Upgrading the Organic Fraction of Municipal Solid Waste by Low Temperature Hydrothermal Processes

Gregor Sailer,Siham Ouardi,Stefan Pelz,Monika Bosilj,Sebastian Paczkowski,Hans Oechsner,Joachim Müller,Victoria Knappe,Jens Poetsch

doi:10.3390/en14113041

Abstract

In comparison to lignocellulosic biomass, which is suitable for thermo-chemical valorization, the organic fraction of municipal solid waste (OFMSW) is mainly treated via composting or anaerobic digestion (AD). An efficient utilization of OFMSW is difficult due to variations in its composition. Based on the characteristics of OFMSW, hydrothermal treatment (HTT) experiments at temperatures < 200 °C as an alternative OFMSW-processing were evaluated in this study. The raw OFMSW was characterized with a dry matter (DM)-based organic dry matter (oDM) content of 77.88 ± 1.37 %DM and a higher heating value (HHV) of 15,417 ± 1258 J/gDM. Through HTT at 150, 170 and 185 °C, the oDM contents as well as H/C and O/C ratios were lowered while the HHV increased up to 16,716 ± 257 J/gDM. HTT led to improved fuel properties concerning ash melting, corrosion stress and emission behavior. Negative consequences of the HTT process were higher contents of ash in the biochar as well as accumulated heavy metals. In the sense of a bioeconomy, it could be beneficial to first convert raw OFMSW into CH4 through AD followed by HTT of the AD-digestate for the generation of solid fuels and liquid products. This could increase the overall utilization efficiency of OFMSW.

Highlights

In Germany, the Recycling Law [1] is the key element for the waste management industry and it implements EU-Directives into national law
The average treatment temperatures of Hydrothermal carbonization (HTC) processes are usually between 180 to 300 ◦ C, leading to several different chemical and physical reactions that influence the characteristics of the substrate
Low carbonization rates were achieved through hydrothermal treatment (HTT)

Summary

Introduction

In Germany, the Recycling Law [1] is the key element for the waste management industry and it implements EU-Directives into national law. The main research subject of this study is the separately collected organic fraction of municipal solid waste (OFMSW). Collected OFMSW (biowaste bin) is categorized as a municipal waste mainly originating from households. OFMSW is usually assigned to the category of separately collected bio- and green waste and represents a partial amount of this category [2,3]. The residual waste bin often contains biogenic ingredients that could have been collected via biowaste bin. According to the Ordinance on the List of

Methods

Results

Conclusion