【作者】 刘丹；

【导师】 李文哲；

【作者基本信息】 东北农业大学 ， 生物质转化与利用工程， 2014， 博士

【摘要】 随着人们生活水平的提高,我国餐厨废弃物的产量日益增加。大量的餐厨废弃物如果得不到及时有效地处理就会对生态环境及人类健康造成严重的影响。厌氧发酵技术处理餐厨废弃物既能获得生物质能源沼气又能减轻其造成的环境污染,是解决我国能源紧缺和环境污染问题的有效的手段。目前国内外学者已经开展了针对餐厨废弃物厌氧发酵的研究,根据以往研究,餐厨废弃厌氧发酵有机负荷一般不能超过3kgVS· m-3· d-1,有机负荷过高会导致发酵失败。这是由于餐厨废弃物易降解有机质含量高,发酵时酸化速度快,在发酵过程中难以实现酸碱平衡而导致酸败。有机负荷的制约致使厌氧发酵反应器的容积利用率低,无法实现餐厨废弃物的稳定高效产甲烷,因此,探讨提高餐厨废弃厌氧发酵有机负荷的工艺途径,对提高反应器的容积利用率具有重要意义。为了获得提高餐厨废弃物厌氧发酵有机负荷的工艺路线,本研究首先深入研究了餐厨废弃物中三大主要有机成分淀粉、蛋白质和脂肪单独厌氧发酵特性及其产甲烷潜力,并在此基础上采用混料试验设计探讨有机成分组成对产气性能的影响,并确定适宜的有机成分配比；其次针对餐厨废弃物厌氧发酵过程中容易酸化,反应器难以顺利启动的问题,以单因素试验结果为基础,通过响应曲面法考察接种比例、浓度和温度影响因子对餐厨废弃物厌氧发酵启动过程的交互作用,优化其工艺参数并确定启动条件；再次为了实现对餐厨废弃物的连续稳定产甲烷,以提高厌氧发酵反应器利用效率为目标,在考察半连续式单相厌氧发酵时有机负荷对餐厨废弃物厌氧发酵过程中产酸和产甲烷的影响规律基础上,确定了采用两相污泥回流工艺处理餐厨废弃物,实现了产酸相丁酸型定向酸化,同时产甲烷相中的碱度和微生物的数量显著增加,大大提高了厌氧发酵处理餐厨废弃物的效率。本文主要研究内容及成果如下：(1)研究发现以餐厨废弃物为原料进行厌氧发酵时,其三种主要成分脂肪、淀粉、蛋白质的比例影响发酵过程的进行,比例不当时,会受到长链脂肪酸、挥发性脂肪酸和氨氮的不同程度抑制。当三种有机成分比例适当时,可以发生协同促进作用,有效避免中间代谢产物的抑制,从而可适当提高有机负荷。经优化得最优混合配比为脂肪：淀粉：蛋白质等于36：30：33,此时VS产甲烷率、VS降解率分别为451.36和79.62%。实际的餐厨废弃物蛋白质含量偏低、淀粉的含量偏高,为了实现餐厨废弃物高负荷厌氧发酵,应采取与含氮量较高的原料混合发酵。与最优混合比例相比,实际的餐厨废弃物蛋白质含量偏低、淀粉的含量偏高。(2)餐厨废弃物厌氧发酵过程中容易产乳酸,乳酸菌主要是餐厨废弃物自身携带。乳酸在厌氧发酵过程中降解率最高,主要转化为乙酸和丙酸,两者的比例接近1：3。乳酸负荷在1Ommol· L-1· d-1的运行条件下发酵30d后厌氧体系也出现了缓冲能力不足的现象,其根源是乳酸降解后所产丙酸在厌氧体系内不能及时转化造成累积,因此应尽量避免丙酸和乳酸进入到厌氧体系。(3)餐厨废弃物厌氧发酵启动试验研究结果。在接种比例小于50：50,体系pH在5.5以下,厌氧体系酸化；当接种比例大于50：50,体系pH维持在7.0以上时,产气状态良好,甲烷含量能达到60%。应用响应曲面法中的Box-Behnken设计,以回归模型为基础,对原料浓度、温度和接种率水平组合进行多目标优化,最终确定最优的工艺参数如下：原料浓度为5%、温度为35℃、接种率为65%。在最优条件下,经试验验证得到了与预测值相吻合的结果,VS产甲烷率、VS降解率平均值分别为469.87mL/g和81.95%。(4)在批式启动试验的基础上,探讨单相厌氧发酵时有机负荷对厌氧发酵各阶段间的平衡影响。当有机负荷小于4kg·m-3·d-1时,体系以产甲烷发酵为主。当有机负荷大于4kgVS· m-3·d-1时,厌氧体系主要以产酸发酵为主。pH小于5.5时为乙酸型发酵,pH在5.0左右为丁酸型发酵,pH在4.5以下为乳酸型发酵。(5)两相污泥回流发酵系统延长了污泥停留时间,所能承受的有机负荷为7.36kgVS·m-3·d-1；此负荷下平均VS甲烷产率为399.95mL·g-1。厌氧体系内的挥发性固体浓度和所能承受的有机负荷之间存在指数函数关系,关系式为y=1.61e0.23x(相关系数R2=0.99187,P<0.0001),其中x代表有机负荷、y代表挥发性固体浓度。由此推断湿法发酵所能承受的最大有机负荷为8kgVS·m-3·d-1。更多还原

【Abstract】 In China, with the improvement of people’s living standard, the output of food wastes is increasing day by day. The ecological environment and human health would be badly affected if the massive food wastes couldn’t be treated timely and effectively. Using anaerobic fermentation technology to treat food waste, can not only obtain biogas but also alleviate environmental pollution, so, it is effective to solve the problem of energy shortage and environmental pollution. Currently, lots of studies on anaerobic fermentation technology of food wastes have been completed. The present researches indicate that anaerobic digestion of food wastes will soon be prone to acidification because of its easy degradability and higher content of organic matter. The inhibition of acidification on fermentation may be reduced to some extent by the method of adding chemical reagent to adjust pH to be neutral. However, the cost and ion concentration of biogas slurry would be enhanced, and it is not conducive to the further utilization of digestion residue. In addition, this way is limited to improve contribution of reactor’s organic loading, the capacity utilization is still very low, and it is unable to achieve sTablele and efficient production of methane with food wastes.In order to obtain the process of improving efficiency of food wastes anaerobic digestion, a large number of experiments have been conducted in this research. First, single fermentation characteristics and methanogenesis potential of starch, protein and fat were investigated, and then the influence of organic ingredients on gas yield property was determined using mixture design experiments, thus the suiTablele ratio of organic compounds was ascertained. Second, on the basis of single factor results, the interaction of inoculation proportion, concentration and temperature on initiating process of food wastes anaerobic fermentation was explored with response surface method, the process parameters was optimized and initiating condition was confirmed in the meantime, this experiment was to solve the problems that food waste was easily going to acidification in the process of anaerobic digestion and the reactor’s initiating was difficult. Third, for the sake of realizing continuous and sTablele methane yield, and also with the purpose of boosting the utilization ratio of anaerobic fermentation reactor, the effect rule of organic loading on production of acid and methane was explored in the process of anaerobic digestion with food waste using semi-continuous single-phase anaerobic fermentation. On this basis, two-phase sludge return process was adopted to treat food waste, this made butyrate type directional acidification of acidification phase come to be true, meanwhile, alkalinity and the number of microorganism of methanogenesis phase raised significantly, and the efficiency of anaerobic fermentation for treating food waste was greatly improved. The main research contents and achievements are as follow:(1) The study result indicated that while food waste was used as anaerobic digestion material, fermentation process would be affected by the mixing ratio of fat, starch and protein. It was inhibited in different degree by long-chain fatty acid, volatile fatty acid and ammonia nitrogen when the ratio was unsuiTablele. While the ratio was appropriate, the inhibition of intermediate meTableolites could be avoided effectively on account of the synergistic effect, and then the organic loading was boosted appropriately. The optimum mixing ration was as follow:fat:starch:protein was36:30:33, the corresponding maximum biochemical methane potential and VS degradation ration were451.36and79.62%, respectively. The protein content of actual food waste was a little lower, but the starch content was higher, therefore, in order to enhanced the organic loading, mixing fermentation of food waste and high nitrogen content material should be put to use. Comparing with the optimum mixing ratio, the protein content of actual food waste was lower and the starch content was high.(2) Lactic acid was easily generated in the process of anaerobic digestion with food waste, the lactic acid bacteria was mainly carried by food waste. The degradation ration of lactic acid was highest, lactic acid mainly converted into acetic acid and propionic acid, and both ratio was close to1:3. Under the condition that the lactic acid loading was10mmol·L-1·d-1, the phenomenon of insufficient buffer ability appeared in the anaerobic system after30days of fermentation, the cause was that propionic acid could not be conversed timely and caused accumulation which was yield after the degradation of lactic acid, accordingly, propionic acid and lactic acid should be prevented to go into anaerobic system.(3) The result of initiating experiment of anaerobic fermentation with food waste manifested that anaerobic system would turn into acidification while inoculation ratio was less than50:50and pH was lower than5.5. Conversely, when inoculation ratio was more than50:50and pH was higher than7.0, gas yield situation was in good condition and methane content could reach60%. Multi-objective optimization of level combination of material concentration, temperature and inoculation ratio was conducted using Box-Behnken design method and on the basis of regression model, and the optimum process parameters were determined as follow:material concentration, temperature and inoculation ratio were5%,35℃and65%, respectively. Under optimum condition, the result of verification test which was consistent with predicted value was obtained, that was the average values of VS methane yield ration and VS degradation ratio were469.87mL/g and81.95%, respectively.(4) On the basis of batch initiating experiment, the effect of organic loading of single-phase anaerobic fermentation on the balance of each stage of anaerobic digestion was explored. Result showed that while organic loading was less than4kg·m-3·d-1, methanogenesis fermentation was the main characteristic for anaerobic system, on the contrary, acidification fermentation was the main characteristic. When pH was less than5.5, the fermentation characteristic of anaerobic system was acetic acid type, When pH was5.0, it was butyrate acid type, and When pH was lower than5.0, it was butyrate acid type lactic acid type.(5) The sludge retention time of two-phase sludge return fermentation system was extended, the organic loading that system could sustain was7.36kgVS·m-3·d-1, under this organic loading the average VS methane yield ration was399.95mL·g-1. There was exponential function relationship between VS concentration and organic loading that system could sustain, and the expression was y=1.61e023x (correlation coefficient R2=0.99187, P<0.0001). Where x represented organic loading and y represented VS concentration. So, it could be concluded that the maximum organic loading that wet fermentation could sustain was8kgVS·m-3·d-1.更多还原