Enhanced denitrifying phosphorus removal and mass balance in a worm reactor

Phosphorus release is one of the disadvantages during worm predation, which has an adverse effect on wastewater treatment. In order to investigate and reveal the effects and mechanisms of worm predation on phosphorus transformation, batch experiments were conducted on a long-running worm reactor (WR). Denitrifying phosphorus removal (DPR) was observed in WR for the first time owing to the special reactor configuration and operating conditions. After DPR in WR, the concentration of supernatant phosphorus increased to 42.2 ± 1.1 mg L⁻¹ owing to bacterial phosphorus release and worm predation, which further promoted DPR in the subsequent cycle. DPR rate in the WR was 12.3 times higher than that in the blank reactor (BR). In addition, the synergistic effects of worm predation and bacterial metabolism on sludge reduction and nutrients transformation were analyzed. The sludge reduction of WR was 84.5% higher than that of BR. Bacterial metabolism played an important role in the removal of supernatant nutrients, which consumed 60.2% of total nitrogen and 55.5% of chemical oxygen demand derived from the reduced sludge. The study suggested that under certain conditions, WR could be functionalized as a bacteria selection tank to further improve the wastewater treatment efficiency. Bacterial metabolism was essential for supernatant nutrients removal during worm predation.