Poultry Processing Waste Conversion into Biochar and Compost: Processes Optimization and Products Characterization

The production of biochar and compost from poultry waste (PW) such as poultry litter (PL) and poultry manure (PM) is done through slow pyrolysis and composting processes which are two farm-based, value-added approaches to recycle these harmful organic wastes and to produce economic value products. This paper aims to compare these two methods of PW valorization and to evaluate the yields and qualities of the two agricultural- use products (biochar and compost). First, the raw PL, PM samples and a mixture of both (50:50) were characterized, and the proximate analyses indicate high volatiles contents (around 82%) and a low ash content (less than 7%), whereas the ultimate analyses reveal high carbon (between 24.48 and 35.13%) and nitrogen contents (between 1.33 and 3.58%). The energy content of the studied samples indicates good HHV (13.19 MJ/KG for PM and 16.51 MJ/kg for PL). Pyrolysis experiments were conducted in a laboratory-scale pyrolysis pilot plant from 300 to 500 °C to examine the effect of final temperature on the quality PL and PM biochars and to identify the optimal pyrolysis conditions for a maximum production of biochar. As peak pyrolysis temperature increased incrementally from 300 to 500 °C, the biochar yield decreased. The generated biochars showed a maximum yield at 300 °C with 45 wt.% for PL, 40 wt.% for PM and 38.75 wt.% for the co-pyrolysis of both PM and PL. Regarding the final biochar characteristics, to produce agricultural use PL biochar, 300 °C should be selected in pyrolysis. Composting experiments were performed for PL, PM and a mixture of them for 95 days. The main composting process phases were followed and identified using the temperature, the pH and the compost moisture content. The final compost characteristics and functional composition using FTIR spectroscopy were determined, and the potential to be applied as fertilizer was evaluated. By comparing the yields and qualities of biochars and composts obtained from each PW recovery technique, it was found that the pyrolysis process represents a more cost-effective and appropriate alternative on an industrial and commercial scale compared to the composting process, which is limited and only used in the agricultural field.