Abstract
This work assessed and compared the leaching properties of two types of compost and stabilized waste from a mechanical-biological treatment (MBT) plant. The first type of compost and the MBT waste were produced by aerobic treatments, while the second type of compost was generated from a combination of anaerobic and aerobic biodegradation processes. Both static-batch leaching tests, carried out applying a single liquid to solid (L/S) ratio equal to 10 L kg-1, and dynamic column percolation tests, investigating constituents release as a function of different L/S ratios, were performed. The three materials were also characterized in order to investigate their biological stability degree, organic matter content, and metals total content. As expected, due to the differences in feed input waste or treatment conditions, the three types of samples showed different characteristics and leaching concentrations. However, the leaching behavior of the three types of treated materials presented similar trends of dissolved organic carbon (DOC) and metals (Cu, Ni, Pb, Zn) leaching as a function of the L/S ratio. A screening model proposed and developed for MBT waste in a previous study, which allows the description DOC release as a function of the L/S ratio, was applied and discussed. The comparison of model predictions with the experimental leaching data highlighted that for all three samples the screening model describes quite well the release trends of metals.
Highlights
In the last decades, since the issuing of the European Landfill Directive 1999/31/EC, Member States took action in order to divert biodegradable municipal waste from landfills
A 0.001 M CaCl2 solution was added to air-dried samples grinded to a size lower than 4 mm at a liquid to solid ratio equal to 10 ml/g and bottles containing the mixture were slowly shaken for 24 hours
Sample characteristics and leaching properties The three considered organic waste samples showed different biological reactivity degrees in the following increasing order: Compost A < mechanical–biological treatment (MBT) waste < Compost B, with dynamic respiration index (DRI) values equal to 620, 1456 and 2857 mgO2 kgVS-1 h-1, respectively. This variability was related to the different nature of the input to the biological processes, to the heterogeneity of the feedstock, which in turn is influenced by the location and seasonal period of sampling, as well as to the type of treatment, i.e. the duration of the process and the type of treatment applied
Summary
Since the issuing of the European Landfill Directive 1999/31/EC, Member States took action in order to divert biodegradable municipal waste from landfills. 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). The leaching of soluble constituents from waste materials upon contact with water, regarded as the main mechanism of release, may result in a potential risk to the Investigating the leaching properties of MBT wastes
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