摘要
随着社会的发展和人们生活水平的提高,餐厨垃圾在城市生活垃圾中的比例越来越大。餐厨垃圾中有机物和水分含量高,若不经过合理处置会给周围的环境卫生和人身健康造成严重危害。目前,国内外实际应用的餐厨垃圾集中处理技术主要包括填埋、焚烧、堆肥、粉碎、饲料化和厌氧消化技术,与其它技术相比,厌氧消化处理技术具有减少处理量、回收清洁能源和残余物制备有机复混肥等优点,它符合节能减排、清洁生产和循环经济等和谐处理技术的要求,能实现真正意义上的垃圾无害化、减量化、资源化。但由于餐厨垃圾原料的特殊性,研究其厌氧发酵关键参数对于餐厨垃圾厌氧消化系统的正常启动和稳定运行十分重要。
本文在借鉴前人研究的基础之上对餐厨垃圾厌氧发酵关键技术问题进行试验研究,为实现分散餐厨垃圾的厌氧消化处理提供基础技术支撑。论文试验主要分为接种物驯化、新鲜餐厨垃圾厌氧发酵和风干餐厨垃圾厌氧发酵三部分,在接种物的驯化试验中,研究了不同来源、不同驯化方式对接种物的影响;在新鲜餐厨垃圾厌氧发酵试验中,通过正交试验研究了接种率、含水率、温度、搅拌因素对厌氧发酵过程的影响,对参数进行了试验研究与优化;在风干餐厨垃圾厌氧发酵试验中,研究了接种率、含水率对厌氧发酵过程的影响。论文的主要研究内容与结论有:
(1)通过收集、阅读大量的国内外文献的相关资料,对目前餐厨垃圾在全球范围的产生量、处理状况、处理技术现状做了比较全面的概述和总结,针对厌氧发酵技术的机理和影响因素也做了详细的总结。
(2)通过对厌氧发酵接种物的驯化研究发现,不同来源、不同驯化方式对接种物最终效果有很大的影响。试验结果表明:经驯化后的污泥菌群呈分散分布,且形状单一;以每天添加餐厨垃圾20 g,连续投加20 d的驯化方式最好,且以厌氧发酵池内的污泥最为明显,产甲烷活性达到0.406 LCH_4/(gVSS·d),活性等级为优。
(3)在厌氧发酵过程中,与新鲜餐厨垃圾相比,风干餐厨垃圾更具有优势,能有效地缓解酸化初期的酸中毒现象。全部厌氧发酵试验前后TN明显提高,COD去除率最高可达91.8%,系统碱度提高25%以上,使得系统有较高的缓冲能力。
(4)适宜的接种率和搅拌频率有利于细菌和微生物的生长,若过多不仅增加成本、降低处理效率,而且还可能影响厌氧发酵的进行。接种率为55%时,只有在含水率为92%、温度为55℃条件下才能实现厌氧发酵顺利进行,其余条件均无法实现。低固体含量较易实现厌氧发酵,无论是新鲜餐厨垃圾还是风干餐厨垃圾,固体含量为16%时,只有在接种率为75%条件下才能顺利实现厌氧发酵。
(5)通过正交试验,得出对于新鲜餐厨垃圾的厌氧发酵系统而言,接种率为75%、含水率为92%、搅拌为2次/d、温度为55℃是最优试验组合。
(6)在整个试验过程中发现,pH值是厌氧消化过程中一个重要的控制参数,它的大小及其稳定性对产气效果有很大影响,因此对厌氧消化过程中的最佳pH值进行预测并进行有效控制至关重要。
With the development of society and improvement of people's living standards, the proportion of food waste in municipal solid waste increases fast. The food waste, without appropriate treatment to the relative high organic substance and moisture content, will make serious threat to both environment and human health. Nowadays, there are many technologies applied to treat the food waste at home and abroad, including landfill, incineration, compost, comminution, feed and anaerobic digestion. However, compared with other technologies, the technology of anaerobic digestion, which accords with the demand of harmonious treatment technology in circular economy, including energy saving, emission reduction, and cleaner production, and will realize harmless, reduction, recycling to the waste, have many advantages, such as reducing treatment capacity, recycling clean energy, making organic compound fertilizer, etc. Moreover, due to the special components of food waste, it is very important to study the key parameter of anaerobic digestion for the normal start-up and stable operation in food waste anaerobic digestion system.
This thesis, at the basis of previous researches, mainly studied the key parameters of food waste anaerobic digestion, to provide the basic technical support to deal with the treatment of the decentralized food waste in anaerobic digestion. Three main tests were carried out in the study, including the test of domestication inoculum that studied the effect of different sources and domestication ways to the inoculum, the test of fresh food waste anaerobic digestion that studied the effect of inoculation rate, moisture content, temperature, stir factor on anaerobic digestion process by oethogonal and optimized the parameters, and the test of air-dried food waste anaerobic digestion, which investigated the effect of inoculation rate and moisture content on anaerobic digestion proces. The main content and conclusions includes:
(1) Comprehensive overview and summary of production, treatment status and technology about global food waste, at the basis of collecting and reading literature at home and abroad, was stated in this thesis. The mechanism and influencing factors about technology of anaerobic digestion was also summarized in detail.
(2) The result of domestication inoculum test showed that different sources and ways of domestication had a great effect on the final status of the inoculum. Moreover, the bacteria flora in domesticated sludge was distributed dispersedly with single shape, and the best way of domestication, which making the activity of methanogenic reached optimal level at 0.406LCH_4/(gVSS·d), was to continuously add food waste 20g per day for 20 days, taking sludge from anaerobic digestion tank as inoculum.
(3) In the process of anaerobic digestion, the obvious advantage of air-dried food waste, compared with fresh food waste, was that it could effectively alleviate the acidosis at the initial acidification phase. It was found that TN had obviously increased, the highest rate of COD removal reached 91.8%, and the alkalinity had been improved to more than 25%, which made the system a higher buffer capacity.
(4) It was found that suitable inoculation rate and stir frequency were favorable to the growth of mushroom, and the overabuandance might increase the cost, reduce the efficiency of treatment, and even effect the process of anaerobic digestion. If the inoculation rate was 55%, the process of anaerobic digestion, only with the moisture content at 92% and temperature at 55℃, could operate normally. In addition, no matter the food waste was fresh or air-dried, of which the low solid content could goes well while the high content were more inclined to get acidified. When the solid content was 16%, anaerobic digestion system with inoculation rate at 75% only could operate normally.
(5) The orthogonal test showed that the optimal combination, in the fresh food waste anaerobic digestion system, was inoculation rate at 75%, moisture content at 92%, stir frequency at twice per day, temperature at 55℃.
(6) During the study, it was found that pH, whose value and stabilization had a significant influence on the methane production, was an important parameter that needs to be predicted, controlled to get the optimal value in the process of anaerobic digestion.
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