Freshwater microalgae growth and Carbon dioxide Sequestration

對永續發展、環境保護及生命支持系統(life supported system)之維護，藻類生物科技(eco-tech)在二氧化碳減量上，展現了肩負眾人期望的替代選項以維護生態系中碳循環之生態功能。本研究基於生態系統動態平衡觀念下，使用跨領域科技的研究優勢探討自然水體培養基質，發展有效利用空氣中二氧化碳的生態科技潛力，進一步推測解決現在科學下無法了解的神祕碳儲存(Unidentified carbon sink)問題。 本研究以三個不同的研究重點：藻類生長與測量(Algae Growth and measurement)、生物固定二氧化碳(CO2 biofixation)和生物統計學(Biostatistics)，研究淡水藻類於淡水水體(freshwater body)的生長與碳循環之生態功能。利用天然水體培養基質且不添加額外營養鹽，在實驗室建立最簡單生態系統之連續攪拌混合反應槽(CSTR)模擬自然界中湖泊之自然水體。本生態系統模擬證明淡水水體中藻類不只增加生物質量(Biomass) 並可提升生物固碳。連續攪拌混合反應槽之二氧化碳利用率(CO2 uptake rate)可達到175 mgL-1day-1，以及其穩定的二氧化碳消耗效率(CO2 Consumption efficiency )高達131%，顯示連續攪拌混合反應槽在生物固碳作用的優越能力。在數學統計分析中，本研究也確認，由實驗室建立的仿生態系統之生物反應器(bio-reactor)，比文獻中提及的一般人工培養基質，具有更佳的二氧化碳利用率與消耗效率，其原因為大自然反應程序被複製到實驗室中顯示出生態系自然選擇(natural selection ) 演化的最佳化原則。 大規模培養藻類來進行生物固碳作用(CO2 biofixation)，代表了先進的生物、生化與生態處理程序，可直接利用大氣中的二氧化碳。本研究證實所有消耗的碳源均來自空氣，證明生態系的自然基質可利用碳循環消耗二氧化碳做為碳源，比人工培養基質具有較高的固碳效率。這項研究也顯示，在天然培養基質中，藻類固碳作用已經超越了培養基質中的碳營養限制( limited carbon nutritious)，而直接吸收空氣中的二氧化碳，佔藻類生物量中碳含量的100%。經過一系列有系統的生物統計迴歸分析與通過F test的迴歸係數(-0.01 by TSS and -0.02 by VSS)檢定，證明二氧化碳消耗效率隨時間變化的一致性。更進一步地，以碳質量平衡(carbon mass balance)之數學計算其二氧化碳儲存量，不只解釋推論科學界的神祕儲存謎團，並且探討解答淡水藻類的二氧化碳固存生態角色(algal niche)。因此，配合集水區經營管理的科技以應用淡水藻類二氧化碳封存的生態工程於永續工程之國土規劃中，以解決大氣中二氧化碳所產生的溫室氣體及極端氣候效應。 關鍵詞：藻類，生物質量，天然水體培養基質，藻類生態角色，生物固碳作用，生物反應器，淡水水體，生物科技。 (Translated by許振峰Jerry、周孟融Caroline)For the sustainable development and environment protection, and life support system, microalgae biotechnology appears as a promising alternative for carbon dioxide (CO2) mitigation. This study took advantage of the multidisciplinary technology to accomplish the management with multiple purposes based on dynamic balancing in ecosystem to maintain the ecological functions of the carbon cycle. This study is based on the concept of ecosystem homeostasis, using interdisciplinary scientific and technological research. This study demonstrated that in natural freshwater medium, the extent of microalgal carbon fixation transcended the substrate limitation by directly absorbing CO2 from air and thus the carbon in the microalgal biomass (100%) was solely derived from atmosphere. Furthermore, our results suggested that the freshwater microalgal carbon fixation could account for a significant portion of the “remaining unidentified” carbon sink. The work focuses on three distinctively different processes (i.e Algae Growth and measurement, CO2 biofixation and Biostatistics) to study on freshwater algae function. The utilization of natural water medium, which came from water body directly without any extra nutrition addition, demonstrated the potential to adopt the algal function for CO2 bio-fixation in a lab reactor. The continuously stirred tank reactor (CSTR) achieved the high algal biomass production. The growth system was achieved high CO2 uptake rate of 175 mg/L/day and stable consumption efficiency of 131. CSTR was displayed the impressive potential of the CO2 biofixation. By the mathematical/ statistical analyses, this study confirmed the lab systems which mimicked the ecosystem could have better uptake rates and consumption efficiencies than the general systems in literature with artificial medium because the natural process was replicated inside the lab. Biofixation of CO2 by microalgae mass cultures represents an advanced, physicochemical, biological and ecological process that enables directly to utilize CO2 from the atmosphere. This study demonstrated that over 100% carbon source from the air was consumed. We found the natural medium system achieved much higher carbon fixation efficiency than artificial medium using CO2 as the sole carbon source. This study demonstrated that in natural medium, the microalgal carbon fixation transcended the substrate limitation of the medium, directly absorbed the CO2 from air and achieved the 100% carbon of algae biomass. Furthermore, we demonstrated the consistency of CO2 consumption efficiency with time by regression analyses and passed the statistical F tests with a near zero negative of regression coefficients (-0.01 by TSS and -0.02 by VSS) for systematical succession. The results of the present investigation of the freshwater algal niche of CO2 sequestration could explain the discrepancy of the “remaining” sink mystery conceptually and mathematically. Thus, the freshwater algal niche of CO2 sequestration can be employed to reduce the greenhouse gas of atmospheric CO2 and in ecological engineering measures including land use planning of watershed management.Content Page Abstract i Contents v List of tables xi List of figures x Chapter 1 Introduction 1 Chapter 2 Literature review 3 Chapter 3 Methodology 32 Chapter 4 Growth and measurement 37 4.1. Chlorophyll is not accurate measurement for algal biomass 38 4.2. Biomass of algae growth on natural water medium 48 Chapter 5 CO2 biofixation 64 5.1. Freshwater microalgae niche of air carbon dioxide mitigation 65 5.2. CO2 fixation of freshwater algae growth 79 Chapter 6 Biostatistics analysis 102 6.1. Statistical study of relationships between microalgal biomass and growth conditions 103 6.2. Factor study of algal CO2 fixation in algae growth 109 Chapter 7 Conclusions 121 References 12