Rapid sludge treatment through phagotrophic algae cultivation using waste activated sludge pretreated with...

The mixotrophic alga Ochromonas danica efficiently synthesizes lipids through phagotrophy and osmotrophy. This study explored its growth using alkali-pretreated waste activated sludge (WAS). Pretreatment at pH 12 for 24 h released 56.4% of WAS organics as microbial cells and dissolved substrates. During 96-hour cultivation, O. danica consumed 91.5% of liberated cells and 63.0% of dissolved organics, converting 28.6% of WAS organics into algal biomass containing 42.4% lipids (dry weight). This algal assimilation step proved pivotal in an integrated 30-day process (1-day alkali treatment, 4-day algal growth, 25-day anaerobic digestion), which achieved 61% total organic reduction - a 2.7-fold acceleration over anaerobic digestion with untreated sludge (23% in 30 days) and a 1.3-fold acceleration over anaerobic digestion with alkali treatment alone (48% in 30 days). The synergy between alkaline solubilization and algal phagotrophy thus simultaneously enhance WAS organics reduction while producing lipid-rich biomass, presenting a time-efficient strategy for sludge management.