FISH investigation of the bacterial groups anammox and Azoarcus-Thauera at treatment of landfill leachate

Abstract

The landfill leachate is heavily polluted wastewater produced in the landfills. The management of the purification of the leachate is especially challenging and that is why new approaches and indicators are needed. The quantity, localization, interaction, clustering of the key microbial groups, responsible for the critical transformation processes can be used as indication leading to better performance of the technology. This study is focused on two bacterial groups (Anammox and Azoarcus-Thauera cluster) which have potential to serve as indicators for the landfill leachate treatment. Their quantity and activity were studied by FISH during lab-scale treatment of leachate from the Municipal Enterprise for Waste Treatment (MEWT), Sofia, Bulgaria. Two activated sludges (AS) were used – one from the MEWT and another form the WWTP (wastewater treatment plant) of Sofia. The obtained results showed that 74% of the COD was eliminated when leachate was diluted 50 and 25 times and 31% - when undiluted leachate was used. At the end of the process (21 day) the Azoarcus-Thauera group formed large aggregations in the AS from MEWT. They were 17.50% of the bacteria there while in the AS from the WWTP of Sofia they represented only 2.61%. The quantity of the anammox bacteria remained almost unchanged during the process and was 10.75% of the community from MEWT which eliminated 98 mg/L more ammonium ions at the end of the process and 6% from the community from the WWTP of Sofia. The two studied groups gave more complex information about the processes in the AS related to the elimination of the nitrogen and carbon containing pollutants. They could be used for better management of the biological processes during landfill leachate treatment. Key words: landfill leachate; anammox, Azoarcus-Thauera; activated sludge; fluorescence in-situ hybridization