Abstract
Dry anaerobic co-digestion of citrus wastes (CW) with chicken feather (CF), wheat straw (WS) and manure bedded with straw (MS) was investigated in batch and continuous processes. Experiments were designed with different mixing ratios considering the inhibitory effect of CW, C/N ratio, and total solid content of individual feedstocks. Best mixing ratio (CF:CW:WS:MS) of 1:1:6:0, enhanced methane yield by 14% compared to the expected yield calculated according to the methane yields obtained from the individual fractions. The process performance of this mixture was then investigated in continuous plug flow reactors at different organic loading rates (OLR) with feedstock total solid contents of 21% TS (RTS21) and 32% TS (RTS32). At OLR of 2 gVS/L/d, a methane yield of 362 NmlCH4/gVSadded was obtained from RTS21, which is 13.5% higher than the yield obtained from RTS32 (319 NmlCH4/gVSadded). However, it was not possible to achieve a stable process when the OLR was further increased to 3.8 gVS/L/d; there were increased total VFAs concentrations and a decline in the biogas production.
Highlights
Appropriate mixing ratio for dry codigestion of inhibitory and recalcitrant wastes was acquired for improved methane yield
Solid waste streams like chicken feathers (CFs), manure bedded with straw (MS), wheat straw (WS) and other agricultural and forest residues are readily available; they account for the largest potential feedstock as sources of biomass energy
All the different mixing ratios examined in this study had a C/N ratio between 12 and 21 which is within the optimal C/N range required for a stable anaerobic digestion process [22, 24]
Summary
Appropriate mixing ratio for dry codigestion of inhibitory and recalcitrant wastes was acquired for improved methane yield This is to circumvent some problems associated with pretreatment of these wastes and make the dry digestion process more economical. Global emissions from solid wastes are estimated to be between 20 and 40 million tons of C H4 per year [1] Biogas production from these waste streams through anaerobic digestion processes reduces greenhouse gas emissions and solve the problem of global energy challenge and environmental threat [2]. Large volume of fruit wastes are generated globally; over 40 million tons of industrial citrus wastes (CW) are globally generated [6] Converting these waste streams into energy through anaerobic digestion is a feasible option with low capital investment thereby ascribing value to these wastes
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