acid solution was negatively correlated with these parameters. In soils fertilized with recycled P products obtained by a chemical procedure (magnesium-ammonium-phosphate), soil P was extracted mainly by alkali extractants, while in soils fertilized with P products obtained by thermal procedures (i.e. sewage sludge ashes), soil P was extracted by the acid solution and was of low plant availability. Sequential chemical fractionation of soil P is suitable for characterizing the plant availability of P from recycled P products. The increase in the alkali soluble fraction in soil characterizes the portion of P available to plants, while the acid soluble fraction characterizes the recalcitrant portion. Phosphorus from fertilizers obtained by chemical procedures, like magnesium-ammonium-phosphate, is mainly extracted by alkali solutions and is comparable to water-soluble P fertilizers, while P from products obtained by thermal processes is mainly extracted by acid solutions and remains mostly unavailable to plants.

Characteristics and speciation of heavy metals in fly ash and FGD gypsum from Chinese coal-fired power plants

This research focused on the distribution and chemical speciation of Cr, Pb, Cd, Cu, Zn, and As in fly ash and flue gas desulfurization gypsum (FGD gypsum) from a large-scale pulverized coal-fired (PC) power plants in Anhui Province of eastern China. The partitioning behavior of the heavy metals (HMs) revealed that trace metals were mainly retained in coal combustion ash (88.9–98.7%) and FGD gypsum (1.26–4.33%). Other fly ashes generated from different PC boilers and a circulated fluidized boiler (CFB) were collected to comparatively study the ash mineralogy and chemistry. The PC fly ashes were dominated by glassy materials including cenospheres, pleiospheres, ferrospheres, solid spheres, and Fe-bearing spinel, while irregular glassy particles and unburned carbon were observed in the CFB ashes. The results of SEM-EDS found that PC ash mainly consisted of <100-µm-diameter aluminosilicate spherical particles. In contrast, CFB ash was primarily comprised of fine irregular Al-Si-Ca-O agglomerates. FGD gypsums, occurring as large flaky crystals, were primarily composed of CaSO4·2H2O with minor quartz and calcite. According to the sequential chemical extraction procedure, the amount of HMs occurring as oxidizable associations of fluidized ash was higher than that of PC ash, which might be associated with the lower flame temperature in CFB boiler. The percentage of Cr (43.1–53.2%), Cu (79–87.8%), Zn (67.8–89.6%), and As (64.5–75.6%) as effective fraction was notably higher in FGD gypsums compared with fly ashes. The leaching tests revealed that all combustion residues were non-hazardous materials. The RACs (risk assessment codes) of Cr, Pb, Cd, and As in fly ashes indicated that they posed no risk or low risk to the ecosystem, while the HMs in all FGD gypsums showed a medium risk or high risk to the ecosystem. Therefore, the reuse of FGD gypsums should be carefully evaluated since the environmental stability of HMs in gypsums was weaker compared with fly ashes.

Environmental factors controlling potentially toxic element behaviour in urban soils, El Tebbin, Egypt

This study focuses on the assessment of surface soils from industrially polluted region (El Tebbin) of southern Cairo, Egypt. The impact of agricultural, residential and industrial land use on soils developed from Nile river sediments has significantly compromised their function. Previous evidence has shown that the food chain is contaminated and enhances risk of contaminant exposure of the residential communities. This study investigates factors controlling potentially toxic element (PTE) distribution (Co, Ni, Pb, Cd, Zn, Cr and Cu) in El Tebbin soils and provide estimates of their mobility and bioavailability. The PTE concentrations are characterised by high variability as result of the variety of natural and anthropogenic influences. Highest spatial variability is found for Zn, Cd, Pb and Cu (C.V = 260.0%, 280.4%, 140.8% and 159.6% respectively) and enrichment factors indicate strong anthropogenic inputs. For Co and Ni, relatively low spatial variability (C.V = 65.8% and 45.0% respectively) with depletion in Ni suggests a relatively minor contribution from anthropogenic sources. For Cr, a more uniform distribution pattern showing depletion to minimal enrichment across the study area (C.V = 19.2%) reflects almost exclusive lithogenic control. Using principle component analysis (PCA) to explore concentration data reveals that the major inputs affecting PTE distribution are modified by primary soil properties (texture and pH). Their relative bioavailability (identified through sequential chemical extraction) relates strongly to local input sources. Those elements dominated by lithogenic input (Ni and Co) were found predominantly in soil residual fractions (95.6% and 90.5% respectively), while elements with stronger anthropogenic contributions (Cd, Zn, Pb and Cu) showed much higher portion in the more mobile and bioavailable fractions obtained from sequential chemical extraction, with average proportions of the totals being 62.6%, 57%, 40.7% and 39.2% respectively. Those PTEs with strong anthropogenic influence are potentially much more mobile for bioaccumulation in food chain with increased health risk for exposed residents and are confirmed by elevated concentrations of Cd, Zn, Pb and Cu recorded in local plant species. The main pollution sources were further highlighted by cluster analysis and showed vehicle traffic and specific industrial activities but which varied significantly from site to site. The identification of sources through the approach developed here allows prioritisation of monitoring and regulatory decisions by the local government to reduce further environmental exposure of the local population.

Metal(loid) speciation in a river subjected to industrial anthropopressure: chemometric and environmental studies

High-performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) was applied to the speciation of arsenic [As(III), As(V), and AsB (arsenobetaine)], MMA (monomethylarsonic acid), DMA (dimethylarsinic acid), antimony [Sb(III) and Sb(V)], and chromium [Cr(III) and Cr(VI)] in water and bottom sediment samples collected from the urban Bytomka River (Poland). The main objective of the study was the research of As, Cr and Sb species in the Bytomka River, as well as the simplified three-stage sequential chemical extraction of bottom sediments according to the Institute for Reference Materials and Measurements (BCR). The contents of V, Mn, Co, Ni, Cu, Zn, Rb, Sr, Ag, Cd, Te, Ba, Tl, Pb, Fe, Ga, and U in the water and bottom sediments were tested using the ICP-MS technique. The risk assessment code (RAC) indicated a medium risk for As and a high risk for Sb to the environment. Sequential chemical extraction of bottom sediments showed that As and Cr were strongly demobilized. Sb was mainly bound with the ion-exchange fraction and posed a serious threat to the environment. Chemometric analysis with the (dis)similarity analysis and principal component analysis (PCA) allowed for visualization of the variability and correlations of the analyzed elements.

Abundance and distribution pattern of rare earth elements and yttrium in vitrain band of high-rank coal from the Qinshui basin, northern China

Vitrain bands are clean and contain less ash than the bulk coal. A comprehensive study on rare earth elements and yttrium (REY) in vitrain may provide insights into the REY affinity. In this study, abundance and distribution pattern of REY in bulk coal, vitrain band and HCl-HF demineralized vitrain band was investigated. The coal studied in the present work was low-ash (ash yields ranging from 4.13 to12.86%, with 8.59% as the average), high-rank (anthracite to semi-anthracite, with volatile matter yields of 7.52–13.42%, 9.58% on average) coal of Permian Shanxi Formation, collected from the Sihe and Zhaozhuang mines, southern Qinshui Basin. The major minerals identified by powder XRD are illite and kaolinite, with small amount of ankerite, chlorite, calcite, siderite and pyrite. In comparison to the bulk coal, vitrain band displays a lower REY content and smaller compositional range. The bulk coal has N-, H- and L-type REY patterns based on Seredin-Dai’s classification, while the REY distribution for the vitrain band is commonly characterized by an H-type pattern. Moreover, the LaN/LuN ratio in the vitrain band is usually lower than that in the bulk coal. This probably suggests that the organic component has a higher HREY association than LREY compared to the inorganic part. The limited impact of HCl-HF demineralization on content and distribution pattern of REY in vitrain band probably reflects the weak acid solubility of REY in the vitrain band. The sequential chemical extraction procedure reveals that the clays and the residual organics, which have a stronger association with LREY and HREY respectively, are the dominant carriers of total REY in the studied bulk coals.

Quantitative characterization of aluminosilicate gels in alkali-activated incineration bottom ash through sequential chemical extractions and deconvoluted nuclear magnetic resonance spectra

It has been reported that incineration bottom ash (IBA) from municipal solid waste can be a potential precursor for the synthesis of alkali-activated materials. It has been reported that the resulting alkali-activated IBA (AA-IBA) binder consists of 20 wt% calcium-containing phases. It is expected that aluminosilicate phases may coexist in the complex AA-IBA binder. Differentiating aluminosilicate phases from C-(A)-S-H phases could be challenging, for in general the two phases largely overlap in the spectra. In this study, aluminosilicate gels in a complex AA-IBA are separated and quantitatively characterized based on sequential chemical extractions, thermogravimetric analysis and nuclear magnetic resonance spectral subtraction and deconvolution. It concludes that the resulting AA-IBA binder consists of 17 wt% aluminosilicate gel with a Si/Al ratio of 2.52 resembling an aged alkali-activated coal fly ash. As understanding gel compositions in a binder is important, the methodology developed in this study is of significance and would benefit the development of alternative binders incorporating solid wastes and industry by-products.

Enhanced characterisation for the management of industrial steel processing by products: potential of sequential chemical extraction

There is a pressing need for innovative waste management approaches as environmental regulations become more stringent worldwide alongside increasing demand for a more circular economy. Sequential chemical extraction (SE) analysis, which has previously been applied to environmental media such as soils and sediments, offers the potential to provide an understanding of the composition of solid steel processing by products, aiding the waste classification process and improving environmental protection. The definition of seven-phase associations through a SE method evaluated in this study were for (1) water soluble, (2) ion exchangeable, (3) carbonate, (4) amorphous Fe–Mn oxides, (5) crystalline Fe–Mn oxides, (6) sulphides and (7) silicate residues. Steel waste by-products (flue dust and filter cake) were evaluated for both extracted components (ICP analysis) and residual phases (using powder X-ray diffraction, SEM and FTIR), to model the transformations taking place during extraction. The presence and removal of important potentially toxic element (PTE) host solid phases were confirmed during extraction. The SE protocol provides key information, particularly for the association of potentially toxic elements with the first three extracts, which are most sensitive in waste management processes. The water-soluble phase is the most available followed by ion-exchangeable and carbonate fractions, all representing phases more sensitive to environmental change, in particular to pH. This study demonstrates that the distribution of potentially toxic elements such as zinc, lead and copper between sensitive and immobile phases can be reliably obtained in technological process by-products. We demonstrate that despite heterogeneity as a major variable, even for fine particulate matter, SE can provide more refined classification with information to identify reuse potential and ultimately minimise hazardous waste streams.

Effect of biochar on fraction and species of antimony in contaminated soil

Antimony (Sb) is a highly toxic heavy metal, and its amount in soil is increasing due to anthropogenic activities. Excessive Sb intake could ultimately threat human health. Recently, biochar (BC) has been accepted for remediation of Sb-contaminated soil. Understanding the interaction between BC and Sb and the effect of BC-induced changes in soil properties on immobilization/mobilization of Sb will help, therefore, to elucidate the mechanism of BC in immobilization/mobilization of Sb in contaminated soils. Wheat straw-derived BC (SBC) and fruit (apple) tree-derived BC (FBC) were obtained at the pyrolysis temperatures of 500 °C. Sb-contaminated soil was incubated with/without 0.5, 5, or 10 wt% of SBC and FBC for 130 days. Change of soil properties induced by BC was explored during the incubation. Dynamic change of Sb fraction and speciation were assessed by the sequential chemical extraction and citric acid extraction, respectively. The X-ray photoelectron spectroscopy (XPS) was employed to check elemental change of soil with 10% SBC at different incubation times. The correlation analysis and principal component analysis (PCA) were used to analyze relationship between Sb immobilization/mobilization and change of soil properties induced by BC. The obvious change of soil properties can be observed when the soil was treated with 10% BC instead of 5 and 0.5% BC. During the first 20 days with SBC incubation and 50 days with FBC incubation, Sb mobilization increased may be because of the electrostatic repulsion of functional groups in BC; OM and functional group of BC govern the reduction reactions, anionic competition, electrostatic repulsion, and biological reduction in soil induced by BC. By contrast, after 20 days with SBC incubation and 50 days with FBC incubation, the mobilization of Sb decreased, which may be attributed to the formation of complexes between Sb and OM of BC, secondary mineral precipitation, and organic complex between Sb and humus acid in soil induced by BC. It is noteworthy that the application of BC has a potential mobilizing risk for Sb and the final effect depends on BC characteristic and the change of soil properties induced by BC. The possible risks induced by BC should be considered before applying the BC to Sb-contaminated soil.

Wheat straw biochar reduces environmental cadmium bioavailability

Cadmium contamination in waters and soils can lead to food chain accumulation and ultimately deterioration in human health; means for reducing bioavailable Cd are desperately required, and biochars may play a role. Long-term (240 d) lab incubation experiments were utilized to explain wheat straw-derived biochar effects on Cd sorption and decreasing Cd bioavailability in soils and solutions (0, 5, and 15% biochar as wt:wt or wt:vol, respectively), and to identify Cd forms present using both the European Community Bureau of Reference (BCR) chemical sequential extraction procedure and synchrotron-based X-ray absorption spectroscopy (XAS). Biochar Cd removal was up to ~90% from Cd-containing solutions and contaminated soil as compared to the control. Based on the wet chemical sequential extraction procedure in conjunction with XAS, biochar application promoted the formation of (oxy)hydroxide, carbonate, and organically bound Cd phases. As a material, biochar may be promoted as a tool for reducing and removing bioavailable Cd from contaminated waters and soils. Thus, biochar may play a role in reducing Cd bioaccumulation, trophic transfer, and improving environmental quality and human health.

Fractionation and identification of iron-phosphorus compounds in sewage sludge

Iron (Fe) salts are widely used to remove phosphorus (P) in wastewater treatment plants (WWTPs). Understanding the existing species of iron-phosphorus compounds (FePs) in sludge is conducive to P recovery. In this study, the chemical equilibrium modeling software, sequential chemical extraction methods and instrumental analytical techniques were used to establish a reliable method for fractionation and identification of FePs in sewage sludge. Five FePs-containing sludge samples obtained in the laboratory or from WWTPs were investigated. Modified chemical extraction methods for P and Fe fractionations combined with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis are preferable for qualitative and quantitative identification of FePs in sewage sludge. The analytical results revealed that more than half of P was bound to Fe in all the sludge samples. Approximately 83% and 14% of Fe was present as iron phosphates in the samples prepared in the laboratory with Fe(III) dosed to a phosphate solution and lab-scale secondary effluent, respectively. Ferrihydrite and hematite were the dominant iron oxides in these two samples, respectively. In the sludge samples collected from WWTPs, Fe bound to iron oxides (71%), mainly hematite, was the dominant Fe fraction in the returned sludge. Mature iron hydroxyphosphate together with some lepidocrocite was the dominant FePs in both the thickened sludge and mixed sludge before digestion.

Fate of 14C-acetyl sulfamethoxazole during the activated sludge process.

Compared to antibiotic parent molecule, human metabolites are generally more polar and sometimes not less toxic in wastewater. However, most researches focus on the fate of parent molecule. Therefore, behaviors of human metabolites are little known. Moreover, though much has been done on the fate of antibiotics during activated sludge process, there are still some limitations and gaps. In the present study, [Ring-14C] acetyl sulfamethoxazole (14C-Ac-SMX) was used to investigate the fate of human metabolite of SMX during activated sludge process at environmentally relevant concentration. At the end of 216h, 3.1% of the spiked activity in the initial aqueous phase was mineralized, 50% was adsorbed onto the solid phase, and 36.5% still remained in the aqueous phase, indicating that adsorption, not biodegradation, was the main dissipation pathway. In the existence of microbial activities, accumulation into the solid phase was much higher, which was less bioavailable by chemical sequential extraction. The multimedia kinetic model simultaneously depicted the fate of Ac-SMX in the gas, aqueous, and solid phases, and demonstrated that microbially accelerated accumulation onto the solid phase was attributed to lower desorption rate from the solid phase to the aqueous phase, where adsorption rate was not the key factor. Therefore, Ac-SMX cannot be efficiently mineralized and remain in the aqueous or the solid phases. The accumulation in the solid phase is less bioavailable and is hard to be desorbed in the existence of microbial activities, and should not be easily degraded, and may lead to the development of antibiotic-resistant bacteria and genes after discharge into the environment.

Chemical controls on dissolved phosphorus mobilization in a calcareous agricultural stream during base flow

This study explores the sources and mechanisms of dissolved phosphorus (P) mobilization under base flow conditions in a headwater stream. We characterized the relevant chemical species and processes within the watershed to investigate connections between stream sediment, surface water, and groundwater with respect to P dynamics. Waters were monitored monthly during the 2017 snow-free period for temperature, pH, dissolved oxygen, conductivity, soluble reactive P (SRP), total P, strong acid anions, strong base cations, dissolved organic carbon (DOC), Al, Fe, and Mn. Phosphorus speciation within sediment samples was determined by sequential chemical extractions. The emerging groundwater was under-saturated by up to 40% with respect to O2, with pH = 7.24, T = 7.0 °C, and SRP = 3.0 μg L−1. Groundwater PCO2 was up to ~35× the ambient PCO2 (410 ppm). Degassing of CO2 from the emerging groundwater resulted in a significant increase in pH downstream, and an increase in the SRP concentration from 3.0 to a maximum of 40.6 μg L−1. Laboratory experiments, using homogenized stream sediment, identified a reduction in the P adsorption capacity, and an increase in desorption of native P with increasing pH from ~7.25 (emerging groundwater) to ~8.50 (air-equilibrated surface water). These data allow us to identify the pH-dependent desorption from P-laden sediment as the most significant source of dissolved P in the headwater stream under base flow conditions.

Mobility and Behaviour of Metals in Copper Mine Tailings and Soil at Khetri, India

The mobility and behaviour of metals (Cu, Zn, Ni, Cr, and Pb) in mine tailings and neighbouring soils were studied in the Khetri copper mine region, Rajasthan, India. Single reagent extraction was used to assess the mobility and availability of metals, while sequential chemical fractionation (water soluble, acidic, and reducible) was used to evaluate their behaviour in the environment. Samples were divided into two different physical grain size fractions to assess the impact of grain size on extraction. The mobility trend in both tailings and soil followed the order Ni > Zn > Cu. Metals of lithogenic origin (Cr and Pb) were less extracted in the water soluble fraction or non-residual fractions than those associated with mining. The acid leachable fraction was high in the tailings due to the presence of sulphide minerals. Hence, acidification of tailings would enhance leaching of metals. Results of single and sequential chemical extraction indicate that the Cu, Zn, and Ni are anthropogenic, as they were mostly associated with the non-residual fraction of the soil.

Distribution of arsenic in an argillaceous sample using sequential chemical extractions: application to the Hydrogeological Experimental Site of Poitiers (HESP)

Arsenic mobility and transport into groundwater is highly dependent on its chemical distribution in sediments. In this study, a combination of sequential extraction and mineralogical investigation by X-ray diffraction on a sample collected from the hydrogeological experiment site of Poitiers (France) was tested to evaluate and predict the mobility of arsenic in different conditions. Results showed that the highest fraction of As (~35 %) was released by 25 % nitric acid however this fraction is poorly mobile under natural chemical conditions due to its high stability. Exchangeable As (~14 %) and As bound to iron and aluminium oxides (~12 %) exhibited a significant fraction that could be of high concern in case of change in the ionic composition and redox conditions, respectively. Soluble fraction comprised only 1 % of As which was in accordance with the composition of groundwater in the site.