Removal of complex phosphorus compounds such as phosphonates, phosphinates, phosphites, etc. from industrial process effluents with simultaneous phosphorus recovery through the use of boron-doped diamond electrodes and suitable precipitants or adsorbents. This is the aim of the "ElPhoDia" project funded by Deutsche Bundesstiftung Umwelt (DBU).

Phosphorus is currently being discussed primarily as a critical raw material, most of which is used as a fertilizer in agriculture and ultimately ends up in sewage sludge from municipal waste water treatment via our food. Phosphorus derivatives such as phosphonates, phosphinates, phosphites etc. play an important role for the industry. Consequently, decisive amounts of phosphorus compounds can be found in various industrial effluents. To date, there are no technical processes that can degrade the above-mentioned compounds in industrial wastewater. Up to now, the only solution for companies in many cases has been very energy-intensive and cost-intensive wastewater disposal.

Approach
This is where the ElPhoDia research project "Electrochemical degradation of phosphonates in industrial process wastewater using diamond electrodes" comes in. Under the leadership of the Fraunhofer Project Group for Recyclable Material Cycles and Resource Strategy IWKS, the researchers are developing an electrochemical process together with DiaCCon for the degradation of inorganic or organic phosphorus derivatives from industrial wastewater in order to recover phosphorus later using suitable precipitants and adsorbents. The flow cells with diamond coating - so-called diamond electrodes - manufactured by the company DiaCCon are the basis for this.

Use of diamond electrodes
In order to precipitate the phosphate from the industrial waste water, it is necessary to convert the organic and inorganic phosphates into ortho-phosphate. Electrochemical oxidation with the aid of diamond electrodes is used for this purpose. In contrast to conventional electrodes, diamond electrodes produce strongly oxidative species (OH radicals) and are thus able to degrade a large number of chemical compounds. The electrodes are already being used on an industrial scale in the field of wastewater treatment to remove organic pollutants or to reduce the chemical oxygen demand (COD).

Innovative character of the project
The novelty of the project includes the overall concept from the decomposition of pollutants to the recovery of phosphorus in industrial wastewater streams that have received little or no attention so far. In the chemical industry, the application of the process described here would considerably reduce the volume of waste water to be disposed of. In addition, the biology of the wastewater treatment plant is relieved. A further positive effect may be the hygienisation of the cooling water, since the use of antifouling reagents can be reduced or even eliminated. In addition, no further chemicals are required for electrochemical degradation and no secondary waste materials need to be disposed of. The option of direct reuse of the recovered phosphates is to be examined. An establishment in the field of phosphorus-based compounds would support the recovery of the critical resource phosphorus and at the same time conserve the resource water. The precipitated ortho-phosphates can also be recycled within the company or processed into fertilisers.

Project partners
DiaCCon is a leading manufacturer of diamond electrodes for electrochemical synthesis and water purification and for contract coating of wear parts (mechanical seals and bearings). Especially in the development of electrodes coated with electrically conductive diamond, DiaCCon can look back on several years of development activity and can call itself one of the technological market leaders with worldwide sales. In addition to project coordination, the Fraunhofer Project Group IWKS of the Fraunhofer Institute for Silicate Research ISC is responsible for the treatment of industrial waste water and for the development of concepts for the recovery and recycling of the residues resulting from the processes.

Associated partners
In order to be able to develop the technology as close to application as possible, samples will be provided by Mitsubishi Hitachi Power Systems Europe GmbH (MHPSE) and Clariant Produkte Deutschland GmbH. In the further phases of the project, both companies will be involved in the development of a pilot plant. The project duration of ElPhoDia is 18 months. The project is funded by the Deutsche Bundesstiftung Umwelt (DBU).