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.

Active water treatment is far more common. Chemicals called coagulants or flocculants are added to waste water in order to quickly clump small metal particles together. These clumps are then left to settle before they are removed, dried out and eventually disposed of - either underground in the mine, or 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 issuess. Hence, our team at Exeter have spent the Summer working on a cost effective solution.

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.