Enhancement of biomethane production during anaerobic digestion of chicken manure using a biocomposite hydrogel with iron-modified biochar

Abstract

A biocomposite hydrogel was developed by crosslinking cellulose, starch, and iron-modified biochar as an additive for enhancing anaerobic digestion (AD) of chicken manure (CM). The hydrogel had an iron content of 2.2 wt% and electrical conductivity of 0.73 mS/cm. The hydrogel showed high hydrophilicity and could adsorb water up to 63 % of its original dry mass. The results showed that the addition of a small amount of hydrogel in the AD could significantly increase the CH₄ yield and concentration, and decrease the CO₂ and H₂S contents in the biogas. The maximum methane yield and concentration during AD of CM at ∼8 % solid content and 55 °C were 275.13 mL/g VS and 63.3 %, which were achieved by adding the hydrogel at 0.66 wt% of the slurry. The yield and concentration of methane produced by the AD with 0.66 wt% hydrogel increased by 34.5 % and 7.7 %, compared to the control without the hydrogel, which produced 204.49 mL/g VS methane with 58.8 % CH₄ in the biogas over the 21 days. The addition of 0.66 wt% hydrogel could reduce 51.1 % of the H₂S in the biogas produced by the 21-day AD of CM, compared to the control without the hydrogel containing an average of 1243 ppm H₂S. Also, it was shown that the addition of the hydrogel formed by cross-linking activated biochar, CMC, and starch to AD at a concentration of 0.66 wt% increased the biomethane yield by 23.33 % compared with the addition of the same amounts of the non-crosslinked raw hydrogel ingredients.