A summary of all results including a comparison to the criteria set by the IBI 13 can be found in Tables 1 (summary), 2 (New, High, Low, Third Feedstock and High-2 biochars) and 3 (Old biochar). All biochars and feedstocks used in 2012 and 2013 (Table 2) were well within the criterion set by the IBI and there were little differences among biochars. Old biochar (Table 3), the first biochar submitted for testing, was made from used shipping pallets and construction wastes and was determined to have elevated levels of the metals arsenic, chromium, copper, and lead. Old biochar also had the lowest levels of organic carbon (63.2%) as determined by loss on ignition. This biochar had the highest levels of extractable phosphorus (850 mg/kg) and CEC (34.8 cmol/kg), as well as the highest percentage of fine particles (<0.5 mm, 48%). Old biochar was also the only biochar to fail the germination test (Figure 3) and it was determined that Eisenia fetida (soil invertebrate) significantly avoided the 2.8% Old biochar amendment, whereas they preferred the 2.8% amendment of the New biochar (Figure 2).

Test Category A: Basic Biochar Utility Properties

Biochar production via pyrolysis is essentially the carbonization of biomass. The carbonization process allows for the transformation of structured organic molecules of wood and cellulose materials into carbon, or carbon-containing residues, which are often aromatic in nature 14-18. Carbonization is obtained through the elimination of water and volatile substances from the biomass feedstock, due to the action of heat during the pyrolysis process 19. All of the biochars produced at the commercial greenhouse contained a relatively low moisture percentage (<5%) with the exception of Old biochar. All biochars are categorized by the IBI as Class A (>60%) in terms of their composition of organic carbon as a result of complete carbonization of the feedstock material via pyrolysis. Thus due to the high percentage of organic carbon, all biochars produced have a low percentage of ash (<2.5%), which is the inorganic or mineral component of the biochar 13. Although these low ash biochars do not provide substantial amounts of nutrients directly to the soil as do their high-ash biochar (often made from manures and bones) counterparts; the carbon content of these biochars is much higher and therefore they have higher long-term nutrient retention abilities 20-22.

The hydrogen to carbon ratio (H:C) is a term often used to measure the degree of aromaticity and maturation of the biochar, which has been linked to their long-term stability in the environment 18. For biomass feedstock containing cellulose and lignin, the H:C ratios are approximately 1.5. However, pyrolysis of these materials at temperatures greater than 400 °C is expected to produce biochars with H:C ratios <0.5. It has been reported that an H:C ratio < 0.1 indicates a graphite-like structure in the biochar 23. All biochars in this report have H:C ratios less than 0.02, indicating that these biochars are highly aromatic in nature and will have long-term stability in the environment.

Soil pH is a measure of soil acidity, and unfortunately many agricultural soils in Canada and worldwide are acidic (pH < 7), meaning that they are not ideal for crop growth. Biochars with an alkaline pH (> 7), such as those being produced at the greenhouse, can be added to acidic soils to increase the soil pH to levels that are more appropriate for plant growth.

Another important soil characteristic for plant growth is particle size distribution (PSD). Biochars that have a higher percentage of coarse particles may favorably increase soil aeration and prevent biochar movement into the subsoil over time, thereby increasing the length of time biochar offers benefits to plant growth 24. However, smaller particle sizes are favored for biochars that are being produced for remediation purposes with the intent to sorb contaminants and minimize their bioavailability, as contaminants are more easily able to access pore space for binding 3,25,26. Also smaller particles sizes increases the number of biochar particles per unit volume of soil which is favorable for contaminant sorption27. As in a previous study3, fine particles are defined as those < 0.25 mm and coarse particles as > 0.5 mm. The biochars named New-, High- and Third Feedstock have a high proportion of coarse particles (~98%), and a low proportion of fine particles (~2%). The biochar produced at a slightly lower temperature, had 89% coarse and 11% fine particles sizes. All of these biochars may offer substantial improvements to soil texture and aeration especially in degraded or clay type soils. The Old biochar had a PSD that differed substantially from the others, having 52% coarse and 48% fine particles. A biochar with this PSD may be preferable for use at contaminated sites, where contaminant sorption is the primary focus.

Test Category B: Toxicant Reporting

Biological testing of biochar is important to assess the toxicity (if any) of these materials to soil invertebrates and plants. To date, there is little existing literature on the potential impact of biochar on terrestrial organisms and their associated response, and often the literature that does exist presents conflicting results. Exposure to contaminants may inhibit earthworms ability to perform essential soil functions such as decomposition, nutrient mineralization, and soil structure improvements 28. New biochar showed no detrimental effects on the earthworm Eisenia fetida as assessed by earthworm avoidance, however worms significantly avoided Old biochar (Figure 2). Germination assays are a technique used to evaluate the toxicity of a particular material to plants. Potting soil served as a better control than filter paper as the filter paper often encouraged mold formation. Pumpkin and alfalfa seeds germinated well with 67% ± 12% and 81% ± 6% germination, respectively. Roots also proliferated well with average lengths after seven days being 14 cm ± 0.6 cm and 55 cm ± 8 cm for pumpkins and alfalfa, respectively. As with the earthworm avoidance studies Old biochar showed toxicity to plants and all other biochars evaluated showed no detrimental effects to seed germination as measured by percent germination and root length after seven days (Figure 3).

Although some types of biochar have the potential to sorb organic contaminants and reduce their toxicity in the environment, careful characterization of the biochar is required to ensure that it does not contain harmful contaminants such as PAHs, PCBs, and metals as a result of contaminated feedstocks or pyrolysis conditions. None of the biochars produced at the greenhouse had PAH concentrations exceeding IBI guidelines. Old biochar was determined to have elevated levels of PCBs and the metals arsenic, chromium, copper, and lead, however none of the biochars produced from the other two biomass materials contained metals above IBI guidelines. Old biochar was produced from used shipping pallets and construction wastes which is likely the source of the metal contamination. Although Old biochar would not be suitable for use in agricultural soils or home gardens, all other biochars could be used for these purposes.

Test Category C: Biochar Advanced Analysis and Soil Enhancement Properties

Biochars containing a high concentration of ammonium and nitrate may be applied to agricultural soils to offset the requirements for synthetic fertilizers. However, if biochar contains an excess of these nitrogen compounds then application on a large scale could increase the atmospheric N 2 O concentration and contaminate drinking water sources with nitrates. None of the biochars studied contained elevated amounts of ammonium or nitrate.

Phosphorus is an essential component for many physiological processes related to proper energy utilization in both plants and animals. Biochars with moderate amounts of available phosphorus will act as important plant fertilizers. In Ontario, soils containing 15–30 mg/kg phosphorus are considered low, 31–60 mg/kg moderate, and 61–100 mg/kg high. Old biochar was highest in available phosphorus at 850 mg/kg and may not be suitable for adding to soils already classified as high in phosphorus. However, all other biochars tested had a much lower amount of available phosphorus and would not be expected to cause problems when added at rates up to 10% (w/w).

The components of biochar (except moisture) that are released during pyrolysis are referred to as volatile matter. These components are typically a mix of short and long chain hydrocarbons, aromatic hydrocarbons with minor amounts of sulfur. Volatile matter was determined via proximate analysis which also determines the moisture and ash content of biochars (section 2.2). The volatile content affects the stability of the material 29, N availability and plant growth 30 . In theory, biochars high in volatile matter are less stable and have a higher proportion of labile carbon that provides energy for microbial growth and limits the availability of nitrogen necessary for plant growth. A study by Deenik et al., (2010) considered 35% volatile matter to be high (inducing nitrogen deficiency), and 10% volatile matter to be low. All biochar in this report contained less than 20% volatile matter, and hence would not be expected to limit plant growth. Proximate analysis determination of volatile matter is most important for biochars with low ash concentrations such as those produced at the commercial greenhouse.

Specific surface area (SSA) is a measure of the porosity of a biochar. It includes not only the external biochar surface area, but also the surface area within the pore spaces and is an important characteristic used to predict the ability of a biochar to sorb organic contaminants. Contaminant sorption has been attributed to π-π interactions (attractive, non-covalent binding) between the aromatic ring(s) of the contaminant and those of the biochar 31. Activated carbon (AC) is a charcoal-like material that is treated during its production to maximize its porosity and therefore has higher SSAs than most biochars. Although all the of biochars presented in this report have SSAs in the 300 m2/g range (i.e. much less than that of AC; ~800 m2/g), as reported in Denyes et al., 2012 and 2013, the biochars, Old and New, have both shown significant potential to serve as a soil amendment for the remediation of PCBs.

Cation exchange capacity (CEC) is a measure of the number of cations (positively charged ions) that a soil particle is capable of holding at a given pH. The ability of the soil to hold cations is due to electrostatic interactions with negatively charged sites on the surface of a particle, such as hydroxyl (OH-) and carboxyl (COO-) groups 32, 33. The CEC of the soil can be linked to the ability of the soil to hold nutrients and retain cations from fertilizers which are essential for plant growth. Also, many environmental contaminants such as lead, cadmium and zinc have positive charges; therefore soils with a high CEC may function to prevent the leaching of these contaminants into drinking water sources. Biochars have been reported to increase the CEC of soils, due to the slow oxidation of the biochar surface which increases the number of negatively charged sites, and therefore may reduce fertilizer requirements and immobilize positively charged contaminants in soils 32 . Typically, sandy soils have a CEC between 1–5 cmol/kg, loam soils 5–15 cmol/kg, clay type soils >30 cmol/kg and organic matter 200–400 cmol/kg. The methods for determining the CEC of biochar are still in their infancy and therefore should be considered in relative terms. The CEC of the biochars produced at the greenhouse are higher than the CEC of PCB-contaminated soils (Denyes et al., 2012), but lower than compost amended soils.



Figure 1. Earthworm avoidance wheel. The wheels are produced from steel and the worms are allowed to move throughout the compartments via multiple holes which are approximately 5 cm in diameter.



Figure 2. Earthworm avoidance assay of Old and New type biochars. The biochar titled “Old” was produced via construction wastes, whereas the biochar titles “New” was produced from sawdust materials. * indicates a significant difference between unamended potting soil and potting soil amended with 2.8% of either biochar (p < 0.05).



Figure 3. Percent germination of two different plant species. Pumpkin (Cucurbita pepo spp. pepo) and alfalfa (Medicago sativa) were grown in triplicate in various biochars produced at a commercial greenhouse for seven days. Old and New refer to biochars made from different feedstocks, whereas Low and High refer to different temperatures of pyrolysis. * indicates significantly difference from the controls (potting soil and filter paper).

Sample Feedstock Pyrolysis Temperature Organic Matter (LOI) pH CEC PSD PSD SSA Coarse Fine °C % cmol/kg % % m2/g Old 1 >700 63.2 9.3 34.8 51.7 48.3 373.6 New 2 700 97.8 9 16 98.7 1.3 324.6 Low Temp 2 500 96.7 8.7 15.9 86.2 13.8 336.9 High Temp 2 >700 97.9 8.4 11.1 98.1 1.9 419.5 Third Feedstock 3 700 96.2 9.6 13.2 97.6 2.4 244.4 High Temp-2 3 >700 97.1 9.1 17.1 97.9 1.9 428 LOI: Loss on Ignition, CEC: Cation Exchange Capacity, PSD: Particle Size Distribution, SSA: Specific Surface Area

Table 1. Feedstock type, pyrolysis temperature and physical characteristics of the six biochars.

Requirement IBI Biochar Feedstock Range Unit Criteria Range Test Category A: Basic Biochar Utility Properties - Required for All Biochars Moisture Declaration <0.1–4.3 % Organic Carbon Class 1 > 60% 96.2–97.8 (LOI) % Class 2 > 30% 92.44–97.93(Pro/Ult) Class 3 > 10 < 30% H:C org 0.7 max 0.01–0.02 Ratio Total Ash Declaration 1.38–2.26 % Total N Declaration 0.28–1.06 % pH Declaration 8.4–9.6 pH Particle Size Distribution Declaration 86–98 % Coarse 1.3–14 % Fine Test Category B: Toxicant Reporting- Required for All Feedstocks Germination Pass/Fail Pass Earthworm Avoidance Declaration No Avoidance Polyaromatic Hydrocarbons (PAHs) 6–20 <2.0 mg/kg Polychlorinated Biphenyls (PCBs) 0.2–0.5 <0.1 mg/kg Arsenic 12–100 <1.0 <1.0 mg/kg Cadmium 1.4–39 <1.0 <1.0 mg/kg Chromium 64–1,200 <2.0 <2.0–2.6 mg/kg Cobalt 40–150 <1.0 <1.0 mg/kg Copper 63–1,500 3.6-6.5 <2.0–5.9 mg/kg Lead 70–500 <2.0–2.7 <2.0–8.1 mg/kg Mercury 1,000–17,000 <5.0–294 ng/g Molybdenum 5–20 <2.0 <2.0 mg/kg Selenium 1–36 <10 <10 mg/kg Zinc 200–7,000 5.6–56.2 7.8–30.5 mg/kg Chlorine Declaration mg/kg Sodium Declaration 137-878 <75-770 mg/kg Test Category C: Biochar Advanced Analysis and Soil Enhancement Properties- Optional for All Biochars Mineral N (Ammonium and Nitrate) Declaration <0.2–6.1 mg/kg Total Phosphorus Declaration 69.5–276 52.5–74 mg/kg Available Phosphorus Declaration 9–80 mg/kg Volatile Matter Declaration 12.47–19.09 % Specific Surface Area Declaration 244–428 m2/g Cation Exchange Capacity Declaration 11.1–17.1 cmol/kg

Table 2. Summary Criteria and Characteristics for New, High, Low, Third and High-2 Biochars and Feedstocks. All biochars listed in this table are produced from similar feedstocks at the same pyrolysis facility.

Requirement IBI Biochar Range Feedstock Range Unit Criteria Test Category A- Basic Biochar Utility Properties - Required for All Biochars Moisture Declaration 20 % Organic Carbon Class 1 > 60% 63.2 (LOI) % Class 2 > 30% Class 3 > 10 < 30% H:C org 0.7 max Ratio Total Ash Declaration % Total N Declaration % pH Declaration 9.3 pH Particle Size Distribution Declaration 52 % Coarse 48 % Fine Test Category B: Toxicant Reporting- Required for All Feedstocks Germination Pass/Fail Fail Earthworm Avoidance Declaration Avoided Polyaromatic Hydrocarbons (PAHs) 6–20 mg/kg Polychlorinated Biphenyls (PCBs) 0.2–0.5 1.2 mg/kg Arsenic 12–100 167 <1.0 mg/kg Cadmium 1.4–39 <1.0 <1.0 mg/kg Chromium 64–1,200 206 <20 mg/kg Cobalt 40–150 5.3 <5.0 mg/kg Copper 63–1,500 558 <5.0 mg/kg Lead 70–500 314 <10 mg/kg Mercury 1,000–17,000 <5.0 ng/g Molybdenum 5–20 <2.0 <2.0 mg/kg Selenium 1–36 <10 <10 mg/kg Zinc 200–7,000 498 <15 mg/kg Chlorine Declaration mg/kg Sodium Declaration 6460 <75 mg/kg Test Category C: Biochar Advanced Analysis and Soil Enhancement Properties- Optional for All Biochars Mineral N (Ammonium and Nitrate) Declaration 2.6 mg/kg Total Phosphorus Declaration mg/kg Available Phosphorus Declaration 850 mg/kg Volatile Matter Declaration % Specific Surface Area Declaration 373.6 m2/g Cation Exchange Capacity Declaration 34.8 cmol/kg

Table 3. Summary Criteria and Characteristics for Old Biochar and Feedstock. The biochar listed in this table was produced from construction wastes at the same pyrolysis facility as the biochars listed in Table 2.