Mitigating long-term emissions of landfill aftercare: Preliminary results from experiments combining microbial electrochemical technologies and in situ aeration.

Landfills still represent the main option for waste disposal in many parts of the world. Anyway, they often pose a significant pollution risk and contribute to potential environmental and human health impacts via gaseous and liquid (leachate) emission pathways if not properly managed. Some innovative technologies can help to reduce these emissions, such as in situ aeration and the application of microbial electrochemical technologies (METs). METs are an emerging field that open the possibility to control microbial reactions, enhancing electron flows from electron donors towards electron acceptors. To this end, several materials with different electrochemically-active properties are used, such as electrical conductivity, capacitance, surface electroactivity and charge. The present project named LA-LA-LAND (Landfill electron-Lapping for a LANDscape requalification) was aimed to apply METs to treat leachate-saturated zones in old landfills. A MET prototype was constructed using a granular anode (graphite) and a cylindrical air-cathode (electroactive biochar). The METs were integrated to three identical laboratory-scale landfill bioreactors coupled with the in situ aeration technique, while three control reactors run without MET. The maximum values of current and power density obtained were 0.015 A·m-2 and 0.00035 W·m-2. The influence of the MET system on the organic matter removal was evident in two reactors, where this technology was applied, with respect to the control ones: total organic carbon decreased on average 13%, while it reduced less than 5% in the control reactors. This preliminary experiment pointed out some critical aspects of MET configuration, such as the weakness of the cathode architecture, which was prone to be flooded by leachate, blocking the aeration flux.

Denitrification of low C/N landfill leachate in lab-scale landfill simulation bioreactors.

Old landfill leachate can be characterized by high ammonia nitrogen concentrations and limited biodegradable carbon availability. A promising and cost-effective option for ammonia nitrogen removal involves ex situ nitrification and in situ denitrification. This study aimed to investigate the denitrification capacity of old MSW in six landfill bioreactors with very low COD/NO3--N mass ratios that ranged between 0.12 and 3.99 g/g. In particular, this study is novel in that it tested COD/NO3--N mass ratios lower than previous studies. The experiment lasted 83 days. The results showed that denitrification occurred in all bioreactors and even at considerably low concentrations of biodegradable organic matter (BOD5 ≤ 9 mg O2/L). In all but one case, when nitrate removal stopped at 55% due to the absence of leachate recirculation, nitrate removal was higher than 95%. The average nitrate removal rates (ANRRs), calculated under significantly different conditions, ranged from 33 to 135 mg NO3--N/L/d. The initial COD concentration and COD/NO3--N ratio did not appear to affect the ANRRs, which were influenced by the initial nitrate concentration and leachate recirculation. The maximum ANRR (135 mg NO3--N/L/d) was measured with the highest initial nitrate concentration (4491 mg NO3--N/L) and the lowest COD/NO3--N mass ratio (0.12 g COD/g NO3--N). The lowest ANRR (33 mg NO3--N/L/d) was calculated for a bioreactor with no leachate recirculation. Sulphate production observed in some bioreactors may suggest that, together with the heterotrophic pathway, autotrophic denitrification contributed to the removal of nitrate, especially in bioreactors with low COD/NO3--N mass ratio.

3D geophysical imaging for site-specific characterization plan of an old landfill.

As it is well-known, the characterization plan of an old landfill site is the first stage of the project for the treatment and reclamation of contaminated lands. It is a preliminary in-situ study, with collection of data related to pollution phenomena, and is aimed at defining the physical properties and the geometry of fill materials as well as the possible migration paths of pollutants to the surrounding environmental targets (subsoil and groundwater). To properly evaluate the extent and potential for subsoil contamination, waste volume and possible leachate emissions from the landfill have to be assessed. In such perspective, the integrated use of geophysical methods is an important tool as it allows a detailed 3D representation of the whole system, i.e. waste body and hosting environment (surrounding rocks). This paper presents a very accurate physical and structural characterization of an old landfill and encasing rocks obtained by an integrated analysis of data coming from a multi-methodological geophysical exploration. Moreover, drillings were carried out for waste sampling and characterization of the landfill body, as well as for calibration of the geophysical modeling.

Improving methane production from digested manure biofibers by mechanical and thermal alkaline pretreatment.

Animal manure digestion is associated with limited methane production, due to the high content in fibers, which are hardly degradable lignocellulosic compounds. In this study, different mechanical and thermal alkaline pretreatment methods were applied to partially degradable fibers, separated from the effluent stream of biogas reactors. Batch and continuous experiments were conducted to evaluate the efficiency of these pretreatments. In batch experiments, the mechanical pretreatment improved the degradability up to 45%. Even higher efficiency was shown by applying thermal alkaline pretreatments, enhancing fibers degradability by more than 4-fold. In continuous experiments, the thermal alkaline pretreatment, using 6% NaOH at 55°C was proven to be the most efficient pretreatment method as the methane production was increased by 26%. The findings demonstrated that the methane production of the biogas plants can be increased by further exploiting the fraction of the digested manure fibers which are discarded in the post-storage tank.

Tests for the evaluation of ammonium attenuation in MSW landfill leachate by adsorption into bentonite in a landfill liner.

Uncontrolled leachate emissions are one of the key factors in the environmental impact of municipal solid waste (MSW) landfills. The concentration of ammonium, given the anaerobic conditions in traditional landfills, can remain significantly high for a very long period of time, as degradation does not take place and volatilisation is not significant (the pH is not high enough to considerably shift the equilibrium towards un-ionised ammonia). Recent years have witnessed a continuous enhancement of landfill technology in order to minimize uncontrolled emissions into the environment; bottom lining systems have been improved and more attention has been devoted to the study of the attenuation of the different chemicals in leachate in case of migration through the mineral barrier. Different natural materials have been considered for use as components of landfill liners in the last years and tested in order to evaluate the performance of the different alternatives. Among those materials, bentonite is often used, coupled with other materials in two different ways: in addition to in situ soil or in geocomposite clay liner (GCL). A lab-scale test was carried out in order to further investigate the influence of bentonite on the attenuation of ammonium in leachate passing through a landfill liner. Two different tests were conducted: a standardized batch test with pulverized bentonite and a batch test with compacted bentonite. The latter was proposed in order to better simulate the real conditions in a landfill liner. The two tests produced values for the partition coefficient K(d) higher than the average measured for other natural materials usually utilized as components of landfill liners. Moreover, the two tests showed similar results, thus providing a further validation of the suitability of the standard batch test with pulverized bentonite. A thorough knowledge of attenuation processes of ammonium in landfill liners is the basis for the application of risk analysis models for the evaluation of the failure of bottom liners or their components.