Aquaculture wastewater treatment using microalgae cultivated in open raceway ponds
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Date
2025-06-30
Authors
Kedoui Sara
MessaoudI Hana
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Abstract
This study evaluates the efficiency of local microalgae strains for treating raw, unfiltered Tilapia aquaculture wastewater (TWW) using laboratory-scale raceway ponds. Initially, the
halotolerance of two strains (4CNR and 5CNR) was assessed under 10 g/L NaCl, confirming their tolerance but revealing optimal growth in freshwater conditions. The 5CNR strain was then selected, along with a freshwater strain (2ST), to evaluate growth and nutrient removal in BG11 medium and non-sterile TWW. Both strains showed strong growth in BG11, with 5CNR achieving higher biomass (1007.14 mg/L) and 2ST slightly higher cell density. In TWW, both strains exhibited reduced growth and fluctuating kinetics. Correlation analysis indicated that optical density (OD) is a reliable proxy for biomass in defined media like BG11 but not in complex, non-sterile media such as TWW. In raceway pond trials, the inoculated strains outcompeted the native algal population. Under batch conditions, 2ST achieved superior removal of phosphate, nitrate, and nitrite compared to the control. However, in semi-continuous mode, low nutrient input and limited biomass recovery prevented steady-state establishment. This led to modest performance, with biomass productivity at 0.087 g/L·day and nutrient removal rates of 0.006 mg/L·day for NH₄⁺, 1.89 for NO₂⁻, 9.7 for NO₃⁻, and 0.07 for PO₄³⁻