Advanced microbiological tools for tracking complex wastewater treatment efficiency through the combination of physicochemical and biological technologies

Landfill leachate is a strongly polluted complex wastewater generated due to rain percolation, which treatment is not completely solved, yet. Its non-biodegradable character makes it necessary to design a specific treatment train by combining conventional and advanced processes for reducing operating costs, allowing its reuse and potentially recovering nutrients. This work presents a strategy based on a coagulation/flocculation pre-treatment step, an advanced oxidation process combined with an advanced bioreactor for landfill leachate remediation at pilot scale. In the physicochemical step, 30% of DOC and 45% of turbidity removal were obtained with 0.5 g/L of FeCl3 at pH 5. The comparison between ozonation and solar photo-Fenton processes as second step showed the highest biodegradability improvement in the last one. Subsequently, a continuous flow rate in the bioreactor was established in 9.6 mL/min (around 60% of DOC elimination). 150 g of sodium bicarbonate was added to the feeding stream to favor the autotrophic bacteria action. The maximum treatment capacity attained was 0.71 mg of COD/L.h and 1.40 mg N-NH4+/L.h with a hydraulic residence time of 2.7 days. The main innovation of this work lays in the application of advanced microbiological techniques such as Quantitative Polymerase Chain Reaction (qPCR) and massive sequencing allowing the characterization and identification of the new microbial population capable of facing the treatment of landfill leachate. The phylum Proteobacteria, responsible for nitrogen fixation, was the most abundant found in the bioreactor at the end of its continuous operation (45.8% of abundance). This information is especially valuable for the design of advanced specific biological systems.