Abstract

This study evaluated the effects of cassava mill effluent (CME) on the growth of the microalgae Chlorella vulgaris and Euglena viridis. The microalgae were cultured in seven CME concentrations (0, 5, 10, 25, 50, 75, and 100%), each in triplicate, and monitored over 14 days. Growth was determined at two-day intervals using a 721 visible spectrophotometer. Dry weight, percentage yield, percentage inhibition, and analysis of variance (ANOVA) were computed, while pH, electrical conductivity (EC), and total dissolved solids (TDS) were measured using standard methods. Both species exhibited rapid growth between days 2 and 4, followed by fluctuating growth from days 6 to 12 and a decline by day 14, particularly at 75% and 100% CME. ANOVA showed significant differences in growth among effluent concentrations and exposure periods (p < 0.001). Growth responses demonstrated a concentration-dependent hormetic pattern, with significant stimulation at low CME concentrations (5–50%) and reduced growth or inhibition at higher concentrations (75–100%). Euglena viridis exhibited a stronger growth response and higher biomass yield than C. vulgaris. Physicochemical characteristics also varied with CME concentration. pH decreased with increasing effluent concentration, ranging from 8.36 to 3.58 in E. viridis cultures and from 6.05 to 3.62 in C. vulgaris cultures. Conversely, EC increased from 417 to 3950 μS/cm and 437 to 3908 μS/cm, while TDS increased from 208 to 1975 mg/L and 218 to 1954 mg/L, respectively. These findings demonstrate that diluted cassava mill effluent can enhance microalgal growth, whereas higher concentrations create conditions that suppress growth, highlighting the importance of effluent dilution for potential phycoremediation and biomass production applications.

Keywords: Cassava mill effluent, Microalgae, Euglena viridis, Chlorella vulgaris, Phycoremediation