Biosolids-Derived Biochar Improves Biomethane Production in the Anaerobic Digestion of Chicken Manure

Abstract

Anaerobic digestion has attracted great interest for use in the management of organic wastes and the production of biomethane. However, this process is facing challenges, such as a high concentration of ammonia nitrogen, which affects the methanogenesis process and, thus, the production of methane. This study investigates the use of biosolid-derived biochar for mitigating ammonia stress and improving methane production during the anaerobic digestion of chicken manure, using both pristine biochar and biochar modified with a potassium hydroxide (KOH) solution. Batch mesophilic anaerobic digestion (37 °C) was carried out over 18 days. When compared to chicken-manure-only controls, a significant increase in methane formation was observed in the digesters amended with biochar and KOH-modified biochar, producing 220 L kg−1 volatile solids (VSs) and 262 L kg−1 VSs of methane, respectively, compared to 139 L kg−1 VSs from the control digesters. The use of biochar and KOH-modified biochar resulted in a significant reduction of 8 days in the lag phase. The total ammonia nitrogen (TAN) concentration was reduced in the digesters with biochar and KOH-modified biochar by 25% and 35.5%, respectively. The quantitative polymerase chain reaction (QPCR) data revealed that the number of 16S rRNA gene copies was around 50,000 and 41,000 times higher in the biochar and KOH-modified biochar digesters, respectively, compared to the control digesters on day 18. The taxonomic profiles indicated that the BC and KOH-BC digesters contained a mixture of methanogenic pathways, including acetoclastic (Methanosaetaceae), hydrogenotrophic (Methanosarcinaceae), and methylation (Methanofastidiosaceae). This mix of pathways suggests a more robust archaeal community and, hence, more efficient methanogenesis. The results show that the addition of biosolids biochar enhances anaerobic digestion, mitigates ammonia stress to methanogens, and significantly increases biogas production.

Source-Separated Industrial Wastewater Is a Candidate for Biogas Production through Anaerobic Digestion

“…To investigate this potential in a configuration applicable to a commercial scale, BMP and semi-continuous digestion using source-separated wastewater were undertaken. In this study, initial BMP showed biogas yields approaching those of similar tests in the literature [25,110,111] but lower than expected biogas and methane yields under semi-continuous feeding conditions. This may be caused by the combination of operating conditions, inoculum, and feedstock composition unique to this study.…”

“…This was performed by adding new substrate to the existing reactor sludge once biogas production had ceased [57,58]. Acclimatisation was especially important for the digesters containing biochar, as it is necessary for microbes to colonise pores in the biochar [25]. For the sequential runs, each reactor was fed the same quantity of substrate as originally fed and biochar in the same 2:1 gTS ratio as appropriate.…”

“…As biochar was regularly added to the digesters, imperfect mixing could cause settling and accumulation of solid particles. The effective use of biochar as an additive [25][26][27][28], especially in large-scale continuous systems, should be investigated further. Using this work as a base, longer-term studies at a larger scale would provide important data around the impacts and effective methods of process control [128], requirements and results of maintenance and shutdowns [128], and seasonal shifts in conditions and feedstocks as weather and product demands change [129,130].…”

“…After conversion from biomass at high temperatures (300-1000 • C) in low oxygen environments, this product has a high surface area and can be further treated to modify characteristics including pH, porosity, and adsorption potential. Biochars from various sources, with and without treatment, have been shown to increase biogas yields by up to 88% in inhibitory conditions [24][25][26] through various mechanisms, including adsorbing inhibitors, controlling pH, providing electron transfer sites, and sheltering microbes [27,28]. Currently, most anaerobic digestion studies investigating biochar use lignocellulosic substrates, such as wood and woody agricultural waste, for the formation of biochar [24,27,[29][30][31], with some biochar being made from manure [32].…”

“…Comparison of biochars produced from different sources shows visible structural differences, varying chemical composition, and a range of effects upon application [35]. The few studies of biosolids biochar as an additive for biogas production have used manure [25] or sewage sludge as the digestion substrate [36,37].…”