Pyrolysis of Solid Digestate from Sewage Sludge and Lignocellulosic Biomass: Kinetic and Thermodynamic Analysis, Characterization of Biochar

Aleksandra Petrovič,Lidija Čuček,Robert Bedoić,Irena Ban,Tjaša Cenčič Predikaka,Marjana Simonič,Sabina Vohl

doi:10.3390/su13179642

Aleksandra Petrovič, Lidija Čuček + Show 5 more

Open Access

https://doi.org/10.3390/su13179642

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Journal: Sustainability	Publication Date: Aug 27, 2021
Citations: 23	License type: CC BY 4.0

Affiliation: University of Maribor, University of Zagreb

Abstract

This study investigates the pyrolysis behavior and reaction kinetics of two different types of solid digestates from: (i) sewage sludge and (ii) a mixture of sewage sludge and lignocellulosic biomass—Typha latifolia plant. Thermogravimetric data in the temperature range 25–800 °C were analyzed using Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose kinetic methods, and the thermodynamic parameters (ΔH, ΔG, and ΔS) were also determined. Biochars were characterized using different chemical methods (FTIR, SEM–EDS, XRD, heavy metal, and nutrient analysis) and tested as soil enhancers using a germination test. Finally, their potential for biosorption of NH4+, PO43−, Cu2+, and Cd2+ ions was studied. Kinetic and thermodynamic parameters revealed a complex degradation mechanism of digestates, as they showed higher activation energies than undigested materials. Values for sewage sludge digestate were between 57 and 351 kJ/mol, and for digestate composed of sewage sludge and T. latifolia between 62 and 401 kJ/mol. Characterizations of biochars revealed high nutrient content and promising potential for further use. The advantage of biochar obtained from a digestate mixture of sewage sludge and lignocellulosic biomass is the lower content of heavy metals. Biosorption tests showed low biosorption capacity of digestate-derived biochars and their modifications for NH4+ and PO43− ions, but high biosorption capacity for Cu2+ and Cd2+ ions. Modification with KOH was more efficient than modification with HCl. The digestate-derived biochars exhibited excellent performance in germination tests, especially at concentrations between 6 and 10 wt.%.

Highlights

IntroductionThe continuous growth of the human population is correlated with an increase in primary energy consumption, where the main sources of energy are (still) of fossil origin, and are responsible for the majority of greenhouse gas (GHG) emissions into the atmosphere [1]
The continuous growth of the human population is correlated with an increase in primary energy consumption, where the main sources of energy are of fossil origin, and are responsible for the majority of greenhouse gas (GHG) emissions into the atmosphere [1].Renewable energy sources, such as solar [2], wind, geothermal, hydropower energy, and energy recovered from biomass and different wastes [3], are promising alternatives to fossil fuels, offering solutions to the above challenges
A much lower P uptake was reported in another study, less than 1 mg/g was adsorbed at an concentration

Summary

Introduction

The continuous growth of the human population is correlated with an increase in primary energy consumption, where the main sources of energy are (still) of fossil origin, and are responsible for the majority of greenhouse gas (GHG) emissions into the atmosphere [1]. Renewable energy sources, such as solar [2], wind, geothermal, hydropower energy, and energy recovered from biomass and different wastes [3], are promising alternatives to fossil fuels, offering solutions to the above challenges. Promoting the production of renewable resources and converting them into valuable products and bioenergy to satisfy sustainable development is the goal of the European Bioeconomy Strategy, which was accepted by the European Commission [9]

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