Comparative characterization of biochars produced at three selected pyrolysis temperatures from common woody and herbaceous waste streams.

Matthew Askeland,Jorge Paz-Ferreiro,Bradley Clarke

doi:10.7717/peerj.6784

Abstract

Biochar, the product of biomass pyrolysis, has been explored as a soil amendment and carbon capture vessel. Recent literature has aligned biochar as a novel sorbent for a host of environmental contaminants. Through the variation of pyrolysis conditions, biochars can be engineered to have qualities desirable in sorbents whilst maintaining their agronomic benefits. This study focuses on identifying the effects that feedstock type and process temperature have on biochar characteristics which may in turn shed light on their potential environmental applications. Using this approach, six biochars were created from two waste biomasses. The biochars exhibited wide ranges of pH (5.6–11.1), surface area (16.2–397.4 m2/g), electrical conductivity (19–2,826 µS/cm), fixed carbon (72–97%), heavy metal and polycyclic aromatic hydrocarbons (PAHs). Statistically significant trends (P < 0.05) in biochar characteristics dependent upon increasing pyrolysis temperature and feedstock type were identified. Arsenic (>13 mg/kg), chromium (>93 mg/kg), copper (>143 mg/kg) and PAH (>6 mg/kg) concentrations presented themselves as obstacles to land application in a small number of biochars with respects to International Biochar Initiative (IBI) guidelines. However, it was demonstrated that these could be eliminated through employing pyrolysis processes which encompass higher temperatures (>500 °C) and ensuring the use of contaminant-free feedstocks. The variation in surface areas, carbonized fractions and surface functional groups achieved suggest that using the correct feedstock and process, biochar could be produced in Victoria (Australia) from common organic waste streams to the ends of acting as a sorbent, soil enhancer, and a waste management strategy.

Highlights

Biochar is the carbonaceous solid resulting from the thermochemical conversion of biomass in an oxygen-limited environment (International Biochar Initiative, 2013)
Six biochars of varying physiochemical properties were successfully engineered through slow pyrolysis at three selected temperatures, using waste feedstocks common in Victoria, Australia
It was found that both temperature and feedstock type were influential on the types of biochars created from selected biomasses and could in turn determine their suitability for environmental application

Summary

Introduction

Biochar is the carbonaceous solid resulting from the thermochemical conversion of biomass in an oxygen-limited environment (International Biochar Initiative, 2013). Waste biomass is the largest and most sustainable biomass source, with 220 billion dry tons being produced globally each year (Azargohar et al, 2013). Application of biochar to soil has been demonstrated to improve soil fertility by increasing cation exchange capacity (CEC), How to cite this article Askeland M, Clarke B, Paz-Ferreiro J. Comparative characterization of biochars produced at three selected pyrolysis temperatures from common woody and herbaceous waste streams. Incorporation of biochar into biocomposites has expanded biochars applications further into the material sciences (Das & Sarmah, 2015; Das, Sarmah & Bhattacharyya, 2016). Biochar can be used as a novel material for remediation, where contaminant sorption to biochar surfaces reduces bioavailability and mobility (Paz-Ferreiro et al, 2014; Srinivasan & Sarmah, 2015). Biochar characterisation studies with respects to the effect of feedstock and temperature are imperative for adequate decision making in proceeding towards engineering the biochars of the future (Gascó et al, 2018; Lu et al, 2018)

Methods

Results

Conclusion