Applied Design

A 2016 report written by Harvard Law School shows that South Africa Have failed to adress the adverse environmental and health effects of more than 130 years of gold mining in and around Johannesburg.

Mining, and more specifically the contaminated waste created by the mining industry, causes damage to the environment that is largely irreversible. Mine waste, or tailings, can contain as many as three dozen hazardous chemicals, including lead, arsenic, mercury and cyanide to name but a few.

Unfortunately, governments in less economically developed countries (LEDCs) are not acting quickly enough on what is already a huge and growing environmental catastrophe. With the World's leading mining country being South Africa, this lack of action taken by the govermnent is putting lives at risk.

Current Methods

There are two routes that current treatments can take: active treatment methods require energy and chemical usage, whereas passive treatment methods use only natural processes, which can include gravity, plants, or even microorganisms.

Such passive processes include Vertical Flow Ponds (VFP’s). The project, which was formed by the University of Newcastle in 2013, was piloted by the Department of Environment, Food and Rural Affairs in partnership with the Coal Authority, the Environment Agency and the National Trust after receiving finding of £1 million to remove heavy metal pollutants leaching from disused mines (Anon., 2013). The scheme bio-remediates water to firstly remove metal contaminants and then allow the outflow to enter wetland where it is filtered through limestone and compost. (Adam Jarvis, 2015).

In addition to this there is ongoing research conducted by the GW4 Alliance into using algae as a form of wastewater treatment. Dr Chris Byran and Dr Mark van der Giezen along with researchers from Bristol, Cardiff and Bath Universities as well as Plymouth Marine Laboratories took samples form the Wheal Jane tin mine and attempted culture algae in them. Testing proved that algae was capable of growing in the mine water and showed that the presence of metals resulted into a greater conversion of bio-mass to bio-crude, which is used to make bio-fuels. The research which has attracted the attention of industry and academics alike is hoped to be applied to waste streams in the future.

Active water treatment is far more common. Clarifying agents such as coagulants or flocculants are will later clump together and are then left to settle before they are removed, dried out and eventually disposed of – most commonly in a waste disposal site. This method is dependent on the desired water quality, and sometimes other methods are used such as ion exchangers, membrane filters, and reverse osmosis.

However, these methods have proven to have high maintenance and running costs. Hence governments of LEDCs would be unlikely to invest in such technologies when there may be more pressing issues. Additionally the storage of residual waste and its future effect on the environment is becoming a growing concern.

With this in mind our team at Exeter have spent the summer working on developing a cost effective and sustainable solution which will have a reduced effect on the environment than compared to the existing technologies in use.

Our Solution

The Pili+ Filtration System offers a cheap to run, cheap to produce alternative to current methods of decontaminating mine waste. It is comprised of three modular components, each of which will be easy to replace or adapt in the event of damage or situational change.

The first component is the hydrocyclone. The hydrocyclone relies on its conical geometry to filter larger particulates, such as sand, from contaminated water. This function is required to prevent blockages in the fluidised media reactor, component two. We have chosen to use a hydrocyclone because it has no moving parts, requires only a pump, and small versions can easily be 3D printed, or manufactured using simple and affordable methods. This makes it perfect for useage in LEDCs where resources are scarce yet situation is critical.

The second component, as mentioned previously, is the fluidised media reactor (FMR). The fluidised media reactor is a piece of cylindrical housing apparatus designed to contain our genetically modified bacteria. The water, now free of large particulates, is fed into the top of the FMR. It travels down through the central pipe, and slowly rises back through the outer pipe, in which the bacteria are contained. The E.Coli are grown on a sponge material, using mouthwash which stresses the bacteria and promotes the development of a biofilm. Here, we have optimised the flow rateto ensure that the bacteria have a high probability of binding to the targeted metal ions.

The third component has been designed to ensure the containment of the genetically modified bacteria.

References (Harvard)

1. Wolkersdorfer, C., Chapter 11: Mine Water Treatment and Ground Water Protection in Water Management at Abandoned Flooded Underground Mines: Fundamentals, Tracer Tests, Modelling, Water Treatment, A. International Mine Water and I. ebrary, Editors. 2008, Springer: Berlin. p. 235.