Development of a portable LED fluorescence LIDAR system for Chlorophyll-a measurement in algal growth monitoring

• Main Author: Cadondon, Jumar G.
• Format: text
• Published: Animo Repository 2019
• Subjects: Chlorophyll—Analysis; Algal blooms—Monitoring—Philippines; Physics
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/6302; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/13372/viewcontent/Chapter1_VI_Development_of_aPortable_LED2.pdf
• Institution: De La Salle University

Algal blooms pose a major problem, as often instigated by pollution, changing temperature and growth dynamics of algae which leads to social and health problems. Given the importance of knowing how these blooms affect aquatic life, several active and passive remote sensing techniques using a variety of fluorescence measurements have been developed. Variation in chlorophyll-a is one major variable in algal blooms and water quality assessment in natural waters. Seasonal appearance of algal bloom has been observed in the Philippines. However, despite its possible consequences, there has been no studies on the non-invasive and in-situ technique that provides chlorophyll-a concentration in the country. This study focused on the development of the first portable LED fluorescence LIDAR system for chlorophyll-a measurement in algal growth monitoring. Unlike other LIDAR systems, which provides high power output, the transmitting pulsed light source is a 385-nm CW with bandwidth of 10.92 ns and repetition frequency of 475 kHz. An optical filter arrangement was used for the green alga, Chlamydomonas reinhardtii Dangeard (680-nm filter) and commercialized AZTEC Spirulina powder (700-nm filter) for chlorophyll-a measurements. An FPGA high photon counting board with resolution of 0.75nm was used to count the backscattered fluorescence LIDAR signal from the photomultiplier tube (PMT). C. reinhardtii, a green alga, was cultured at 12.5 % inoculum and prepared in an 8- L tank system with three replications. Environmental parameters such as temperature and relative humidity were simultaneously measured during (12h/12h) light/dark cycle conditions. The fluorescence LIDAR signal measurements of C. reinhardtii was conducted in this study during night conditions only, to lessen background noise measurements. Excitation emission matrix (EEM) fluorescence measurements coupled with Parallel Factor Analysis (PARAFAC) was used to extract components of algal organic matter and pigments. Several protein-like and humic-like substances, fluorescence indices, and chlorophyll-a pigment at excitation wavelength of 385-nm were used to correlate the growth dynamics of C. reinhardtii Also, cell density by absorbance spectroscopy (optical density) was also used to determine their growth phases. On the other hand, Spirulina powder was used to determine the linear relationship of the different chlorophyll-a measurements with the fluorescence LIDAR signal measurements at varying freeze-dried biomass. Commercialized AZTEC Spirulina at varying concentrations from 20 mg/L to 2000 mg/L also showed high correlation between range-resolved fluorescence LIDAR signal and EEM chlorophyll-a pigment (R2 = 0.9650), absorbance/optical density (R2 = 0.8958), and corrected chlorophyll-a concentration (R2 = 0.9421). The range-resolved fluorescence LIDAR signal of C. reinhardtii showed high exponential correlation with the EEM chlorophyll-a pigment at 680-nm having a coefficient of 0.8609 during the lag phase to stationary peak. On the other hand, a correlation of R2 = 0.9480 was obtained between the fluorescence LIDAR signal and absorbance/ optical density on the same growth phases. This is due to the algal organic matter component such protein-like, humic-like substances observed in all samples. It was observed that the UV-C humic-like component of AOM in C. reinhardtii showed high correlation (R2 = 0.8982) with the fluorescence LIDAR signal. However, during death phase, a linear correlation was observed between the maximum range-resolved fluorescence LIDAR signal and the EEM chlorophyll-a pigment (R2 = 0.9809) and absorbance/optical density (R2 = 0.9779) measured at 680-nm. Using the exponential correlation equation between the range-resolved fluorescence LIDAR signal and corrected chlorophyll-a concentration of Spirulina powder, the chlorophyll-a concentration of C. reinhardtii was estimated. The estimated chlorophyll-a concentration showed positive correlation (R2 = 0.8554) with the absorbance measurements using cell density of C. reinhardtii during the lag phase to stationary peak. This shows the exponential growth of C. reinhardtii as it reaches it optimal peak at Day 12. Also, a polynomial trend with correlation coefficient of R2 = 0.9863 between the estimated chlorophyll-a concentration and absorbance/optical density during death phase. The variance in the chlorophyll-a concentration can be attributed with algal organic matter, some physical parameters such as light, temperature, and humidity concentrations. Also, the bacterial populations, possible contaminations, types of invertebrates present in the algal samples can also be probable. From the values, the developed fluorescence LIDAR system for chlorophyll-a measurement shows its possible use as a monitoring technique.