Evaluating the bio-removal of crude oil by vetiver grass (Vetiveria zizanioides L.) in interaction with bacterial consortium exposed to contaminated artificial soils

Rhizobacterial-assisted phytoremediation for accelerated petroleum-hydrocarbon removal in crude-oil sludge

Almost over ten years, environmental experts have concentrated on implementing risk-based management strategies for the remediation of sites contaminated with total petroleum hydrocarbons (TPHs), which can potentially have detrimental ecological impacts. Phytoremediation widely recognized as a green technology a plant-based and economically efficient technology, emerges as a promising method to offer an alternative to existing treatment technologies in TPH contaminated ecosystems. The utilization of Scirpus grossus, a perennial plant, has been proposed as a practical, safe, and cost-effective method for remediating soil contaminated with petroleum hydrocarbons. This study aimed to evaluate the efficacy of S. grossus in removing total petroleum hydrocarbons (TPH) in real crude-oil sludge. Employing a batch phytoremediation system with S. grossus, the experiment was conducted in crates within a greenhouse, maintaining ambient temperatures (30 °C-35 °C) for a duration of 28 days. Each crate was populated with 9-month-old plants of uniform size, initially cultivated in the greenhouse before being transplanted into crates containing 100 % crude-oil sludge with an initial TPH concentration of 37,554 mg/kg for the treatment phase. TPH removal rates were assessed after 14, 21, and 28 days of exposure, resulting in removal rates of 67 %, 74 %, and 75 %, respectively. The highest concentration of rhizobacteria recorded in both sample (with contaminants and without contaminants) were 5.56 × 104 and 5.72 × 104 CFU/mL respectively. Furthermore, TPH extraction from both stems and roots of S. grossus was analysed, revealing the highest TPH concentration of 15,319 mg/kg and about 8000 mg/kg of TPH at day 28 by roots and stem sample respectively. In conclusion, S. grossus demonstrated substantial potential in effectively mitigating the toxicity of TPH in real crude-oil sludge contamination scenarios.

Enhanced phytoremediation of atrazine-contaminated soil by vetiver (Chrysopogon zizanioides L.) and associated bacteria

The intensive and long-term use of atrazine (ATZ) has led to the contamination of agricultural soils and non-target organisms, posing a series of threats to human health through the transmission of the food chain. In this study, a 60-day greenhouse pot experiment was carried out to explore the phytoremediation by Chrysopogon zizanioides L. (vetiver). The uptake, accumulation, distribution, and removal of ATZ were investigated, and the degradation mechanisms were elucidated. The results showed that the growth of vetiver was inhibited in the first 10 days of the incubation; subsequently, the plant recovered rapidly with time going. Vetiver grass was capable of taking up ATZ from the soil, with root concentration factor ranging from 2.36 to 15.55, and translocating to the shoots, with shoot concentration factor ranging from 7.51 to 17.52. The dissipation of ATZ in the rhizosphere soil (97.51%) was significantly higher than that in the vetiver-unplanted soil (85.14%) at day 60. Metabolites were identified as hydroxyatrazine (HA), deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA) in the samples of the shoots and roots of vetiver as well as the soils treated with ATZ. HA, DEA, DIA, and DDA were reported first time as metabolites of ATZ in shoots and roots of vetiver grown in soil. The presence of vetiver changed the formation and distribution of the dealkylated products in the rhizosphere soil, which remarkably enhanced the occurrence of DEA, DIA, and DDA. Arthrobacter, Bradyrhizobium, Nocardioides, and Rhodococcus were the major atrazine-degrading bacterial genera, which might be responsible for ATZ degradation in the rhizosphere soil. Our findings suggested that vetiver grass can significantly promote ATZ degradation in the soil, and it could be a strategy for remediation of the atrazine-contaminated agricultural soil.

Modelling of n-Hexadecane bioremediation from soil by slurry bioreactors using artificial neural network method

Diesel oil is known to be one of the major petroleum products that can pollute water and soil. Soil pollution caused by petroleum hydrocarbons has substantially impacted the environment, especially in the Middle East. In this study, modeling and optimization of hexadecane removal from soil was performed using two pure cultures of Acinetobacter and Acromobacter and consortium culture of both bacterial species using artificial neural network (ANN) method. Then the best ANN structure was proposed based on mean square error (MSE) as well as correlation coefficient (R) for pure cultures of Acinetobacter and Acromobacter as well as their consortium. The results showed that the correlations between the actual data and the data predicted by ANN (R2) in Acromobacter, Acinetobacter and consortium of both cultures were 0.50, 0.47 and 0.63, respectively. Despite the low correlation between the experimental data and the data predicted by the ANN, the correlation coefficient and the precision of ANN for the consortium was higher. As a result, ANN had desirable precision to predict hexadecan removal by the cobsertium culture of Ochromobater and Acintobacter.