A Novel Membrane Biofilm Reactor for Microalgae Cultivation and Harvest and Wastewater Treatment

藻类产业是全球经济的重要组成部分。除了生物产品外，藻类在生物能源和废物管理部门（从废水中去除营养物质和减少温室气体（CO2））中的应用也日益得到认可。然而，悬浮微藻培养的细胞浓度很稀，通常小于0.5-2 g/L。因此，在开放池塘或封闭光生物反应器中生长的微藻需要大量的水和大量的能量投入，用于种植、收获和脱水。据估计，20-30%的微藻生产成本和约90%的设备成本分别与藻类生物量的收获和脱水有关。因此，为了提高微藻生产的经济性，迫切需要新的微藻栽培、收获和脱水技术。藻类生物膜系统作为开放池塘和封闭光生物反应器的替代方案，因其具有生物量密度高、易于收获、生物量生产力提高等独特的特点，近年来备受关注。微藻生物膜（MB）的主要优势在于较高的细胞浓度（高达悬浮细胞浓度的100倍），这大大减少了收获的努力，因为MB可以简单地从表面刮掉或抽真空，无需进一步浓缩即可使用。然而，MB的高细胞密度需要更大的CO2量和更快的传递速率来促进生物膜的生长。传统的CO2气体直接鼓泡进入光生物反应器或微藻池的策略转移和利用效率较低，50% ~ 90%的CO2存在于大气中。因此，新的二氧化碳输送技术对于提高二氧化碳的转移和利用效率以及降低能源成本至关重要，特别是对于MB系统。提出的研究项目重点是开发一种新型的膜碳酸微藻生物膜生物反应器（MCMBR），用于微藻的培养、收获和废水处理。这种新系统利用疏水透气膜将分子CO2输送到生长在膜外表面的MB中，而营养物质（N和P）和光子则从相反的方向输送到MB中。这种新型生物反应器系统结合了高细胞密度生物膜系统的优点和通过膜（通过协同效应）的高CO2转移和利用效率，并且具有低能耗，因此可以实现目前微藻技术无法实现的更高工艺效率。本研究的成果是开发一种新型MCMBR系统，用于微藻的培养、收获、废水处理和温室气体（CO2）减排。这项研究将有利于加拿大的环境和能源行业，并在对加拿大至关重要的领域培养高素质人才。

The algae industry is an important part of the global economy. In addition to bioproducts, algae are increasingly recognized for their use in the bioenergy and waste management sectors (nutrients removal from wastewater and abatement of greenhouse gas (CO2)). However, the cell concentration of suspended microalgae culture is very dilute and usually less than 0.5-2 g/L. Consequently, microalgae grown in open ponds or closed photobioreactors require large volumes of water and a significant amount of energy input for cultivation, harvest, and dewatering. It is estimated that 20-30% microalgae production cost and about 90% of the equipment cost are associated with the harvest and dewatering of algal biomass, respectively. Thus, novel technologies for microalgae cultivation, harvest, and dewatering are highly desirable to improve the economy of microalgae production. As an alternative to open ponds and closed photobioreactors, algal biofilm systems have drawn great attention in recent years, due to their unique features, such as high biomass density, easy biomass harvest, and increased biomass productivity. The key advantage of microalgal biofilm (MB) lies in the higher cell concentration (up to 100 times of suspended cell concentrations), which greatly reduces harvesting effort as the MB can simply be scraped or vacuumed off the surface and can be used without the need for further concentration. However, the high cell density in MB requires a larger amount and faster transfer rate of CO2 for biofilm growth. The traditional strategies of directly bubbling CO2 gas into photobioreactors or microalgae ponds have a low transfer and utilization efficiency with 50% to 90% CO2 existing back to atmosphere. Thus, novel CO2 delivery technologies are vital to increase CO2 transfer and utilization efficiencies and reduce energy cost, particularly for MB systems. The proposed research program focuses on the development of a novel membrane carbonated microalgal biofilm bioreactor (MCMBR) for microalgae cultivation, harvest, and wastewater treatment. This novel system utilizes hydrophobic gas permeable membranes to deliver molecular CO2 into MB grown on outside surfaces of the membrane, while nutrients (N and P) and photons are transported into the MB from an opposite direction. This novel bioreactor system combines the advantages of high cell density biofilm systems and a high CO2 transfer and utilization efficiency through membranes (via a synergistic effect) and has a low energy consumption and thus can achieve a much higher process efficiency that is not achievable with current microalgal technologies. The outcome of this research is the development of a novel MCMBR system for microalgae cultivation, harvest, wastewater treatment, and greenhouse gas (CO2) abatement. This research will benefit the Canadian environmental and energy industries and train highly qualified personnel (HQP) in areas that are critical to Canada.