Large scale bioaugmentation of soil contaminated with petroleum hydrocarbons using a mixed microbial consortium

•Bioaugmentation of hydrocarbon-contaminated soil with a bacterial consortium.•Repeated field studies showed TPH levels were reduced to <1000 mg kg−1.•A phytotoxicity bioassay confirmed successful degradation in the field.•TPH analysis 3 years after treatment confirmed that TPH levels have remained low.

Singapore is a highly industrialised country with an important oil industry resulting in a significant environmental impact, creating vast amounts of hydrocarbon waste that needs to be remediated. Here we report on the commercial scale bioremediation of a soil contaminated with processed petroleum hydrocarbons at a petroleum facility located offshore from Singapore. Initial laboratory results indicated the efficacy of an adapted consortium in terms of degradation of petroleum hydrocarbons, with complete degradation of the contaminants occurring after 21 days. Microbial counts confirmed a bacterial increase during the degradation and an ecotoxicological assessment using Brassica rapa confirmed a reduction in the toxicity of the treated soil. In field studies for example, initial processed petroleum hydrocarbon concentrations of 26,240; 622,657; and 978,399 mg kg−1 in 250 tonnes of soil were degraded to <1000 mg kg−1 in 9, 12 and 17 weeks, respectively following the bioaugmentation treatment. A 100% germination rate of Brassica rapa was also observed in the field for all the treated soil batches except for soils further contaminated with oil tank bottom sludge. Moreover, further total petroleum hydrocarbons (TPH) analysis performed 3 years after the treatment confirmed that their concentrations have remained low (7-35 mg kg−1) all over the site. To the author's knowledge, this is among the first studies to report large scale successful bioaugmentation of TPH-contaminated soil in Singapore.