Sludge-Grown Algae for Culturing Aquatic Organisms: Part I. Algal Growth in Sludge Extracts

Area of Science:

• Environmental Microbiology
• Aquaculture Nutrition
• Waste Valorization

Background:

• Sewage sludge presents a potential nutrient source for microalgae cultivation.
• Microalgae are a valuable feed source for aquatic organisms.
• Sustainable waste management strategies are crucial for environmental protection.

Purpose of the Study:

• To assess the feasibility of using sewage sludge as a culture medium for microalgae (Chlorella-HKBU).
• To evaluate the growth performance of microalgae cultured in sludge-based media.
• To investigate the potential of sludge-grown microalgae as feed for aquatic organisms.

Main Methods:

• Preparation of sludge extracts for microalgae culture.
• Comparison of two culturing techniques: aeration and shaking.
• Optimization of aeration rates (0.5, 1.0, 1.5 liters/min) for microalgae growth.
• Analysis of algal growth parameters (lag phase, log phase, final cell density).
• Monitoring of pH and ammonia nitrogen removal rates.
• Quantification of heavy metal content in sludge-grown algae.

Main Results:

• Aeration significantly shortened lag and log phases compared to shaking.
• Optimal aeration rates (1.0 and 1.5 liters/min) resulted in higher final cell densities.
• Ammonia nitrogen removal rates ranged from 62% to 70%.
• Significant levels of heavy metals (Zn, Cu, Ni, Mn, Cr, Fe) were detected in the sludge-grown algae.

Conclusions:

• Sewage sludge can be utilized as a culture medium for microalgae, with aeration enhancing growth.
• The high heavy metal content in microalgae grown on sewage sludge may limit their use as feed for higher trophic organisms.
• Further research is needed to mitigate heavy metal accumulation and assess the overall safety for aquaculture applications.