The Effect of Co2 Injection Duration on The Growth and Quality of Chaetoceros Muelleri at Intermediate Scale

This study aimed to analyze the effect of variations in the duration and frequency of carbon dioxide (CO2) gas injection on the productivity of the microalga Chaetoceros muelleri at an intermediate scale. This experimental study used a Completely Randomized Design (CRD) with five treatments using a CO2 concentration of 50% v/v and three replications, namely P0 (Control/no CO₂ injection), P1 (6 seconds/1.2 hours), P2 (10 seconds/2 hours), P3 (20 seconds/4 hours), and P4 (40 seconds/8 hours). The parameters observed included daily cell density trends, chlorophyll content, dry biomass, final harvest weight, and water quality stability (pH, DO, temperature, and light intensity). Data were analyzed using ANOVA followed by Duncan’s test. The results showed that CO₂ injection duration had a significant effect (P<0.05) only on chlorophyll content and total harvest weight, but did not significantly affect water quality parameters, indicating that the culture medium remained stable. Microalgal cell density in all treatments reached its highest peak on Day 7, with the maximum population recorded in treatment P1 (6 seconds/1.2 hours) at 4,330,000 cells/mL, which also produced the highest chlorophyll content of 76.04 mg/g. In contrast, the highest final harvest weight was significantly obtained with the longer injection duration, namely treatment P4 (40 seconds/8 hours), at 5.42 g/L. It can be concluded that the short injection duration of 6 seconds/1.2 hours (P1) was optimal for stimulating the logarithmic growth phase and chlorophyll content, whereas the longer duration of 40 seconds/8 hours (P4) was more effective for maximizing final harvest weight.