2015 Sustainable Remediation Project Recognition Award – Coffey for "Solar Thermal Aerobic Recirculation Remediation System"
by Andrew Labbett & Michael Blackham, Coffey
Market and technology drivers
In the petrochemical industry, many decommissioned sites exist with residual contamination, which typically manifests itself as a groundwater plume. Active remediation systems can be costly to install and operate, and often have a high carbon energy cost. Consequently numerous legacy sites are being left in a derelict state for years to bio-remediate through natural processes. During this time, these sites pose an ongoing environment and community risk. Furthermore, the financial and reputational costs of these legacy sites for petrochemical companies can be significant.
Many operational petrochemical and service station sites are also allowed to remain in a contaminated state, providing the existing contamination is managed appropriately. While this approach can be financially viable while the sites are being operated, leaving this contamination unchecked can increase remediation costs, if and when sites are divested or re-developed.
Remediation technologies – particularly those adopted on petrochemical industry sites – typically utilise extraction and treatment equipment with intrinsic high energy consumption to operate aggressive remediation strategies. Driven by regulatory compliance and enforced clean-up requirements, these reactionary and energy-intensive approaches often ignore the energy cost and greenhouse gas emissions associated with remediation.
At many sites where the bulk of the primary and secondary contaminant sources have been removed, longer timeframes may be required for close out, due to the need to treat lower level contamination that is less responsive to common remedial approaches. The cost and greenhouse gas impact of continuing to operate standard approaches such as air-sparging or pump-and-treat at these sites can mean that any apparent improvement to the environment can be outweighed by the environmental impact due to energy usage.
Addressing these challenges – The “STAR” System
To address these market challenges, Coffey has developed an efficient, but low cost active remediation system for enhanced bioremediation at contaminated petrochemical sites, known as the Solar Thermal Aerobic Recirculation (“STAR”) remediation system. The development of this product was commissioned in 2013 and is currently being trialled at a former petrol station in Western Australia. A world-first, this system has the potential to change the remediation landscape, by providing clients with a low-cost, low environmental impact, low social impact and faster solution for the clean-up of hydrocarbon contaminated sites.
We have taken the important step of filing a patent application with the Australian Patent Office, demonstrating the technical details, method and advance in the science of remediating contaminated sites.
How the STAR system works
The STAR system utilises alternative (solar) energy sources combined with enhanced bioremediation, to minimise energy usage and reduce the greenhouse gas emissions that arise from conventional fossil-fuel derived electricity.
Enhanced bioremediation is a process that increases the activity of the microbes that reduce contaminant mass through bio-degradation. These microbes already exist in the sub-surface, and can be stimulated through environmental control by adding nutrients and oxygen (where aerobic biodegradation is required), and by increasing the sub-surface temperature to a more optimal range, typically between 25°C and 35°C.
The STAR system boasts a fully automated recirculation system that utilises solar powered groundwater pumps to extract contaminated groundwater from the downgradient fringe of the plume. The extracted groundwater is heated - at no energy cost - through an array of parallel solar water heating panels, before passing through an eductor, which acts as an oxygenation and optional nutrient dosing system. The water is then reinjected into the source zone of the plume. The oxygenation system entrains air (the oxygen source) into the heated groundwater prior to re-injection, and can also be used for transporting liquid nutrients into the system if required.
All major elements of the system are solar powered, making the system operation carbon-neutral. This is a significant advantage in the present “green-demanding” commercial environment.
Site adaptability is also an important consideration. The equipment is mounted on flat-packing stands for easy establishment and decommissioning at non-operational sites, however the same equipment can also be roof mounted at operational sites to reduce site space impact. Using equipment that is commonly seen mounted on roofs also reduces the perception of the equipment being used for remediation purposes.
Based on the current field trials being conducted in Western Australia, water temperature increases of more than 7°C are achievable where ambient temperatures are in the low 20s centigrade, with water recirculation rates of up to 30,000 litres per day being achieved with a two-pump system. Groundwater temperature increases of 3 to 5°C have also been recorded.
Retail petroleum site divestment – Site divestment is a primary market for this technology. Whether the sites are operational, decommissioned, leased or owned, the STAR system could be readily utilised for polishing residual contaminant loads in groundwater - a common issue that can lead to a stalled site divestment process.
Management of former landfills - Landfill leachate treatment and recirculation is also a potential application. Bioreactor landfills involve the addition of moisture to landfilled waste to create an environment more favourable for microorganisms responsible for waste decomposition. Councils who manage old landfills could therefore utilise the STAR system to improve landfill biodegradation rates and reduce methane production.
Industrial brownfields and other petrochemical sites – The appeal of this product is broad, with the potential for brownfields and other petrochemical sites to utilise the STAR system to enhance bioremediation of plumes that may migrate beyond site boundaries.
The STAR system is considered to be in keeping with sustainable remediation frameworks, in terms of environmental, economic and social indicators.
|Low environmental impact||Because of the system’s reliance on solar energy, greenhouse gas emissions generated during operation are close to zero. The only moving parts are below ground electrical pumps; hence the STAR system is noise-free. The system’s closed loop configuration means that it also generates no vapour emissions and no waste products.|
|Low cost||The combined capital and installation costs of a basic STAR system are about the same as a single chemical amendment injection phase of work, which is typically around $50k to $100k. Given that multiple injection events are required for most sites, the cost savings using the STAR system is likely to be in the order of several tens to hundreds of thousands of dollars at most sites. The reduction in overall timeframe also reduces the number and cost of groundwater monitoring events, which can lead to significantly earlier site divestment and redevelopment dates.|
|Low social impact||Given that the only moving parts of the system are high-reliability solar driven submersible pumps, maintenance is minimised. Assuming that the levels of biological fouling are manageable, quarterly operations and maintenance visits may be all that is required for most sites. Impacts on local neighbourhoods are therefore minimal and health and safety risks are low. Utilisation of the STAR system also enables the spirit of the ‘polluter pays principle’ and associated social justice to be upheld, with ultimate remediation timeframes at legacy sites reducing from periods in the order of 10 to 15 years to approximately 3 to 5 years.|
Coffey currently has a pilot project operating in Perth. Water temperature increases of several degrees have been recorded over the treatment area along with good evidence of enhanced biodegradation occurring. By late 2015 the pilot trial phase will be nearing completion, and the site data will be available for publication.
A second system is currently being constructed, which is expected to be operational by September 2015.