Date Published: March 22, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Enlan Zhang, Jiajia Li, Keqiang Zhang, Feng Wang, Houhua Yang, Suli Zhi, Guangqing Liu.
Sweet potato vine (SPV) is an abundant agricultural waste, which is easy to obtain at low cost and has the potential to produce clean energy via anaerobic digestion (AD). The main objectives of this study were to reveal methane production and process stability of SPV and the mixtures with animal manure under various total solid conditions, to verify synergetic effect in co-digestion of SPV and manure in AD systems, and to determine the kinetics characteristics during the full AD process. The results showed that SPV was desirable feedstock for AD with 200.22 mL/g VSadded of methane yield in wet anaerobic digestion and 12.20 Lmethane/Lworking volume in dry anaerobic digestion (D-AD). Synergistic effects were found in semi-dry anaerobic digestion and D-AD with each two mixing feedstock. In contrast with SPV mono-digestion, co-digestion with manure increased methane yield within the range of 14.34–49.11% in different AD digesters. The values of final volatile fatty acids to total alkalinity (TA) were below 0.4 and the values of final pH were within the range of 7.4–8.2 in all the reactors, which supported a positive relationship between carbohydrate hydrolysis and methanogenesis during AD process. The mathematical modified first order model was applied to estimate substrate biodegradability and methane production potential well with conversion constant ranged from 0.0003 to 0.0953 1/day, which indicated that co-digestion increased hydrolysis efficiency and metabolic activity. This work provides useful information to improve the utilization and stability of digestion using SPV and livestock or poultry manure as substrates.
Total solid (TS) concentration is one of the most important parameters in the efficiency assessment of anaerobic digestion. It is widely accepted including wet, semi-dry, and dry anaerobic digestion, when TS of substrate are < 10, 10–15, or > 15%, respectively (Li et al. 2011; Liotta et al. 2015). Wet anaerobic digestion (W-AD) is widely applied to treat livestock and poultry breeding wastewater, food waste and energy crop due to high methane yield per unit substrate, low level of sludge generation and convenient operation and maintenance (Zhang et al. 2000; Demirel and Scherer 2009; Nagao et al. 2012). However, for feedstock with low moisture content, such as crop straw and municipal sludge, dry anaerobic digestion (D-AD) is a better choice because of low consumption of water, small reactor requirement and high volumetric methane production (Guendouz et al. 2010; Brown and Li 2013). In addition, the storage and recovery of anaerobic sludge activity has aroused the concern of researchers (Li et al. 2014), which help to solve the demand for large amounts of activated sludge and accelerate the start-up of D-AD reactors.
In view of substrate utilization efficiency, the increase of TS concentration had the negative effect to methane production performance. Usually, there are a series of important parameters to evaluate the operation stability, including pH, VFAs, TA and ammonia concentration (Callaghan et al. 2002; Weiland 2010). As shown in Table 3, suitable pH range and VFAs/TA ratio guaranteed gas production efficiency. However, methane productivity was restricted when FA value was over 380 mg/kg in the reactors, which was also supported by Bujoczek et al. (2000).