Sources and levels of potentially toxic elements in the biodegradable fraction of autoclaved non-segregated household waste and its compost/digestate

Abstract

Waste that reflected the average UK composition of household waste was treated by autoclaving at the three set pressure/temperature levels of 2.7 bar/130 degrees C, 6.2 bar/160 degrees C and 15.5 bar/200 degrees C. The biodegradable fraction of the autoclaved household waste (;floc') was manually separated by screening and underwent characterization for its Cd, Cr, Cu, Pb, Hg, Ni, and Zn content. Autoclaving did not guarantee the production of compost/digestate that met the UK specification for compost, BSi PAS100, without restrictions being made on the composition of the waste feedstock. Results indicate that the levels of Zn and Cd associated with floc materials alone could lead to compost limit values being exceeded. For all other potentially toxic elements (PTEs), the estimated excessive (i.e. above levels of compliance) PTEs levels for compost/digestate were mainly due to external (i.e. non-floc) materials, primarily electronic/electrical waste. Batteries may have also contributed to the high levels of Zn and Hg. In this study, for all PTEs examined, with the exception of Cd and Zn, autoclaving had a performance comparable to that of the most effective mechanical biological treatment systems.

Hydrothermal Carbonization of Autoclaved Municipal Solid Waste Pulp and Anaerobically Treated Pulp Digestate

“…have not yet been demonstrated as commercially viable including secondary fiber [8][9][10] , ethanol 11-4 12 , anaerobic digestion (AD) [13][14][15][16] , compost [17][18] , and others. Anaerobic digestion has been demonstrated effective for reducing the biodegradable fraction of MSW to biogas yet produces a significant digestate fraction that requires further re-use or disposal.…”

Evaluating an anaerobic digestion (AD) feedstock derived from a novel non-source segregated municipal solid waste (MSW) product

“…As the novel fibrous material was produced from non-source segregated MSW, it is anticipated that bulk and chemical contaminants present within the MSW may become incorporated within the material during the process of roto-autoclaving, and remain after subsequent mechanical separation procedures (Papadimitriou et al, 2008). There are numerous potential sources of heavy metals within MSW, e.g.…”

“…glass, plastic, ferrous metals, non-ferrous metals, textiles), and result in the production of a single unified organic material product (Garcia et al, 2012). To date studies of this treatment method have often been carried out using synthesised waste materials, at relatively small lab, or pilot, scale (Houltman et al, 2016;Papadimitriou et al, 2008;Papadimitriou, 2010).…”

Mesophilic and Thermophilic Anaerobic Digestion of Organic Fraction Separated during Mechanical Heat Treatment of Municipal Waste

“…Depending on the technological process and the composition of the waste, this fraction constitutes up to 61.5% of the initial weight of waste [3]. This fraction consists mainly of thermally processed organic waste, such as paper, kitchen and garden waste and other organics, which are turned into a very homogenous fibrous material under the influence of temperature [4]. According to Papadimitriou [1], a properly conducted MHT process enables approximately 80% of the initial waste stream to be recycled/recovered.…”

“…Due to the fact that MHT is a technology in the developmental phase, there is a need to expand knowledge in this field. The uniqueness of the organic remaining fraction obtained during MHT of municipal waste, including its homogeneity and fibrous structure, makes it impossible to determine the impact Although autoclaving dissolves paints on cans and other packages and thus could contribute to heavy metal pollution of organic fiber [4,5], contamination resulting from autoclaving is similar to that from the most effective mechanical-biological treatment systems [4]. The process of autoclaving disrupts the lignocellulosic structure in organic waste [6], which theoretically facilitates the decomposition of organic matter, both in aerobic and anaerobic conditions.…”