Abstract
Goat manure (GM) is an excellent raw material for anaerobic digestion because of its high total nitrogen content and fermentation stability. Several comparative assays were conducted on the anaerobic co-digestion of GM with three crop residues (CRs), namely, wheat straw (WS), corn stalks (CS) and rice straw (RS), under different mixing ratios. All digesters were implemented simultaneously under mesophilic temperature at 35±1 °C with a total solid concentration of 8%. Result showed that the combination of GM with CS or RS significantly improved biogas production at all carbon-to-nitrogen (C/N) ratios. GM/CS (30:70), GM/CS (70:30), GM/RS (30:70) and GM/RS (50:50) produced the highest biogas yields from different co-substrates (14840, 16023, 15608 and 15698 mL, respectively) after 55 d of fermentation. Biogas yields of GM/WS 30:70 (C/N 35.61), GM/CS 70:30 (C/N 21.19) and GM/RS 50:50 (C/N 26.23) were 1.62, 2.11 and 1.83 times higher than that of CRs, respectively. These values were determined to be the optimal C/N ratios for co-digestion. However, compared with treatments of GM/CS and GM/RS treatments, biogas generated from GM/WS was only slightly higher than the single digestion of GM or WS. This result was caused by the high total carbon content (35.83%) and lignin content (24.34%) in WS, which inhibited biodegradation.
Highlights
China is one of the largest agricultural countries in the world
The cumulative biogas productions for Goat manure (GM)/Wheat straw (WS) 10:90, 30:70, 50:50, 70:30 and 90:10 were 11890, 12765, 11253, 12685 and 9650 mL, respectively (Fig. 2A). These results showed an increase of 51.0%, 62.1%, 42.9%, 61.1% and 22.6% compared with single WS (7874 mL), and an increase of 51.0%, 62.1%, 42.9%, and 22.6% compared with single GM (10375 mL)
The results suggested that the ideal C/N ratio range is between 20 to 35 in the co-digestion of GM with crop residues (CRs), which was consistent with the report of Verma [29], which revealed that the optimum C/N ratios in anaerobic digesters were between 20 to 30
Summary
China is one of the largest agricultural countries in the world. The production of net available crop residues (CRs) in China is estimated to be over 800 million t/yr [1], which ranks first in the world. Compared with the single digestion of feedstock, the co-digestion of CRs and animal manures increases the rate of biogas production because of the greater balance between carbon and nitrogen [7] and improves AD efficiency [8]. High TN content is beneficial to co-digestion with CRs because it decreases the carbon-to-nitrogen (C/N) ratios of single CRs substrates. Various raw materials, such as agricultural waste, animal manures, sewage sludge and food waste have been reported as potentially feasible for co-digestion [7,13,14,15,16,17,18,19,20], the suitable mixing ratios of multi-component substrates between GM and various CRs are largely unknown. We investigated the biogas-producing efficiency of anaerobic co-digestion influenced by different GM and CR mixing ratios. An optimum co-digestion condition for biogas production was proposed
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