Cleaner, faster, better

Remediation specialists Rick Parkman and Richard Bewley look at innovative techniques and technologies bringing greater efficiencies and clever solutions to environmental clean-up.

Huge variations in emerging types and amounts of contaminants are demanding new and innovative clean‑up methods. Clients are also looking for greater cost efficiencies and faster solutions, perhaps more than ever before. The projects below describe some of the most innovative approaches to these challenges, and while the projects are unique, the processes are replicable.

The magic of mushrooms

Bioremediation uses naturally occurring organisms like bacteria or fungi to break down contaminants, with new and innovative processes constantly emerging. AECOM helped an oil industry client stop residual hydrocarbon, including gasoline and refined motor oil, seeping into soil and groundwater at one of its refinery sites in the US by using white rot fungi mixed with woodchips — a viable alternative to many mainstream applications by being cheaper and more effective.

By applying the fungi woodchip mix in an eight-foot deep trench across the affected area, the fungus consumed the woodchips by releasing a rotting enzyme which then broke down the complex cellulose and hydrocarbons into simpler molecules, enabling indigenous bacteria to digest these in-situ, into carbon dioxide and water. This was cheaper and more effective than conventional pumping systems used by many refineries. It’s an approach that could, potentially, be applied to a range of projects, from small-scale oil leaks from overland pipelines, through to more substantial contamination in rivers and streams affected by major hydrocarbon spills.

Nanotechnology: a smarter future?

Nanotechnology creates ‘smart particles’ that can deliver complex chemical remedies to areas of contamination that are difficult to access. Although in its infancy, it’s possible that nanotechnology can engineer solutions that address contamination at both the macro and micro level — for example, on sites with various types of soils or bodies of groundwater spread across wide areas that are contaminated with many different chemicals. We’re working with a leading university in the US on ground-breaking nanotechnology research. The research focuses on the environmental impact, transport, toxicity and safe handling of nanoscale zero valent iron (nZVI) — a material that is proving effective in treating contaminated groundwater and soils for chemicals such as chlorinated solvents, widely used in industry. Our environmental scientists and engineers are pilot testing the use of nZVI for cleaning sites with contaminated groundwater.

There are plenty of discussions that still need to take place around nanotechnology — there’s a moratorium on development in the UK, for example — and the long term impacts of such solutions are difficult to assess. Yet, the benefits of this technology should not be written off. More research is needed, but these smart particles may well prove to be the future of remediation.

Injecting innovation

For nearly 100 years, Glasgow, Scotland, was the world’s largest producer of chromium. During this time, more than a million tonnes of chromite ore processing residue (COPR) was used as in-fill material across the city’s southeast. These contained massive concentrations of hexavalent chromium (Cr VI) — a known carcinogen.

One area of contamination was found in the Clyde Gateway redevelopment. The AECOM team needed to reduce the amount of hexavalent chromium from the saturated COPR waste deposits leaching into groundwater at the site and nearby River Clyde. Because the hexavalent chromium was situated within COPR deposits, traditional methods of cleaning the contaminant were ineffective. Instead, an innovative form of calcium polysulphide, CaSx, also known as lime sulphur, was injected into the contaminated soil across three treatment areas. Because the product was relatively new, comprehensive bench tests and field trials were conducted to confirm its effectiveness and to reassure the client and regulators.

In total, more than 115,000 tonnes of COPR were treated with this method, reducing hexavalent chromium concentrations in the groundwater to below target levels across the treated area. This innovative in‑situ remediation also required just 10 per cent of the volume of the conventional form of CaSx to achieve a similar effect.

Knee deep in sludge: floating bioreactor

Contaminated sediments in waterways such as canals, rivers and lakes pose complex problems for remediators. Getting to the contaminants is difficult — not only are they underwater, they may be distributed across the length of a waterway.

Our floating bioreactor combines a process for in-situ remediation of such hard-to-reach contaminated sediments with the tools for performing the process. How does it work? The bioreactor sits on floating pontoons. A pressurised pump then lifts the sediments from the water bottom and pushes them through on-board cleaning to strip them of volatile compounds, before resettling them in a controlled way to avoid producing clouds of suspended sediments.

Contaminated sediments often contain compounds that reduce the oxygen in the water, killing fish and other wildlife, so the bioreactor also includes aeration in its cleaning processes, and has proved cheaper and more effective than conventional methods such as extraction and hydraulic dredging.