Nutrient removal by alginate-immobilized Chlorella vulgaris: response to different wastewater matrices

BACKGROUND Immobilized algae are a promising tool to treat wastewater within a short time (<12 h) and simplify biomass harvesting compared with suspended algae. The potential of alginate-entrapped Chlorella vulgaris to bioremediate secondary (with and without nutrient supplementation), primary and two lagoon municipal wastewaters was investigated. The capability of the system to adapt to these wastewaters was analysed by determining biotic and abiotic nutrient removal, and further evaluated by comparison with suspended cells. RESULTS The algal nitrogen (N) content (4.6-7.8 wt%) was closely related to the wastewater ammonium concentration (R-2 = 0.97). The algal cells did not adapt N uptake as effectively to wastewater nitrate concentration because both abiotic N and phosphorus (P) removal increased. The algal P content (1.2-3.2 wt%) varied in response to the wastewater P and was inversely related to the initial cellular P content. The algae thus adapted nutrient uptake to the wastewater N:P level and ratio when ammonium predominated. Biomass production (35-73 mg L-1 d(-1)) increased with dissolved organic and inorganic carbon with little impact from other wastewater characteristics. Immobilization did not affect N and P uptake per cell compared with suspended algae. CONCLUSION Decoupling biotic and abiotic removal showed adaptation to the N:P of the wastewater and luxury P uptake had significant impact during treatment of different wastewater matrices, these traits were not affected by immobilization. Immobilization enables increased N and P removal rates compared with suspended algal systems as nutrient uptake per cell is not affected and higher concentrations of algal biomass within the reactor are facilitated. (c) 2020 Society of Chemical Industry