BIOCHAR - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 113

B IOCHAR P RODUCT AND T ESTING S TANDARDIZATION
Biochar is produced from feedstock of different origin and quality, mixing thereof, and
by pyrolysis conducted under different set of conditions and systems. As such, biochars
encompass wide variety of characteristics and may differ markedly in their properties and
impact. The International Biochar Initiative (IBI) organization recently published guidelines
to establish common definition for feedstock, biochar, as well as to standardize biochar
testing methods, provide minimal characterization recording and reporting requirements, and
labeling standard for the biochar products (IBI, 2012). IBI distinguishes between ‗processed'
and ‗unprocessed' feedstock, where the former includes any chemical and/or biological
process the feedstock was exposed to prior to pyrolysis, e.g. paper pulp sludge, manures,
distillers grains, and biomass portion of municipal solid waste. In addition, animal parts and
any biomass grown on contaminated soils are considered processed feedstock and as such are
subject to a more rigorous and frequent testing requirements. IBI proposed three test
categories to provide uniform presentation format for (a) basic biochar properties, (b)
toxicology, and (c) characterization of properties relevant to soil fertility. Much of the
categories, tests, and limits are adopted from existing standards and limits previously
established for toxicants in soil and soil amendments such as land application of biosolids,
compost, and wood ash. The basic category (A) include essential properties of biochar used in
soil analysis: moisture content, elemental analysis (C, H, N), organic C, pH, electrical
conductivity, liming capacity, particle size distribution, ash content, and H:C org molar ratio.
Organic carbon is divided into three categories: Category 1: carbon content >60, Category 2:
between 30 to 60, and Category 3: between 10 to 30% organic C by weight (dry basis). While
information about all other properties in the basic category needs to be reported only, biochar
is required to have a H:C org molar ratio of <0.7. The H:C org ratio is considered an intrinsic
indicator for the degree of organic carbon stability that is correlated with the production of
fused aromatic ring structures from the thermochemical alteration of the feedstock (IBI,
2012). A ratio of 0.7 is used to distinguish between biochar and biomass that has not been
thermochemically altered, or material that was altered to an insufficient lesser degree (IBI,
2012). As several studies had shown, biomass pyrolyzed at 300 or 350 °C results in H:C org
ratios higher than 0.7; such ratio may lead to the biochar production at high temperatures, that
will positively affect biochar carbon stability; however, it is likely to adversely affect biochar
properties of agronomic benefits, such as nutrient availability and CEC (Wu et al., 2012;
Rutherford et al., 2004; Rutherford et al., 2008). The basic category is followed by the
biochar toxicity assessment test category (B), which include earthworm avoidance test,
germination inhibition test, testing for polycyclic aromatic hydrocarbons (PAHs),
polychlorinated biphenyls (PCBs), dioxins and furans, and content of metals and non-metal
elements of environmental concern (e.g. Hg, As, Se, Cd, and Pb). While values of B, Cl, and
Na only need to be declared, numerical values of Maximum Allowable Thresholds (MAT) for
selected chemical compounds or elements are given as a range based on established
thresholds for such toxicant in soil (Table 1). The ranges published by IBI are based on MAT
values from Australia, Canada, EU, UK, and USA where long established regulation for such
toxicants in soils and or other substrates exist. Category C is optional and provides
information about volatile matter, mineral N, total K, total and available P, and total and
external surface area (no threshold values exist).