Prototyping of co-composting as a cost-effective treatment option for full-scale on-site remediation at a decommissioned refinery

Abstract

The costs for managing process wastes and their environmental and social impacts is contributing to the poor economics of petroleum hydrocarbon refining. The hypothesis tested was that oily sludge co-composted at a pilot scale would enable a proof of concept (prototype) for remediation at commercial field scale. The aims of the study were to translate pilot-scale outcomes to commercial terms for full scale treatment, as well as studying leachability of the contaminants, and biodegradation of the petroleum fractions. A co-composting experiment, based on a relatively simple windrow design with readily available organic amendments, demonstrated the potential to cost effectively remediate oil-contaminated soil and sludge on-site at a petroleum refinery. An initial mesophilic - thermophilic phase, characterised by high windrow temperatures (up to 60–65 °C), incorporating weekly windrow turning, resulted in fast rates of removal of total petroleum hydrocarbons (TPH) (>3000 mg kg−1. day−1) and polycyclic aromatic hydrocarbons (PAHs) (9 mg kg−1. day−1) over the first month. The remaining period of the biphasic degradation process was passive i.e. without windrow turning. At the end of the experiment, TPH in the composted windrows of organic amended sludge were decreased from 62% (w/w) (in air dried sludge), the highest reported in the oil composting literature, to 1% in the final mix, meeting the targeted solid waste disposal criteria of 1% TPH. PAHs were reduced by 96% to below relevant solid waste and contaminated soil health investigation levels (HILs) to considerably less than 100 mg kg−1. The major conclusion was that the study enabled costings for commercial scale-up to be developed indicating on-site treatment could be achieved at approximately $AUD 150 compared to off-site treatment at $AUD 1250 per tonne.