Nutrient rich biomass and effluent sludge wastes co-utilization for production of biochar fertilizer through different thermal treatments

Effective valorization of nutrient rich wastes for the fertilizer application is a promising method towards sustainable development. Nutrient rich wastes were mainly researched for production of biochar straight (single nutrient) fertilizer through slow pyrolysis. Appropriate waste feedstocks and cleaner thermal processing need to be explored for value addition. In present study, potassium (K) containing banana peduncle and phosphorus (P) rich effluent sludge (chemical fertilizer industry) wastes co-utilized for development of biochar complex fertilizer. Different thermal treatments viz slow pyrolysis (700 °C) and thermal plasma processing (1200–1500 °C) were trialed for production of biochars with desired characteristics. Plasma processing produced biochar with higher total P (8.53 – 11.81 %) and K (17.13 – 21.9 %) than slow pyrolysis (P-4.2 % and K-11.5 %). In contrast, slow pyrolysis resulted higher biochar yield (42 %) and total carbon content (34.1 %) than in plasma (28 – 34 % and 10.9 – 21.8 %). Bio-available phosphorus of effluent sludge (600 mg/kg) enhanced to 4500 – 6000 and 5600 mg/kg in plasma and slow pyrolysis biochars. XRD analysis indicates the presence of P as hydroxyapatite in sludge and biochars. The K was dominantly present as kalicinite (KHCO3) in slow pyrolysis and fairchildite [K2 Ca (CO3)2] specifically in plasma biochar. Biochars contained lesser total (0.18 –1.55 %) and leachable (0.014 – 0.034 %) fluoride than effluent sludge i.e. 3.45 and 0.076 %. These results demonstrate utilization potential of aforementioned wastes and thermal processes for the production of K and P enriched biochar complex fertilizer. Its application will be suitable for non-food crops and degraded soil reclamation due to toxic constituents.