Remediation Of Polluted Sites Research Articles

Fulvic acid enhancing pyrene biodegradation by immobilized Stenotrophomonas maltophilia: Effect and mechanism

Immobilization technology is a promising way to improve effectiveness and stability of microbial remediation for polycyclic aromatic hydrocarbons (PAHs), in which carrier material is one of key factors restricting removal efficiency. In this study, fulvic acid-wheat straw biochar (FA/WS) composites were applied for immobilization of an efficient PAHs degrading bacterium Stenotrophomonas maltophilia (SPM). FA/WS&SPM showed superior degradation capacity than free bacteria and biochar-immobilized bacteria, with the removal efficiency of pyrene (20 mg L-1) reaching 90.5 % (7 days). Transcriptome analysis revealed that FA in the carrier materials can promote transportation and degradation of pyrene, and cell growth, as well as inhibit cell apoptosis. Enzyme activity and degradation products detection showed that SPM utilized both phthalic acid and salicylic acid metabolic pathways to degrade pyrene. Practicality of FA/WS&SPM for different kinds of PAHs remediation had been verified in contaminated soil, demonstrating a great potential in the field of PAHs polluted sites remediation.

Chrome shaving-derived biochar as efficient persulfate activator: Ti-induced charge distribution modulation for 1O2 dominated nonradical process

Efficient degradation of organic contaminants by oxidative radicals remains a challenge due to invalid consumption of radicals and easy generation of secondary halogenated pollutants. In this work, an efficient and recyclable bimetallic biochar (Cr-Ti/BC) was developed through peroxydisulfate (PDS) activation via nonradical pathway for sulfamethoxazole (SMX) degradation. The Cr-Ti/BC exhibited excellent catalytic activity for 99.9 % of SMX removal with a high kobs of 0.13 min−1, and negligible inhibitory effects were observed under various pH condition. The activation mechanisms were (i) metastable reactive intermediates (Cr-Ti/BC-PDS) formation via an interaction between Cr-Ti/BC and PDS on the active defective sites (e.g., OH/COC, COOH, CO, nitric oxides, graphitic N, and pyridinic N), and (ii) 1O2 generation through electron transfer between Cr-Ti/BC-PDS intermediates and dissolved oxygen. The high reusability and strong stability of Cr-Ti/BC also verified the outstanding advantage of the Cr-Ti/BC during practical application. This study not only is the first study the catalytic performance of Cr and Ti co-doped biochar for PDS activation, but also successfully provides a promising strategy to induce a nonradical pathway for PDS activation, which is of great significance for the subsequent method design, and thus paving the path for exploiting advanced oxidation systems in practical application for organic contaminant removal toward polluted site remediation.

Characterization and degradation mechanism of bimetallic iron-based/AC activated persulfate for PAHs-contaminated soil remediation

In this research, a novel iron based bimetallic nanoparticles (Fe–Ni) supported on activated carbon (AC) were synthesized and employed as an activator of persulfate in polycyclic aromatic hydrocarbons (PAHs) polluted sites remediation. AC-supported Fe–Ni activator was prepared according to two-step reduction method: the liquid phase reduction and H2- reduction under high temperature (600 °C), which was defined as Fe–Ni/AC. Characterizations using micropore physisorption analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM) showed that the synthetic material had large specific surface area, nano-size and carbon-encapsulated metal particles, moreover, the lattice fringes of metals were clearly defined. The PAH compound types and their concentrations were determined by gas chromatography mass spectrometry (GC-MS) with SIM mode, the method detection limit (MDL) was estimated to about 0.21 μg/kg for PAHs, and the average recovery of PAHs was 96.3%. Mechanisms of PAH oxidation degradation with the reaction system of Fe–Ni/AC activated persulfate were discussed, the results showed that short-life free radicals, such as SO4−·, OH·, and OOH· were generated simultaneously, which acted as strong oxidizing radicals, resulting in the oxidation and almost complete opening of the PAH rings.

Co-transport of phenanthrene and pentachlorophenol by natural soil nanoparticles through saturated sand columns

Mobile colloids such as nanoparticles (NPs) are often considered to affect the fate and transport of various contaminants by serving as carriers. Many studies have focused on the effect of engineered NPs on contaminant transport. To date, very little information is available on the co-transport of natural soil NPs with typical organic contaminants. This study investigated the co-transport of phenanthrene (PHE) and pentachlorophenol (PCP) by three soil NPs through saturated sand columns. Soil NPs with high organic matter and particle concentration were the most effective in transporting PHE through columns. In addition, soil NPs significantly increased the transport of low-level PHE (0.2 mg L−1) but there was no obvious increase at 1.0 mg L−1 PHE. This is attributed to a higher ratio of NP-associated PHE to total PHE at a low-level than at a high-level during transport. In contrast to PHE, the chemical speciation of PCP determined its mobility, which was highly dependent on solution pH. At pH 6.5, anionic PCP became dominant and soluble in the effluent. This could account for the negligible effect of soil NPs on PCP mobility. At pH 4.0, however, neutral molecular PCP dominated and, as expected, decreased mobility of PCP occurred. Soil NPs considerably enhanced the transport of neutral PCP in NP-associated forms compared to controls, due to the high hydrophobicity and sorption affinity of PCP to NPs. The mobility of soil NPs was little affected by PHE and PCP under tested conditions. This study indicated that highly mobile soil NPs may be effective carriers for organic contaminants and give a new direction to polluted site remediation by using a natural material, e.g., soil.

Brief Introduction of Pollution Sites Remediation and Risk Assessment and Its Policy Making in United States

Site remediation has become an imperative part of environmental protection in China due to recent economic development, urban spreading, new industries replacing old ones, relocation of old industrial sites, and increased environmental conscience. This paper mainly introduced the concept, method, calculation, risk assessment and management for polluted sites remediation based on experience from California, USA. Further, the paper presented the concept of vapor intrusion and how to use vapor intrusion methodology to determine site remediation standard. Mathematical modeling approaches were also discussed in terms of how to determine the residual pollutant concentrations in soil and how to calculate indoor vapor concentrations. Based on risk assessment, California Environmental Protection Agency, Water Resources Control Board issued a 'Low Threat Underground Storage Tank Case Closure Policy' for impacted underground storage tank sites. The numerical criteria in the Policy were based on calculations of human health risk assessment. Finally, a real case study in California, USA, was presented to demonstrate how the risk assessment calculations were applied in polluted site remediation, which helps to answer the question of 'how clean is clean'.

How to manage potential groundwater contaminations by As, Fe and Mn in lower Po Plain: a proposal from the case study of Cremona

The Legislative Decree 152/06 on environmental regulations also governs polluted site remediation (Part IV). A potentially contaminated site is defined when concentrations exceed the limits reported in the Attachment 5 (Title V). Nevertheless, the Legislative Decree 152/06 considers the possibility of higher limits than Attachment 5 for trace elements in the case of natural high contents by the definition of natural background levels. The lower Po Plain is characterized by high natural concentrations of As, Fe and Mn in groundwater and, at the same time, is one of the most important areas for the Italian productive system, and thus, possible direct sources of As, Fe and Mn or indirect anthropogenic influences could also exist. Therefore, an operative tool is required to determine the natural background levels and to understand if measured high concentrations are attributable to natural backgrounds or to anthropogenic sources/influences, and consequently, to decide on the beginning of the administrative procedure requested by the Legislative Decree 152/09 through the site characterization phase. This work presents a proposal of procedure to manage potentially contaminated site by As, Fe and Mn in the lower Po Plain, that was developed in the framework of a scientific collaboration between the Province of Cremona and the University of Milano-Bicocca. The procedure involves the following four steps, preceded by the derivation of natural background levels as step zero: (1) comparing new measurements to natural background levels; (2) testing the presence of direct anthropogenic sources of As, Fe and Mn; (3) excluding false positives and (4) testing the presence of indirect anthropogenic influences on As, Fe and Mn concentrations. The operative application of the proposed procedure is actually under consideration by the Province of Cremona.

Sequestering ability of polyaminopolycarboxylic ligands towards dioxouranium(VI) cation

In the present paper, some results of an investigation (at t = 25 °C by potentiometry, ISE-H + glass electrode) on the sequestering ability of five different polyaminopolycarboxylic ligands [Nitrilotriacetate (NTA), ethylenediamine- N,N,N′ ,N′-tetraacetate (EDTA), ethylene glycol-bis(2-aminoethylether)- N,N,N′ ,N′-tetraacetate (EGTA), diethylenetriamine- N,N,N′ ,N″ ,N″-pentaacetate (DTPA), triethylenetetraamine- N,N,N′ ,N″ ,N′′′ ,N′′′-hexaacetate (TTHA)] towards dioxouranium(VI) cation in sodium chloride aqueous solutions, at I = 0.7 mol L −1 are reported. Calculations performed on potentiometric data gave evidence of the formation of the following species (log β in parenthesis): UO 2(NTA)H 0 (12.27); UO 2(NTA) − (8.21); UO 2(NTA)OH 2− (2.39); UO 2(EDTA)H − (15.19); UO 2(EDTA) 2− (9.81); UO 2(EDTA)OH 3− (3.58); UO 2(EGTA)H − (17.35); UO 2(EGTA) 2− (11.60); UO 2(EGTA)OH 3− (2.77); UO 2(DTPA)H 2 − (22.14); UO 2(DTPA)H 2− (17.86); UO 2(DTPA) 3− (11.79); UO 2(DTPA)OH 4− (3.09); UO 2(TTHA)H 3 − (28.41); UO 2(TTHA)H 2 2− (24.73); UO 2(TTHA)H 3− (19.14); UO 2(TTHA) 4− (12.12). In presence of complexones, the formation of scarcely soluble species occurs at higher pH values than in simple UO 2 2+ aqueous solutions. The stability of dioxouranium(VI)–polyaminopolycarboxylate species follows the trend: TTHA > DTPA > EGTA > EDTA > NTA, it is dependent on the ligand structure and this dependence was modeled. Polyaminopolycarboxylate ligands are good sequestering agents towards UO 2 2+, indicating the possibility of being employed in the UO 2 2+ polluted sites remediation, and in the chelating therapy in medicine. A literature data critical evaluation was made, evidencing the high discrepancies occurring between different authors in both the stability constant values and the proposed speciation models.