Assessment of biogas production from MBT waste under different operating conditions

Abstract

In this work, the influence of different operating conditions on the biogas production from mechanically-biologically treated (MBT) wastes is investigated. Specifically, different lab-scale anaerobic tests varying the water content (26-43% w/w up to 75% w/w), the temperature (from 20 to 25°C up to 55°C) and the amount of inoculum have been performed on waste samples collected from a full-scale Italian MBT plant. For each test, the gas generation yield and, where applicable, the first-order gas generation rates were determined. Nearly all tests were characterised by a quite long lag-phase. This result was mainly ascribed to the inhibition effects resulting from the high concentrations of volatile fatty acids (VFAs) and ammonia detected in the different stages of the experiments. Furthermore, water content was found as one of the key factor limiting the anaerobic biological process. Indeed, the experimental results showed that when the moisture was lower than 32% w/w, the methanogenic microbial activity was completely inhibited. For the higher water content tested (75% w/w), high values of accumulated gas volume (up to 150Nl/kgTS) and a relatively short time period to deplete the MBT waste gas generation capacity were observed. At these test conditions, the effect of temperature became evident, leading to gas generation rates of 0.007d(-1) at room temperature that increased to 0.03-0.05d(-1) at 37°C and to 0.04-0.11d(-1) at 55°C. Overall, the obtained results highlighted that the operative conditions can drastically affect the gas production from MBT wastes. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of disposed waste, the presence and type of temporary and final cover systems.

Investigating the leaching properties of MBT wastes and composts from aerobic/anaerobic processes

“…The MBT waste, analyzed in the work of Pantini et al (2015a), after completion of the stabilization process, was sampled in one of the four MBT plants located in Rome, having a maximum treatment capacity of 750 Mg MSW d -1 . Focusing on the biological process, after metal removal by belt-type electromagnetic separators, the biodegradable fraction (i.e.…”

“…The results obtained from column and batch tests were interpolated through the model developed by Pantini et al (2015a) in order to find the key mechanisms governing elements release and to compare the leaching behaviour of the three investigated samples.…”

“…Many studies investigated the recovery of MBT waste for land reclamation purposes obtaining positive performances, such as in landfills as cover layer material (Angermeier et al, 2011) or applied to degraded and/or contaminated soils for organic matter supply and for metals recovery, respectively (Farrell and Jones, 2010). In this light, assessing the environmental performance of different types treated biowastes is essential for increasing the material recovery by keeping the soil quality and preventing the risk to human health (Smith, 2009, Pantini et al 2015a and, based on the previous targets, defining end-of-waste criteria (EU, 2008). To date, the latter have not been issued at a European level, whereas some Member States (e.g.…”

“…The experimental leaching data were then elaborated through a screening model proposed and developed in a previous study (Pantini et al, 2015b), which assesses organic carbon and metals release as a function of the L/S ratio. The experimental and modeled results obtained for the two composts were then compared with those found for an MBT waste (Pantini et al, 2015a), in order to point out analogies and differences in the release of constituents from the different types of organic wastes.…”

Evaluation of the effects of bio stabilised waste on soil in terms of heavy metal accumulation and leaching

“…plastic pieces) and heavy metals compared to compost (Di Lonardo et al, 2012). However, the interest in the possibility of recovering MBT waste is increasing (MacLeod et al, 2008), especially considering the large amounts that are being produced in efforts to divert waste from landfills (Farrell and Jones, 2010;Pantini et al, 2015a;2015b). One of the possible ways to recover MBT waste is as landfill cover material for promoting vegetation growth (Angermeier et al, 2010); application to degraded and/or contaminated soils of these organic rich fractions has been also proposed (Farrell and Jones, 2010).…”