Diagnostic screening of organic contaminant level in solidified/stabilized pre-treated oil-based drill cuttings

The reuse of solidified/stabilized low-temperature thermally desorbed (pre-treated) oil-based drill cuttings for construction purposes is becoming increasingly attractive in recent times; though, without screening a priori the levels of target residual organic contaminants against environmental guidelines to ensure compliance. In this study, pre-treated oil-based drill cuttings were collected from a waste treatment facility in the Niger Delta Province (5.317^oN; 6.467^oE), Nigeria and subjected to cement-based solidification/stabilization (S/S) followed by chemical leaching and screening of the data against local environmental guidelines. S/S was done with drill cuttings contents of 0 (control), 2, 4, 6, 8, and 10 % as part replacement for fine aggregate at 0.6:1, 0.65:1, 0.7:1, 0.75:1, and 0.8:1 water-to-cement ratios using 1:2:4 mix design for a grade-20 concrete. Afterwards, the surface microstructure, elemental composition, and unconfined compressive strength (UCS) of the solidified/stabilized matrix were determined. Amounts of heavy metals and total petroleum hydrocarbons (TPH) leached were also assessed. Results showed that the 2 % drill cuttings addition yielded the highest UCS (22.22-26.22 N/mm²) at water-to-cement ratio of 0.6:1, which were well above the recommended minimum UCS of 20 N/mm² for a grade-20 concrete. The average amount of residual TPH in the solidified/stabilized matrix (62.41 mg/kg) was slightly higher than the local regulatory target value of 50 mg/kg; suggesting that the cement-based S/S failed to immobilize completely all the hydrocarbons in the pre-treated oil-based drill cuttings. This shows that the solidified/stabilized matrix is not in compliance with environmental guidelines on TPH for sustainable reuse as construction materials.