Application of phagotrophic algae in waste activated sludge conversion and stabilization

Area of Science:

• Environmental Microbiology
• Biotechnology
• Wastewater Treatment Engineering

Background:

• Waste activated sludge (WAS) contains abundant bacteria, posing disposal challenges.
• Current sludge treatment methods like aerobic digestion are energy-intensive and slow.
• Phagotrophic algae offer a potential biological solution for consuming microbial biomass in WAS.

Purpose of the Study:

• To develop and evaluate a combined ultrasonication-phagotrophic algal process for efficient WAS conversion.
• To assess the effectiveness of this process in reducing sludge volatile solids (VS) and producing algal biomass.
• To compare the energy efficiency and performance of this novel process against conventional aerobic digestion.

Main Methods:

• Ultrasonic pretreatment of WAS to release volatile solids and bacteria.
• Cultivation of the phagotrophic alga *Ochromonas danica* to consume released VS.
• Measurement of VS reduction, algal yield, and oxygen uptake for stabilization.

Main Results:

• The process consumed over 80% of released VS by *Ochromonas danica*, achieving approximately 30% algal cell yield.
• A 42.4% reduction in WAS VS was achieved in 1 day, significantly faster than aerobic digestion (27% in 10 days).
• Stabilized solids required 65%-92% less oxygen uptake, indicating substantially reduced aeration costs.

Conclusions:

• The ultrasonication-phagotrophic algal process offers an efficient and sustainable method for WAS treatment.
• This approach significantly reduces sludge volume and energy requirements for stabilization.
• The process generates microalgal biomass, providing a valuable co-product for potential reuse.