Technology

ADVANCED OXIDATION PROCESSES FOR THE OXIDATION OF COMPLEX ORGANIC COMPOUNDS

The residuals of drugs can be persistent in the environment for a very long period. This means that their biological degradation (mineralization) takes place very slowly. High stability of these organic compounds is a consequence of their complex structure. To enhance their degradation, we therefore propose advanced chemical oxidation processes. The use of advanced oxidation processes can result in:

  • Complete degradation of complex molecules (into CO2 and H2O),
  • Their easier further biological degradability by partial degradation of the complex molecules on smaller parts,
  • Reduction of their toxicity with partial degradation of complex molecules on smaller ones.

 

Degradation of substances in advanced oxidation processes usually takes place based on the formation and use of hydroxyl radicals (HO), as well as other reactive forms of oxygen (O, HO2, O3, H2O2). The formation of free radicals can be achieved with the use of technologies, which combine ozone, UV, hydrogen peroxide, ultrasound, electrocavitation, photocatalysis, nonthermal plasma, etc.

 

Formation of hydroxyl radicals from water with the help of electric energy.

Recently, a recognition is gaining the use of electrolytic cells with different electrode materials. They enable the formation of HO radicals directly from water with the help of electric power. In the case of wastewater treatment, HOradicals are formed directly from wastewater.

 

Within the LIFE PhamDegrade project, the company ARHEL will test the performance of electrolytic cells with different electrode materials, first in a laboratory scale. A degradation efficiency of individual pharmaceuticals in different working conditions will be evaluated in cooperation with the Faculty of Pharmacy and their Department for Biopharmaceutics and Pharmacokinetics.

THE FORMATION OF ELECTROCHEMICAL OXIDANTS IN ELECTROLYTIC CELL

The electrolytic cells are known mostly for their formation of oxygen and hydrogen from water. An electrolytic cell is composed of two electrodes, electrolyte and voltage generator. The chemical reactions start after both electrodes are immersed into electrolyte and connected to the voltage generator. Different types of chemical reactions can take place, depending on the sort of used electrodes and chemical composition of the electrolyte. In our case, wastewater is the electrolyte.

 

Boron-doped diamond anodes (BDDA) allow to directly produce hydroxyl (HO) radicals from water electrolysis with very high current efficiencies. This has been explained by a very high overvoltage for oxygen production and many other anodic electrode processes on diamond anodes. The other electrochemical oxidants, which are emerging in water, are short lived forms of free radicals, like reactive forms of oxygen (O, HO2) and somewhat more persistent substances like Cl2, ClO-, HClO, O3, H2O2, S2O82-, and others. The development of later depends on the composition of dissolved substances in water.

Hydoxyl radical formation in electrolytic cell Arhel

The formation of hydroxyl radicals in the electrolytic cell using boron doped diamond electrode.

DEGRADATION OF SUBSTANCES WITH THE HELP OF HYDROXYL RADICALS

Hydroxyl radicals are very strong oxidants. This means that they represent a very reactive molecules in aerobic processes of chemical degradation of substances. We can name them reactive electrophiles (they have preferences towards electrons), which rapidly and unselectively react with nearly all organic compounds, rich with electrons.

Complex organic compounds in water, like residuals of drugs, can be degraded in their presence to carbon dioxide and water, or to smaller molecules, which are less toxic and further easier biologically degradable. The procedure is efficient also in the processes of disinfection or elimination of harmful bacteria. Besides HO• radicals, the reactive electrochemical oxidants are also ozone, hydrogen peroxide, chlorine and its compounds, etc.

Carbamazepine degradation Arhel

Timeline demonstration of the reduction of carbamazepine concentration in water with the use of electrolytic cell equipped with BDDA.

ELECTROLYTIC CELLS WITH ADVANCED ELECTRODE MATERIALS

There are several different electrodes in use, like graphite, platinum, mixed metal oxide, etc., for the purpose of degradation of persistent organic molecules, discoloration or water disinfection. Boron doped diamond anode (BDDA) enters recently in the forefront as the anode material with the highest potential of forming hydroxyl radicals. Diamond is non-conductive material. After doping with boron, it becomes conductive and applicable in electrolysis.

The advantage of boron doped diamond electrodes, in comparison to others, is their exceptional chemical inertness and durability. Chemical inertness signifies that there are no metal ions releasing into water during the operation, which would represent additional water load. At the same time they are long lasting. In comparison with other electrode materials, BDDA has the highest capacity of formation of hydroxyl radicals, which are though short-lived and do not represent any hazard at the outflow of purified water.

ADVANTAGES OF THE APPLICATION OF ELECTROCHEMICAL PROCESSES

  • In the process of electrolysis, reactive oxidizing substances, necessary for the degradation of pollutants, are generated directly in the water and there is no need to add them in the form of chemicals.
  • The pollutants are completely removed from water with oxidation, by the help of reactive oxidizing substances and are therefore not just transferred into another media.
  • Short reaction times. The kinetics of electrochemical processes is up to 100 times faster compared kinetics of biological processes. In the short time and small volume, also very persistent pollutants can be degraded.
  • Since there is no need for the use of chemicals, there is no additional hazards, which are present at the transport and storage of chemicals as chlorine and ozone.
  • The degree of treatment and thereby the use of energy can be adapted to the actual needs of the treatment, like the reduction of toxicity, with partial degradation of molecules.
  • The operation of the system can be adapted to the actual needs for water, e.g. disinfection of water with regard to the used quantity.
  • Boron doped diamond electrodes are inert and do not release additional pollutants into the water.

WHERE CAN WE USE ELECTROCHEMICAL PROCESSES FOR TREATMENT OF WATER?

  • In the tertiary treatment of wastewater for the removal of persistent micro pollutants as residuals of pharmaceutical drugs and phytopharmaceuticals and other recalcitrant organic molecules.
  • In the treatment of wastewater from individual technological lines to reach better degradation of wastewater before its inflow into biological treatment plant (residuals of active pharmaceutical substances, pigments and other persistent organic compounds).
  • In the water conditioning for the use in industrial processes (food industry, pharmacy).
  • In the disinfection of treated water for its reuse for irrigation of plants.
  • In disinfection of pool water.
  • In disinfection of drinking water.