微藻动态载体高密度富集的污水深度净化研究

Microalgae-based wastewater treatment technologies provide an elegant solution for advanced wastewater purification with features of low energy & resources consumption, capture of CO2 and production of high value biomass, etc. However, low culture density, difficulty in biomass harvesting and community control handicapped its potential of industrial application. Aiming at high density microalgae enrichment, this study will theoretically figure out key scientific issues toward the culture density, biomass separation and community control. Then, the controlling factors (carrier filling ratio, turbulence and bacteria/higher microorganisms) on the development of photo-biofilm will be experimentally explored. It is followed by the exploration on mechanisms and operational conditions of autofloccutation and selective sedimentation, which could not only resolve the biomass loss problem, but also provide a powerful method in regulating the cell growth rate/phase and activities. Furthermore, microalgae community structure and its changes under mixed culture condition with real wastewater will be revealed. This will provide critical information on determining the ultimate utilization of the harvested microalgae biomass(for example, methane-producing or oil-producing), and lay the foundation for the subsequent exploration for enrichment of the targeted species.

微藻污水深度净化有着低能耗、低消耗、固定CO2，产生生物质能等独特优势。然而，培养密度低、藻细胞分离困难及混合培养种群控制困难等问题却限制了其工程化应用的潜力。本课题以微藻高密度富集培养为核心，理论上解答"藻细胞培养密度低"、"藻细胞分离困难"及"混合培养种群控制困难"等关键科学问题。实验上揭示载体填充比、水流紊动性及细菌/高等微生物对光生物膜发展的影响；探明自发性絮凝和选择性沉淀等高效"原位"分离手段的机理和控制条件，从而解决藻细胞流失难题，并为调控藻细胞的生长速率、生长阶段和活性等要素提供强有力的手段；探究实际污水混合培养下的微藻群落结构及其变化，为确定藻细胞的最终利用方式（如产甲烷或产油）提供关键信息，并为后续实现目标种属的富集奠定基础。

藻细胞分离采收困难是微藻生物技术在污水深度处理和生物质能生产中难以工程化的主要瓶颈。本项目在序批式光生物反应器通过调控沉淀时间及体积交换比创造了淘汰缓慢沉降种属的环境压力，在混合培养中实现了对可沉降微藻种属的选择性富集。所富集的可沉降微藻具有极佳的沉降性能，重力沉降效率>97%，SVI为17-50。研究发现，高体积交换比是实现快速富集可沉降微藻的关键运行参数。体积交换比也是序批式光生物反应器中微藻种属结构的控制因素。高体积交换比（0.5，0.7）能在反应器中形成较高的硅酸盐浓度，利于可沉降硅藻成为优势种属。低体积交换比（0.2）利于可沉降蓝藻成为优势种属。在高效沉降分离的基础上，实现了5-11 g/L的高密度培养。培养密度为传统高效藻类塘（0.2-0.6 g/L）的10倍以上。可沉降微藻在水力停留时间≥2 d的处理能力上，稳定实现了出水硝酸氮≤2.2 mg/L，出水磷酸盐<0.1 mg/L的处理效果。所富集的直链硅藻具有良好的生物柴油生产潜力，在本研究的实验条件下实现了12.4-14.6 mg/L/d的油脂产率，显著高于文献报道的以二/三级出水为底物培养的其他产油藻的油脂产率（0.3-4.9 mg/L/d）。水中可利用无机碳源不足是硝酸氮去除不彻底和油脂含量（10%）偏低的主要原因。可通过人工补充CO2等方式加以克服。总之，本课题的研究成果为克服藻细胞分离采收问题提供了简单、高效的方法，具有良好的工程化前景。