Biochemical Engineering Journal, 2018, n. 137
In this study, the effects on process performance and changes in microbial populations with the addition
of biochar to the anaerobic digestion of sludge and orange peels were evaluated. Biochar had a positive
influence in batch digestions, leading to a decrease in the lag phase and an increase in methane yields;
this was even more evident for citrus peel wastes, which reached an increase of approximately 33% when
10 g L−1 of biochar was added and 56% when 30 g L−1 was added. Particle size analysis performed for the
experiments shows greater surface area available in biochar systems for biomass immobilization.
Analysis of the microbial communities by means of 16S rRNA gene pyrosequencing shows that
the biochar addition favoured the electro-active microorganisms consortia creating a synthrophic
metabolism between eubacterial and archaeal populations, which resulted in an improvement of the
anaerobic digestion performance.
The codigestion of the mixture under a semicontinuous regimen showed an improvement in methane
yields of approximately 60% and at hydraulic retention times of 30–20 days (reaching methane production
values above 500 L CH4 kg VS−1 at an OLR of 1.49 kg VS m−3 d−1). The enhancement observe in biochar
supplemented fermentations may be explained by the adsorption of inhibitors and the relatively high
surface area favoured the adhesion and growth of microorganisms.
This research was possible thanks to the financial support of the "Ministerio de Economía y Competitividad" and Fondo Europeo de Desarrollo Regional through the project (ref: CTQ2015-68925-R) and ‘Junta de Castilla y León, Consejería de Educación’ (ref: LE060U16) projects cofinanced by FEDER funds. A. Sotres thanks the regional ‘Junta de Castilla y León’for the postdoctoral contract associated with project ref: LE060U16
