Sustainable treatment of oil contaminated waste: oil-based mud (OBM) drill cuttings and soil.
Nwinee, Sarah Ateduobie
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NWINEE, S.A. 2018. Sustainable treatment of oil contaminated waste: oil-based mud (OBM) drill cuttings and soil. Robert Gordon University, PhD thesis.
Environmental pollution from oilfield drilling waste poses potential hazards which can lead to ecological imbalance. The predominant pollutant from oilfield waste is petroleum hydrocarbons. Some effects of petroleum hydrocarbon contamination in soil include loss of nutrients, reduced fertility, foul odour, flora/fauna imbalance and potential for transport and distribution to other media. Several studies have been carried out to develop technologies for the reduction of petroleum hydrocarbons in oil based mud (OBM) drill cuttings and soil. Soil washing using biosurfactant is one of such technological developments. Biosurfactants are surface active compounds produced from biological origin. They are amphiphilic molecules, consisting of hydrophilic and hydrophobic moieties. The major advantage biosurfactants have over their synthetic counterpart is that they have low toxicity and are biodegradable. They can be produced from natural and renewable feedstock (agricultural and industrial waste). This work focused on the production, purification and characterisation of rhamnolipid (RL) biosurfactant, produced from Pseudomonas aeruginosa ST5 and Pseudomonas aeruginosa PS1, and its consequent application for the removal of total petroleum hydrocarbon (TPH) in OBM drill cuttings and petroleum contaminated soil. First, the OBM drill cuttings and soil were characterised to investigate the following parameters; particle size analysis by laser diffraction and sieve, morphology and elemental content (qualitative) by Scanning Electron Microscope – Energy Dispersive X-ray Analysis (SEM-EDXA), elemental content by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis (quantitative), hydrocarbon profile by Gas Chromatography–Mass Spectrometry (GC-MS) and TPH by Fourier-Transform Infrared Spectroscopy (FT-IR). Second, the rhamnolipid was produced from both bacteria using mineral salts media with glycerol as carbon source in shake flask cultivation process. Approximately 3.5 g/L yield of crude ST5 rhamnolipid extract (ST5-RL) was determined from the culture broth from Ps. ST5 and PS1. Thin layer chromatography analysis carried out on the crude ST5 rhamnolipid extract detected two fractions with retardation factors 0.76 and 0.39, which were purified by column chromatography and confirmed to be monorhamnolipid (R1) and dirhamnolipid (R2) respectively, consequent upon structural characterization using FTIR, NMR and LC-MS/MS. The surfactant potential of R1, R2 and ST5-RL were determined by investigating their surface active properties such as critical micelle concentration (where R1 = 28 ppm, R2 = 24 ppm and ST5-RL = 48 ppm), surface tension and emulsification index after 24 hours (E24). The crude ST5 rhamnolipid, R1 and R2 were applied for the removal of total petroleum hydrocarbon (TPH) in diesel contaminated soil at 10, 100 and 1000 ppm concentration levels. R1 and R2 both showed TPH removals at approximately 77% at 10 ppm, approximately 87% at 100 ppm and approximately 91% at 1000 ppm. However, ST5-RL showed over 90% TPH reduction from the oil contaminated soil at 10, 100 and 1000 ppm, validating the potential of RL in the removal of TPH from soil without purification. Approximately 91% of TPH was removed at the optimum washing condition using ST5-RL. The rhamnolipids were able to remove TPH from the sample by the mechanism of solubilisation. Also, the biocidal effect of RL and RL-washings (from the soil treatment) at 10, 100 and 1000 ppm was studied by carrying out cytotoxicity test on breast cancer MDA-MB-231 cells using MTT assay. The unused RL showed significant anti-proliferative against the cancer cells at 100 and 1000 ppm, while RL-washings showed significant anti-proliferative against the cancer cells at only 1000ppm. The RL was seen to be safe at 10 and 100ppm where over 90% TPH was achieved. This result shows the crude ST5 rhamnolipid is safe to use at concentrations not exceeding 100ppm. The study shows that biosurfactants can be applied to remove TPH from the environment at room temperature.