Water treatment and disinfection
Rivers and wells, which are primarily used as sources of drinking water in Southern Africa, often contain high concentrations of organic pollutants, heavy metals and pathogens. In the first step of the water treatment, organic constituents and heavy metals are removed using a combination of electrocoagulation, flocculation and filtration. Subsequently, diamond-coated electrodes are utilized for disinfection in order to kill fungi, algae, bacteria and viruses with the aid of electrochemical oxidation (see adjacent Figure above). The special challenge lies in designing components able to withstand the conditions prevailing in remote regions.
In September 2018, the first demonstrator built by South African partners was erected in Waterval near Johannesburg (see adjacent Figure below). Solar cells and a battery will enable self-sufficient operation independent of unreliable or non-existent power networks.
Improved long-term stability of diamond electrodes
Within the framework of the project, the Fraunhofer IST developed a new concept for improving the long-term stability of diamond electrodes. The novel diamond electrodes consist of silicon base bodies with a coating of electrically conductive diamond which is only a few micrometers thick. In order that diamond growth is able to take place in the hot-wire CVD process, a pretreatment step, known as nucleation, is required. The denser and more homogeneously the diamond nuclei are applied to the base body, the faster the growth of a defect-free diamond layer and the longer the achievable service life.
Nucleation through bombardment with hydrocarbon ions
In the “SafeWaterAfrica” project, the “Hot Filament Bias Enhanced Nucleation (HFBEN)” process was used for the first time for the nucleation of the diamond electrodes. Nucleus formation takes place directly in the coating reactor through bombardment with hydrocarbon ions which are created in an additional plasma. The advantage of the HFBEN process is that it produces particularly high and uniform nucleus densities, thereby enabling the growth of low-defect diamond coatings with potentially improved service life.
Following the successful installation of the first demonstrator, a second demonstrator is now being set up in Mozambique. In a test phase with a duration of several months, the demonstrators will be tested as regards water quality, failsafe performance and operating costs. Simultaneously, business models will be developed in order to transfer the technology to real application following conclusion of the project in November 2019.
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 689925.