Evaluation of the Growth Potential of Local Algal Genera (Spirogyra, Zygnema, and Oedogonium) in Wastewater from Kesses, Kenya

Abstract

The remediation of nutrient-rich wastewater using indigenous microalgae faces significant economic bottlenecks due to energy-intensive biomass harvesting methods. This study investigated the biological feasibility and growth dynamics of three locally isolated, easily harvestable freshwater filamentous green macroalgae genera (Spirogyra, Zygnema, and Oedogonium) cultivated in domestic sewage. Wild algal strains were harvested from the Kesses region of Uasin Gishu County, Kenya, and cultured under controlled laboratory conditions using secondary effluent collected from the First Maturity Pond of the Moi University Waste Stabilization system. Algal growth and metabolic vitality were monitored daily over a 7-day experimental period by quantifying chlorophyll a concentrations as a definitive proxy for biomass proliferation. A Friedman test was applied to evaluate the statistical significance of temporal variations in pigment accumulation. The empirical results demonstrated that all three genera underwent a distinct, statistically significant exponential growth phase driven by wastewater nutrient assimilation (p<0.01). Both Spirogyra and Zygnema exhibited peak chlorophyll a accumulation on day 4 (with median values of 37.84 mg m−3 and 34.14 mg m−3, respectively), which directly coincided with their maximum internal nitrate sequestration capacity. Conversely, Oedogonium adapted more rapidly to the waste stream, mirroring the control growth kinetics of a synthetic medium to achieve its maximum chlorophyll a concentration by day 3 (median = 39.31 mg m−3). Following these genus-specific peaks, ambient nutrient depletion triggered a sharp metabolic decline, with day 7 exhibiting the lowest pigment concentration across all treatments. These findings confirm that native Kenyan strains of Spirogyra, Zygnema, and Oedogonium can effectively exploit domestic sewage as a cost-free growth medium. Furthermore, this study establishes the first empirical baseline for the phycoremediation potential of the genus Zygnema in East African lagoon systems. Because these macroscopic, interlocking filaments can be recovered using simple mechanical screening or gravity settling, integrating them into decentralized waste stabilization ponds offers a low-cost, low-energy alternative for institutional wastewater polishing. This approach simultaneously mitigates downstream eutrophication in the Lake Victoria basin while generating scalable, non-crop biomass suitable for downstream bioenergy and bio-fertilizer valorization.