Competitive sorption of lead and methylene blue onto black soil and their interaction with dissolved organic matter using two-dimensional correlation analyses

Molecular size-dependent compositions and lead (II) binding behaviors of two origins of organic fertilizers-derived dissolved organic matter

The application of organic fertilizers caused large amounts of dissolved organic matter (DOM) entering the soil environment and influencing the behaviors and fates of heavy metals. Here, we investigated the molecular weight-dependent (high molecular weight [HMW], 1 kDa-0.7 µm; low molecular weight [LMW], <1 kDa) compositions and lead (Pb) binding behaviors of DOM derived from sheep manure-based (SMOF) and shrimp peptide-based organic fertilizers (SPOF) using chromophoric and fluorescent spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and two-dimensional correlation spectroscopy (2D-COS). Results showed that SMOF released more DOM with higher aromaticity and hydrophobicity, containing more fluvic-like components, carboxylic-rich alicyclic molecules (CRAMs) and lignin phenolic compounds compared to SPOF-DOM with more microbially-transformed heteroatom-containing compounds (CHON, CHONS and CHOS). Furthermore, there was more aromatic compounds with ample carboxyl and hydroxyl groups in HMW-DOM but abundant protein-like components and heteroatom-containing compounds (CHONS and CHOS) in LMW-DOM. SMOF-DOM exhibited more obvious MW-dependent heterogeneity in molecular components compared to SPOF-DOM with higher molecular diversity. Moreover, 2D-COS indicated phenol and carboxyl groups in SMOF-DOM and polysaccharides in SPOF-DOM exhibited superior binding affinities for Pb. Pb binding to HMW-DOM derived from SMOF first occurred in the phenolic groups in fulvic-like substances, while polysaccharides in LMW-DOM first participated in the binding of Pb. In contrast, irrespective of MWs, polysaccharides and humic-like substances with aromatic (CC) groups in SPOF-DOM displayed a faster response to Pb. Furthermore, the polysaccharides which preferentially participated in the binding of Pb to SPOF-DOM and SMOF-derived LMW-DOM may pose a higher risk of Pb in the environment. These results were helpful to understand the effects of sources and size-dependent compositions of DOM on the associated risks of heavy metals in the environments.

Spectral change of dissolved organic matter after extracted by solid-phase extraction and its feasibility in predicting the acute toxicity of polar organic pollutants in textile wastewater

Spectroscopic parameters can be used as proxies to effectively trace the occurrence of organic trace contaminants, but their suitability for predicting the toxicity of discharged industrial wastewater with similar spectra is still unknown. In this study, the organic contaminants in treated textile wastewater were subdivided and extracted by four commonly-used solid-phase extraction (SPE) cartridges, and the resulting spectral change and toxicity of textile effluent were analyzed and compared. After SPE, the spectra of the percolates from the four cartridges showed obvious differences with respect to the substances causing the spectral changes and being more readily adsorbed by the WAX cartridges. Non-target screening results showed source differences in organic micropollutants, which were one of the main contributors leading to their spectral properties and spectral variations after SPE in the effluents. Two fluorescence parameters (C1 and humic-like) identified by the excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were closely correlated to the toxicity endpoints for Scenedesmus obliquus (inhibition ratios of cell growth and Chlorophyll-a synthesis), which can be applied to quantitatively predict the change of toxicity effect caused by polar organic pollutants. The results would provide novel insights into the spectral feature analysis and toxicity prediction of the residual DOM in industrial wastewater.

Sorption of Pb(II) onto biochar is enhanced through co-sorption of dissolved organic matter

Biochar plays an important role in controlling migration of pollutants in soils. However, little information is available on the interactions between soil-derived dissolved organic matter (DOM), biochar and soluble metal species. The aim of this work was to present the adsorption process of soil DOM by biochar (corn straw biochar produced at 700 °C) and to determine whether co-sorption of DOM would change the affinity for Pb(II). The adsorption rates of biochar and biochar + DOM for Pb(II) were best fitted with a pseudo-second order kinetic model, and the equilibrium adsorption isotherm data agreed well with both the Langmuir and Freundlich models. Adsorption of DOM to biochar reached equilibrium after 15 h with an uptake of 52% of the supplied DOM. We used fluorescence excitation-emission matrices (EEMs) with parallel factor (PARAFAC) analysis to demonstrate that protein-like, fulvic acid-like and humic acid-like substances were the primary constituents of the DOM, which were quenched over time in the presence of biochar. Synchronous fluorescence spectra indicated that the protein-like structures were the predominant fluorescence substances in DOM. Two-dimensional correlation spectroscopy (2D-COS) showed the binding of DOM to biochar resulted in the quenching of fluorescence in the order: protein-like substances > humic-like substances (280 > 355 nm). Data supports the notion that DOM can increase the adsorption capacity of biochar for metal-ions.

The pH dependence and role of fluorinated substituent of enoxacin binding to ferrihydrite

The sorption of antibiotics on iron (hydr)oxides is an important process that influences their environmental fate. Ferrihydrite (Fh) nanosized iron hydroxide is omnipresent in nature. However, the sorption mechanism of fluoroquinolone (FQ) antibiotics on Fh is unclear. Here, a combined experimental and computational study was conducted to investigate the sorption of enoxacin (ENO) as one model of FQs on Fh. Pipemidic acid (PPA), as a structural analog of ENO, was selected to compare the effect of fluorinated substituent on the sorption mechanism. Results indicated that the average K_d values of ENO at pH = 7.0 and 8.0 were 1.72 and 2.75 times higher than those at pH in the ranges of 4.0-6.0 and 9.0-10.0, respectively. The main sorption mechanisms included electrostatic, hydrophobic interaction, and inner-sphere complexation. The fluorinated substituent of ENO facilitated its sorption on Fh through enhancing its hydrophobicity as well as modifying its dissociation constants and charge distribution. The findings give new insights into the significant influence of active fluorinated substituents on the environmental behaviors of fluorinated pharmaceuticals.

Study on the regulation mechanism of cadmium adsorption system mediated by extraneous dissolved organic matter

Adsorption of biochar on heavy metals is one of the hot spots in the application of biochar. However, the mediation of existing extraneous substances in the environment, such as dissolved organic matter (DOM), could regulate and affect the heavy metals adsorption process on biochar. In our study, we mainly focus on the regulation mechanism of modified biochar on the adsorption process of cadmium mediated by exogenous DOM. The modification significantly changed the functional groups composition on biochar, thus improving the adsorption capacity of cadmium on biochar. In the adsorption system concerned, the combination was formed between DOM and cadmium to a certain extent. The combination had a certain correlation with the influence on the adsorption capacity of cadmium onto biochar in the system.

Evaluation of three common alkaline agents for immobilization of multi-metals in a field-contaminated acidic soil

We investigated three common alkaline agents (NaOH, CaO, and Mg(OH)₂) for immobilization of four heavy metals (Pb, Zn, Cu, and Cd) in a field-contaminated soil and elucidated the underpinning principles. NaOH caused the highest pH spike in the soil, while CaO and Mg(OH)₂ served as a longer-lasting source of OH^-. Amending the soil with CaO or Mg(OH)₂ at ≥0.1 mol as OH^- (kg·soil)^-1 for 24 h was able to immobilize all four metals, while NaOH failed. NaOH leached up to 3 times more organic carbon than CaO and Mg(OH)₂, resulting in elevated leachability of the metals. Column elution tests showed that amendments by CaO and Mg(OH)₂ lowered the leachable Pb²⁺, Zn²⁺, Cu²⁺, and Cd²⁺ by 52-54%, 71-75%, 69-73%, and 68%, respectively, after 1440 pore volumes of elution. Sequential extraction revealed that the soil amendments converted the exchangeable fraction of the metals to the much less available forms. XRD and FTIR analyses indicated that formation of metal oxide precipitates and complexation with soil organic matter were responsible for the metals immobilization. Taken together the chemical cost, technical effectiveness, and environmental impact, CaO is the most suitable alkaline agent for remediation of soil contaminated with heavy metals.

Phosphorus sorption - Desorption behaviors in the sediments cultured with Hydrilla verticillata and Scripus triqueter as revealed by phosphorus fraction and dissolved organic matter

The migration of sediment phosphorus (P) could be affected by the existence of aquatic plants. To explore the effects of aquatic plants on the P sorption-desorption behaviors in the sediments, sediment in Caohai wetland was collected and cultured with the submerged plant (Hydrilla verticillata) and emerged plant (Scripus triqueter). Then the sorption and desorption experiments were performed, and physicochemical properties, P fractions, and dissolved organic matter (DOM) characteristics were evaluated. Results showed that the treated sediments exhibited similar P sorption kinetic process fitted well with the two-compartment first-order model. Nevertheless, H. verticillata cultured sediment could be well described by the modified Langmuir isotherm model, while S. triqueter cultured sediment fitted the modified Freundlich equations well. The obvious changing P fractions in cultured sediments were BD-P and NaOH-SRP during sorption. H. verticillata and S. triqueter displayed different sorption-desorption behaviors by altering BD-P, humification index, fluorescence intensity, and PARAFAC component contents in sediments. Compared to raw sediment, H. verticillata presented higher P sorption and lower P release from sediments by decreasing BD-P and increasing DOM (fulvic acid-like and humic-like components) content, while S. triqueter showed adverse P sorption and release effects by reducing DOM components. The growth of submerged plants was suggested to make a positive influence on the high efficiency of P retention capacity and low release risk.

Simultaneous immobilization of multi-metals in a field contaminated acidic soil using carboxymethyl-cellulose-bridged nano-chlorapatite and calcium oxide

We prepared and tested carboxymethyl-cellulose-bridged nano-chlorapatite (CMC-CAP) for simultaneous immobilization of Pb, Zn, Cu, and Cd in a field-contaminated acidic soil. Amending the field-contaminated soil using 0.5 wt.% CMC-CAP and 0.1 wt.% CaO was most effective in immobilizing the four metals, which decreased the leachabilities by 98.2%, 98.3%, 96.3%, and 96.2% for Pb, Zn, Cu, and Cd, respectively, after 1 day of treatment. The acid-leached metals fluctuated in the first 60 days, and then approached to steady state after 180 days, where the acid-leachable concentrations all met the regulation levels, and the immobilization was further consolidated when further aged for 365 days. Column elution tests showed that the soil amendment lowered the peak metal concentrations by > 92.5%, and the total eluted masses by >71.9%. Sequential extraction revealed that the soil amendment converted the exchangeable fractions to the much less available Fe-Mn oxides bound and residual forms, and thus, lowered the risk levels to "low risk" for all the metals. The immobilization of the metals was facilitated through formation of stable metal (chloro)phosphates, surface complexation, and/or ion exchange reactions. Combined CMC-CAP and CaO may serve as an effective formulation for simultaneous and long-term immobilization of multiple heavy metals in acidic soil.

Effect of competitive adsorption on the transport of multiple pollutants through a compacted clay liner

Leachate transport through municipal solid waste (MSW) landfill liners can be slowed considerably by adsorption. MSW landfill leachate contains a large variety of pollutants at very different concentrations, and there will be competitive adsorption as these pollutants are transported through the landfill's compacted clay liner (CCL). In this study, we used batch adsorption tests and geotechnical centrifuge modelling to examine how the adsorption of pollutants commonly found in leachate changed under competitive adsorption conditions and how competitive adsorption affected the CCL breakthrough of multiple pollutants. The results showed that the adsorption of the target pollutant on clay decreased by approximately 30% when competing pollutants were added. The speed at which the pollutants were transported through a 2-m-thick CCL increased, and the breakthrough times reduced by up to 24.8%, when the competing pollutants were mixed. Competitive adsorption significantly promoted the CCL breakthrough of pollutants at low concentrations, but it had limited effect on pollutants at high concentrations.

Microwave-assisted one pot synthesis of β-cyclodextrin modified biochar for concurrent removal of Pb(II) and bisphenol a in water

Herein, β-cyclodextrin (β-CD) functionalized rice husk-derived biochar (BC) was conveniently and fast synthesized via microwave (MW)-assisted one pot process, and employed for simultaneous elimination of bisphenol A (BPA) and plumbum (Pb). Profiting by microwave irradiation, the surface modification was implemented in 15 min and the prepared BC_MW-β-CD presented an excellent adsorption performance with a heterogeneous adsorption capacity of 209.20 mg/g for BPA and a theoretical monolayer uptake of 240.13 mg/g for Pb(II) in the mono-component system. Furthermore, the BC_MW-β-CD could simultaneously achieve efficient cleanup of BPA and Pb(II) through avoiding the competitive behaviors between them, which were due to the different adsorption mechanisms for Pb(II) (i.e. electrostatic attraction and complexation) and BPA (i.e. host-guest supramolecular and π-π interactions). Moreover, the adsorbed BPA and Pb(II) could be sequentially desorbed with mild decrease in the adsorption performance of BC_MW-β-CD even after five cycles in the Pb(II)-BPA multi-component system.

Effect of pH on the adsorption of arsenic(V) and antimony(V) by the black soil in three systems: Performance and mechanism

Arsenic (As) and antimony (Sb) are listed as the priority pollutants by the U.S. Environmental Protection Agency (EPA) and the European Union (EU) due to their toxicity and potential carcinogenicity. It is necessary to investigate their adsorption over soil as such a behavior affects their mobility and bioavailability. In this study, the effect of pH on the adsorption of As(V) and Sb(V) by the black soil was investigated with three systems: the Single system, Binary system, and Sequence system. The operating pH was set at 4.0, 7.0 and 10.0. Based on the Langmuir isothermal and the pseudo-second-order kinetic models, the adsorption for As(V) was always better than Sb(V) in the whole pH range; the best adsorption performance for the two sorbates was achieved at pH of 4.0, followed by 7.0 and 10.0 in the three systems. The reasons could be that the atomic radius of arsenic is smaller than that of antimony, and the positively charged functional groups carried by the inorganic colloids in the soil contributed to binding with the negatively charged As(V)/Sb(V). A lower pH promoted the inorganic colloids to carry more positive charges. Compared to Single system, the maximum adsorption capacity (q_m) and the initial adsorption rates (k₂q_e,cal²) of As(V) and Sb(V) in Binary system decreased obviously, suggesting competitive adsorption occurred when As(V) and Sb(V) coexisted. The findings of this workimprove the understanding of As(V)/Sb(V) adsorption behavior in soil under different situations and would facilitate a comprehensive evaluation on the risk assessment of arsenic and antimony.