No abstract

Polycyclic aromatic hydrocarbons (PAHs) are potent environmental pollutants, and some of them have been identified as carcinogenic and mutagenic. To advance the knowledge of the environmental fate of PAHs, we systematically investigated the influence of different UV wavelengths irradiation on photolysis of PAHs on sandy soil under tow wavelengths (254 and 306 nm) UV irradiation for six PAHs. In addition, kinetic model and influence of several parameters on PAHs photolysis have been studied. The results obtained indicated that UV radiation with a wavelength of 306 nm was more efficient in the photolysis of the polycyclic aromatic hydrocarbons. Our results showed that fluoranthene (Flt) was the fastest in decomposition, has the greatest value for the coefficient of photolysis (7.4 × 10(-3) h(-1)), and has less half-life, reaching 94 h when using a wavelength of 254 nm. The results indicated that the pyrene (Pyr) was more resistant to photolysis in comparison with indeno(1,2,3-cd) pyrene (IP) and fluoranthene (Flt). The results indicate that photolysis is a successful way to remediate the six studied PAHs compounds.

Surface modification of nanoscale zero-valent iron (nZVI) using polymer stabilizers (e.g., sodium carboxymethyl cellulose, CMC) is usually used to minimize aggregation, increase stability, and enhance transport of nZVI. We investigated the stability and dynamic aggregation of bare and CMC–nZVI as affected by variations in pH, ionic strength (IS), and nZVI particle concentration. CMC coating of nZVI resulted in smaller hydrodynamic size and larger zeta potential. The largest hydrodynamic size of nZVI was associated with bare nZVI at high IS (100 mM), pH close to the point of zero charge (PZC, 7.3–7.6), and larger particle concentration (1.0 g L−1). The increase in the zeta potential of CMC–nZVI reached one- to four-fold of that for bare nZVI, and was greater at pH values close to PZC, high IS, and larger particle concentration. The stability of CMC–nZVI was increased by 61.8, 93.1, and 57.5% as compared to that of bare nZVI at IS of 1, 50 and 100 mM, respectively. Calculations of Derjaguin, Landau, Verwey and Overbeek (DLVO) interaction energy were in agreement with stability results, and showed the formation of substantial energy barriers at low IS indicating greater nZVI stability. Our results suggest that at IS above 50 mM and nZVI particle concentration larger than 0.1 g L−1, the likelihood of nZVI aggregation is high. Nevertheless, CMC polymer stabilizer would enhance the stability and transport of nZVI even under these unfavorable solution chemistry conditions.

No abstract

Efficient application of nanoscale zero-valent iron (nZVI) particles in remediation processes relies heavily on the ability to modify the surfaces of nZVI particles to enhance their stability and mobility in subsurface layers. We investigated the effect of sodium carboxy-methyl-cellulose (CMC) polymer stabilizer, pH, particle concentration, and flow rate on the transport of nZVI particles in sand columns. Breakthrough curves (BTCs) of nZVI particles indicated that the transport of nZVI particles was increased by the presence of CMC and by increasing the flow rate. The relative concentration (RC) of the eluted CMC-nZVI nanoparticles was larger at pH 9 as compared to RC at pH 7. This is mainly attributed to the increased nZVI particle stability at higher pH due to the increase in the electrostatic repulsion forces and the formation of larger energy barriers. nZVI particle deposition was larger at 0.1 cm min −1 flow due to the increased residence time, which increases the aggregation and settlement of particles. The amount of CMC-nZVI particles eluted from the sand columns was increased by 52% at the maximum flow rate of 1.0 cm min −1 . Bare nZVI were mostly retained in the first millimeters of the soil column, and the amount eluted did not exceed 1.2% of the total amount added. Our results suggest that surface modification of nZVI particles was necessary to increase stability and enhance transport in sandy soil. Nevertheless, a proper flow rate, suitable for the intended remediation efforts, must be considered to minimize nZVI particle deposition and increase remediation efficiency.