Bioremediation is a process in which the natural microbes in the soil are promoted to digest hydrocarbon based contaminants. Contaminants that fall into this category include polycyclic aromatic hydrocarbons (PAHs), such as those produced as a waste by-product in gas manufacture, and petroleum hydrocarbons (TPHs), such as those typically found at service stations (including petrol, diesel and oils). The bioremediation of these materials does not necessarily occur in-situ. This is where a dedicated bio-pad or treatment pad is required in order to treat the material ex-situ.
The technology is based on soil science principles and involves continually assessing the properties of input material and the material undergoing treatment to ensure the maximum bioremediation rate is achieved.
Although the process may vary slightly for each batch of hydrocarbon contaminated material received, depending on specific contaminants and the matrix material, the following general process is undertaken at the SRF:
- the impacted material is stockpiled on the bio-pad in the treatment area and the following additives are mixed with the material using the Mobile Unit for Soil Treatment (MUST);
- surfactant (EESI18)
- green mulch
- manure (or other microbe source)
- a nitrogen source (e.g., urea).
- Stockpiles are then cultivated via turning with an excavator on a regular basis to allow air into the stockpiles;
- Stockpile soil testing is undertaken on a regular basis to measure the progress of the treated material and analysed for contaminants of concern and, at times, microbiological indicators.
- The process is repeated until validation samples show that the soil has been successfully decontaminated to an acceptable level for re use off-site or in some cases on-site. Validation samples are collected by independent consultants and analysed at NATA approved laboratories.
The stockpiles must remain aerobic via turning of the stockpiles with an excavator to allow the conversion of hydrocarbon compounds to carbon dioxide, water, and microbial cell mass.
There are three potential options for the reuse of treated and validated soil. Remediated soil can be returned to sites where the contaminated soil has been sourced from to allow for the back-filling of excavations, soil may be remediated to NSW guidelines for re-use at landfill as day cover, or it can be re-used on site.
All soil material brought to the Soil Recycling Facility to be treated and recycled will meet the requirements imposed on it by the NSW EPA Environment Protection Licence (EPL number 13413) for the SRF.