Understanding and exploiting biological metal-nanoparticle synthesis for metal recovery

There is increasing concern over environmental copper levels, their toxicity and their adverse effects on humans and wildlife. The environmental quality standard of copper in groundwater in the UK is set low, at 1-28 ug/l, to balance these risks against the interests of industry. Consequently, the currently allowed environmental level of copper effectively pitches the key Scottish industry of salmon fishing against another - the spirits industry, as whisky, vodka and gin production involve a universal step of distillation in copper pot stills. Soluble copper is required in the distilling process as it prevents sulphur-containing compounds from distilling with the alcohol, which would give it an aroma of bad eggs, so a simple change to the material from which the stills are made is not an option. This dissolved copper is then found in the waste, and not the whisky, in concentrations high enough to be toxic to living organisms. Therefore, it is necessary to treat the waste before it can be used as animal feed, fertiliser or released into the environment.

The whisky industry has invested heavily in research to develop an effective method for removing toxic material from the waste of the whisky making process. Current treatments include chemical and physical methods that are expensive and have significant limitations. Cheap and effective treatment methods for copper contaminated waste still need to be developed and employing bacteria for the recycling of such contaminants may provide the solution, allowing the whisky industry to continue its expansion without adverse environmental consequences.

The biological transformation of copper ions to stable copper nanoparticles may provide a cost-effective biological solution for the treatment of distillery coproducts. This biotransformation of metal ions occurs naturally within some bacteria with the formation of solid metal nanoparticles outside of the bacterial cell. Our previous work has shown that distillery coproducts are an excellent nutrient source for our chosen bacterium and that the copper ions in distillery coproducts can be biotransformed to nanoparticles at the same time.

This application requests funding to improve the efficiency of this process to allow its future use on a industrial scale.

Metals have a finite supply, thus metal scarcity and supply security have become worldwide issues. To solve such a global challenge, we have to ensure that we do not drain important resources by prioritizing the desires of the present over the needs of the future. Thus we need to move to a circular, more sustainable economy where we use the resources we have more wisely. One of the founding principles of a circular economy is that waste is an unused feedstock; that organic and inorganic components can be engineered to fit within a materials cycle, by the design, engineering and re-purposing of waste streams. Biological nutrients are non-toxic and can be composted, whereas technical nutrients can be designed to enable their reuse with minimal energy.

However, what if it was the 'compost' itself that provided energy to designed microbes that were then able to engineer the reuse of materials? That is the aim of this proposal. To use the new tools and techniques provided by advances in biology to engineer a bacterium with the ability to recycle metals from waste streams.

Certain bacteria have the ability to reduce metal cations and form precipitates of zero-valence, pure metals, as part of their survival mechanism to defend against toxic levels of metal cations. We will use a modular approach, commonly used in Synthetic Biology, to enable us to design, build and test methods to enhance the bioproduction of these high-value metal nanoparticles. We will also compare this method to a more traditional strain enhancement approach and use the data provided through proteomics to further inform design. Thus we will provide the next step towards a biological waste treatment method with high value metal recovery.

This project will address the important challenge of remediating contaminated wastes to recover materials for future use and economic gain.

Industrial Impact: Diageo plc. is a global leading company in beverage alcohol. Having promised not to increase the production of waste while still planning ambitious expansion the company has effectively committed to around a 50% reduction in waste. It is therefore seeking to invest in research that may provide new ways to remove contaminating copper ions from its co-products, allowing their use as animal feed and fertilizer, with the recovery of valuable copper. Importantly, Diageo is a committed member of the Scotch Whisky Association and sees the development of such a technology as vital for the industry rather than as a USP for itself and would therefore share such a technology to further promote the iconic, high quality product of Scotch Whisky worth £4.23bn in annual exports. In addition to whisky, gin and vodka require similar distillation steps in copper pot stills, producing similar contaminated co-products, and thus the adoption of new bioremediation technology would have manufacturing impact outside of Scotland.

CuNPs are of interest in the electronics field, especially the market of conductive inks, which is expected to grow to $2.4 billion by the end of this year. Currently, conductive inks used for printed electronics are based on silver particles. However, 80% of the cost of the silver inks is the metal and this price is unpredictable. Research into alternatives has led to silver-coated copper nanoparticles. They use less than 10% silver loading; however the processing costs are higher, which means savings of only 10-15% on standard silver inks. Therefore, there is a new market arising for CuNPs (currently $8500 per kg, compared with approximately $17 for micron size particles) and the substantially lower costs of bioproduction suggests that they might offer a viable and cost-effective alternative to the chemically synthesized particles currently in use.

Our abilities to manipulate bacteria in combination with their ability to synthesise nanoparticles could provide access to a host of novel nanoparticles. While we cannot predict their properties at this stage it is possible that they may be similar to those of critical metals already in use. This would allow the novel biogenic nanoparticles to replace scarce materials, which have prices dictated by countries outside of the UK, and thus ensure resource security.

Public and Social Impact: The environmental quality standard for copper in groundwater in the UK, is set reassuring low and new bioremediation technologies would not benefit public health as alternatives are available. However, the resource efficiency KTN estimates that world wide mining activities are responsible for 5% of global carbon dioxide emissions, consume limited fossil fuel resources and produce other damaging 'greenhouse gases', recovery of metals would reduce the burden on mining and its environmental impact.

Economic Impact: The industrial impacts described will produce economic benefits to Scotland and the UK and concurrent social benefits to some of the less affluent areas of the UK, creating employment and reducing healthcare needs, which in turn leads to economic benefits at a national and international level. The recovery of materials from waste streams has obvious economic benefits and the development of new process routes for the production of lower cost and/or higher performance metal nanoparticles may contribute towards wealth generation in a number of possible sectors.

Policy Makers: Impact on policymakers on future technology options in: contaminated waste remediation (e.g. DEFRA); eco-friendly/economic production routes for nano-materials (BIS and DEFRA); advancing biotechnology/synthetic biology in the public interest and in the development of a range of high-value products that rely on nanoparticles (BIS, DH and DECC).