Biochar enhanced thermophilic anaerobic digestion of food waste: Focusing on biochar particle size, microbial community analysis and pilot-scale application

Syntrophic interactions in anaerobic digestion: how biochar properties affect them?

“…The large surface area of biochar benefits microbial attachment, growth and enrichment in AD, thereby promoting methane production (FAGBOHUNGBE et al, 2016). Supporting this theory, increased rates of methanogenesis between 23% and 47% have been observed when biochar particle size was reduced, mainly resulting from the increased surface area of biochar (LÜ et al, 2019;ZHANG et al, 2020). To this, the surface areas of biochar varying from 37.2 to 248.6 m 2 /g have been shown in literature to promote microbial growth and enhance methane production (Wang et al, 2019aa, Johnravindar et al, 2021.…”

“…Moreover, the floating of biochar having a relatively large particle size, e.g., diameter > 1 cm, and a density of <1000 kg/m 3 (e.g. 847 kg/m 3 ) was not found to be conducive to microbial growth (ZHANG et al, 2020). This indicated that the biochars derived from pyrolysis or gasification processes need simple pretreatment (e.g.…”

“…Biochar addition to AD has been shown to promote syntrophic VFA oxidation, methane production and process stability (HU et al, 2020;KAUR et al, 2020). Suggested mechanisms for the increased methane production by addition of biochar include (a) reduction of acid and ammonia stress by virtue of the buffering capacity of biochar and consequent increase in methanogenic activity in the AD reactor (LÜ et al, 2016;LUO et al, 2015;SUNYOTO et al, 2016), (b) acting as a conductor for electron transfer between different microbial groups colonizing the biochar surface, thereby increasing the rate of methanogenesis (BAEK et al, 2018), (c) facilitating growth of bacteria and methanogens via biochar's immobilization effect and microbial enrichment ability (LÜ et al, 2019;ZHANG et al, 2020), and (d) enabling the capacity of fermentative bacteria to metabolize long-chain VFA during AD (KAUR et al, 2020;LÜ et al, 2019). Table 2 provides a summary of reports on biochar addition in AD and its impact on enhancing methane production.…”

Monitoring of Food Waste Anaerobic Digestion Performance: Conventional Co-Substrates vs. Unmarketable Biochar Additions

“…When it comes to the technical side, diverse researchers have confirmed that carbonaceous material has been widely tested to reinforce buffering capacity, delay the accumulation of volatile fatty acids (VFAs), and mitigate ammonia inhibition, which strengthens the durability of the AD process [35]. In the same context, Zhang et al, (2020) linked the biological and physiochemical aspects, and reported that biochar's high surface area ensured a high degree of inhibitive compound adsorption, reduced acidification, and then ensured a high-performing process, as well as highly qualified AD effluents [36]. Admittedly, while biochar addition has significant benefits in terms of enhancing anaerobic treatment, it is also worth mentioning that the nature of the initial feedstocks used, as well as the selected process and the operational conditions, ultimately raise further concerns in relation to UBc exploitation.…”

“…Few researchers have tested the effect of biochar size on AD performance. However, Zhang et al, (2020) revealed that biochar with different particle sizes (<50 µm to 3 cm) substantially improved methane yield [36]. Accordingly, UBc-residue upcycling as a co-substrate of FW anaerobic treatment was tested during the experimental work described in this paper to identify whether or not the unmarketable carbonaceous material could provide the digester with the required features.…”