Enhancement of resource recovery and sludge digestion by cultivation of phagotrophic algae with alkali-pretreated waste activated sludge and waste ketchup

Abstract

Abstract The reclamation of waste activated sludge (WAS) organics is often impeded by the long time required for the solid organic matter to solubilize. Here we introduce a fast approach to reclaim WAS by using phagotrophic algae. Phagotrophic algae have unique ability of growing by ingesting insoluble organic particles, which makes the solubilization of WAS organic matter unnecessary and largely accelerates the WAS digestion rate. To facilitate this approach, alkali treatment was evaluated at different pH and time and optimized at pH 10 for 6 h to release microbial cells and other organics from the WAS flocs. Then the alkali-treated WAS was fed to phagotrophic algae. In later experiments, the addition of readily consumable organics, such as waste ketchup (WK), was found to enhance the percentage reduction of WAS organics and algae yield. With WK addition at 0.118:1 (w/w) WK-to-WAS organics, 46–49% of the WAS organic matter was digested within 22 h. The lipid content was 20.8% in the treated biosolids, increased from 6.8% in the original WAS. With the fast digestion rate and high lipid production ability, this new approach has strong potential to improve WAS digestion and utilization.