Abstract:
This study aims to improve the cultivation of the microalga Chlorococcum humicola in airlift photobioreactors were investigated. The study was divided into two parts as (1) algal biofilm reduction on the surface of photobioreactors, and (2) the feasibility of using the effluent from nitrification in a recirculating aquaculture system as the nutrient source during C. humicola cultivation. The first method for algal biofilm reduction utilized suspended carrier addition to increase physical abrasion on the photobioreactor surface. Results indicated that suspended carriers such as MB5 and beads were suitable for use in airlift photobioreactors, with an optimal amount of suspended carrier determined at 5% and aeration rate maintained at 0.8 vvm. Algal cultivation after suspended carrier addition improved algal biomass concentration by 21% to 25% compared to cultivation without suspended carriers. The second method considered for algal biofilm reduction involved addition of surfactant in the algal growth medium. Addition of SDS at 0.0082 mM effectively controlled biofilm wall growth formation in both stirred-tank and airlift photobioreactors made from acrylic or glass, with photobioreactor volumes ranging from 2 to 60 L, and increased algal biomass concentrations from 68% to 158% in acrylic photobioreactors and from 28% to 43% in glass photobioreactors. The second part of this research focused on the feasibility of using the effluent from nitrification in a recirculating aquaculture system as the nutrient source for C. humicola cultivation. Effluent from a nitrifying unit, after filtration through nylon cloth, was used to cultivate C. humicola for 24 days in airlift photobioreactors with MB5 addition. Algal productivities in this study were significantly lower than reported using BG-11 growth medium but algal biomass concentrations were comparable to previous studies. Findings indicated the potential of reutilizing aquaculture effluent for algal cultivation, thereby adding value to aquaculture waste, reducing nitrogen and phosphorus discharge into the environment, and decreasing culture expense by 527.50 Baht per kilogram of algae compared to cultivation using BG-11 growth medium. Average nitrate and phosphate removal efficiencies were determined at 82.8% and 89.1%, respectively. Results demonstrated the concept of adding value to aquaculture waste by reutilization for algal biomass production. This increased the economic efficiency of aquaculture cultivation and achieved environmental protection by reducing nitrate and phosphorus discharge, thereby promoting the concept of sustainable aquaculture.