Biochar production from co-pyrolysis of coffee ground and native microalgae consortium

Abstract

In this study, coffee ground (CG), a kind of solid waste, was co-pyrolyzed with native microalgae consortium (NMC) of which the main population were Spirogyra sp., Cladophora sp., Microspora, and Rhizoclonium at various mass ratios to improve the biochar qualities such as biochar yield, pH, nitrogen content, and BET surface area. The biochar production was undertaken from 150 g raw material in a slow pyrolysis cylindrical fixed bed reactor at 5–10 °C/min heating rate with 100 ml/min flow rate of nitrogen as sweeping gas. The reactor temperature was heated up to 400 °C with a holding time of 1 h. Increase of NMC resulted in higher percentage of biochar yield but in terms of higher heating value (HHV), the biochar from pure CG gave a high HHV of 32.14 MJ/kg which was suitable to be used as solid fuel and the value decreased with the NMC composition. The pH value and nitrogen content in the biochar were found to be improved with the increase in NMC content or decrease in CG/NMC ratio. The pores generated in the co-pyrolyzed biochars were mesopores of which the specific surface area and the total pore volume increased with the NMC content then the biochars were suitable for soil amendment and taken as adsorber to remove some toxic organic and inorganic pollutants in water and air treatments. In the case of the biochar electrical conductivity, since the value of the was higher with the increase of NMC content, the amount of the biochar having NMC composition for soil amendment should be carefully estimated to avoid high soil salinity and nutrient imbalances.