Optimization of PAHs oxidation from contaminated soil using modified nanoscale zero-valent iron combined with potassium permanganate.

A novel synergistic oxidation technology based on modified nanoscale zero-valent iron (nZVI) and potassium permanganate (KMnO4) was developed for polycyclic aromatic hydrocarbons (PAHs) remediation in actual contaminated soil. In this study, three surfactants were used as dispersants to modify nZVI, including poly acrylic (PAA), sorbitan monolaurate (SPAN-20) and sugar esters (SE). The following parameters were studied to optimize the coupling oxidation process: dispersants/nZVI ratio, dosage of oxidant based on soil oxidation demand (SOD), amount of modified nanomaterials added in the coupling system. By using zeta potential, XRD, SEM, BET characterization methods, the results show that nZVI successfully coated with 5% PAA, 20% SE and 10% SPAN-20 have the best stability and mobility to effectively reduce the agglomeration effect. The conditions for treating PAH contaminated soil with the three best modified nanocomposites combined with KMnO4 were studied. The optimal conditions were defined as [SE-nZVI] = 10% and [KMnO4] = 40% SODmax for 24 h at 25 °C. The synergistic oxidation process under these optimal conditions and the two unoptimized processes of KMnO4 and nZVI-KMnO4 degraded 85%, 58.9% and 62% of PAHs, respectively. This showed that the treatment effect of the optimized oxidation process was improved by 1.3-1.5 times. Further, by using gas chromatography-mass spectrometry (GC-MS), adsorption and electrophilic substitution reaction were speculated as the oxidation mechanism of PAHs treated by the coupling system of SE-nZVI-KMnO4. PAHs could finally be decomposed into 9-methylene-9H-fluorene, fluoranthene and 1,5-diphenyl-1,4-pentadiyn-3-one and reached a safer status in the soil.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems.

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters ßm and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (Km) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.

The performance of emerging materials derived from waste organism blood and saponified modified orange peel for immobilization of available Cd in soil.

Waste organism blood (WOB) and orange peel are emerging stabilization materials obtained as by-products from agricultural processes, which are quite suitable for heavy metal immobilization in soil. In this work, waste organism blood and chemically modified orange peel (SOP) were investigated as potential sorbents for immobilization of available Cd in soil. Application of 5% WOB and SOP effectively immobilized cadmium (Cd) with an associated regulation of soil pH, among which the pH of acidic soil increased most significantly. While the application of 3% SOP alone stabilized almost the same amount of available Cd compared to WOB, it caused the highest stabilization rate of 58.85% when applied at 5%. By contrast, SOP combined with WOB (the mass ratio of the material is 1 : 1) at a 5% addition rate stabilized the available Cd in soils remarkably, with a stabilization rate of 57.74%. This study revealed that the soil particles after stabilization have a more compact and flaky structure, and the SOP and WOB had a particular pore structure, which was helpful for the adsorption of available Cd in soil. This study put forward new insights into the potential effects of Cd immobilization in contaminated soil by newly emerging stabilization biomass materials (WOB and SOP).

[Characteristics and Influencing Factors of Polycyclic Aromatic Hydrocarbons in Surface Soils from Typical Industrial Areas of Chengdu].

To improve the pollution signature database for polycyclic aromatic hydrocarbons (PAHs) in typical industrial areas in China, surface soil samples were collected from four typical petroleum-processing industrial areas of Chengdu. The concentration and composition of 16 PAHs listed for prior control by the United States Environmental Protection Agency (US EPA) were determined using high-performance liquid chromatography (HPLC). The result showed that the concentration of PAHs in surface soils of the four industrial areas ranged from 191.2 to 1604.2 µg·kg-1, with an average of (583.6±365.6) µg·kg-1. The PAHs in the present study were mainly composed of medium-molecular-weight PAHs and high-molecular-weight PAHs. Among the PAHs detected in the study soils, phenanthrene (PHE), pyrene (PYR), fluoranthene (FLT), and benzo[b]fluoranthene (BbF) were the major pollutants presenting a potential pollution risk. Selected mathematical statistical methods were used to analyze the relationship between soil organic matter (SOM), soil particle diameter and PAH content, and to simultaneously identify the factors influencing PAHs in the soils. SOM was shown to be a favorable absorbent, predicting the migration and transformation behavior of PAHs in surface soil and soil ecological risk (i.e., PAH carcinogenicity) to some extent. Compared with SOM, the correlation between PAHs and soil particle size was relatively low, showing a weak positive correlation with silt, a weakly negatively correlation with clay, and no significant correlation with sand. These results provide a basis for soil remediation practices and further research in such industrial areas.

Response of energy microalgae Chlamydomonas reinhardtii to nitrogen and phosphorus stress.

Microalgae can effectively absorb nitrogen (N) and phosphorus (P) in wastewater, while growth characteristics can be affected by such nutrients. The influences of the N and P concentration on growth, biomass yield, protein yield, and cell ultrastructure of Chlamydomonas reinhardtii (C. reinhardtii) were investigated in this study. The results showed that, in the optimum conditions (24-72 mg/L for N and 4.5-13.5 mg/L for P), the final biomass and protein content of C. reinhardtii could reach maximum value, and the cell organelles (chloroplast, mitochondria,etc.) showed good structures with larger chloroplasts, and more and neater thylakoids. However, if the concentration of nutrients was much higher or lower than the optimal value, it would cause adverse effects on the growth of C. reinhardtii, especially in high nitrogen (1000 mg/L) and low phosphorus (0.5 mg/L) conditions. Under these extreme conditions, the ultrastructure of the cells was also damaged significantly as follows: the majority of the organelles were deformed, the chloroplast membrane became shrunken, and the mitochondria became swollen, even partial disintegrated (differing slightly under high-N and low-P conditions); furthermore, it is found that C. reinhardtii was more sensitive to low-P stress. On the basis of these results, our findings have general implications in the application of wastewater treatment.