Physicochemical and biological characterization of waste and leachate from landfill simulation reactors

This thesis reports a laboratory scale bioreactor experiment which sought to determine whether excavated waste from old landfills could contribute to the accelerated degradation of new residual waste fractions. The solid waste as well as the ensuing leachate were analysed and characterised according to their physicochemical and microbial parameters, in order to define if the old waste could provide inoculum to promote the biodegradation of the new waste. Four bioreactors (R1, R2, R3, R4) simulating anaerobic landfill conditions were set up in the LISA lab (Laboratorio di Ingegneria Sanitaria e Ambientale). Each bioreactor was filled with a different waste fraction: R1 - old waste excavated from an old sector of the Villadose landfill, R2 - new waste light fraction, R3 - new waste stabilised fraction from the Sarzano mechanical biological treatment plant and R4 - a mixture of all individual waste fractions. Samples were collected and analysed at the start of the experiment t0 days, in the middle t50 days and at the end t100 days. R4 which contained waste particular to this research and representing the real waste composition in the newly constructed sectors of the Villadose landfill underwent rapid degradation and stabilisation with the first 100 days of operation. Comparatively, R2 which only contained new residual waste maintained more elevated BOD5, COD and TKN values. The accelerated degradation in R4 suggested that the added presence of old waste fractions provided microbial communities which enhanced stabilisation processes. The results from illumina sequencing revealed the abundant presence of facultative aerobic hydrolytic acidifier bacteria such as Rummeliibacillus, which dominated the R4 landfill leachate at t50 days (92.40 ± 0.79 %). The surge up of this microbial species could have been caused by metabolic cooperation with microbial communities in old waste. Further research is needed to establish the precise inoculum present in old waste, responsible for the accelerated stabilization of new waste.