产酸沼渣再利用稻秸两级联合产酸工艺研究

VFAs Production Technology by Two-stage Fermentation from Rice Straw Based on Digestate Reuse

摘要:

秸秆厌氧产挥发性脂肪酸（Volatile fatty acids, VFAs）工艺可生产具有较高经济价值的混合短链脂肪酸，但存在发酵周期短、秸秆降解率低等不足。为了提高VFAs产率和秸秆利用率，对产酸沼渣开展了二次产酸利用试验。将秸秆在3种预处理、3种产酸温度得到的产酸沼渣，统一在35℃进行二次产酸发酵，以考察各预处理组的二次产酸效果。结果表明，各组在二次产酸时均能获得更为稳定和适宜的pH值，水热组和2%HCl组在二次产酸时均有更佳产酸表现，1%Ca(OH) 2组在两级均采用35℃温度时获最大产酸量。采用两级联合产酸工艺，可将1% Ca(OH) 2预处理组的0.07~0.20g/g的一次产酸率提高至0.27~0.38g/g的总固体产酸率。以初始100g原秸秆计算，1%Ca(OH)2、35℃发酵时一次产酸和二次产酸量分别为12.24g和11.69g，两级联合的总产酸量为23.93g，采用两级联合产酸比一次产酸的产酸量提高了95.5%，二次产酸使得木质纤维素各组分降解利用更为充分。

Abstract:

Volatile fatty acids (VFAs) production process via anaerobic digestion from rice straw is highly promising due to the preferable economic value of mixed shortchain fatty acids. However, the VFA fermentation has critical disadvantage as low digestion rate of rice straw owing to the relatively short digestion time. To increase the VFAs yield and enhance rice straw utilization, the anaerobic digestion (AD) digestate from the VFAs production was exploited for the second stage VFAs production. The first stage VFAs production was conducted by three different pretreatment methods and three different fermentation temperatures, thus the AD digestate of all sets after fermentation was used as substrates for the second stage VFAs production, and VFAs potential production for all AD digestate sets still needed to be investigated. The AD digestate of all sets was directly fermented at the same temperature of 35℃ for the second stage VFAs production without further additional pretreatment. The results revealed that all sets can have more stable and suitable pH value at the second stage. Both hydrothermal and 2% HCl sets had higher VFAs yield at the second stage. The maximum VFAs yield was achieved under the condition of 1% Ca(OH)2 pretreatment and temperature of 35℃. By combining the two stages together, the total VFAs yield of 1% Ca(OH)2 group was enhanced from 0.07~0.20g/g at the first stage to 0.27~0.38g/g in total. The mass balance analysis was based on the hypotheses that the initial substrate was 100g rice straw and 1% Ca(OH)2 pretreatment was chosen at the first stage. The 1% Ca(OH)2 and 35℃ group produced 12.24g VFAs at the first stage and 11.69g VFAs at the second stage. The VFAs yield for the combined twostage was 95.5% greater than that of the first stage. The research result could provide useful reference for enhancing VFAs yield by further fermentation of the AD digestate obtained from the first stage.