Effect of wood biochar dosage and re-use on high-solids anaerobic digestion of chicken litter

Abstract The use of biochar (pyrolysed biomass) in anaerobic digesters can improve the efficiency of methane production at a low cost. However, the biochar dosage and the ability to re-use biochar affects the viability of this process improvement. This study shows the effects of high dosages of both pristine and re-used wood-pellet biochar on the performance of high-solids anaerobic digesters processing chicken litter. Performance was assessed on a basis of methane yield per gram of volatile solids and the volumetric efficiency. The 90-day methane yield increased by 39% with a pristine biochar dosage of 1 gTS−char/gTS−feed but unchanged under pristine biochar at lower dosages and re-used biochar at all three dosages. The use of pristine biochar at the highest dosage increased propionate degradation compared with other treatments. In addition, the highest dosage of pristine biochar causes the largest reduction in lag time compared with the control, a reduction of 35%. Lowering the biochar dosage affects the concentration of methanogens on the biochar. Methanosaetaceae and hydrogenotrophic methanogens had greater concentrations on the biochar at dosages of 0.25 and 0.5 gTS−char/gTS−feed. The addition of both pristine and re-used biochar at all three dosages investigated allows for shorter retention times and a greater number of batches to be processed per annum compared with digesters without biochar.