Investigation into the Sources of Biochar Water-Soluble Organic Compounds and Their Potential Toxicity on Aquatic Microorganisms

Abstract

During biochar production, a number of pyrolysis intermediates recondense on the surface of biochar where potentially they may play an interesting role in soil and freshwater environments. This study investigated the sources of biochar water-soluble organic compounds (WSOC) as a function of biomass materials including cellulose and lignin and also as a function of pyrolysis temperature from 300 to 500°C in relation to their potential toxicity to freshwater blue-green algae, Synechococcus. The amount of WSOC extracted from biochar, irrespective of biomass starting material, decreased significantly as a function of pyrolysis temperature. For biochars produced at pyrolysis temperatures below 400 °C, algal bioassays and advanced mass spectrometry analyses revealed that toxic WSOC extracted from pinewood-derived biochar was most likely due to mono-, di-, and trisubstituted phenolic compounds derived from lignin, while toxic WSOC extracted from cellulose-derived biochar was acidic and bio-oil like in nature. For pinewood biochar produced at temperatures above 400 °C, WSOC contained small to nondetectable (500 °C) amounts of phenolic compounds and decreased from 664.5 ± 6.2 mg DOC/kg biochar (300 °C) to 75.39 ± 0.42 mg DOC/kg biochar (500 °C) with no observable toxicity on blue-green algae growth. Additionally, this study investigated toxicity caused by an imperfect reactor condition, such as the presence of cold spots and insufficient evacuation of pyrolysis intermediates, leading to a significant amount of toxic WSOC.

Source and Biological Response of Biochar Organic Compounds Released into Water; Relationships with Bio-Oil Composition and Carbonization Degree

“…The series of peaks in BC350 extracts were predominantly associated to carboxylic acids, which were the main components of the low molecular weight fraction of BC WSOCs, with C1-12 straightchain and branched, saturated and unsaturated aliphatic acids, and aromatic acids like benzoic acid and its C1-2 alkylated derivatives. The composition of the OL was more complex ( None of these species characterized the BC WSOCs, but minor contribution of some of these compounds was evidenced in other studies 8 . Low molecular weight aliphatic aldehydes (C3-4), ketones and diketones (C4-6) were detected in the OL, but not in BC WSOCs, indicating that, if retained by the BC after their production, they could be released preferentially as VOCs.…”

“…In conclusion, WSOCs influence the suitability of BC for environmental applications. Previous studies proposed that high amounts of PAHs 49 , phenolic and carboxylic acids 4,8 in BC WSOCs caused harmful effects on cress seeds. In this study, fulvic-like WSOCs and concentrations of VFA< 3mg/g induced statistically significant positive effects on the seedlings of cress, corroborating the hypothesis that the complex biological effects of BC WSOCs are the results of an interaction between contrasting factors.…”

“…Uchimiya et al 10 demonstrated the existence of polyaromatic moieties in the dissolved organic carbon (DOC) extracted from a BCamended soil, attributed to unique structures of pyrogenic DOC. Vapors re-condensation and pyrolysis temperature were found to be of primary importance for the production of BC suitable for soil application 5,8,11 . The contact of the pyrolysis vapors with the carbonized biomass inside the reactor and their removal is critical to prevent BC contamination 5,8 .…”

“…Temperature and residence time are crucial process parameters. At temperatures higher than 400°C a sharp decrease in VOCs adsorbed on BC was evidenced 8,11 . High nitrogen flow can reduce the content of PAHs 12,13 .…”

Use of fecal and sawdust biochar as a new perfume delivery system

“…The main difference is the detection of short chain fatty acids and C16 and C18 fatty acids in biochar 300 containing feces; in sawdust only, methyl or methoxy alkyl phenols can be detected. The toxicity and properties of different biochar types is a topic that is becoming documented more frequently …”