Co-pyrolysis of agro-industrial waste and chemical and physical characterisation of biochars

Faced with the growing volume of agro-industrial waste, biochar production offers a sustainable solution for soil conditioning. However, biochar properties are highly dependent on the feedstock and pyrolysis conditions, requiring detailed characterisation. This study characterised biochars, produced via pyrolysis and co-pyrolysis, to evaluate their potential as soil conditioners. The biochars were derived from poultry litter, coconut fibre, rotary sieve residue, and charcoal fines, individually and in co-pyrolysed combinations (with poultry litter as the base) at 500 °C. Comprehensive analyses included yield, pH, EC, CEC, BET surface area, neutralising value, elemental composition (CHN), and structural/morphological evaluations (XRD, FTIR, SEM). The results revealed diverse physicochemical properties influenced by the feedstock. Coconut fibre biochar (F) exhibited high fixed carbon (70.83 %) and BET surface area (67.62 m 2 /g), indicating strong water retention potential. Biochars derived from poultry litter and their co-pyrolysed counterparts demonstrated significant neutralising value (up to 32.52 % CaCO3 equivalent), making them promising for acidic soil correction. Co-pyrolysis proved effective in optimising specific characteristics, notably improving cation exchange capacity with combinations such as poultry litter and charcoal fines (CM) or rotary sieve residue (CR). Multivariate analysis further confirmed the suitability of biochar F for water retention, while specific co-pyrolysed biochars (e.g., C + M 0.5:0.5; C + R 0.75:0.25) were identified as ideal for nutrient retention. These findings underscore the critical role of detailed characterisation for efficient biochar application. Co-pyrolysis emerges as a valuable strategy to tailor biochar properties, contributing to sustainable agro-industrial waste management and improved soil quality. • Some biochars compromise soil physical conditioning due to excessive ash content. • Biomass and combinations were compared to optimise the quality of produced biochars. • Co-pyrolysis yielded biochars with distinct characteristics compared to simple pyrolysis due to synergy. • Nutrient supply and water retention capacity, alongside immediate analysis, were key criteria in biochar selection. • Co-pyrolysis involving a higher proportion of poultry litter provided greater nutrient retention capacity.