Nutrient removal using algal-bacterial mixed culture.

Area of Science:

• Environmental Science
• Biotechnology
• Water Treatment

Background:

• Nutrient pollution from nitrate (N) and phosphate (P) is a major environmental concern.
• Chemical Oxygen Demand (COD) also contributes to water pollution.
• Algae-bacteria symbiotic systems offer a potential solution for simultaneous pollutant removal.

Purpose of the Study:

• To investigate simultaneous removal of N, P, and COD using algae and bacteria in photobioreactors.
• To evaluate the effect of biomass recycling on pollutant removal efficiency.
• To understand the mechanisms behind nutrient uptake in these systems.

Main Methods:

• Operation of photobioreactors in semi-batch mode with a 2-day hydraulic retention time.
• Two operational phases: 33% biomass recycle and no biomass recycle.
• Use of synthetic wastewater with varying initial N, P, and COD concentrations.

Main Results:

• Achieved >90% removal of N and P, and >80% removal of COD.
• Nutrient removal efficiency was high even at elevated initial N and P concentrations.
• Biomass growth did not correlate with increased nutrient concentrations; 'luxury uptake' was observed.
• No significant advantage of biomass recycling was demonstrated.

Conclusions:

• Algae-bacteria photobioreactors are highly effective for simultaneous N, P, and COD removal.
• Nutrient removal is primarily driven by 'luxury uptake' rather than solely stoichiometric requirements for biomass growth.
• Biomass recycling does not appear to enhance the removal efficiency in this specific system.