聚羟基烷酸脂论文：两段式和三段式工艺制取聚羟基烷酸酯的试验研究.doc

聚羟基烷酸脂论文：两段式和三段式工艺制取聚羟基烷酸酯的试验研究【中文摘要】聚羟基烷酸酯(PHA)是一类羟基脂肪酸的聚合物,当外界环境较恶劣时,部分微生物可以在体内以内碳源的形式贮存PHA。PHA具有生物相容性和可生物降解性,同时根据单体组分的不同还可以具有同石化塑料相类似的多种物理性质,可以代替现行的难降解塑料,以此可缓解环境固体废弃物污染。然而目前PHA商业化生产都采用纯菌发酵的方式,成本较高,阻碍了PHA的大规模应用。采用活性污泥混合菌群生产PHA可以采用廉价的有机废物为底物,有望大大降低PHA的生产成本。两段式PHA生产工艺包括有机废物厌氧酸化和PHA生产两步,后者在时间上分为污泥适应阶段和PHA积累阶段,适应阶段采用均衡营养比例而PHA积累阶段则限制进水中营养元素。本研究发现在PHA积累阶段一步减少进水中80%(相对于均衡比例)的氨氮,比逐步减少可以更有效的促进PHA积累;在每周期底物都可以消耗完毕的条件下,无论底物为乙酸钠还是污泥水解液,该阶段反应器厌氧-好氧运行与好氧运行得到的结果几乎没有区别;研究还发现适应期污泥龄较长时可以保证反应器长时间的稳定运行,而污泥龄较短时易引发污泥膨胀,污泥龄低于5天引发的污泥膨胀会使得污泥产PHA能力下降。以污泥水解液为底物时,其中VFAs可以得到的快速的吸收,PHA积累与其中氨氮水平有很大关系。三段式PHA生产工艺包括有机废物厌氧酸化、菌群富集和PHA积累,其中菌群富集是最重要的一步。本研究以乙酸钠为底物考察以SBR富集产PHA菌群时,发现反应器易于发生污泥膨胀。在污泥龄为1天、底物负荷较高(6.6 g COD/L/d)时,反应器膨胀非常严重,大量泡沫产生,污泥很快丧失了产PHA能力;而污泥龄为10天、负荷较低(2.7 g COD/L/d)条件下得到的膨胀污泥则具有较高的PHA合成能力,好氧SBR运行102天时污泥积累PHA最大含量达到了53%,PHA平均积累速率为0.19 mg COD/mg X/h,PHA产率为0.76 mg COD/mg COD,而与此SBR同步运行的厌氧-好氧SBR则运行55天左右后突然崩溃,污泥浓度甚至不足500 mg/L。以蔗糖模拟糖蜜废水经厌氧酸化用于PHA合成时,产酸反应器启动运行1个月后逐渐稳定为乙醇型发酵,此时出水经中空纤维膜过滤后用于SBR富集产PHA混合菌群和PHA积累,实现了生物制氢与PHA合成系统的耦合。SBR运行负荷为4.2-4.5 g COD/L/d,污泥龄为10天,启动运行1个月内污泥浓度从3300 mg/L增大到8000 mg/L以上,尽管底物充盈时溶解氧控制于3.0 mg/L左右,然而30天时SBR依然发生了污泥膨胀,这可能是污泥浓度过大导致的。对比发现,膨胀后的污泥在底物吸收、PHA合成以及生长方面比非膨胀污泥快了1倍左右。本实验在SBR运行25天时,系统每消耗1 kg COD的蔗糖,约生产16 L氢气和0.1 kg COD的PHA,其中单体HV质量比约占24%左右。【英文摘要】Polyhydroxyalkanoates (PHAs) are a class of polymers, which can be accumulated as internal carbon sources by part microorganisms under adverse circumstances. PHAs are biocompatible and biodegradable and can also possess the similar properties with the petro made plastics, which enables them to substitute the current plastics to reduce solid wastes. However, PHAs in market are all commercially produced by pure cultures, which bring about high costs and hampered their large-scale application. PHA production by mixed microbial cultures can be completed in open reactors and future more, more cheap organic wastes can be used. This would make cost reduction possible.Two-stage PHA production process includes acidogenic fermentation of organic wastes and PHA production, and the latter is composed by sludge acclimation and PHA accumulation. In sludge acclimation, nutrients are balanced while in PHA accumulation, nutrients are unbalanced. In this study, results showed that direct limitation of ammonia by 80% (compared with balance level) in influent could better stimulate PHA accumulation than gradual limitation. When there was no substrate left in every cycle, little difference was observed in PHA accumulation between anaerobic-aerobic and aerobic operation with substrate as acetate or sludge alkaline fermentation liquids. It can also be drawn that long sludge retention time would guarantee longterm stability of the reactor, while low sludge retention time would bring about sludge bulking. Especially, when sludge retention time was lower than 5 days, the PHA storage capacity would be damaged. VFAs could be uptaken rapidly and the PHA accumulation depended highly on the level of ammonia when the substrate was sludge alkaline fermentation liquids.Three-stage PHA production process includes acidogenic fermentation of organic wastes, culture selection and PHA accumulation, and stage of culture selection is the most important. It was observed that bulking sludge was easily established when selecting cultures in SBR with actate as substrate. Under SRT of 1d and high organic loading rate (6.6 g COD/L/d), the bulking was more severe with a great deal of foam and poor PHA storage ability. While, under SRT of 10 d and low organic loading rate (2.7 g COD/L/d), bulking sludge possessed high PHA storage capacity. After 102 daysoperation, sludge from SBR could accumulate PHA to 53% of TSS, under ammonia starvation, with average storage rate of 0.19 mg COD/mg X/h and yield of 0.76 mg COD/mg COD. However, another SBR operated in parallel with anaerobic-aecobic pattern suddenly failed after 55 daysoperation.When using cane sugar to simulate molassess as the substrate, after anaerobic fermented, for PHA production, the CSTR gradually stablized towards ethonal-type fermantation one month after startup. The effluent was clarified with hollow fiber membrane and then was used for culture selection and PHA accumulation, thus coupling bio-hydrogen production with PHA production system was achieved. The TSS in SBR rised up to more than 8000 mg/L from 3300 mg/L with organic loading rate of 4.2-4.5 g COD/L/d and SRT of 10 d. Although DO was maintained above 3 mg/L in feast phase, sludge bulking still happened after 30 daysoperation. This may be caused by high sludge concentration. Bulking sludge exhibited higher rates in substrate uptake, PHA storage and biomass proliferation than well-settling sludge, about 2 times than the latter. When SBR run 25 days after inoculation, the whole system could produce 16 L H2 and 0.1 kg COD PHA using 1 kg COD cane sugar. The HV weight proportion of PHA was 24% approximately.【关键词】聚羟基烷酸脂 混合菌群 污泥膨胀 生物制氢 PHA合成【英文关键词】polyhydroxyalkanoates mixed microbial culture sludge bulking bio-hydrogen production PHA synthesis【目录】两段式和三段式工艺制取聚羟基烷酸酯的试验研究摘要4-6Abstract6-7第1章 绪论11-311.1 课题背景11-121.1.1 课题来源111.1.2 课题研究目的和意义11-121.2 PHA 概述12-191.2.1 PHA 结构与性质12-141.2.2 细胞储存PHA 的微生物学意义14-151.2.3 微生物合成PHA 的代谢机制15-181.2.4 PHA 的提取回收18-191.3 混合菌群合成PHA 国内外研究现状19-291.3.1 底物选择19-201.3.2 工艺流程20-221.3.3 工艺运行策略22-251.3.4 影响因素25-291.4 主要研究内容29-31第2章 实验材料与方法31-362.1 实验装置及运行工况31-332.1.1 实验装置31-322.1.2 主要设备仪器32-332.2 检测方法33-362.2.1 PHA 的检测332.2.2 乙醇-VFAs 的检测33-342.2.3 气体成分检测342.2.4 其他常规指标的测定与分析方法34-36第3章 两段式PHA 制取工艺优化36-493.1 氨氮限制方式对PHA 积累的影响36-393.1.1 实验工艺控制36-373.1.2 污泥性状的变迁37-383.1.3 限制进水氨氮下PHA 的循环积累38-393.2 PHA 积累期厌氧-好氧与好氧运行方式的对比39-413.2.1 实验工艺控制39-403.2.2 底物消耗与PHA 积累40-413.3 短污泥龄、短周期的污泥适应期41-453.3.1 实验工艺控制423.3.2 污泥性状的变迁42-433.3.3 底物消耗与PHA 积累43-453.4 污泥水解液用于两段式工艺45-483.4.1 实验工艺控制45-463.4.2 底物为污泥水解液时PHA 积累情况46-483.5 本章小结48-49第4章 以乙酸钠为底物富集产PHA 混合菌群49-634.1 实验工艺控制49-5