【作者】 蔡萌萌；

【导师】 蔡宏；

【作者基本信息】 哈尔滨工业大学 ， 环境工程， 2009， 博士

【摘要】 塑料制品是人们日常生活和工农业生产的必需品。广为使用的石油基塑料造成了严重的环境污染,消耗了大量不可再生资源。聚羟基烷酸酯(Polyhydroxyalkanoates, PHA)是一种生物制备型的环境友好塑料,可完全生物降解,具有和传统塑料相近的物化性质和加工特性,所需底物为可再生有机质。因此PHA是石油基塑料的理想替代品,具有广阔应用前景。纯菌种合成PHA是目前工业化制备PHA的主流。高昂的生产成本制约了PHA作为日常用品得到广泛应用。此外,市政废水处理厂每天产生大量剩余污泥,污泥处置费用高。选择廉价的、可再生且来源广泛的废物作为PHA合成用底物、利用活性污泥中的混合菌群作接种体合成PHA、优化PHA合成工艺的运行条件,都有利于大幅降低PHA生产成本,实现废物和剩余污泥的减量化和资源化。本研究的目的即为同时实现PHA生产低成本化,以及废物及剩余污泥资源化。主要研究内容和结论如下:通过剩余污泥利用人工废水合成PHA的小试研究,考察了影响PHA产量、底物转化率和PHA单体组分含量的工艺参数。结果表明,好氧、高碳氮比、多次投加碳源底物、弱碱性条件有助于提高PHA产量。在此条件下,活性污泥合成PHA的产量与纯菌种合成PHA的产量及物化性质接近,且PHA合成产率高于纯菌种。通过工艺调控,活性污泥可以合成含有特定单体组分的PHA。好氧时,短链脂肪酸中碳原子的数目决定聚(-β-羟基丁酸-co-β-羟基戊酸)(Poly(β-hydroxybutyrate-co-β-hydroxyvalerate),PHBV)中的单体组分。溶解氧浓度(dissolved oxygen, DO)降低、pH值升高,PHBV共聚物中的羟基戊酰含量(hydroxyvalerate%, HV%)会增加,且与碳源类型无关;污泥来源、碳源与氮磷浓度比的变化会影响羟基烷酸(hydroxyalkanoate, HA)单体组分的含量。结合上述试验结果,采用批式好氧动态底物投加工艺,对剩余污泥作为接种体利用污泥消化液中的挥发性有机酸(volatile fatty acids, VFAs)以及食品废液合成PHA进行了工艺优化研究。通过投加镁盐形成鸟粪石沉淀,污泥消化液中过量的氮磷得到去除和回收,以提高污泥消化液的碳氮比。碱性条件和较高的消化温度可以提高污泥消化液中的VFAs产量以及氨氮去除率。污泥消化液中VFAs的主要成分是乙酸。利用剩余污泥消化液中的VFAs合成的PHA的最大产量可达到56.5%(占VSS比重)。活性污泥和纯菌种利用麦芽废物作碳源合成的PHA产量比其它种类的食品废液都高。随后对剩余污泥利用实际废液合成的PHA产物进行了物化加工性质分析。为了优化活性污泥合成PHA的单体组分,在总结了纯菌种合成PHA的代谢机理的基础上,模拟了活性污泥合成PHA的生化代谢途径。为了预测活性污泥合成PHA的产量和产率,通过改进活性污泥三号模型(Activated Sludge Modeling 3, ASM3模型)和优化PHA合成工艺参数,建立了活性污泥合成PHA的反应动力学模型。并通过小试试验验证了该模型的准确性。研究结果表明,污泥在厌氧时摄取乙酸会合成HV的代谢机理是,通过“琥珀酰-CoA→丙酰-CoA”反应,部分乙酸转化为丙酰-CoA,成为PHBV中HV的前体物。外界工艺条件改变,会影响活性污泥中的混合菌群的结构和代谢途径,进而改变活性污泥合成的HA单体组分。通过试验验证,活性污泥合成PHA的动力学模型可以较为准确地预测PHA的产量、产率、底物转化率和细胞生长量。剩余污泥利用污泥消化液合成PHA工艺的工业化,有助于实现实际废液和剩余污泥的资源化,推动PHA作为普通包装材料得到应用,具有良好的经济效益和社会价值。相对于纯菌种以及活性污泥利用人工废水合成PHA,剩余污泥利用污泥消化液合成PHA工艺,可以节约的成本包括:合成PHA的碳源成本、PHA合成反应构筑物建造和运行成本、剩余污泥处置成本、微生物筛选/富集培养成本,同时得到鸟粪石结晶沉淀副产品。更多还原

【Abstract】 Plastic product is applied widely in the daily life and industrial and agricultural manufacture. In response to the problem and harmful effects of the plastic wastes on the environment, there is considerable interest in the development of biodegradable plastics. Among the various biodegradable polymer materials, polyhydroxyalkanoates (PHA) provide a good fully degradable alternative to petrochemical plastics. The properties of PHA are very similar to those of polyethylene (PE) and polypropylene (PP). PHA is fully biodegradable, and transformed from renewable raw materials. Thus, PHA is a kind of environmental- friendly plastics and a good substitute to the traditional plastics, therefore having the potential to be widely applied in the future.Recently, PHA has been industrially produced mainly by pure cultures as inoculation. Wider use of PHA is prevented mainly by their high production cost compared with the oil-derived plastics. Otherwise, the excess sludge generated from the world-wide municipal wastewater treatment plants is plenty and the disposal cost for the excess sludge is very high. Choosing cheap, reusable and common waste material as the carbon source, using the populations in the activated sludge as inoculation, and optimizing the PHA production process parameters is attractive to produce PHA with significant reduced cost, to reduce and reuse waste material, and to decrease both the environment harm and the consumption of the non-renewable resource resulting from the traditional plastics.The aim of this study is to realize the reduction of both costs for PHA production and the amount of real waste, as well as the reuse of excess sludge. The main content and results are listed as following:The PHA production by excess sludge process parameters influencing the PHA yield, PHA productivity, carbon source transform rate and the copolymer composition was discussed from the lab-scale experiments utilizing synthesized wastewater. Results showed that, adjusting these process parameters is essential for increasing PHA yield and regulating the monomer composition of the PHA copolymer. Aerobic, high ratio of carbon to nitrogen and dynamic feeding pattern was helpful to increase the PHA yield. Under these conditions, the yield of PHA produced by activated sludge was similar to that obtained from pure culture. Moreover, the specific PHB production rate was one order of magnitude higher than that reported for pure cultures. Certain monomer composition of PHA could be obtained by control the process operation parameters. Aerobically, the fraction of the hydroxyvalerate monomer in Poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) depends on the carbon atom number of the short chain fatty acids. The variation of dissolved oxygen (DO) concentration influenceed the metabolic pathway of PHA production by activated sludge significantly. The increase of pH value and the decrease of DO led to the increase of HV% in PHBV, which was independent of the type of carbon source. The sludge source as inoculation and the ratio of carbon to nitrogen also influenced the composition of PHBV.According to the experiment results of the above studies and the mechanism analysis of both metabolic and kinetic modeling for PHA production by activated sludge, a new process was developed to optimize the yield of PHA and the monomer composition using real wastewater as carbon source. One of the real wastewater was excess sludge fermentation liquid generating from alkaline anaerobic thermophilic sludge digestion, and the other was food waste. The excess sludge as inoculation was not acclimated before being used to synthesize PHA. To increasing the ratio of carbon to nitrogen in the sludge fermentation liquid, the excess ammonia and phosphate was recovered by adding Mg2+ to form the deposition of strive. Alkaline and thermophilic condition could enhance the yield of volatile fatty acids (VFAs) and the removal rate of the ammonia in the excess sludge fermentation liquid. The main component of the VFAs in the sludge fermentation liquid was acetate. The maximum yield of PHA produced by excess sludge from sludge fermentation liquid was 56.5% (fraction of the Volatile Suspended Sludge, wt%). Malt waste was the most popular carbon source for PHA production by excess sludge and the pure culture, which means malt waste led to the maximum PHA yield by these bacterial. The PHA product generated from real waste by excess sludge was analysized to penetrate their physical-chemical characteristics.To regulate the PHA copolymer composition, the metabolic pathway for PHA synthesis by activated sludge was simulated based on the metabolic mechanism analysis of PHA synthesis by pure culture. To optimize and forecast the yield and productivity of PHA produced by activated sludge, based on the modification of the Activated Sludge Modeling Number 3 (ASM3), a simple kinetic mathematical model was developed for PHB production process by mixed cultures with sufficient accuracy for supporting model-based optimization studies. The mechanism for the acetate uptaken from the outside was transformed anaerobically to be form hydroxyvalerate (HV) was explained as such: intracellular acetate was metabolized through a converse reaction in TCA cycle as“succinyl-CoA→propionyl-CoA”to become propionyl-CoA, which is the prior of HV in PHBV. The change of process operation conditions influenced the community structure and metabolic pathway of the mixed cultures in the activated sludge, led to the variation of hydroxyalkanoate (HA) composition and yield. The kinetic model presented here for PHA production by activated sludge could forecast the PHA yield, PHA productivity, the carbon source transform rate and the biomass yield for accurately, which was improved by lab-scale experiments.The industrial-scale production of PHA from sludge fermentation liquid by excess sludge establishs the sustainably economical and social value, due to the realization of the reduction and reuse of real waste and excess sludge, as well as the wide application potential of PHA product as common package material. Comparing with the PHA production by pure culture and by activated sludge from synthesized wastewater, the PHA production cost by excess sludge as inoculation and sludge fermentation liquid as carbon source was low enough. The saving cost of the PHA production by excess sludge from sludge fermentation liquid includes, the carbon substrate cost, the PHA production process configuration and operation cost, the excess sludge disposal cost, the bacterial selection and enrich cost. The strive is the byproduct during operation.更多还原