Clean Leachate - cleaning the landfill leachate waters

Project CleanLeachte is a project of applied research aimed at cleaning the landfill leachate waters, which we were dealing with in the years 2010 - 2012 under the Seventh Research Framework Programme for SME. Within the project cooperate four SME participants and two research institutions.

We was take part in the development of the structural housing for the electrolytic cell and the sensors and actuators that are required to make CleanLeachate system fully automated. German company EUT was take part in the research and development of the electrolytic cell. Dutch company Magneto was tasked with the development and production of propriate electrodes for electrolytic cell. And england company Ential was tasked with formulating the exploitation strategy of CleanLeachate product.

RTD performers were German Fraunhofer, which was placed to carry out the required research and testing with landfill leachate samples, and development of the electrolytic cell also. And Spanish Cric, which was undertaking the development of the automated systems, including integrating sensors and actuators, within the CleanLeachate apparatus.

The leachates from landfills show very diverse in composition depending on the type of waste, age and seasonal climate. But the common features of raw leachate from landfill are its high concentrations of ammoniacal nitrogen (even 20 000 mg/L). Of the toxic pollutants that are present in landfill leachate, NH3-N, which is stable under anaerobic conditions and therefore typically accumulates in leachate, has been identified not only as a major long-term pollutant but also as the primary cause of acute toxicity. When present at a concentration higher than 100 mg/L, untreated NH3-N is highly toxic to aquatic organisms.

Conventional landfill leachate treatments can be classified into two major groups:
(a) biodegradation - aerobic processes (lagooning, activated sludge processes, sequencing batch reactors) and anaerobic processes
(b) chemical and physical methods - chemical oxidation, adsorption, chemical precipitation and air stripping. Two of the most recent developments are the membrane bioreactors and the reverse osmosis.
These are compared in the table below in terms of their effectiveness.

Electrochemical methods are one of the most promising advanced techniques that can be used for purification of landfill leachates. The rate of supply the reactant is known as an electric power. And the oxidizing/reducing force as an electric potential (voltage). Advantage of these methods lies in the separation of electrode reactions which allows to make otherwise the difficult or unfeasible reactions. Another advantages lies in their versatility, selectivity and minimize of penetration the chemicals into the environment.   The CleanLeachate project represents a new approach to the AOP (Advanced Oxidation Processes) methods as it is one in which oxidising OH radicals are produced electrochemically in an anodic reaction directly from water within the landfill leachate that is to be treated according to the equation H2O → OH• + e- + H+ The electrochemical production of hydroxyl radicals eliminates the need for the addition of chemical substances, which in turn ensures that the overall running costs of the process are kept as low as possible. The reduction of COD values of wastewaters, using electrochemical methods to cause direct cold electrochemical oxidation, also called mineralisation, of organic substances has long been striven for. According to this process, electrode materials with a very high oxygen overvoltage are necessary. Electrodes made of boron doped diamond (BDD) show the largest overvoltage for oxygen production from water and also exhibit high chemical and mechanical stability.

The electrodes are mounted in our electrolytic cell either side of a membrane, as shown in the diagram, and the leachate waste stream will be introduced so that it first contacts the anode and then the cathode. The reduction of remaining organic pollutants can be achieved at the cathode, but may also be used to reduce other hazardous compounds that may be evolved during the reaction at the anode.

Previous research carried out on electrolysis of some waste waters from the motor industry showed that the COD reduction was simultaneous with the evolution and increase of the concentration of chloride ions and AOX (chlorinated organic compounds). Whilst COD removal was achieved at a high current efficiency, the presence of chloride ions in the electrolyzed solution meant that AOX was formed during the initial stages of COD removal, as shown in the graph beside. The chlorinated organic compounds are, however, also eventually destroyed by OH• radicals, thus finally reducing the AOX value.

As diamond electrodes also possess a high overvoltage for cathodic hydrogen production, thus enabling cathodic reactions which are impossible by use of other electrode materials, we are going to use the cathode reaction to remove any AOX that may be formed during the oxidation process in leachate that contains elevated levels of chloride ions. This will further enhance the energy savings of our method, over other previously explored electrolysis options, through the decreased time taken for AOX destruction, and thus decreased time the leachate must be processed for prior to discharge. With reference to the graph displayed above, at the time point when the COD value has decreased to zero, reactions at the cathode in our proposed cell should mean that the AOX levels have also reached zero. In the displayed results this would be a 29% reduction in reaction time. 

Clean Leachate project aims to bring to the market an automated, modular, mobile landfill leachate treatment unit that is more efficient and less costly than other methods currently used due to the novel electrolytic cell that reduces required reaction times. This technology has the potential to be applied in other sectors such as treatment of waste from the food processing industry (dairy washings, meat offal and vegetable waste waters), liquid waste from the brewing industry, petrochemical wastes and treatment of pulp, paper mill sludges, pharmaceutical sector and other.

The benefits for ASIO company consist in extending the range of products and technologies in the field of wastewater treatment, and also in the production and distribution of these equipment and spare parts.

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