Activated sludge microbial communities and hydrolytic potential in a full-scale SBR system treating landfill leachate.

Landfill leachate, due to its recalcitrant nature and toxicity, poses a serious environmental threat, which requires the implementation of effective treatment processes. In this work, a full-scale treatment system consisting of two Sequencing Batch Reactors (SBRs) was used for the processing of landfill leachate of intermediate to mature age (BOD/COD ratio of 0.16). Biosystem operation resulted in BOD 5 , COD and TKN removal efficiencies of 81%, 39% and 76%, respectively, whereas the low residual NO 3 - -N concentration in the effluent (4.01 ± 0.10 mg/L) was indicative of the efficient denitrification process. Assessment of hydrolytic potential of activated sludge revealed high endocellular and extracellular lipase activities, which reached values up to 206 and 141 U/g protein respectively, possibly as the consequence of plastics degradation during maturation process. Implementation of Illumina sequencing indicated the predominance of Alphaproteobacteria , accompanied by members of Bacteroidetes , Betaproteobacteria and Chloroflexi . Paracoccus was the predominant genus identified, followed by representatives of the genera Bellilinea , Flavobacterium , Thauera and Truepera . Nitrosomonas was the major ammonia-oxidizing bacterium (AOB), while nitrite oxidation was mainly achieved by the uncultured nitrite-oxidizing bacterium (NOB) Candidatus Nitrotoga.