Plant-based oil-sorbents harbor native microbial communities effective in spilled oil-bioremediation under nitrogen starvation and heavy metal-stresses

Costus speciosus (Koen ex. Retz.) Sm.: a suitable plant species for remediation of crude oil and mercury-contaminated soil

The aim of this study was to evaluate the efficiency of Costus speciosus (Koen ex. Retz.) Sm. in the degradation of crude oil and reduction of mercury (Hg) from the contaminated soil in pot experiments in the net house for 180 days. C. speciosus was transplanted in soil containing 19150 mg kg-1 crude oil and 3.2 mg kg-1 Hg. The study includes the evaluation of plant biomass, height, root length, total petroleum hydrocarbon (TPH) degradation, and Hg reduction in soil, TPH, and Hg accumulation in plants grown in fertilized and unfertilized pots, chlorophyll production, and rhizospheric most probable number (MPN) at 60-day interval. The average biomass production and heights of C. speciosus in contaminated treatments were significantly (p < 0.05) lower compared to the unvegetated control. Plants grown in contaminated soil showed relatively reduced root surface area compared to the uncontaminated treatments. TPH degradation in planted fertilized, unplanted, and planted unfertilized pot was 63%, 0.8%, and 38%, respectively. However, compared to unvegetated treatments, TPH degradation was significantly higher (p < 0.05) in vegetated treatments. A comparison of fertilized and unfertilized soils showed that TPH accumulation in plant roots and shoots was relatively higher in fertilized soils. Hg degradation in soil was significantly (p < 0.05) more in planted treatment compared to unplanted treatments. The fertilized soil showed relatively more Hg degradation in soil and its accumulation in roots and shoots of plants in comparison to unfertilized soil. MPN in treatments with plants was significantly greater (p < 0.05) than without plants. The plant's ability to produce biomass, chlorophyll, break down crude oil, reduce Hg levels in soil, and accumulate TPH and Hg in roots and shoots of the plant all point to the possibility of using this plant to remove TPH and Hg from soil.

Adsorption of Sb(III) and Pb(II) in wastewater by magnetic γ-Fe2O3-loaded sludge biochar: Performance and mechanisms

Magnetically modified carbon-based adsorbent (BC@γ-Fe2O3) was prepared through facile route using activated sludge biomass and evaluated for the simultaneous removal of Sb(III) and Pb(II). BC@γ-Fe2O3 exhibited outstanding Sb(III) and Pb(II) adsorption capacity when 200 mg of adsorbent was employed at pH 5.0 for 240 min, with the removal efficiency higher than 90%. The experiments demonstrated the excellent reusability and the potent anti-interference properties of the prepared absorbent. Freundlich and pseudo-second-order kinetic were prior to describe the adsorption process. The adsorption of Sb(III) and Pb(II) onto BC@γ-Fe2O3 was spontaneous and endothermic. BC@γ-Fe2O3 with high specific surface area revealed the exceptional competence to absorb Sb(III) and Pb(II) through pore filling, electrostatic adsorption and complexation. The adsorption mechanisms of Sb(III) and Pb(II) showed similarities with slight disparities. The removal of Sb(III) involved the Fe-O-Sb bond and π-π bond, while the adsorption of Pb(II) was closely related to ion exchange. Moreover, Sb(III) was oxidized to Sb(V) in a minor part during adsorption. The Fe-O-Cl active sites on BC allowed for the binding of γ-Fe2O3, guaranteeing the abundant adsorption sites and stability. BC@γ-Fe2O3 provides an efficient and green insight into the simultaneous removal of complex heavy metals with promising application in wastewater treatment.

Changes in Lolium perenne L. rhizosphere microbiome during phytoremediation of Cd- and Hg-contaminated soils

The contamination of soil and water by metals such as mercury (Hg) and cadmium (Cd) has been increasing in recent years, because of anthropogenic activities such as mining and agriculture, respectively. In this work, the changes in the rhizosphere microbiome of Lolium perenne L. during the phytoremediation of soils contaminated with Hg and Cd were evaluated. For this, two soil types were sampled, one inoculated with mycorrhizae and one without. The soils were contaminated with Hg and Cd, and L. perenne seeds were sown and harvested after 30 days. To assess changes in the microbiome, DNA isolation tests were performed, for which samples were subjected to two-step PCR amplification with specific 16S rDNA V3-V4 primers (337F and 805R). With mycorrhizae, changes had been found in the absorption processes of metals and a new distribution. While with respect to microorganisms, families such as the Enterobacteriaceae have been shown to have biosorption and efflux effects on metals such as Hg and Cd. Mycorrhizae then improve the efficiency of removal and allow the plant to better distribute the absorbed concentrations. Overall, L. perenne is a species with a high potential for phytoremediation of Cd- and Hg-contaminated soils in the tropics. Inoculation with mycorrhizae modifies the phytoremediation mechanisms of the plant and the composition of microorganisms in the rhizosphere. Mycorrhizal inoculation and changes in the microbiome were associated with increased plant tolerance to Cd and Hg. Microorganism-assisted phytoremediation is an appropriate alternative for L. perenne.

Integration of biosorption and biodegradation in a fed-batch mode for the enhanced crude oil remediation

Microbial bioremediation of oil-contaminated sites is still a challenge due to the slower rate and susceptibility of microbes to a higher concentration of oil. The poor bioavailability, hydrophobicity, and non-polar nature of oil slow down microbial biodegradation. In this study, biodegradation of crude oil is performed in fed-batch mode using an oil-degrader Pseudomonas aeruginosa to address the issue of substrate toxicity. The slower biodegradation was integrated with faster biosorption for effective oil remediation. Highly fibrous and porous sugarcane bagasse was surface modified with hydrophobic octyl groups to improve the surface-oil interactions. The microbe showed 2 folds enhanced oil degradation in the fed-batch study, which was further increased by 1·5 folds in the integrated biosorption coupled biodegradation approach. The biosorption-assisted biodegradation approach supported the microbial growth to 2 folds higher than the fed-batch study without biosorbent. The analysis of biosurfactant production indicated the 3 folds higher concentration in fed-batch modes as compared to batch study. In the integrated strategy, the concentration of contaminant (oil) reduces to quite a tolerable level to microbes, which improved effective metabolism and thus overall biodegradation. This study puts forward a promising strategy for improved degradation of hazardous hydrophobic contaminants in a sustainable, economic and eco-friendly manner.

Self-cleaning of very heavily oil-polluted sites proceeds even under heavy-metal stress while involved bacteria exhibit bizarre pleomorphism

Two substrates saturated with crude oil, a desert soil sample (17.3% oil) and an olive-pomace (plant-based oil sorbent) sample (41% oil) showed effective self-cleaning via their own native microorganisms. The oil in such systems did not gather in one compact layer as it may be expected, but became dispensed as vesicles of varying dimensions connected together with narrow tunnels. Bacteria colonized the oil vesicles but only at the borders between the oil and the watery substrates. Through this architectural arrangement, the cells were capable of absorbing oil through their oil-contact surfaces and oxygen, water and water soluble nutrients through their substrate-contact surfaces. The cells involved were those of indigenous hydrocarbonoclastic bacterial communities. Many of those bacteria also tolerated and removed the amended heavy-metals, Hg²⁺, Cd²⁺, Pb²⁺, AsO₄^3- and AsO₃^3-. In the presence of heavy-metals, some of the bacterial species particularly of the pseudomonads exhibited bizarre pleomorphic cell-forms. It was concluded that even environments toxified with extremely high oil concentrations and heavy-metals can be remediated rather effectively via their already existing native microorganisms.