Bioremediation of petroleum contaminated soils using native plants and their rhizobacteria in the Sudd region of South-Sudan

Abstract

Crude oil extraction in Sudd wetland covers an estimated area of 1,834,000 ha currently producing between 298,000 to 390,000 barrels per day. It estimated that almost the entire area is contaminated with crude oil. Incidentally, in the region, ordinary citizens subsist on agriculture for livelihoods. Hence, need for rehabilitation of oil-contaminated soils. Globally, green technologies such as bioremediation are encouraged for rehabilitation of soils contaminated with Petroleum Hydrocarbons (PHC). This study determined: i) Plant species abundance in PHC contaminated soil for selection of phytoremediation species. ii) The capability of native plant species for bioremediation. iii) Biostimulation rate of cattle manure for enhancing phytoremediation, and iv) Characterizing the rhizobacteria community for bioremediation. The study sampled three land use types (oil drilled, cultivated and natural) for plant species and soil samples (objective 1) and conducted screen house experiments (objectives 2 to 4). There were 23 herbaceous plant species in the sampled fields but only six (Sorghum arundinaceum, Oryza longistaminata, Hyparrhenia rufa, Nicotiana tabacum, Gossypium barbadense and Abelmoschus ficulneus) were abundant in fields contaminated with PHC. Petroleum hydrocarbon contamination at concentration of 7002 mgkg-1 detected as far as cultivated land from drilling points, was higher than the critical value of 5000 mgkg-1 soil (Sudan) and 5600 mgkg-1 (International). In the screen house experiment, plant species H. rufa removed about 74.4 % of PHC in 75 gkg-1soil followed by G. barbadense (66.3 %), O. longistaminata (56.2 %), T. diversifolia (55.9 %), and S. arundinaceum (50.2 %). All the seeds planted in soil with PHC concentration at 125 gkg-1 failed to germinate. Biostimulation with cattle-manure at 2 tha-1 significantly increased removal of PHC. Pyrosequencing of 16S rRNA generated abundance of rhizobacteria community in manure treated hydrocarbon contaminated soil as shown by Chao1 values (H. rufa, 10310; T. diversifolia, 9795; G barbadense, 9540; O longistaminata, 9168; and S. arundinaceum, 8260). Rhizobacteria genera Pseudomonas, Luteimonas, Sphingomonas, Mycrobacterium, Rhodococcus, Bacillus and Fusibacter were more prevalent in manure treated hydrocarbon contaminated soil. In conclusion, use of plant species H. rufa, T. diversifolia, G. barbadense, O. longistaminata and S. arundinaceum biostimulated with 2 tha-1 of cattle-manure greatly improves bioremediation of PHC contaminated soils in the Sudd region of South Sudan.