Unlocking the Potential: Algal Biomass Cultivation and Growth Kinetics Using Tanning Process Water

Abstract

A basic kinetic model has been applied to microalgae to predict the growth parameters in Zarrouk Media composition (ZMC) and precipitated chrome tanning effluent (PCTE). The model was fitted with the experimental data of Spirulina cultivation to estimate growth parameters: nutrient adsorption constant (K_a) (h^–1), nutrient desorption constant (K_d) (h^–1), rate of respiration (rR_c)(h^–1), efficiency of bio-synthesis (β) (g g^–1), respiration rate (h^–1)(rR_c), rate of maximum photosynthesis (p_max) (h^–1), coefficient for light-absorption (α) (m² g^–1), photon efficiency (g.μmol^–1 photons^–1) (φ_m), etc. The model suggests a higher nutrient adsorption rate in ZMC (0.75 h^–1) as compared to PCTE (1.40 × 10^–2 h^–1). The rate of respiration of Spirulina decreased due to cultivation in PCTE from 5.36 × 10^–3 to 1.91 × 10^–3 h^–1. The biosynthetic efficiency of Spirulina decreased from 8.72 to 2.002 due to cultivation in PCTE media. The maximum photosynthetic rate h^–1 was slightly higher in ZMC as compared to PCTE media. The model parameter values were lower for Spirulina in PCTE than those in ZMC. Spirulina’s cell density was lower in PCTE compared to ZMC, as the doubling time was increased from 9.97 h^–1 to 31.47 h^–1. Moreover, the optimum pH for growth was also shifted from 9.5 to 10.5. The higher dose of PCTE (Cl^– > 2.96 × 10³ mg L^–1) restricted cell growth. Adding Cr(III) in ZMC has a higher impact on cell growth than Cr(VI). The model parameters with Cr(III) and Cr(VI) also showed a decrease in values except rR_c and β have higher values for Cr(VI) as compared to Cr(III) added ZMC due to the non-interaction of Cr(VI) with algae. The model-predicted cell growth rates closely align with experimental results, with deviations within an ±7% margin. The addition of heavy metals to ZMC disrupts nutrient interactions and transport mechanisms during Spirulina cell growth.