High solids anaerobic digestion (AD) of chicken manure (CM) is often challenging due to ammonia-N inhibition and accumulation of volatile fatty acids (VFAs). This study evaluated the effect of adding biochars from different feedstock to ameliorate semi-dry AD of fresh CM during batch fermentation. Experiments were performed in 300 mL at two total solid (TS) levels (12% and 15%) under mesophilic (36 ±1ᵒC) conditions for 55 d, using activated sludge as inoculum. Treatments included: fresh CM (at 12% or 15% TS) mixed separately with rice husks char (RB), wood char (WB) and bamboo char (BB) at biochar dosages of 2.5%, 5% and 10% of TS in the CM, inoculum only and inoculum plus CM without addition of char as the control. Results indicated that addition of biochar reduced the lag phases to 4-5.4 d and AD performances were significantly improved with total volatile solids removal of 53-67% and 62-71%, and cumulative methane of 277-380 mL/gVS (CH4 content ≈ 51-63%) and 297-438 mL/gVS (CH4 content ≈ 49-67%) at 12% and 15% TS, respectively. Biochar buffered over acidification and stabilized pH in the range of 6.5-7.8 but mild ammonia inhibition still occurred in all biochar treatments due to the high residual total ammonia-N (4.3 g-5.6 g/L). For all the investigated parameters, WB amended digesters exhibited the best results owing to its high specific surface area, porosity, cationic exchange capacity, and elemental composition which were superior to those of RB and BB. At 10% dosage of all tested biochars, the AD process was more stable and methane content neared optimal of >65% CH4. Therefore, addition of biochar from lignocellulosic materials at a given threshold dosage could promote semi-dry and dry biogas production from chicken manure and thus add value to this waste which in most cases is improperly managed.
Keywords: Biochar amendment; Biomethane production; High-solid anaerobic digestion; Mesophilic conditions; Poultry manure management.
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