Optimization of Biochar Production by Co-Torrefaction of Microalgae and Lignocellulosic Biomass Using Response Surface Methodology

Abstract

Co-torrefaction of microalgae and lignocellulosic biomass was evaluated as a method to process microalgae sludge produced from various effluents and to obtain biochars with suitable properties for energy or material valorization. The influence of four independent variables on biochar yield and properties was evaluated by a set of experiments defined by response surface methodology (RSM). The biochars were characterized for proximate and ultimate composition, HHV, and methylene blue adsorption capacity. HHV of the biochars was positively correlated with carbonization temperature, residence time, and lignocellulosic biomass content in the feed. Co-torrefaction conditions that led to a higher yield of biochar (76.5%) with good calorific value (17.4 MJ Kg−1) were 250 °C, 60 min of residence time, 5% feed moisture, and 50% lignocellulosic biomass. The energy efficiency of the process was higher for lower temperatures (92.6%) but decreased abruptly with the increase of the moisture content of the feed mixture (16.9 to 57.3% for 70% moisture). Biochars produced using algal biomass grown in contaminated effluents presented high ash content and low calorific value. Dye removal efficiency by the produced biochars was tested, reaching 95% methylene blue adsorption capacity for the biochars produced with the least severe torrefaction conditions.

Biochar Production Technologies from Agricultural Waste, Its Utilization in Agriculture and Current Global Biochar Market: A Comprehensive Review

“…Response surface approach can optimise biochar preparation from the stem of Eichhornia crassipes for Cd2+ adsorption [103]. Biochar production can be optimised by Co-Torrefaction of Microalgae and Lignocellulosic Biomass Using Response Surface methodology [104].…”

An Optimized Method for Evaluating the Preparation of High-Quality Fuel from Various Types of Biomass through Torrefaction

“…These results indicate a reduction in the ash content of 15.71% and 14.88%, respectively, while maintaining a high yield and HHV. Viegas et al [23] optimized the torrefaction of mixed biomass of microalgae and lignocellulosic biomass using RSM, finding that at 250 • C, 60 min, and 50% lignocellulosic biomass, the highest yield and HHV of the mixed biochar were achieved, at 76.5% and 17.4 MJ/kg, respectively. In another study [24], the torrefaction process of olive waste was optimized using a numerical modeling method, with the optimal operating conditions being 275 • C and 30 min, resulting in an 18.18% increase in HHV.…”

A Framework for Assessing Hydrochars from Hydrothermal Carbonisation of Agrowaste with the Use of MCDA: Application with the Hierarchical SMAA-PROMETHEE Method

“…The most common properties of hydrochars and their production methods that are reported in the literature are the following: temperature ( • C), residence time (h), pH, ash content (%), yield (%), elemental composition (e.g., C, N, H, O, S), Volatile Matter (VM-%), Fixed Carbon (FC-%), electrical conductivity, H/C and O/C atomic ratios, heating value, surface area (SSA), particle size distributions, density, porosity, biomass/water ratios, water holding capacity, Cation Exchange Capacity (CEC), the presence of metals (e.g., Ag, Cu, Pb, Zn, Cd, Fe, Mn), and morphological features [6][7][8][9][10][11][12][13][14]. It is evident that depending on the hydrochar type and production method used, an assessment and comparison of different products could be performed based on their physicochemical characteristics only.…”