孢子化技術於MICP處理之可行性探討

Abstract

微生物誘導碳酸鈣沉澱 (Microbially Induced Carbonate Precipitation, MICP) 為一種具環境友善與可持續性的地盤改良技術，其透過尿素酶細菌分解尿素產生碳酸鈣以膠結土壤。然而，現行 MICP 工法多以營養細胞型菌液為主，受限於其對環境條件高度敏感，在保存、運輸與反應控制上皆面臨挑戰，並易造成沉澱集中與改良不均等問題。為突破此瓶頸，本研究提出以 Sporosarcina pasteurii 孢子替代營養細胞作為改良菌體來源，並進行一系列涵蓋孢子形成、乾燥保存、萌發特性與應用效果之系統性實驗，評估孢子型菌液於 MICP 工法中之可行性與工程潛力。

本研究首先針對五種誘導培養基進行篩選，並以不同培養天數與加熱條件處理後之平板計數及顯微鏡影像評估孢子形成率。結果顯示，以 NB_ion 培養基培養五天最具孢子形成之表現，且經 50°C 加熱 15 分鐘可有效抑制營養細胞，以製備純孢子型菌液。於乾燥處理部分，經比較四種不同處理方式，選定冷凍預處理後冷凍乾燥法為最適方法，其能成功將孢子保存為粉末型態，且復水後仍保有良好萌發能力。應用層面以小型土壤試體進行改良實驗，分別針對營養細胞與孢子型菌液設計不同養護天數組別，評估其碳酸鈣沉澱量與深度分佈變異。結果顯示，養護七日後孢子組之碳酸鈣總量與營養細胞組相近，且沿深度之含量變異性較小，變異係數 (Coefficient of Variation) 明顯較低，顯示孢子型菌液具延遲活化特性，有助於提升沉澱均勻性與改良品質穩定性。

整體而言，孢子型菌液具備高保存性、反應時程延長與空間分布均勻之優勢，為 MICP 工法提供具實務可行性與應用潛力之替代菌體形式。本研究成果有助於突破 MICP 技術現有瓶頸，推動其於地盤改良工程中之應用深化與規模化發展。

Microbially Induced Carbonate Precipitation (MICP) is a ground improvement technique considered to have potential environmental friendliness and sustainability. It utilizes urease-producing bacteria to hydrolyze urea, resulting in calcium carbonate precipitation that binds soil particles. However, current MICP applications predominantly rely on vegetative bacterial cells, which are highly sensitive to environmental conditions and face challenges in preservation, transportation, and reaction control. These limitations often lead to concentrated precipitation near injection points and non-uniform soil improvement. To address these issues, this study proposes using Sporosarcina pasteurii spores as an alternative bacterial form, and conducts a series of systematic experiments covering spore formation, drying preservation, germination capacity, and application performance to evaluate the feasibility and engineering potential of spore-based MICP treatment. The study first screened five types of spore-inducing media, and evaluated spore formation efficiency by subjecting cultures to varying incubation durations and heat treatment conditions, followed by plate counting and microscopic observation. Results indicated that cultivation in NB_ion medium for five days followed by heat treatment at 50°C for 15 minutes effectively suppressed vegetative cells and produced a stable, spore-only bacterial suspension. For drying preservation, four methods were compared, and freeze-drying after pre-freezing was selected as the optimal approach. It successfully preserved spores in powder form while maintaining high germination capacity upon rehydration. In the application phase, small-scale sand specimens were treated with both vegetative and spore-based bacterial solutions under different curing durations. The total calcium carbonate content and its depth-wise distribution were analyzed. After seven days of curing, the spore-treated group achieved a comparable calcium carbonate yield to the vegetative group, while exhibiting lower variation along depth, as evidenced by a lower coefficient of variation (CV). These findings highlight the delayed activation characteristics of spores, which contribute to more uniform precipitation and improved treatment quality. Overall, spore-based bacterial solutions offer high storability, extended reaction control, and better spatial distribution of precipitation, making them a viable and promising alternative for MICP applications. The results of this study help address current limitations in bacterial preservation and uniformity control, advancing the practical development and scalability of MICP-based ground improvement.