Adding Value to Sugarcane Bagasse Ash: Potential Integration of Biogas Scrubbing with Vinasse Anaerobic Digestion

Abstract

One of the byproducts of sugarcane bagasse combustion in sugarcane mills is sugarcane bagasse ash (SCBA), which contains up to ~40 mass% of organic matter. Currently, SCBA is partially used as a soil fertilizer. However, SCBA’s poor content of minerals, which are required by soils, restricts its use in soils, resulting in the disposal of large amounts of SCBA in landfills. Alternatively, SCBA has shown promise for some environmental applications such as wastewater treatment, but its use in gas cleaning deserves further study. The objective of this work was to assess the use of as-received SCBA to remove hydrogen sulfide (H2S) from biogas, thus, to add value to the ash. The experimental procedure consisted of passing biogas containing H2S through a column with SCBA and monitoring the H2S content inline by employing a gas chromatograph until the concentration of H2S, measured after the column, was ~10% of the original concentration. The breakthrough time of the SCBA adsorption curve was ~75% the breakthrough time observed with activated carbon, showing that SCBA could be a cheap alternative to commercial materials that are currently used for biogas scrubbing. This result could positively impact ethanol sugarcane mills that need to clean biogas produced from vinasses, as part of a strategy to integrate biogas production and cleaning operations using low-value residues (i.e., vinasses and ash). SCBA’s capacity for removing H2S from biogas results from the presence of K-compounds (e.g., K2SiO3 and K2Si2O5) on the ash’s surface and its relatively high porosity. Additionally, S-enriched SCBA (due to H2S retention) can expectedly be more beneficial to soils than directly adding the ash since S is an essential nutrient for the growth of plants.