Effect of Pyrolysis Temperature on Chemical and Structural Properties of Raw Agricultural Wastes

Abstract

This study was carried out to assess the effect of charring on chemical and structural properties of raw agricultural wastes at two different temperatures. The agricultural wastes (feather from the poultry unit, maize cob, maize stalk, bamboo, rice straw, cocoa pods, maize husk and used paper from offices) were collected from Teaching and Research Farm, Obafemi Awolowo University (OAU), Ile-Ife, Osun State, Ife excluding the used paper, which was collected from the Academic areas, OAU. The collected waste materials were air-dried, pulverized, ground, and sieved with 2 mm sieve separately. Biochars were produced from raw agricultural wastes at pyrolysis temperatures 400℃ and 450℃. The raw and selected charred agricultural wastes were subjected to chemical and structural analyses. Pyrolysis of the raw materials at the two temperatures led to a significant increase in pH. A significant decrease in organic carbon of all the agricultural waste materials was observed after pyrolysis, a lower C:N was recorded; however, nitrogen content did not change significantly with pyrolysis temperature compared with the raw waste materials. The concentrations of cations like Ca and Mg were unaffected by the pyrolysis temperatures, but significant increase was observed with potassium. The results of FTIR analysis indicated the presence of many surface functional groups in both the raw and charred materials, such as OH, COOH and NH, that could be involved in adsorption and release of plant nutrients in soils, including heavy metals adsorption from soil. However, the intensities of the functional groups were lower in raw agricultural wastes compared with charred agricultural waste. The effect of temperature differences was not significant on the elemental and structural properties; thus, any could be taken as the optimum temperature for effective biochar production. It was concluded that biochar produced from agricultural wastes could be used as liming materials and soil amendments. Also, the presence of carboxylic and phenolic groups in the charred materials will increase the soil cation exchange capacity and improve the nutrient holding capacity of the soil.