CleanLeachate - Electrochemical treatment of landfill leachate

Treatment of landfill leachate

The disposal of waste in a landfill is the most commonly used type of waste disposal worldwide. A major disadvantage of landfill operation is the generation of highly contaminated leachate, which is mainly formed by precipitation. Water contained in the waste and released by biological degradation processes also contribute to the formation of landfill leachate. As a rule, pollutants are discharged with the leachate.

The leachate therefore usually has toxic properties and contains substances that are difficult to biodegrade. Treatment plants with biological processes can only provide limited treatment. In particular, persistent organic substances (measured as chemical oxygen demand, COD), ammonium and halogenated organic substances (measured as adsorbable organically bound halogens, AOX) are present in critical concentrations in landfill leachate and must be removed before discharge into a water body or a municipal biological treatment plant.

The treatment of landfill leachate represents a significant cost factor for the landfill operator. Even after the closure of a landfill site, contaminated leachate continues to be produced for decades and must be treated. Membrane and adsorption processes (e.g. with activated carbon) are often used. In these processes, however, the contaminants are not decomposed, but only concentrated. The concentrate must then be disposed of or treated.

Globally, the amount of waste going to landfill is increasing while legislation is becoming stricter. This leads to a growing demand for cost and energy efficient and reliable processes for the treatment of landfill leachate.

Combination of electrochemical oxidation and reduction

Together with European partners from industry and research, Fraunhofer IGB has developed an electrochemical process within the EU-funded CleanLeachate project that enables reliable treatment of landfill leachate without having to add auxiliary substances to the wastewater. Through electrochemical oxidation at the reactor anode and subsequent reduction at the reactor cathode, ammonium as well as organic water constituents and organically bound halogens can be eliminated from the landfill leachate. In contrast to membrane filtration, electrochemical treatment completely removes the water constituents. No residual substances have to be disposed of.

Divided electrolysis cell

For oxidation and reduction, the electrolysis cell is separated by an ion exchange membrane into two chemical reaction chambers which are flowed through one after the other but form an electric circuit. The pollutants in the water are thus subjected to two treatment processes. The basic principles for the development of the process were initially worked out in laboratory tests. Together with the project partner Eilenburger Elektrolyse- und Umwelttechnik GmbH (EUT) the split electrolysis cell was developed. Six different anode materials provided by the project partner MAGNETO were tested in the laboratory with regard to the degradation of organic substances and ammonium by anodic oxidation. To investigate the dehalogenation of the AOX, stainless steel cathodes of different geometries were investigated.

Pilot plant - test operation on landfill

Based on the laboratory findings, a pilot plant with a flow rate of 20 litres per hour was designed, manufactured by the project partner EUT and tested in continuous operation by the project partner ASIO at a landfill in the Czech Republic. It was possible to optimise the process in such a way that the COD concentrations in the landfill leachate were reduced to below 200 mg/L and the total nitrogen concentrations to below 70 mg/L. Thus, the legal requirements of the Wastewater Ordinance regarding the COD and total nitrogen concentration in the treated landfill leachate were met. The energy required to eliminate pollutants was 43 kWh to break down one kilogram of COD and 22 kWh to break down one kilogram of ammonium.

Outlook

An automated and transportable prototype plant is now available for the further development and market launch of the technology. It could be shown that the electrochemical treatment of landfill leachate is possible while complying with the legal limits. The technology is now to be tested and demonstrated with a variety of industrial process and waste waters in order to gain further experience and basic principles for optimisation.

Project title

CleanLeachate – Combined anode and cathode process to treat landfill leachate

Project duration

December 2010 – November 2011

Coordinator

• Fraunhofer IGB
  

Cooperation partners

• Eilenburger Electrolysis and Environmental Technology GmbH, Eilenburg
• MAGNETO special anodes B.V., Schiedam, Netherlands
  
• ASIO spol. s r.o., Brno, Czech Republic
  
• Initial Projects Limited, Wolverhampton, United Kingdom
  
• Centre de Recerca i Innovació de Catalunya, S.A., Barcelona, Spain.