The contamination of water with hydrocarbons resulting from oil exploration and production highlights the need for efficient and environmentally friendly technology to mitigate this form of water pollution. Floating treatment wetlands are a sustainable approach for remediating contaminated water. In this large-scale study, we used four different plants, Phragmites australis, Typha domingensis, Leptochloa fusca, and Brachiaria mutica, to vegetate a floating mat with an area of 3058 m 2 made from locally sourced materials. The floating treatment wetlands constructed in this manner were used to treat an oil-contaminated water stabilization pit resulting from oil and gas exploration activities in District Chakwal, Pakistan. The plants and the water in the pit were inoculated with a consortium of 10 different hydrocarbon-degrading bacteria. The application of floating treatment wetlands to the pit reduced chemical oxygen demand, biochemical oxygen demand, total dissolved solids, hydrocarbon content, and heavy metals by 97.4%, 98.9%, 82.4%, 99.1%, and 80%, respectively, within 18 months. All plants survived and showed growth, but maximum development and biomass production were exhibited by P. australis. Moreover, the bacteria used for inoculation were able to persist and show degradation activity in the water as well as in the rhizoplane, roots, and shoots of the plants. We conclude that floating treatment wetlands can be applied to oil-contaminated water stabilization pits for affordable and effective water treatment.
Helophytic plants contribute significantly in phytoremediation of a variety of pollutants due to their physiological or biochemical mechanisms. Phenol, which is reported to have negative/deleterious effects on plant metabolism at concentrations higher than 500 mg/L, remains hard to be removed from the environmental compartments using conventional phytoremediation procedures. The present study aims to investigate the feasibility of using P. australis (a helophytic grass) in combination with three bacterial strains namely Acinetobacter lwofii ACRH76, Bacillus cereus LORH97, and Pseudomonas sp. LCRH90, in a floating treatment wetland (FTW) for the removal of phenol from contaminated water. The strains were screened based on their phenol degrading and plant growth promoting activities. We found that inoculated bacteria were able to colonize in the roots and shoots of P. australis, suggesting their potential role in the successful removal of phenol from the contaminated water. Pseudomonas sp. LCRH90 dominated the bacterial community structure followed by A. lowfii ACRH76 and B. cereus LORH97. The removal rate was significantly high when compared with the individual partners, i.e., plants and bacteria separately. The plant biomass, which was drastically reduced in the presence of phenol, recovered significantly with the inoculation of bacterial consortia. Likewise, highest reduction in chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total organic carbon (TOC) is achieved when both plants and bacteria were employed. The study, therefore, suggests that P. australis in combination with efficient bacteria can be a suitable choice to FTWs for phenol-degradation in water.
Inoculation of plants with pollutant-degrading and plant growth-promoting microorganisms is a simple strategy to enhance phytoremediation activity. The objective of this study was to determine the effect of inoculation of different bacterial strains, possessing alkane-degradation and 1-amino-cyclopropane-1 -carboxylic acid (ACC) deaminase activity, on plant growth and phytoremediation activity. Carpet grass (Axonopus affinis) was planted in soil spiked with diesel (1% w/w) for 90 days and inoculated with different bacterial strains, Pseudomonas sp. ITRH25, Pantoea sp. BTRH79 and Burkholderia sp. PsJN, individually and in combination. Generally, bacterial application increased total numbers of culturable hydrocarbon-degrading bacteria in the rhizosphere ofcarpet grass, plant biomass production, hydrocarbon degradation and reduced genotoxicity. Bacterial strains possessing different beneficial traits affect plant growth and phytoremediation activity in different ways. Maximum bacterial population, plant biomass production and hydrocarbon degradation were achieved when carpet grass was inoculated with a consortium of three strains. Enhanced plant biomass production and hydrocarbon degradation were associated with increased numbers of culturable hydrocarbon-degrading bacteria in the rhizosphere of carpet grass. The present study revealed that the combined use of different bacterial strains, exhibiting different beneficial traits, is a highly effective strategy to improve plant growth and phytoremediation activity.
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