Characterization of biochar prepared from biogas digestate. (August 2017)

• Record Type: Journal Article
• Authors: Hung, Chao-Yi; Tsai, Wen-Tien; Chen, Jie-Wei; Lin, Yu-Quan; Chang, Yuan-Ming
• Is Part Of: Waste management. Volume 66(2017)
• Page Start: 53
• Page End: 60
• Publication Date: 2017-08
• Subjects: Solid digestate -- Pyrolysis -- Biochar -- Pore property -- True density -- Biofertilizer; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2017.04.034
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: Solid digestate (SD) is a potential feedstock for preparing biochars. The optimal BET surface area of resulting biochar from SD is over 100 m 2 /g. The higher temperature leads to the increase in true density of resulting biochar, but exhibited a decreased higher heating value. The SD-based biochar may be used as a biofertilizer due to the mesoporosity and the abundant in nutrient minerals. Abstract: In the study, the biogas digestate was evaluated as a potential feedstock for preparing biochars at a broad temperature range of 300–900 °C. The physico-chemical and pore properties of the resulting biochars (denoted as SDBC, solid digestate biochar), including calorific value (higher heating value), surface area/pore volume/pore size distribution, true density, scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray powder diffraction (XRD), were studied. It was found that the higher heating values of the SDBC products were on a decreasing trend as pyrolysis temperature increased, but they indicated an increase in true density. The results are probably associated with the active pyrolysis of the lignocellulosic fragments and the calcination (or shrinkage) processes, thus resulting in the increased contents of aromatic carbon clusters and main mineral constituents remained. Based on the pore properties, pyrolysis temperature at around 800 °C seemed to be the optimal condition for producing SDBC, where its Brunauer-Emmet-Teller (BET) surface area (>100 m 2 /g) largely increased as compared to that of the digestate feedstock (<1 m 2 /g). Furthermore, the main compositions of mineral ash in the resulting biochar could exist as phosphates, carbonates, or oxides of calcium and other alkali/alkaline earth elements. According to the data on EDS and XRD, more pores could be significantly generated under severe pyrolysis (>700 °C) due to the high aromaticity via the thermal decomposition of lignocelluloses and the volatilization of inorganic minerals.