Membrane bioreactors for landfill leachate
Due to its high pollution, land-fill leachate represents a hazard for drinking water and ground water.
The development of a leachate purification process
In consequence all landfill operators are required by law to implement a leachate purification system. An efficient and environmentally sound process has been developed and tested in Austria by EnviCare® Engineering GmbH. In collaboration with the Technical University of Graz, university institutes of Zagreb (Croatia), Aix-la-Chapelle (Germany), and Toulouse (France) two years of research work were dedicated to the development of a leachate purification process.
The membrane bioreactor
First the leachate is drained through pipes running at the landfill bottom to large storage puffer basins. Pumps are feeding the multi-stage purification unit. Organic carbon compounds, ammonium, and a large share of the halogenated hydrocarbons are degraded mainly to gaseous carbon dioxide and nitrogen with the help of bacteria. In order to cope with the great contaminant load, the unit must contain large quantities of bacteria, namely 20 to 30 grams per liter, which is seven times more than in a conventional communal sewage purification plant. To provide microorganisms with a perfect environment, the liquid must be thoroughly mixed and oxygen must be supplied. This is done through an air-injector system.
Ceramic mikrofiltration and spiral wound-reverse osmosis
In order to avoid that valuable biomass is washed out along with the pre-cleaned water, the microorganisms are entirely held back by means of a micro filtration technique and are then recirculated to the activated sludge tanks. In a sequential step, the leachate is subjected to a two stage reverse osmosis unit to obtain pure water quality. This plant cleans the highly polluted waste water up to direct discharge quality permanently and successfully since 1994, whereat the effluent is discharged to a small creek.