Allelopathic effect of benzoic acid (hydroponics root exudate) on microalgae growth

Area of Science:

• Environmental Biotechnology
• Microalgal Cultivation
• Wastewater Treatment

Background:

• Hydroponic effluent (HE) is rich in residual nutrients, presenting an opportunity for microalgae cultivation.
• Root exudates, such as benzoic acid, in HE can exhibit toxicity to microalgae, potentially limiting its use.
• Microalgae are crucial for resource recovery and water recycling processes.

Purpose of the Study:

• To investigate the allelopathic effects of benzoic acid on the growth of two microalgal species.
• To determine the potential of HE as a growth medium for microalgae, considering benzoic acid toxicity.
• To evaluate the suitability of HE for resource recovery and water recycling.

Main Methods:

• Batch growth experiments were conducted over 96 hours with varying doses of benzoic acid.
• Biomass concentration was measured for Chlorella pyrenoidosa and Chlorella sorokiniana.
• Allelopathic effects and growth kinetics were analyzed, including the determination of half effective concentration (EC50) and fitting to Haldane's model.

Main Results:

• Both Chlorella species exhibited allelopathic behavior, with growth stimulation and inhibition observed at different benzoic acid concentrations.
• Chlorella sorokiniana achieved higher biomass concentrations (0.09-0.26 g.L⁻¹) than Chlorella pyrenoidosa (0.064-0.037 g.L⁻¹).
• The 96-hour EC50 values were 65.10 mg.L⁻¹ for C. pyrenoidosa and 105.27 mg.L⁻¹ for C. sorokiniana. Haldane's model accurately described the experimental data (r ≈ 0.99).

Conclusions:

• Low concentrations of benzoic acid in HE may not be detrimental and could even stimulate microalgal growth.
• HE shows promise as a sustainable and low-cost growth medium for microalgae-mediated resource recovery and water recycling.
• Further research using real HE is recommended to validate its practical application in large-scale systems.