自製濁度計量測三種微藻濃度變化之研究

Abstract

微藻一直是健康食品的重要原料，近年更發現部分微藻含有大量油脂適合產製生質柴油，吸引大量資金投入微藻養殖產業。然而微藻養殖需要人工耗時費力進行濃度變化的檢測工作，不易達成自動生產目標。微藻皆以單一物種養殖，適合使用濁度進行微藻濃度評估，過去以濁度法評估微藻濃度時，皆以濁度計或濁度儀進行藻水的濁度檢測，必須採樣且無法連續計測；近年研發出之手持式濁度計，省去檢測過程之採樣並可測得即時濁度。 本研究使用捷騰光電公司研發的TBS-200濁度感測器，搭配必要之類比數位轉換元件、顯示模組、微控制器等，自製手持式濁度計。針對使用過程中環境光可能的干擾，以及感測器的輸出電阻進行實驗，決定自製儀器的計測方式與感測器規格。製作適用於微藻濃度計測的手持濁度計，其成本低於新台幣2000元。 本研究選擇周氏扁藻(Tetraselmis)、等鞭金藻(Isochrysis)、紅球藻(Haematococcus)等三種具經濟價值之微藻進行計測研究。以微藻檢測中常用的鏡檢法計測藻個數，乾燥秤重法檢測藻重量，自製濁度計及市售HACH 2100N實驗室濁度儀計測濁度，評估以自製濁度計計測濁度方式，監測三種微藻濃度的可行性。 實驗結果，使用自製濁度計需以黑樣本瓶進行計測降低環境光干擾；藻水濁度大於50 NTU時濁度讀值的變異係數會小於10%，呈現較穩定的結果。微藻的大小對濁度影響顯著。自製濁度計的讀值低於HACH 2100N濁度儀計測結果；濁度與藻個數的二次多項式迴歸為正相關，R^2值分別為周氏扁藻0.99、等鞭金藻0.983、紅球藻0.976，與藻重量的二次多項式迴歸結果，R^2值分別為周氏扁藻0.937、等鞭金藻0.981、紅球藻0.963，證實本研究之自製濁度計應可作為快速評估純種微藻濃度之工具。

Micro-algae have long been important ingredients of health food. In addition, considerable amount of lipid in their cells is found to be a promising source of bio-diesel fuel, therefore ever-increasing budget has been put into micro-algae culture industry in recent years. Nevertheless, given that recording and monitoring concentration of suspending cells remain tasks performed manually, both laborious and time-consuming, the ideal goal of automated micro-algae production would be arduous to achieve. Monoculture is the typical way adopted in micro-algae culturing, as such, turbidity is a suitable indicator in evaluating cell density of an alga-suspension. Although several kinds of turbidimeters have been available in practical use, most of them mandate repeated samplings that are inconvenient in a budget-limited, field-based, full-time monitoring program. With the handheld turbidimeter entering the market, such impediment seemingly would no longer exist, not only does it simplify routine monitoring by omitting the necessity of repeated samplings but it also can provide instantaneous and less interrupted recording data. In this study, several inexpensive, sturdy and ready-made components including TBS-200 Turbidity sensor(Solteam Opto. Co.), Analog-to-Digital Convertor(ADC), LCD module, Microcontrolling Unit(MCU) etc, are used to assemble a low-cost prototype of handheld turbidimeter. The possible disturbance of ambient light and its effect on output electric resistance of the turbidity sensor are especially taken into account on experiment designing. The prime cost of such a workable handheld turbidimeter is less than 2000 NT dollars. Three species of micro-algae with economic potential, including Tetraselmis, Isochrysis and Haematococcus are selected in our study. In addition to cell counts determined under microscopic examination and net weight obtained from desiccated alga mass, the turbidity data measured repectively by laboratory turbidimeter HACH 2100N and our prototype turbidimeter are compared in order to assess feasibility of the latter in monitoring micro-algae concentration. The results reveal that to eliminate the disturbance caused by ambient light the sensor of our prototype handheld turbidimeter must be operated in a black sampling bottle. The coefficient of variation of readings is less than 10% when the turbidity is more than 50 NTU. Different grain sizes of various micro-algae species also have a remarkable influence on turbidity readings. Our prototype handheld turbidimeter shows a consistently lower reading value than that of HACH 2100N. Analysis between turbidity readings and cell counts with quadriatic regression manifests a positive correlation, the R2 value for three micro-algae species are : Tetraselmis 0,99; Isochrysis 0.983; Haematococcus 0.976. The R2 value for turbidity and net weight are: Tetraselmis 0,937; Isochrysis 0.981; Haematococcus 0.963. These results support the conclusion that our prototype handheld turbidimeter could be a useful tool to promptly evaluate the concentration of single-species microalgae.