WaterPlasma

Water decontamination technology for the removal of recalcitrant xenobiotic compounds based on atmospheric plasma technology

WaterPlasma.

Currently available wastewater treatments based on physico-chemical and biological processes are limited, since they are unable to efficiently remove recalcitrant xenobiotics substances. To be able to comply with EU regulations in the future the WaterPlasma project aims at developing an innovative decontamination process based on a one atmosphere uniform glow discharge (“OAUGD”) plasma reactor that makes it possible to eliminate recalcitrant molecules without the need of chemicals and filters or without resulting in residual materials.

Plasma-chemical degradation of organic contaminants in water

en
Schematic view of a plasma reactor for water purification.
Degradation kinetics of 1 mg/L methylene blue (efficiency 90 % reduction of 4 g/kWh).
Degradation kinetics of 1 mg/L methylene blue (efficiency 90 % reduction of 4 g/kWh).
Degradation of 0.8 mg/L cyanide in water using plasma treatment.
Degradation of 0.8 mg/L cyanide in water using plasma treatment.

The use of atmospheric pressure plasma processes could provide an environmentally compatible and cost-effective alternative. Ions, highly reactive radicals and short-wave radiation, that degrade the contents of the wastewater are formed simply by applying a high voltage, which is igniting a plasma discharge in ambient air or oxygen. This renders the use of chemicals and their subsequent disposal unnecessary. The aim of the EU-funded “WaterPlasma” project was therefore to develop a plasma process for purifying water and a suitable plasma reactor as a prototype.

 

New type of plasma reactor

The special design of the plasma reactor insures an effective transmission rate of the highly reactive species formed in the plasma to the contaminated water. This is achieved by forming the plasma in direct contact with a flowing water film. The water to be purified falls through the plasma zone by the force of gravity, directly onto the outer surface of a grounded electrode (stainless steel cylinder). Hydroxyl radicals, among others, are created in the plasma and transmitted to the water. By means of their high oxidation potential these radicals and short wavelength UV radiation break down the dissolved contaminants until they are mineralized.

 

Energy-efficient and effective degradation

A method for comparing the efficiency of advanced oxidation processes is the measurement of the energy input that is required to decolor methylene blue by one order of magnitude [1]. Using the plasma process 4 g/kWh is achieved. This value is nearly one order of magnitude better than the energy efficiency measured with a UV H2O2 treatment of methylene blue [2]. In another application of the water plasma method the project showed that cyanide is broken down by 90 percent within 2 minutes [3].

 

Outlook

Unlike well-established advanced oxidation processes the plasma process for water decontamination has no barrier between the plasma and the medium that is to be purified. It therefore requires almost no maintenance and is characterized by a long life. A very high degree of efficiency is achieved even without the introduction of hazardous substances such as hydrogen peroxide or ozone. As a result of the project a demonstrator is now available that is suitable for purifying substantial quantities of contaminated water (240 L/h). At the moment further possible applications for the procedure are being examined.

Project information

Project title

WaterPlasma – Water decontamination technology for the removal of recalcitrant xenobiotic compounds based on atmospheric plasma technology

Project duration

01.01.2011 – 31.12.2012

Project coordination

Ventilaqua – Tratamento de Águas e Efluentes Lda

Funding

The research leading to results in this project receives funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 262033

References

[1] Malik, M. A. (2010) Water purification by plasmas: Which reactors are most energy efficient?, Plasma Chem Plasma Proc. 30: 21-31

[2] Siemens Industry (2011) New actinometry procedure for industrial UV applications, http://www.industry.siemens.com/topics/global/en/fairs/siww/water-convention/Documents/09_Poster_New-Actinometry-Procedure.pdf
[3] Valsero, M. H.; Molina, R.; Schikora, H.; Müller, M.; Bayona, J. M. (2013) Removal of cyanide from water by means of plasma discharge technology, Water Research 47: 1-7