Bioremediation of Total Polycyclic Aromatic Hydrocarbon Contaminated Soil Using Nitrified Sawdust and Pseudomonas auriginosa

Bioremediation involving bioaugmentation and biostimulation are eco-friendly existing methods for degrading polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. This study investigates the efficiency of Pseudomonas auriginosa and nutrient-enriched sawdust (SD) in biodegrading ∑PAHs in contaminated soil (CS). Four compost mixtures of CS/SD (1:0, 3:1, 1:1, 1:3) were applied for 2, 4, 6, 8-week bio-cleanup after inoculation. Results show ∑PAHs concentrations decreased with increasing time of treatment for all four compost in experimental and control setups. The removal efficiency of ∑PAHs was clearly associated with nutrient-enriched sawdust and Pseudomonas auriginosa, especially for 3:1, 1:1, and 1:3 ratios. Both factors had a significant effect (p = 0.05) on removal efficiency compared to the control setup. The highest (78.5%) and lowest (37.8%) ∑PAHs removal efficiency were observed for CS/SD ratios of 1:3 and 1:0 respectively after 8-week treatment. In this instance, this study recommends a CS/SD ratio of 1:3 at 8-week treatment to achieve maximum removal efficiency of ∑PAHs in contaminated soils.

Heavy Metal Pollution of Topsoil in the Vicinity of an Industrial Estate Co-Located with a Housing Estate in Southwestern Nigeria

Heavy metals were determined in topsoils around a major industrial estate co-located with a housing estate in the southwestern region of Nigerian. Samples were collected on three-monthly basis for 18 months, from the industrial waste dumpsites, industrial area, residential area, around an effluent channel, outskirts of the estate and control sites. Average levels of Cu (2850 ± 3340 mg/kg), Pb (768 ± 450 mg/kg) and Ni (105 ± 30 mg/kg) at the dumpsites were significantly higher than other locations. At the industrial area and effluent channels, Pb and Cr levels were slightly elevated compared with other metals. Metal levels at the residential area and outskirts of the estate were about the levels in the control. Generally, the degree of contamination within the vicinity of the estate was of the order Cu>Pb>Ni>Cd>Co>Cr. Average total bioavailable (non-residual) fraction of the metals consisted of 52.0% of the metal load, with this fraction for Cd and Pb being 73.9% and 60.7% respectively. Topsoils around the dumpsite were evidently polluted with high levels of copper and lead. Seepage of leachate from the dumpsite has the potential of contaminating ground water reserves. Improper disposal of industrial solid wastes appears to be the likely source of metal pollution in the industrial estate. Heavy metal pollution in the estate can therefore be significantly reduced by prompt and proper disposal of generated solid wastes, and the application of particulate scrubbers in the industries.

Leachate Quality Characteristics: A Case Study of Two Industrial Solid Waste Dumpsites

The study evaluates the associated environmental risk of two industrial solid waste dumpsites. The Toxicity Characteristic Leaching Procedure (TCLP) and American Society for Testing and Materials (ASTM) extraction test were used to characterize leachate quality on six solid waste samples obtained in July 2005, March 2006 and July 2006. Solid waste compositions varied with 58% metal scraps, 30% vegetation matter, 10% plastics and 2% paper materials. Statistical T-test (95% confidence limit) showed no significance difference in physico-chemical quality of the leachates obtained by both methods from both sites. Leachates obtained by the TCLP extraction accounted for a total of 92.4% of the overall metal load as against 6.01% for the ASTM method. This disparity is due to the acidic nature of the TCLP procedure which enhances more efficient extraction of metals than the ASTM method. Solid waste deposits at SITE-1 were considered hazardous to the environment, given that the upper 90% UCL values for lead exceeded the TCLP characteristic regulatory levels. These may pose a risk to vegetations and ground water reserve within the vicinity of the dumpsite on the long run. The risk may be such as bioaccumulation of lead in the food chain. Therefore, constant monitoring and possible remediation measures should be carried out to contained contamination.

Distribution of Soil-Bound Lead Arising from Rainfall-Runoff Events at Impact Berm of a Military Shooting Range

Surface runoff from rainfall event is an important indicator of metal mobility in soil, which may enhance non-point source contamination of soil. This study is designed to assess the mobility of soil-bound lead through simulated rainfall runoff experiment and its spatial distribution within the vicinity of a berm at a major military shooting range. Contamination was more significant at the impact area of berm, indicating threefold increase in Pb (17,500 ± 3811 μg/g) within a space of ten years. However, the non-impact area (459 ± 147 μg/g) was less contaminated. Other metals (Cu, Cd, Cr, Ni and Zn) analyzed were about background levels except for Cu at impact area. The enrichment ratio of Pb in runoff sediments was mostly high for the 0.43 mm sediment fractions independent of rainfall condition. Principal component analysis (PCA) biplot showed strong correlation between spatial distributions of metals around the vicinity of the berm (farmlands behind the berm) with concentrations on the impact berm soil. Surface runoff simulated on impact area soil had high concentrations of Pb (40.4 - 65.6 μg/mL) which could further lead to enrichment of soil-Pb levels within the vicinity of the berm. Decontamination measure is therefore required to minimize extensive contamination of surrounding soils of the impact berm due to rainfall runoff events.