再生水补水条件下过量营养盐生态影响的热力学评价研究

When reclaimed water is used for supplementation of water body, the problem of increased eutrophication potential caused by excess nutrient has received lots of attention. The occurrence of eutrophication is affected by many factors, thus quantitatively evaluate the ecological impact of nutrients is faced with problems. Based on the idea that the ecological impact of any contamination is the state change of water system from thermodynamic equilibrium to imbalances, this project studied the thermodynamic assessment of ecological impact of excess nutrients. By studying the conversion process of nitrogen and phosphorus uptake by typical algae in the water body, the conversion principle of biomass for nutrients was identified, and then the model of algae growth was proposed. For analysis of photosynthesis and energy transformation processes of typical algae growth, the biomass energy storage characteristics of algae cells was revealed, then the calculation model of energy consumption for algae growth was established. Afterwards, by studying the thermodynamic characteristics and entropy balance principle of algae growth, the calculation method of entropy increase under conditions of nitrogen limitation and phosphorus limitation were proposed. Finally, combined with the process analysis of a water body supplemented by reclaimed water, the model of thermodynamic assessment was established, and then the model was applied and verified. The results will provide new approaches and methodologies for environmental impact assessment and regulation of the ecological utilization for reclaimed water.

再生水用于水体补水，过量营养盐引起富营养化潜能增大的问题广受关注，但富营养化是否发生受多方面因素影响，使得营养盐生态影响的定量评价面临困难。本项目基于任何污染物的生态影响均为水体系统从热力学平衡转向失衡状态的观点，研究过量营养盐生态影响的热力学评价方法。通过水中典型藻类的氮磷摄取过程研究，判明营养盐的生物质转化原理，提出藻类生长过程模型；分析典型藻类生长的光合作用和能量迁移转化过程，揭示藻类细胞的生物质能量储存特性，建立藻类生长的能耗计算模型；研究藻类生长的热力学过程特点和熵平衡原理，提出氮、磷元素限制条件下的营养盐摄取过程熵增计算方法；结合再生水补水过程分析，构建热力学评价模型体系和模型计算方法，完成模型的应用与验证。研究成果将为再生水生态利用的环境影响评价与调控提供新的途径与方法。

水体富营养化问题使得对生态水体的环境影响评价迫在眉睫。本项目基于藻类的生长模型和氮磷摄取过程，研究了过量营养盐生态影响的热力学评价方法。本课题首先通过实验优选出小球藻作为典型藻种，通过测定其生长速率、外部氮磷浓度，得到了在自养和异养条件下普通小球藻的生长参数，建立了藻类生长的Monod模型。发现培养基中初始营养物含量的增加会提高普通小球藻的生长速率，影响微藻的干重和细胞内氮、磷的元素构成，并总结出普通小球藻的化学通式。然后分析了营养物浓度对藻类光合作用效率的影响，得到在实验氮磷浓度梯度下，初始氮浓度的供给对普通小球藻光合作用效率的影响更为显著；光合作用效率和电子传递速率与藻类的叶绿素含量变化一致。通过测定不同氮磷浓度下，藻细胞胞内营养物浓度，解释了细胞内部能量储存与氮、磷的关系，结合普通小球藻燃烧热和微量量热实验研究，提出了藻类生长的能耗模型，建立氮（磷）元素限制条件下营养盐摄取过程熵增计算方法。最后，将此方法应用于二级出水补水中营养物对水环境生态影响的案例研究，结果表明单位质量总磷对补水水环境的生态影响最为显著。本课题的研究成果为再生水补水条件下过量营养盐生态影响的热力学评价研究提供了理论基础和科学依据，对利用热力学熵评价水体富营养化的方法发展具有重要的理论意义。