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

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 similar to 8 % solid content and 55 degrees 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.