Remediation of soil chromium (Cr) pollution is becoming more and more urgent. In this study, a multi-loaded nano-zero-valent iron (nZVI) material (CNH) was prepared by carboxymethyl cellulose (CMC) and humic acid (HA) as dispersant and support agent, respectively, and the remediation effect of CNH, HA and CN (CNH without HA) for Cr contaminated soil was investigated within 90 d cycle. After 7 d treatment of CNH, the HOAc-extractable Cr decreased significantly. After the 90 d remediation, the HOAc-extractable Cr decreased most in the treatment of 3% CNH, about 74.48% lower than control. All treatments eventually caused different decline of soil pH, with a range of 0.12–0.54, in which the CNH treatment group had the least depression. HA loading significantly weakened the toxicity of nZVI, resulting in the higher soil microbial quantity and enzyme activities compared with CN. Additionally, the improvement of soil microecology by CNH and HA was positively correlated with the ratio of application, while CN was negatively correlated (except FDA enzyme activity) with these indexes. These results emphasized the potential of the synthesized CNH as a promising material to remediate Cr contaminated soil. Furthermore, details of possible mechanistic insight into the Cr remediation were carefully discussed.

The degree to which droplet shedding (tip-streaming) can modify the size of rising oil droplets has been a topic of growing interest in relation to subsea dispersant injection. We present an experimental and numerical approach predicting oil droplet shedding, covering a wide range of viscosities and interfacial tensions.Shedding was observed within a specific range of droplet sizes when the oil viscosity is sufficiently high and the IFT is sufficiently low. The affected droplets are observed to reduce in size, as smaller satellite droplets are shed, until the parent droplet reaches a stable size.Shedding of smaller droplets is related to the viscosity-dominated modified capillary number (Ca′), especially for low dispersant dosages recommended for subsea dispersant injection. This, in combination with the IFT-dominated Weber number (We), characterise droplets into three possible states: 1) stable (Ca′ < 0.21 &We<12); 2) tip-streaming (Ca′ > 0.21 &We<12); 3) unstable and subject to total breakup (We>12).

Both oil droplets and gas bubbles have simultaneously been quantified in laboratory experiments that simulate deep-water subsea releases of both live oil (saturated with gas) and additional natural gas under high pressure. These data have been used to calculate particle size distributions (50–5000 μm) for both oil and gas. The experiments showed no significant difference in oil droplet sizes versus pressure (from 5 m to 1750 m) for experiments with live oil. For combined releases of live oil and natural gas, oil droplet sizes showed a clear reduction as a function of increased gas void fraction (increased release velocity) and a weak reduction with increased depth (increased gas density/momentum). Oil droplets were reduced by a factor of 3 to 4 during simulated subsea dispersant injection (SSDI) and no significant effect of pressure was observed. This indicates that SSDI effectiveness is not dependent on water depth or pressure.

Toxicity of weathered oil was investigated using Atlantic cod (Gadus morhua) larvae. A novel exposure system was applied to differentiate effects associated with dissolved and droplet oil with and without dispersant. After a 4-day exposure and subsequent 4-day recovery period, survival and growth were determined. Analytical data characterizing test oil composition included polyaromatic hydrocarbons (PAH) based on GC/MS and unresolved hydrocarbon classes obtained by two-dimensional chromatography coupled with flame ionization detection was used as input to an oil solubility model to calculate toxic units (TUs) of dissolved PAHs and whole oil, respectively. Critical target lipid body burdens derived from modeling characterizing the sensitivity of effect endpoints investigated were consistent across treatments and within the range previously reported for pelagic species. Individually measured PAHs captured only 3–11% of the TUs associated with the whole oil highlighting the limitations of traditional total PAH exposure metrics for expressing oil toxicity data.

Knowledge of key species sensitivity for oil spill response (OSR) options is needed to support decision-making and mitigate impact on sensitive life stages of keystone species. Here, Northern shrimp (Pandalus borealis) larvae were exposed for 24 h to a gradient (H-High, M-Medium: 10 times dilution and L-Low: 100 times dilution) of mechanically- (MDO) (H < 6 mg/L total hydrocarbon content) and chemically- (CDO) dispersed oil (Slickgone NS, H < 20 mg/L total hydrocarbon content), followed by a recovery period. Larval mortality, feeding rate and development were evaluated.Overall, the results show that 24 h exposure to field-realistic concentrations of CDO lead to lower survival, reduced feeding rate and slower larval development in P. borealis larvae compared to MDO. These effects persisted during recovery, indicating a higher vulnerability with dispersant use and the need for longer observation periods post-exposure to fully evaluate the consequences for sensitive life-stages from OSR.

As part of a Comparative Risk Assessment (CRA) developed and reported previously, oil spill modeling of a hypothetical blowout at 1400 m in the northeastern Gulf of Mexico was performed to evaluate changes in oil exposures with alternative response options, i.e., combinations of mechanical recovery, in-situ burning, surface dispersant application and subsea dispersant injection (SSDI). To assess if conclusions from this study could be extended to other spill scenarios, sensitivities of the predicted oil fate and exposure metrics to location, release depth, oil and gas flow rate, gas content, orifice size, oil droplet size distribution, and biodegradation rates were examined. Results show that the fraction of oil surfacing is highly sensitive to oil droplet size distribution and depth of release. Across the simulations performed, SSDI use reduced oil droplet sizes released, thereby mitigating surface and shoreline oiling, volatile hydrocarbon exposures, and potential surface water column exposures.

Biodegradation is important for the fate of oil spilled in marine environments, yet parameterization of biodegradation varies across oil spill models, which usually apply constant first-order decay rates to multiple pseudo-components describing an oil. To understand the influence of model parameterization on the fate of subsurface oil droplets, we reviewed existing algorithms and rates and conducted a model sensitivity study. Droplets were simulated from a blowout at 2000 m depth and were either treated with sub-surface dispersant injection (2% dispersant to oil ratio) or untreated. The most important factor affecting oil fate was the size of the droplets, with biodegradation contributing substantially to the fate of droplets ≤0.5 mm. Oil types, which were similar, had limited influence on simulated oil fate. Model results suggest that knowledge of droplet sizes and improved estimation of pseudo-component biodegradation rates and lag times would enhance prediction of the fate and transport of subsurface oil.

Limited experimental and field data are available describing oil droplet formation from subsea releases at high pressure. There are also analytical challenges quantifying oil droplets over a wide size and concentrations range at high pressure. This study quantified oil droplets released from an orifice in seawater at low and high pressure (5 m and 1750 m depth). Oil droplet sizes were quantified using a newly developed sensor (Silhouette camera or SilCam).The droplet sizes measured during experiments at low and high pressure, using the same release conditions, showed no significant difference as a function of pressure. This lack of a pressure effect on oil droplet sizes was observed for both untreated oil and for droplet formation during subsea dispersant injection or SSDI. This strongly indicates that the effectiveness of SSDI is not influenced by water depth or pressure, at least for simulated subsea releases of oil alone (no gas).

The preparation of coal water slurry (CWS) using wastewater, which contains inorganic and organic components, is one method of wastewater utilization. In this study, the effect of inorganic salts on the viscosity of CWS was examined. The results show that monovalent salts (NaCl, KCl) decreased the viscosity of CWS. The viscosity of CWS was not affected by bivalent salts (CaCl₂, MgCl₂). However, CWS combined with trivalent salt (AlCl₃) sharply increased the viscosity. The zeta potential of CWS with inorganic salts increased which can enhance the electric repulsion and beneficial to reduce the viscosity. The content of free water in CWS with trivalent salt decreased, and the freedom of the free water in CWS with trivalent salt decreased which were all bad to the viscosity and the adsorption of the dispersant on the particles. Compared with the surface polarity of the particles without inorganic salts, the surface polarity of the particles with divalent salts was similar to those without inorganic salts. Under the comprehensive influence, divalent salt has little effect on the viscosity of CWS.

Dispersants including Tween 20, Tween 40, Tween 60, and polyacrylic acid (PAA) were used to modify nanoscale zero-valent iron (nZVI). All dispersants dispersed nZVI effectively. PAA-modified nZVI was more stable than nZVI that was modified with Tween surfactant. Iron nanoparticles that were prepared using 0.5–5.0% (vol%) of PAA remained in suspension for more than 2 h. nZVI that was modified using Tween surfactant remained in suspension for 30–60 min, and there was complete sedimentation of bare iron in 10 min. When 2.0–5.0% (vol%) of Tween surfactant was used, the stability of the nZVI that was modified using Tween 20 was much better than that for nZVI that was modified using Tween 40 or Tween 60. The results for the transportation test show that nZVI that was prepared using 2% (vol%) of Tween 20 exhibited the best mobility in porous media. Approximately 83–90% of TCE was degraded by bare, PAA-modified, and Tween 20-modified nZVI, and about 63–67% of TCE was removed by nZVI that was modified using Tween 40 and Tween 60 during 20 days of reaction. The production of cis-dichloroethene (DCE) and 1,1-DCE demonstrates that TCE is removed via reductive dechlorination. The results of this study show that PAA- and Tween 20-modified nZVI are more practical for in situ remediation because they exhibit good mobility and degrade TCE effectively.