Co-pyrolysis of municipal and horticultural wastes for enhanced biochar and bio-oil production: A response surface methodology approach

Abstract

Pyrolytic biochar is a promising approach to the withdrawal of CO2 and reduction of Green House Gases. One of the effective techniques to improve the properties of biochar with desired characteristics is co-pyrolysis of types of biomass. Among the types of biochar, biochar from nitrogen-rich biomass pyrolysis has various applications, including soil amendment and removal of organic pollutants. The aim of this study is co-pyrolysis nutrient-rich municipal (household) and horticultural wastes for N-doped biochar production and provide optimal conditions for the production of pyrolytic products. A series of experiments were designed with municipal and horticultural wastes at different mass ratios in a fast catalytic reactor at 550 °C with varying catalyst amounts (0–15 %) and waste blend ratios (0–100 wt%) were designed using the response surface methodology. The yields of bio-oil, biochar, and biogas were quantitatively and qualitatively assessed. Statistical analysis showed that that the horticultural-to-household wastes ratio has the most critical effect on the biochar yield. The optimum N-doped biochar yield (26 wt%) was achieved at the household-to-horticultural wastes ratio of 1.5 without using the catalyst. Also, the result showed that adding municipal waste increased bio-oil yield significantly from 18 % to 58 %. Moreover, increasing the catalyst amount raised gas yield to 37 %, and horticultural waste favored biochar formation (53 %). The optimized product showed carbon enrichment and oxygenated compound reduction the result is bio-oil production with a higher heating value. Gas chromatography-mass spectrometry (GC–MS) analysis of volatile products indicated that the co-pyrolytic oil was rich in N-containing compounds (Pyrrole, Pyridine, and Indole)which is widely used in pharmaceutical and polymer industries. Synergistic interactions between municipal and horticultural wastes significantly reduced the amount of carboxylic acids, alcohols, ketones, and esters, whereas phenols formation as valuable chemicals were increased. Therefore, this study shows that co-pyrolysis is a suitable approach for household and horticultural waste management that can increase the production of N-doped biochar and also be a sustainable source for the extraction of nitrogen-containing biochemical products.