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===Effect of biochar on retention and fate of other pollutants=== | ===Effect of biochar on retention and fate of other pollutants=== | ||
− | *Nitrogen. Biochar effects on nitrogen retention depend on the properties of the biochar and stormwater runoff. Biochars produced at relatively low temperatures (less than 600<sup>o</sup>C) provide some retention of organic nitrogen and ammonium nitrogen in stormwater runoff (Iqbal et al., 2015; Gai et al., 2014) | + | *Nitrogen. Biochar effects on nitrogen retention depend on the properties of the biochar and stormwater runoff. Biochars produced at relatively low temperatures (less than 600<sup>o</sup>C) provide some retention of organic nitrogen and ammonium nitrogen in stormwater runoff. Mechanisms for nitrogen retention include adsorption of ammounium and nitrogen immobilization. Leaching of nitrogen may decrease due to increased water holding capacity (Iqbal et al., 2015; Gai et al., 2014; Zheng et al., 2013). |
*Metals. Biochar enhance retention of metals in stormwater runoff. (Reddy et al., 2014; Domingues et al., 2017; Iqbal et al., 2015) | *Metals. Biochar enhance retention of metals in stormwater runoff. (Reddy et al., 2014; Domingues et al., 2017; Iqbal et al., 2015) | ||
*Organics. Biochar significantly retains polynuclear aromatic hydrocrabons in stormwater runoff (Reddy et al., 2014; Domingues et al., 2017; Ulrich et al., 2017; Iqbal et al., 2015) | *Organics. Biochar significantly retains polynuclear aromatic hydrocrabons in stormwater runoff (Reddy et al., 2014; Domingues et al., 2017; Ulrich et al., 2017; Iqbal et al., 2015) | ||
*Bacteria and viruses. Biochar effects on bacteria and virus retention are a function of the particle size of the biochar. Fine-grained biochars enhance removal of bacteria in stormwater runoff through straining of microorganisms (Reddy et al., 2014; Sasidharan et al., 2016; Yang et al., 2019). | *Bacteria and viruses. Biochar effects on bacteria and virus retention are a function of the particle size of the biochar. Fine-grained biochars enhance removal of bacteria in stormwater runoff through straining of microorganisms (Reddy et al., 2014; Sasidharan et al., 2016; Yang et al., 2019). | ||
− | * | + | *Dissolved organic carbon. Biochar shows limited retention of dissolved carbon in stormwater runoff (Iqbal et al., 2015). |
+ | *Greenhouse gas emissions. Biochar effectively sequesters carbon and reduces loss of greenhouse gases when incorporated into soil or media, particularly soil with high organic matter content (Zhaoa et al., 2013; Mohanty et al., 2018; 37. Agyarko-Mintah et al., 2017). | ||
==Accessibility== | ==Accessibility== |
Biochar is a charcoal-like substance that’s made by burning organic material from biomass. The two most common proceesses for producing biochar are pyrolysis and gasification. During pyrolysis, the organic material is heated to 250-800oC in a limited oxygen environment. Gasification involves temperatures greater than 700oC in the presence of oxygen.
Biomass waste materials appropriate for biochar production include crop residues (both field residues and processing residues such as nut shells, fruit pits, bagasse, etc), as well as yard, food and forestry wastes, and animal manures. Clean feedstocks with 10 to 20 percent moisture and high lignin content must be used. Examples are field residues and woody biomass. Using contaminated feedstocks, including feedstocks from railway embankments or contaminated land, can introduce toxins into the soil, drastically increase soil pH and/or inhibit plants from absorbing minerals. The most common contaminants are heavy metals—including cadmium, copper, chromium, lead, zinc, mercury, nickel and arsenic, and Polycyclic Aromatic Hydrocarbons (PAHs).
Biochar is black, highly porous, lightweight, fine-grained and has a large surface area. Approximately 70 percent of its composition is carbon. The remaining percentage consists of nitrogen, hydrogen and oxygen among other elements. Biochar’s chemical composition varies depending on the feedstocks used to make it and methods used to heat it.
Biochar benefits for soil may include the following.
Biochar is also found to be beneficial for composting, since it reduces greenhouse gas emissions and prevents the loss of nutrients in the compost material. It also promotes microbial activity, which in turn accelerates the composting process. Plus, it helps reduce the compost’s ammonia losses, bulk density and odor.
The properties of biochar depend on the feedstock and the conditions under which the biochar is produced.
NOTE - this is from one study, just inserted here as an example
NOTE - this is from one study, just inserted here as an example
This section is divided into chemical-physical properties, hydraulic properties, retention-leaching properties, and other properties.
The properties of biochar vary depending on the feedstock and conditions, primarily the pyrolysis temperature, under which the biochar is produced. Consequently there is considerable variability in the chemical and physical properties of different biochars. The table below summarizes data from our literature review. Some conclusions from the literature are summarized below.
Chemical and physical properties of biochar.
Link to this table
Property | Range found in literature1 | Median value from literature |
---|---|---|
Total phosphorus (%) | 0.0061 - 1.086 | 0.0618 |
Total nitrogen (%) | 1.2 - 2.4 | 0.88 |
Total potassium (%) | 0.0079 - 1.367 | 0.181 |
Total carbon (%) | 24.2 - 90.9 | 66 |
Total hydrogen (%) | 0.67 - 4.3 | 2.8 |
Total oxygen (%) | 2.69 - 28.7 | 16.3 |
pH | 6.43 - 10.4 | 9.66 |
Cation exchange capacity (cmol/kg) | 0.1 - 562 | 43.1 |
Surface area (m2/g | 2.78 - 203 | 30.6 |
Electrical conductivity (μs/cm) | 100 - 2221 | 231.5 |
Pore volume (cm3/g) | 0.006 - 0.51 | 0.036 |
Total calcium (%) | 0.0954 - 3.182 | 0.590 |
Total magnesium (%) | 0.0297 - 0.2801 | 0.0587 |
Total copper (%) | 0.0001 - 0.0078 | 0.00025 |
Total zinc (%) | 0.0002 - 0.0152 | 0.00135 |
Total aluminum (%) | 0.001 - 0.1929 | 0.0290 |
Total iron (%) | 0.0009 - 0.2209 | 0.0333 |
Total manganese (%) | 0.0001 - 0.1025 | 0.00145 |
Total sulfur (%) | 0.01 - 0.44 | 0.05 |
Primary references for this data:
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In this section we provide information on effects of biochar on pollutant attenuation and the physical properties of soil and bioretention media.
Biochar is not likely to provide significant phosphorus retention in bioretention practices unless impregnated with cations (e.g. magnesium) during production at relatively low temperatures (e.g. less than 600oC.) |
Biochar may have several properties for managing stormwater, such as increased water and pollutant retention, improving soil physical properties, and attenuating bacteria and pathogens. Biochar has been examined as a potential amendment to engineered media in bioretention or other stormwater control practices. With respect to phosphorus, information from the literature is mixed. Below are summaries from several studies.