餐厨垃圾厌氧发酵过程稳定性及高效产气工艺研究

发布时间：2018-09-14 15:11

【摘要】：能源短缺已成为当今世界面临的重要问题,开发和利用可再生能源是解决化石燃料枯竭的重要途径之一。作为城市污染物之一的餐厨垃圾是厌氧发酵产沼气的良好底物,但餐厨垃圾发酵过程易酸化,发酵稳定性不高,极易失败。本研究以餐厨垃圾作为主要发酵对象,利用实验室批次发酵试验,在分析其单独发酵结果的基础上,利用混合发酵的方法筛选最适合与餐厨垃圾发酵的底物,进而利用碱性物质调节混合原料的初始pH值,探究干扰发酵液酸碱度对发酵效果和发酵前期停滞时间的影响,在此基础上不断改变调控策略及接种物的添加方式,旨在寻去餐厨垃圾混合发酵高效产气的工艺要点,同时提升餐厨垃圾厌氧发酵过程稳定性,为厌氧发酵在城市推广及解决餐厨垃圾城市污染问题提供理论和实践依据。主要结论如下:(1)餐厨垃圾适宜在35℃下进行厌氧发酵。不同温度下餐厨垃圾单独发酵结果表明低温(25℃)发酵对餐厨垃圾不可行,高温(55℃)发酵易发生铵态氮抑制现象,中温(35℃)发酵下效果较为稳定;餐厨垃圾发酵过程酸化速度较快,一般1~3天即可完成,挥发性脂肪酸会迅速产生并达到抑制反应进行的浓度,用Ca(OH)2适当调节发酵液的p H值,可起到改善酸化的效果,调节后产气量及发酵液pH值有上升趋势。(2)牛粪是最适合与餐厨垃圾进行发酵的物料。通过4种碱度较高的常见发酵原料(牛粪、羊粪、鸡粪和废水处理厂剩余污泥)与餐厨垃圾进行不同比例混合发酵研究,结果表明,餐厨垃圾与牛粪、羊粪、鸡粪、污泥混合发酵的效果较餐厨垃圾单独发酵有所提升,但随餐厨垃圾比例的升高,发酵效果变差。当餐厨垃圾比例超过10%,发酵初始系统的碱度极低,当餐厨垃圾比例超过50%,发酵易失败。餐厨垃圾与牛粪1:9混合发酵总产气量最高,为17960mL;其次是餐厨垃圾与鸡粪1:9混合,总产气量为11848mL;餐厨垃圾与羊粪、污泥的最佳混合比例为5:5、3:7,产气量分别为8937mL和9611mL。为了加大餐厨垃圾的处理率,选用餐厨垃圾与牛粪湿重比为5:5进行后续研究。(3)初始pH(6.5、7.0、7.5)调控可以提高餐厨垃圾和牛粪混合发酵的效果。研究发现调节餐厨垃圾与牛粪等比例混合发酵过程的初始pH水平为6.0时,不能起到提高发酵系统的稳定性和产气量的效果。除此之外,与不调节pH相比,产气量分别提高了1.24~7.54倍。初始p H值为7.5时,发酵系统的沼气产量和甲烷产量均最高,分别为14559mL和7043mL。(4)不同时期干扰发酵液pH值(6.5、7.0、7.5、8.0)都可提高混合发酵的产气效率,但对发酵初期停滞时间的改善不明显。结果表明,2种调控方式(酸化过程结束时调节、初始和酸化结束时联合调节)都可提高餐厨垃圾与牛粪混合发酵的产气量,最高沼气产量可达27447mL,最大甲烷产量可达13723mL,Gompertz模型分析得到的停滞时间差别较大,最短为14天,但pH值调控方式的改变对缩短总体停滞时间没有明显影响。当控制pH水平在7.0和7.5时,甲烷产气量均可达13000mL以上,但当只调节一次pH值且p H水平为6.5时,系统的缓冲能力较差,缓冲时间较长,产气量偏低。(5)接种物添加方式与pH调节联合处理可以进一步提高餐厨垃圾与牛粪厌氧发酵的沼气产量,缩短发酵初期的缓冲时间。混合发酵过程两种方法联合处理后,最高沼气产量可达25626mL,Gompertz模型预测的平均滞留时间为19.97天,比仅调节初始pH平均滞留时间(26.73)缩短了6.73天,最高VS降解率和COD降解率可分别达到44.97%和99.84%。当发酵系统酸化较严重时,添加沼液和调节pH方式都可以在一定程度上提高系统的pH、缓解酸化现状,调控次数越多,系统的pH相应越高。在发酵过程中酸化较严重的时期,用新鲜的沼液替换发酵上清液,可以缓解挥发性脂肪酸的抑制现象。
[Abstract]:Energy shortage has become an important problem facing the world today. The development and utilization of renewable energy is one of the important ways to solve fossil fuel depletion. As one of the urban pollutants, kitchen waste is a good substrate for biogas production by anaerobic fermentation. Taking kitchen waste as the main fermentation object, using batch fermentation test in laboratory, on the basis of analyzing its individual fermentation results, the substrate suitable for fermentation with kitchen waste was screened by mixed fermentation method, and then the initial pH value of mixed raw materials was adjusted by alkaline substances, and the fermentation effect and development of disturbing acidity and alkalinity of fermentation broth were explored. On the basis of the influence of the stagnation time in the pre-fermentation period, the control strategy and the inoculum addition method were changed continuously to find out the key points of the high-efficiency gas production by mixed fermentation of kitchen waste, and to improve the stability of the anaerobic fermentation process of kitchen waste, so as to provide theory and theory for the promotion of anaerobic fermentation in the city and to solve the problem of pollution of kitchen waste in the city. The main conclusions are as follows: (1) Anaerobic fermentation of kitchen waste is suitable at 35 C. The results show that low temperature (25 C) fermentation is not feasible for kitchen waste, high temperature (55 C) fermentation is prone to ammonium nitrogen inhibition, and the effect is stable at medium temperature (35 C). In general, it can be finished in 1 to 3 days. Volatile fatty acids will be produced quickly and reach the concentration of inhibiting reaction. Using Ca (OH) 2 to adjust the P H value of fermentation broth properly can improve acidification effect. After adjusting, the gas yield and P H value of fermentation broth will increase. (2) Cattle dung is the most suitable material for fermentation with kitchen waste. Mixed fermentation of common fermentation materials with high alkalinity (cow dung, sheep dung, chicken dung and excess sludge from wastewater treatment plant) and kitchen waste was studied. The results showed that the mixed fermentation effect of kitchen waste with cow dung, sheep dung, chicken dung and sludge was better than that of single fermentation of kitchen waste. When the proportion of kitchen waste exceeded 10%, the basicity of the initial fermentation system was extremely low, and the proportion of kitchen waste exceeded 50%. Fermentation was easy to fail. In order to increase the treatment rate of kitchen waste, the ratio of wet weight of kitchen waste to cattle manure was 5:5 For the follow-up study. (3) Initial pH (6.5, 7.0, 7.5) could improve the effect of mixed fermentation of kitchen waste and cattle manure. When the initial pH level was 6.0, the stability and gas yield of the fermentation system could not be improved. In addition, the gas yield was increased by 1.24-7.54 times compared with that without pH regulation. When the initial pH value was 7.5, the methane yield and methane yield of the fermentation system were the highest, which were 14559 mL and 7043 mL, respectively. (4) The pH value of the fermentation broth was disturbed at different stages (6.5, P 7.0, 7.5, 8.0) could improve the gas production efficiency of mixed fermentation, but the stagnation time of initial fermentation was not significantly improved. The results showed that the gas production of mixed fermentation of kitchen waste and cow manure could be increased by the two control modes (at the end of acidification, at the beginning and at the end of acidification), and the maximum methane production could reach 27447 mL and the maximum methane production could be achieved. The output of methane can reach 1372mL, and the stagnation time obtained by Gompertz model is very different, the shortest is 14 days. However, the change of pH regulation mode has no obvious effect on shortening the total stagnation time. (5) The combined treatment of inoculum addition and pH regulation could further increase the methane production of anaerobic fermentation of kitchen waste and cow dung, shorten the buffer time in the initial fermentation stage. The average retention time was 19.97 days, which was 6.73 days shorter than that of the initial pH (26.73). The highest VS degradation rate and COD degradation rate could reach 44.97% and 99.84% respectively. When the fermentation system was acidified seriously, adding biogas slurry and adjusting pH could increase the pH of the system to a certain extent, alleviate the acidification status and control times. The more the pH of the system is, the higher the pH is. During the period of serious acidification, the inhibition of volatile fatty acids can be alleviated by replacing fermentation supernatant with fresh biogas slurry.
【学位授予单位】：西北农林科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S216.4

【相似文献】