添加尿素和无机盐土对秸秆厌氧消化的影响

Effects of urea and inorganic saline soil on anaerobic digestion of straw

向厌氧消化体系加入外源添加剂是一种有效且简单的用于提高产气效率的方法。为了解决秸秆厌氧消化原料转化率低、易酸化、厌氧消化时间长等问题,该文选取尿素和无机盐土作为秸秆厌氧消化的添加剂,研究比较不同添加量对玉米秸秆厌氧消化过程产气特性、发酵环境、微生物活性以及物能转化效率的影响。结果表明,对于出现酸化问题且甲烷菌活性较低的厌氧消化系统,添加尿素和无机盐土有利于缓解酸化并促进微生物生长繁殖,三磷酸腺苷(ATP)峰值时的微生物数量可增加2.76×1011-5.31×1011个/L。添加一定量的尿素和无机盐土可使产气高峰提前,添加10%的无机盐土处理组与纯秸秆处理相比,产气高峰可提前4d;但酸化也会削弱尿素和无机盐土对产甲烷过程的促进作用,添加量越大,削弱效果越显著。研究结果可为秸秆厌氧消化的工程应用提供参考。

China is a large agricultural country with the most abundant straw resources in the world. In 2010, the amount of collected straw reached 700 million tons, Anaerobic digestion (AD) technology is a widely applied technology can achieve resource utilization of straw, as well as produce clean energy. Straw is one kind of typical carbon-rich biomass, which is easy to acidify in the AD process, even more influence the biogas production and system performance. Additive has the function of adjusting carbon-nitrogen ratio, promoting AD process and relieving acidification process, thus, adding additive has been considered as an alternative method to improve the AD process. In this study, the crushed corn straw were conducted in batch reactor with the feeding concentration of 6%TS at (40±1)℃, urea and inorganic salts soil were used as additives for the straw anaerobic digestion. There are six treatments in this study, including pure straw without adding additive (R1), adding urea with the C/N of 25/1(R2) and 30/1(R3), adding inorganic salts soil of 10%(R4) and 20%(R5)( based on fresh weight of straw), as well as a control only adding inoculum (R6). The pH value, volatile fatty acids (VFAs) concentration, adenosine triphosphate (ATP) concentration, biogas production and other indicators had been measured in the whole process of 49 days. Acidification phenomenon occurred in the second day for all the treatments and 300mL of cultivated inoculum was added for each treatment. The results indicated that adding inorganic salts soil and urea displayed significant buffering action to the straw anaerobic digestion process. The pH value of R1-R5 ranged at 6.11-6.60、6.69-7.09、6.60-7.16、6.30-7.01 and 6.39-6.97 from the third day to the seventh day, respectively. While the VFAs concentration of R1-R5 was 0.38, 0.37, 0.33, 0.22 and 0.17g/L,among which, acetic acid accounting for 60.78% 、 43.82% 、 57.62% 、 21.00% and 27.64%, respectively. According to ATP results, the microorganisms quantity might increased by adding the urea and inorganic salts soil. The ATP peak of R1-R5 was 724, 996, 1236, 1040 and 1248nmol/L, respectively. Compared with the pure straw treatment(R1), R2-R5 made microorganisms quantity increased by 2.76×1011, 5.19×1011, 3.20×1011 and 5.31×1011 of per liter digested liquid, For the anaerobic digestion system with acidification problem and low methanobacteria activity, the promoting action of urea and inorganic salts soil may be influenced and weakened. Compared with the pure straw treatment, the more adding amount of urea and inorganic salts soil, the less of the biogas production, however, it could make the gas peaked one day, two days and four days earlier respectively by adding urea (25:1), adding urea (30:1) and adding 10%inorganic salts soil under the anaerobic digestion system with acidification problem and low methanobacteria activity. In short, it is a good solution to avoid acidification problem by adding urea and inorganic salts soil, the amount and regulation method should be further studied. It is helpful to avoid acidification problem and reduce the interference of promoting effects of adding urea and inorganic salts soil by changing the feeding way (like batch feeding way) and strengthening the microorganisms activity.