POLLUTANTS REMOVAL FROM COMPOSTING PROCESSES USING BIOCHAR FROM LOCALLY AVAILABLE BIO-RESOURCES

Yaime Jefferson Milan

doi:10.7273/000002435

Processing food and organic waste via composting leads to a soil amendment product that positively impacts soil health. However, composting also results in the emission of vapors and gases that cause undesirable odor, affecting the air quality. In this thesis, biochars derived from the carbonization of wheat straw and Douglas Fir were produced and used as an adsorbent to remove targeted gases released by composting facilities. Eight biochars were produced under two treatment conditions: carbonization only (raw) and treatment with ammonia (N-doped). The characterization of the chars obtained was performed through elemental analysis, proximate analysis, gas physisorption analysis, Fourier Transform Infrared Spectroscopy, and pH analysis. Adsorption experiments were performed to analyze the capacity of these biochars to remove hydrogen sulfide (H2S), ammonia (NH3), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). All of these gases are contaminants released during composting of organic wastes. Biochars produced from wheat straw biomass presented higher ash content and pH than those obtained from Douglas fir. Nitrogen-doped chars had greater nitrogen content and higher surface area than the chars produced without doping. The results showed that the pH and nitrogen content were positively correlate with the adsorption capacity of the char to remove H2S and CO2. The best biochars in the removal of H2S were WS N-doped 600 and WS raw 600, with adsorption capacities of 26.7 and 23.9 mg H2S/ g char, respectively. For NH3 and CO2 adsorption tests, the best chars were DF raw 400 (0.20 mg NH3/g char) and WS N‐doped 600 (0.47 mg CO2/g char). The oxygen content in the biochar was positively correlated with NH3 retained. For CH4 and N2O the surface area is positively correlated to the adsorption capacity. Although the adsorption capacity achieved for some gases was low compared with the best chars reported in the literature, our results suggest that it is possible to engineer chars with adsorption capacity high enough that justify their use for gases removal in composting facilities. Activated chars obtained by physical activation with high surface area are needed to enhance CH4 and N2O adsorption. Bio-chars with high surface area and basic functional groups on the surface obtained by activation in the presence of NH3 or ash is needed to achieve high CO2 adsorption capacities. Biochars with acidic functional groups (as those obtained by oxidation at temperatures close to 230 oC) and with high surface area will likely result in higher NH3 adsorption capacity. More work is needed to produce a biochar cocktail to be used for odor removal in composting facilities.

POLLUTANTS REMOVAL FROM COMPOSTING PROCESSES USING BIOCHAR FROM LOCALLY AVAILABLE BIO-RESOURCES

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