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我国农业固体废物年产量高达4×1010 t,“垃圾乱倒、秸秆焚烧、柴草乱跺、粪土乱堆、畜禽乱跑”等现象造成严重的农业面源污染和资源浪费[1]。农业固体废物是重要的生物质资源,富含有机质、氮、磷等营养物质,其能源化利用是未来我国新能源领域的突破点[2-4]。氢能被认为是未来最重要的清洁能源之一,具有能量密度高、热效率高、绿色清洁等特点[5]。暗发酵产氢是在传统厌氧生物处理基础上发展起来的绿色能源制备技术,具有微生物比产氢速率高、不受光照限制、工艺简单和可利用有机物范围广等优势,是农业固体废物能源化利用的理想途径[6-8]。如何提高农业固体废物的暗发酵产氢效率,保证产氢系统高效稳定运行一直是制氢领域的研究热点。
近年来的研究发现,温度、pH是影响暗发酵产氢效率和系统稳定性的重要非生物性因素。张彤[9]研究了pH对常见农业固体废弃物厌氧发酵的影响,发现不同初始pH会显著影响厌氧发酵启动时间。卢怡等[10]研究了农业固体废物厌氧产氢的潜力,以乳酸调控系统pH为4.7~5.5,发现控制体系温度在(25±1) ℃时可以产生氢气。MA等[11]研究了温度对污泥暗发酵的影响,认为最适发酵温度为55 ℃左右。陈智远等[12]研究了不同温度对畜禽粪便厌氧发酵的影响,发现相比25 ℃,粪便在35 ℃条件下厌氧发酵具有明显优势。LI等[13]以加热预处理后的餐厨垃圾为底物进行暗发酵产氢,研究发现,系统pH从4.36升高至5.81,氢浓度升高到26.6%。目前,国内外围绕有机固体废物暗发酵产氢影响因素的研究已有报道,但以典型农业固体废物为研究对象,阐明非生物性因素对不同农业固体废物暗发酵产氢性能和代谢途径影响的研究鲜有报道。
根据农业固体废物的组成与特性,本研究选取畜禽粪便、秸秆、生活垃圾等多种典型农业固体废物为底物,探究温度、初始pH等非生物性因素对暗发酵产氢性能、代谢产物、产氢代谢途径的影响,采用Gompertz模型对暗发酵产氢系统启动时间、最大产氢速率和产氢潜力进行动力学解析,为解决暗发酵产氢的反馈抑制作用,有效提高农业固体废物的氢能源转化效率提供参考。
温度和初始pH对农业固体废物暗发酵产氢的影响
Effects of temperature and initial pH on the hydrogen production by dark fermentation of agricultural solid waste
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摘要: 以猪粪、鸡粪、玉米秸秆、餐厨垃圾和厨余垃圾等5种农业固体废物为底物,采用修正的Gompertz模型,研究了典型农业固体废物暗发酵产氢动力学和代谢产物变化规律,探讨了不同温度和初始pH条件下的主要产氢代谢途径。结果表明:温度和初始pH对农业固体废物暗发酵产氢具有显著影响;高温组累积产气量和氢气百分含量显著高于中温组。在55 ℃高温且pH为6.0的条件下,餐厨垃圾暗发酵产氢效果最佳,累积产气量和氢气百分含量最大,为1 100 mL和73.58%,最大产氢速率和产氢潜力分别为37.11 mL·h−1和660.30 mL;厨余垃圾暗发酵产氢效果次之,鸡粪产氢潜力最差。在暗发酵产氢末期,以鸡粪为底物的代谢产物的氨氮浓度最高,过高的氨氮浓度可能抑制了产氢过程。VFA分析表明:不同底物和条件下丁酸浓度均最高,且含有少量乙醇、乙酸、丙酸等;暗发酵产氢代谢途径是以丁酸型发酵为主的混合型发酵。通过温度、初始pH等非生物性控制因素的优化调控,显著提高了农业固体废物暗发酵产氢潜力和底物利用效率,为生物制氢的技术研发与工程应用提供参考。Abstract: In this study, five kinds of typical agricultural solid wastes including pig feces, chicken feces, corn stover, food waste and kitchen waste were taken as substrates, and the effects of temperature and initial pH on their hydrogen production potential by dark fermentation were determined by using the modified Gompertz model, and the main pathways of hydrogen production and metabolism were analyzed. The results showed that temperature and initial pH had significant effects on the hydrogen production by dark fermentation of agricultural solid wastes. The cumulative gas production and hydrogen content in high temperature group were significantly higher than those in medium temperature group. At high temperature of 55 ℃ and pH 6.0, the best dark fermentation effect of food wastes was achieved, and the highest cumulative gas production and hydrogen content were obtained with respective value of 1 100 mL and 73.58%, and the maximum hydrogen production rate and hydrogen production potential were 37.11 mL·h−1 and 660.30 mL, which were followed by kitchen waste, while chicken feces had the worst hydrogen production potential. The concentration of ammonia nitrogen was the highest at the end of hydrogen production by dark fermentation of chicken feces. Excessive concentration of ammonia nitrogen might inhibit the hydrogen production process. VFA analysis showed that the concentration of butyric acid was the highest under different substrates and conditions, and it also contained a small amount of ethanol, acetic acid, propionic acid. The hydrogen production pathway was a mixed fermentation based on butyric acid fermentation. Through optimizing and controlling the non-biological control factors such as temperature and initial pH, the potential of hydrogen production by dark fermentation of agricultural solid wastes and the utilization efficiency of biomass were significantly improved, which provided a theoretical basis for the research and development of biological hydrogen production technology and engineering application.
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Key words:
- agricultural solid waste /
- dark fermentation /
- pH /
- temperature /
- metabolites /
- dynamic analysis
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表 1 农业固体废物的基本指标
Table 1. Basic characteristics of agricultural solid waste
实验样品 含水率/% TS/(g·L−1) VS/(g·L−1) 灰分/(g·L−1) pH C/N 猪粪 75.13 248.68 198.65 50.03 7.52 12.66 鸡粪 64.55 354.51 173.80 180.71 7.49 8.47 玉米秸秆 8.45 915.51 845.38 70.13 5.24 47.48 餐厨垃圾 81.55 184.47 172.23 11.25 6.34 13.31 厨余垃圾 93.32 66.79 59.45 7.34 6.29 20.00 接种污泥 80.82 191.77 94.47 97.30 8.59 10.21 注:TS为总固体;VS为挥发性固体。 表 2 产氢动力学分析
Table 2. Hydrogen kinetics analysis
处理条件 实验样品 Pmax/mL Rmax/(mL·h−1) λ/h R2 35 ℃中温,初始pH=5.0 猪粪 3.92 0.11 4.67 0.950 35 ℃中温,初始pH=5.0 鸡粪 3.29 0.21 6.13 0.961 35 ℃中温,初始pH=5.0 玉米秸秆 11.51 0.71 6.49 0.994 35 ℃中温,初始pH=5.0 餐厨垃圾 28.89 1.54 13.11 0.955 35 ℃中温,初始pH=5.0 厨余垃圾 24.89 3.62 29.56 0.976 35 ℃中温,初始pH=5.0 接种污泥 0.35 0.09 10.66 1 55 ℃高温,初始pH=5.0 猪粪 28.79 3.53 11.72 0.997 55 ℃高温,初始pH=5.0 鸡粪 12.73 0.63 0.50 0.992 55 ℃高温,初始pH=5.0 玉米秸秆 42.07 1.90 5.59 0.994 55 ℃高温,初始pH=5.0 餐厨垃圾 27.10 3.20 6.39 0.999 55 ℃高温,初始pH=5.0 厨余垃圾 151.55 8.45 6.07 0.969 55 ℃高温,初始pH=5.0 接种污泥 6.67 0.38 2.83 0.971 35 ℃中温,初始pH=6.0 猪粪 51.12 4.01 24.12 0.998 35 ℃中温,初始pH=6.0 鸡粪 2.16 0.14 3.15 0.995 35 ℃中温,初始pH=6.0 玉米秸秆 62.24 4.29 12.92 0.984 35 ℃中温,初始pH=6.0 餐厨垃圾 53.44 3.61 3.61 0.999 35 ℃中温,初始pH=6.0 厨余垃圾 79.49 5.05 9.94 0.996 35 ℃中温,初始pH=6.0 接种污泥 1.55 0.11 1.22 0.997 55 ℃高温,初始pH=6.0 猪粪 40.39 4.48 10.42 0.999 55 ℃高温,初始pH=6.0 鸡粪 84.60 16.19 17.26 0.995 55 ℃高温,初始pH=6.0 玉米秸秆 67.59 9.29 5.80 0.999 55 ℃高温,初始pH=6.0 餐厨垃圾 660.30 37.11 7.66 0.996 55 ℃高温,初始pH=6.0 厨余垃圾 228.17 24.00 6.93 0.995 55 ℃高温,初始pH=6.0 接种污泥 10.16 1.39 11.89 0.999 35 ℃中温,初始pH=7.0 猪粪 30.54 5.59 11.20 0.988 35 ℃中温,初始pH=7.0 鸡粪 18.30 1.27 2.56 0.998 35 ℃中温,初始pH=7.0 玉米秸秆 27.35 2.98 0.43 0.981 35 ℃中温,初始pH=7.0 餐厨垃圾 237.37 22.38 4.97 0.999 35 ℃中温,初始pH=7.0 厨余垃圾 113.49 10.46 4.17 0.997 35 ℃中温,初始pH=7.0 接种污泥 4.23 0.18 0.58 0.979 55 ℃高温,初始pH=7.0 猪粪 130.53 13.33 5.03 0.990 55 ℃高温,初始pH=7.0 鸡粪 24.03 1.49 2.59 0.996 55 ℃高温,初始pH=7.0 玉米秸秆 133.97 9.49 2.96 0.997 55 ℃高温,初始pH=7.0 餐厨垃圾 370.44 20.21 7.18 0.992 55 ℃高温,初始pH=7.0 厨余垃圾 300.31 31.47 3.23 0.999 55 ℃高温,初始pH=7.0 接种污泥 48.72 11.03 12.30 0.999 -
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