Abstract
Crude oil contamination of soil and water resources is a widespread issue. The present study evaluated the degradation of aliphatic hydrocarbons (C11–C36) in crude oil by 17 bacteria isolated from a crude oil–contaminated soil. The results suggested that Pseudomonas sp. and Bacillus amyloliquefaciens were the best hydrocarbon-degrading bacteria in the presence of surfactant Tween-80 (0.1% w/v). Based on the present investigation and a previous study, Pseudomonas sp. + B. amyloliquefaciens and fungus Aspergillus sydowii were identified as best oil degraders and were immobilized in alginate–bentonite beads, guargum–nanobenonite water dispersible granules (WDGs), and carboxy methyl cellulose (CMC)–bentonite composite. Sandy loam soil was fortified with 1, 2, and 5% crude oil, and total petroleum hydrocarbon (TPH) degradation efficiency of free cultures and bio-formulations was evaluated in sandy loam soils. Compared to a half-life (t1/2) of 69.7 days in the control soil (1% oil), free cultures of Pseudomonas sp. + B. amyloliquefaciens and A. sydowii degraded TPH with t1/2 of 10.8 and 19.4 days, respectively. Increasing the oil content slowed down degradation, and the t1/2 in the control and soils inoculated with Pseudomonas sp. + B. amyloliquefaciens and A. sydowii was 72.9, 14.7, and 22.2 days (2%) and 87.0, 23.4, and 30.8 days (5%), respectively. Supplementing soil with ammonium sulfate (1%) enhanced TPH degradation by Pseudomonas sp. + B. amyloliquefaciens (t1/2–10 days) and A. sydowii (t1/2–12.7 days). All three bio-formulations were effective in degrading TPH (1%), and the t1/2 was 10.7–11.9 days (Pseudomonas sp. + B. amyloliquefaciens and 14–20.2 days (A. sydowii) and were at par with free cultures. Microbial diversity analysis based on taxonomic markers and functional markers suggested that the bioaugmentation process helped keep soil in the active stage and restored the original microbial population to some extent. The present study concluded that bio-formulations of crude oil–degrading microbes can be exploited for its degradation in the contaminated environment.
Highlights
Crude oil is a rich source of hydrocarbons and a major source of energy to the ever growing automobile industry
Crude oil was characterized for aliphatic hydrocarbons and chromatograms of certified reference material and crude oil constituents are shown in Supplementary Figure S1
The t1/2 in fungus treatments, compared to T8 (1%), increased by 14.4% (T16) and 58.8% (T19) in respective treatments. These results suggested that bacterial consortium was better in degrading the Total petroleum hydrocarbons (TPHs) content in crude oil–fortified soils, but fungi were more resilient at higher crude oil content and less strained to higher oil content
Summary
Crude oil is a rich source of hydrocarbons and a major source of energy to the ever growing automobile industry. India is not spared from such environmental threats, and several incidences of crude oil spillage have caused serious threat to the environment. It included destruction of more than 300 ha of mangrove across 100 km stretch of coastline in Mumbai due to collision of ships, four sq km spread of crude oil due to rupture of Mumbai–Uran trunk pipeline, and 25 miles of coastlines affected by ship collision in Chennai (THE ECONOMIC TIMES, 2011; THE HINDU, 2011; THE TIMES OF INDIA, 2017; Han et al, 2018). Several acres of paddy fields were ruined following irrigation by the oil slick–laden water from the channel, and few farmers got a compensation of INR 5000–80000 from Oil and Natural Gas Corporation Limited (ONGC) (THE HINDU, 2011). Oil India Limited provided INR 2.5 million as immediate compensation to each of 12 families that completely lost their homes and continue to give INR 50000 per month as livelihood support to each family which are forced to go away from their homes (BBC NEWS, 2020; WIKIPEDIA, 2020)
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