- 學位論文
灼燒牡蠣殼消毒動力學及雨水回收抑菌裝置設計應用
Disinfection Kinetics and Development of a Treatment Module Using Heated Oyster Shell Particles for Microbial Inactivation in Rainwater Harvesting Systems
摘要
雨水收集系統(RWH)容易受到各種來源的汙染，對於雨水收集系統中的水質造成負面影響，進而影響到用戶的使用意願。研究指出雨水收集系統中的污染很大一部分是屬於生物性污染，包括對人體有害之有活性或不具活性之致病菌，但以目前的傳統消毒技術在有效性、成本和操作維護上並不足有效地應用於雨水收集系統中，並有可能產生對人體有害之消毒副產物。有鑑於上述限制，本研究將以低衝擊開發(LID)的方式，探討以灼燒之牡蠣殼(HOSP)顆粒來取代傳統的直接消毒技術，評估其對於抑制雨水收集系統中微生物生長的能力，本研究主要包含三部分，一是比較牡蠣殼灼燒前處理之相關條件對於殺菌能力的影響，二是在可控的批次式反應裝置下探討灼燒牡蠣殼顆粒的消毒動力速率，最後，則是以灼燒牡蠣殼顆粒作為材料，設計開發雨水回收抑制裝置，並在實驗室條件下評估其可行性與消毒能力。 牡蠣殼之灼燒溫度、灼燒牡蠣殼顆粒使用劑量及接觸時間等參數，在文獻中被認為對於抑制孢子生長能力有著顯著地影響，但在本研究中發現不同灼燒溫度的牡蠣殼顆粒抑菌能力並沒有顯著地改變，表示牡蠣殼中的碳酸鹽化合物物質在高溫下會迅速地轉化成氧化物。由批次式實驗的結果發現灼燒牡蠣殼顆粒之劑量與接觸時間，這兩項參數對於批次式系統中抑制微生物生長的能力有所影響，與牡蠣殼中CaO經過水合反應所產生的Ca(OH)2，能夠有效地抑制枯草桿菌孢子的生長。灼燒之牡蠣殼顆粒抑制細菌與病毒生長的能力優於枯草桿菌孢子，研究結果顯示在少於孢子達到3-log抑制效果的牡蠣殼劑量下，即可以完全地抑制細菌及病毒的生長。此外，在250~300小時的接觸實驗下發現灼燒牡蠣殼顆粒之殺菌能力為非線性並會自然地減少，消毒反應動力學近似於Hom’s model。在實驗室環境下研究灼燒牡蠣殼顆粒所開發之裝置實際應用於雨水回收可行性之結果顯示，在低流速及低灼燒牡蠣殼顆粒劑量條件下，使用本研究所開發之雨水回收裝置抑制微生物生長的能力與先前批次式的實驗結果相同。
並列摘要
Rainwater harvesting (RWH) systems are prone to contamination from various sources. Numerous studies have reported on the impact of these contaminants on the quality of rainwater harvested in RWH systems and their ensuing effects on the end user. It is also well documented that a significant portion of these contaminants are biological in nature, which comprise of sizeable fraction of viable and non-viable forms of pathogenic microorganisms capable of causing disease in living beings. Conventional disinfection techniques that treat such contaminants in the harvesting systems are often inadequate in one or more aspects of effectiveness, cost, operation, maintenance, or the production of harmful by-products that are detrimental to human health. In view of these limitations, and in a strategic effort to adopt Low Impact Development (LID) solutions to improve the microbial quality of rainwater contained in RWH storage systems, this study attempts an alternate direct disinfection setup for RWH systems by exploring and exploiting the disinfection potency of heated oyster shell particles (HOSP) against microbes in the harvested rainwater. The study demonstrates this idea in parts, by i) Studying the relative effects of key parameters for oyster shell heat activation and treatment conditions on the disinfection efficiency in aqueous system, ii) Determination of disinfection kinetics of HOSP in aqueous system in controlled batch setup for the purpose of application in disinfection, iii) Designing and developing a simple prototype for a direct rainwater contacting module integrating the heat activated oyster shell compound, i) Finally, a lab-scale controlled operation of the treatment module loaded with HOSP is performed to assess its function and disinfection efficacy. Key factors such as oyster shell baking temperature, HOSP treatment dosage and contact time in aqueous medium were observed to have significant influence on the sporicidal effect, consistent with prior studies on sea shells of comparable origin. Whereas, the effect of oyster shell baking time was identified to be insignificant in comparison, indicating that the rate of conversion of the carbonate compound in the shell material to oxide occurs rapidly at high calcination temperatures. From the effect of HOSP dosage and contact time on the microbicidal effect in batch system, it is understood that soluble compounds resulting from hydration of CaO, i.e. Ca(OH)2, in the treated medium affect B. subtilis spore survival significantly. Vegetative cells of bacteria and viral forms were highly sensitive to HOSP compared to spore form of bacteria. Results showed that complete inactivation of virus and vegetative forms of bacteria were attained rather quickly at HOSP doses at least a magnitude less compared to what was normally applied to achieve 3-log inactivation of spore forms of bacteria. Furthermore, sporicidal effect over a prolonged contact time of 250-300 hours was identified to be nonlinear and decelerating in nature, where Hom’s model of disinfection offered the closest fit compared to other non-linear models of disinfection kinetics such as Modified Chick-Watson or Collin Selleck’s. In the last part, feasibility for rainwater treatment using HOSP loaded treatment module was studied under controlled operational setup. The discharged quantity of the disinfectant and the corresponding disinfection rate observed at lower flow rates through the prototype correspond with the rate of inactivation at low dosage in batch test in the same test medium, indicating operational consistency.