Underwater plasma technology (UWPT) is a basically new type of “incineration” method for aqueous wastes that contain hazardous organic components. The decomposition of the organic materials takes place in an electric plasma zone that is generated directly in the diluted aqueous solutions. Using the technology, the water content of the liquid waste does not need to be evaporated, therefore, the energy consumption of the process is low compared to the traditional combined separation-incineration processes.
In the course of the decomposition of organic materials mostly carbon dioxide, nitrogen and water are formed, while the inorganic salt content of the solution remains unchanged. Halide, sulfur and phosphorus containing liquids can be processed as well. During the underwater treatment no flocculants are to be added. Using underwater plasma treatment, the chemical oxygen demand of even concentrated waste waters can be decreased to virtually zero.

Industrial references:

Paks Nuclear Power Plant (Hungary)
Removal of the EDTA content of Fe-EDTA solutions (a boric acid containing waste solution that is developed during the cleaning of steam generators). About 2000 cubic meter of such radioactive waste has been treated successfully until 2000.
Removal of Co60 isotopes from the concentrate of the primary coolant, by breaking the Co60-EDTA complex. Initial Co60 activity: 20.000 Bq/liter, Co60 activity after treatment: less than 100 Bq/liter. The plasma technology is an important part of the liquid radioactive waste treatment process of the NPP.

MOL Hungarian Oil Company
Decomposition of mercaptan containing MEROX liquid. Initial chemical oxygen demand (COD): 200000 mg/l O2 , COD after the plasma treatment is less than 50 mg/l O2. Removal of methyl alcohol (CH3-OH) from wastewaters. Initial COD: 20000 mg/l O2, COD after the plasma treatment is less than 50 mg/l O2.

CIPLA Pharmaceutical Company, India
Cleaning of a complex pharmaceutical waste water. Initial COD: 5800 mg/l O2. The COD of the wastewater dropped to zero due to the plasma treatment.

Removal of nitrophenols from an armaments industry wastewater
Total initial nitro phenol content of the wastewater: 6524 ppm. The plasma treatment completely eliminated the nitro phenol content of the wastewater.

Principles of operation

The plasma zone is formed on the surface of submerging electrodes, due to the effect of alternating current of sufficient voltage. Because of applying at least 10 Hz frequency alternating current, electrochemical reactions cannot take place, hence hydrogen and oxygen is not generated. The decomposition of the organic components takes place because of the extremely high temperature and UV radiation of the plasma, and can be further intensified by adding oxidizing agents, preferentially hydrogen-peroxide. Applying underwater plasma technology, the decomposition of the organic materials is achieved by breaking atom-atom bonds; at this point underwater plasma technology differs from traditional plasma applications where complete atomization of the molecules happens.

Energy Consumption and costs of Underwater Plasma-technology

An important fact about underwater plasma technology is that the water content of the liquid waste is not evaporated during the treatment, therefore, the energy consumption of the process is low compared to the traditional incineration or distillation-based processes. Furthermore, the energy consumption of the technology heavily depends on the type and capacity of the underwater plasma device as well as on the initial and required final compositions of the actual liquid waste. Currently the G.I.C. Ltd. offers regular 50 Hz and new generation high-frequency plasma apparatuses. The energy consumption of the latter type new generation equipment is about the tenth of the other, while its investment cost is higher. An approximate energy consumption value for the 50 Hz equipment is around 0.9 kWhr/litre, in case of decreasing the COD of a wastewater from 10000 to 100. Accurate investment and operational cost information can be obtained from the G.I.C. Ltd. The basis of the cost calculation is usually a pilot-scale experiment carried out using the actual wastewater sample of the potential user. To carry out the pilot experiment about 20 liter of wastewater sample is needed.
Awards received for UWP technology: Honorable mention of the XIV. Hungarian Prize of Innovation, 2006; International and Hungarian Major Awards of the EKO 2005 Contest of Environmental Innovation; Extra Reward of the IX. Hungarian Prize of Innovation
Patented in: EU (1406843), Hungary (224394), Republic of South Africa (2003/9503), Republic of Korea (2003-7016176), Ukraine (76989), Japan (3841788), Russian Federation (2286949), China (ZL02814452.X).
Patents pending in: Germany (60203393.4-08), Finland (1406843), Norway (20040196), Spain (ES 2236544 T3), France (02749139.8), Belgium (1406843), Canada (2449529), USA (10/482,960).
The electrodes have a Supplementary Protection Certificate since 2005.