Improvement of Biogas Production Using Biochar from Digestate at Different Pyrolysis Temperatures during OFMSW Anaerobic Digestion

Abstract

Anaerobic digestion (AD) was utilized to treat the ever-growing amount of organic fraction of municipal solid waste (OFMSW) generated due to population growth and the expansion of the global economy. The widespread application of AD has led to a continuous increase in residual solid digestate that necessarily requires further disposal. Improving AD efficiency and reducing the large amount of digestate is necessary. This study investigated the chemical and physical characteristics of biochar derived from digestate at different pyrolysis temperatures (300 °C, 500 °C, and 700 °C), as well as corn stover biochar at 500 °C, and their effects on AD performance. The pH value of the biochar increased with an increase in pyrolysis temperature while the electrical conductivity decreased. Macropores dominated the biochar’s pore size, and decreased with an increased pyrolysis temperature. The biochar preparation temperature significantly influenced the AD efficiency. Biochar prepared at 700 °C outperformed the other groups, improving the biogas production yields by 10.0%, effectively shortening the lag time, and increasing the average chemical oxygen demand (COD) degradation rate by 14.0%. The addition of biochar (700 °C) and corn stover biochar increased the relative abundance of the volatile fatty acid (VFAs)-oxidizing bacteria Syntrophomonadaceae, which expedited the acid conversion in AD systems. Biochar facilitated direct interspecies electron transfer between DMER64 and Trichococcus with Methanosaeta, enhancing the biogas production performance. These findings confirmed that the biochar derived from digestate promoted biogas production and acid conversion in the AD system of OFMSW. Furthermore, biochar has an improved AD stability, which represents a promising approach to recycling digestate.

Characterization of biochars of different origin and application to the anaerobic digestion of source-selected organic fraction of municipal solid waste under batch conditions and at different dosages

“…The physicochemical characteristics found in Table 1 show pH values consistent with the literature for both substrates (5.50-5.52) and the inoculum (7.69) (Campuzano and González-Martínez, 2016;Alghashm et al, 2023). The TS and VS of the substrate (31-33 and 21-22 g/L, respectively) are below the typical values for the OFMSW (Campuzano and González-Martínez, 2016) due to the addition of water in the pretreatment of the OFMSW, which reduces the concentration of solids and in turn affects the TS and VS of the inoculum (14.2 and 6.4 g/L, respectively).…”

Geobacter grbiciae—A New Electron Donor in the Formation of Co-Cultures via Direct Interspecies Electron Transfer

“…This stimulatory effect may be ascribed to the establishment of DIET between G. grbiciae and M. barkeri 800 with conductive particle materials acting as electron conduits. Previous studies on DIET have indicated that some (semi) conductive materials (including magnetite, carbon cloth, GAC, and biochar) can accelerate the direct electron transfer between microbes [7,10,13,[18][19][20][21][22][23][24][25][26][27]34,35]. Methane was generated at a faster rate and higher levels in co-cultures supplemented with GAC than in co-cultures supplemented with magnetite during the early growth phase.…”

“…Subsequently, various co-cultures that exchange electrons through DIET have been reported [5,[12][13][14][15][16][17][18] and primarily involve Geobacter species and methanogens. Moreover, the effects of various conductive materials on DIET have also been reported [7,10,[18][19][20][21][22][23][24][25][26][27]. The continuing increase in the number of microbes identified to carry out electron exchange through DIET indicates that DIET is a syntrophic metabolism that is more prevalent in nature than previously thought.…”

Reuse and Valorization of Solid Digestate Ashes from Biogas Production

“…AD represents the most well-known, efficient, and mature technology for OFMSW treatment and is a viable alternative to landfill for different categories of waste (food industry, domestic, and abattoir wastes, etc.). They provide three assets, i.e., safe waste disposal, a sustainable supply for biogas production, and a socially accepted technology [34,35]. On the other hand, a recognized drawback comes in the form of concomitant large production of digestate, leading to a potential environmental problem that requires effective disposal [36].…”