The complexity of hazardous waste management for infrastructure projects is not new. Stakeholders, planning restrictions, design requirements, and budgets all generate problems that can be solved by the creativity and persistence of the design team and client.
In the modern urban context, many of these solutions are found below the ground. This is where another set of challenges can arise – including excavation volumes and contamination legacies.
Straight to landfill vs treatment and reuse
Hazardous waste is managed via multiple processes. “Straight to landfill” can be one approach, which can transfer complex hazardous wastes into another location. But there are options to reduce the risk of the waste in storage (in landfill), as well as to reduce the volume (via treatment and reuse).
Organic contaminants can be found on brownfields sites. It is these organic contaminants that are persistent in the environment (such as PFAS) or hazardous to human health (such as PCBs, PAHs). There are some in situ immobilisation options, but site constraints and project timelines can often not allow for this work to occur.
This is where thermal treatment can be beneficial. Thermal treatment allows the material to be taken off-site in accordance with a traditional remove and dispose approach. With this method, the spoil is transferred to the treatment facility instead of a landfill. Diversion of material from landfills is consistent with best practice, as viewed from social and regulatory perspectives, in line with the National Waste Hierarchy pictured below.
Benefits of thermal treatment
Thermal treatment of the soil removes organic contaminants, which reduces the residual risk of output material. If there is co-mingling with inorganics, then this will continue to be held in the material. However, spoil which is only contaminated with organic materials will become clean fill, when assessed against the Industrial Waste Resource Guidelines (IWRG). IWRG is used to determine if the material is contaminated, and it is the same guidelines used to determine whether the treatment has been effective.
Of the options available to counter the risks of hazardous materials, thermal treatment is able to offer destruction of the contaminant. Thermal treatment severs the chemical bonds of the chemical contaminant, which decomposes into water, carbon oxides, and acid salts. The contaminant no longer exists. Alternatives, such as immobilisation, encapsulation, dilution and storage, reduce the risk, but a residual risk persists.
Thermal treatment process at SOLVE
Contaminated waste from projects is transported to SOLVE Altona and stored in a fully enclosed atmospherically controlled Material Receival Building.
Prior to the treatment, the waste undergoes conditioning which involves – crushing, drying, and screening of the material. The pre-processed material is then fed into the thermal desorber. This increases the volatility of the contaminants, thereby separating the contaminants from the solid material.
The contaminated vapours are collected by gas collection equipment. These vapours are destroyed using a thermal oxidiser which converts them to carbon dioxide and water vapour.
All treated material is then stored in the Treated Material Building for sampling, validation, and waste categorisation. The treated material can then be returned to where it was excavated from, re-used for beneficial purposes, or safely disposed into a landfill if required.
The SOLVE thermal facility at Altona supports the delivery of numerous infrastructure projects across the country and diverts tonnes of material from becoming landfill content. This clean fill can then be used for a very broad range of applications, which will reduce landfill occupancy and landfill toxicity.