Integrated treatment at laboratory scale of a mature landfill leachate via active filtration and anaerobic digestion: Preliminary results

The management of mature landfill leachate (MLL) represents an increasingly crucial issue to tackle. In this study, the feasibility of an integrated treatment was investigated at the laboratory scale using synthetic leachate with the objective of maximizing the recovery of potentially useful compounds present in leachate (especially ammonia nitrogen). First, in order to remove heavy metals, active filtration of the MLL was carried out using zero-valent iron (ZVI) mixed with either lapillus or granular activated carbon (GAC). The average removal rates for the ZVI/lapillus and the ZVI/GAC filter were 33%, 85%, 66%, and 58% and 56%, 91%, 67%, and 75% for COD, Cu, Ni, and Zn, respectively. Then, pre-treated MLL was added during the anaerobic digestion (AD) of cellulose with the aim of providing bacteria with macro (i.e., ammonia nitrogen) and micro (e.g., residual heavy metals) nutrients. After 38 days, the best performance in terms of cumulative methane production (5.3 NL) and methane yield (0.26 NL/gVSadded on average) was recorded in the reactor fed with the lowest dosage (17.9 mL/d) of MLL pre-treated by the ZVI/lapillus filter. The main issue that emerged during AD was the possible inhibition of the process linked to an excessive presence of humic substances; however, in future experiments, this problem can be solved through an optimization of the management of the whole process. The residual digestate from AD, rich in nitrogen and humic substances, may be safely used for agriculture purposes, closing the cycle of MLL management.