A novel integrated treatment for mature landfill leachate via active filtration and anaerobic digestion

The final disposal of end-of-life products in landfills has caused waste accumulation over the years with consequent soil, water and air pollution. Particularly, landfill leachate poses a serious threat to fresh and ground water, air and soil quality. Leachate is the result of the water percolating through landfilled waste which concentrates biological and chemical constituents of waste. Leachate must be collected during landfill operations (and even after landfill closure) and treated before its discharge in the environment. Dissolved organic matter, toxic and persistent organic compounds, ammonium, heavy metals and metalloids, chlorine compounds, dioxins and emerging contaminants are the main pollutants present in leachate. Moreover, leachate coming from mature landfills (i.e., > 10 years old) has slightly alkaline pH and is rich in hardly biodegradable or non-biodegradable organic matter (e.g., humic substances). These peculiarities make mature landfill leachate (MLL) treatment challenging. This thesis investigated an innovative MLL treatment at a laboratory-scale on the basis of Circular Economy principles. A synthetic MLL was pre-treated using active granular filters (Zero Valent Iron, ZVI, mixed with Lapillus and Granular Activated Carbon, GAC, respectively) with the aim of reducing heavy metals and other contaminants refractory to biological treatment. Both filters showed positive results in terms of metals removal. Afterwards, the pre-treated aqueous matrix was used as a nutrient solution useful for the metabolism of bacteria involved in the anaerobic digestion of a biodegradable organic substrate. As a result of the process, produced methane can be used for energy generation and residual digestate can replace fertilisers due to the presence of nitrogen and HSs deriving from the pre-treated MLL. Whilst the digestion of pure cellulose (model organic substrate) was adversely affected by pre-treated MLL addition, conversely, the use of a more realistic substrate (i.e., market waste) seemed to trigger the beneficial effects of pre-treated MLL on the process which resulted stable and efficient. Accordingly, it can be stated that the feasibility of this MLL treatment has been proved at a laboratory-scale. Further research consisting of larger scales experiments and life cycle analyses needs to be carried out in order to optimise operational parameters of both processes prior to a possible full-scale application.