Abstract: With the development of modern energy, the use of clean and renewable new energy has gradually become the main idea to solve environmental and energy problems. Among the many new energy sources, biomass energy not only reduces greenhouse gas emissions, but also has good renewable properties. Microalgae is an ideal preparation of biomass raw materials which can grow fast and are rich in oil. However, their density are close to water making harvesting difficult. Harvesting difficulty is one of the main constraints on the development of the microalgae industry. In this study, a flotation method based on bead flotation is using a re-frying oil emulsion as flotation beads for harvesting Chlorella vulgaris. The re-frying oil will be fully emulsified with pure water in a certain proportion under the action of emulsifier. Combining with the response surface method, the significant factors affecting the harvesting efficiency were screened as pH, stirring rate, and proportion of protoalgae; the significant factors affecting the enrichment ratio were pH, flotation time, and proportion of protoalgae. The optimal harvesting efficiency and enrichment ratio were obtained as 92.79% and 2.07%, respectively. By taking Chlorella vulgaris as the research object, using XDLVO theory (extended Derjaguin-Laudau-Verwey-Overbeek), the mechanism of action between re-frying oil floating beads and Chlorella vulgaris was discussed. The mechanism of harvesting microalgae by re-frying is that microalgae and buoy beads form aggregates by electric neutralization and bridging due to of aluminum ion. The microalgae and the buoy beads first approach each other under the action of kinetic energy provided by stirring, and then by van der Waals force to adhere. The gravitational action reaches the critical value at 14.73 nm. The harvesting cost is only 4.38 ￥/t under the optimal harvesting conditions. This method reduces the harvesting cost and energy consumption which provides a method for the reuse of re-frying oil.

Key words: Microalgae, harvesting, Re-frying oil, Emulsion, Buoy bead flotation method, response surface method

摘要： 随着现代能源发展，使用清洁、可再生的新能源逐渐成为解决环境和能源问题的主要思路。在众多新能源中，生物质能不仅可以降低温室气体排放，还具有良好的可再生特性，小球藻作为一种理想的制备生物质能，不仅生长速度快，且油脂含量高。但因其密度与水接近而导致采收困难，这也成为制约微藻产业发展的主要原因之一。以浮珠浮选法为基础，提出一种以复炸油乳化液为浮珠的浮选法用于采收小球藻，即将复炸油与纯水按照一定比例在乳化剂作用下充分乳化，并结合响应面法，筛选出影响采收率的显著因素为pH、搅拌速率和原藻体积占比；影响富集比的显著因素为pH、浮选时间和原藻体积占比；同时结合多目标优化结果得出最佳采收率和富集比分别为92.79%和2.07%。以小球藻为研究对象，获得复炸油采收微藻机理：微藻与浮珠在铝盐的作用下，通过吸附电中和及桥接作用形成聚合体；微藻与浮珠首先在搅拌提供的动能作用下相互靠近，之后在范德华力作用下发生黏附，在14.73 nm时引力作用达到临界值。在最佳采收条件下，处理成本仅为4.38元/吨，降低采收成本和能耗的同时也为复炸油再利用提供了一种新方法。

关键词: 微藻, 采收, 复炸油, 乳化液, 浮珠浮选法, 响应面法