Clarification of the phosphorus release mechanism for recovering phosphorus from biofilm sludge in alternating aerobic/anaerobic biofilm system.

A novel wastewater treatment plant process was constructed to overcome the challenge of simultaneous nitrate removal and phosphorus (P) recovery. The results revealed that the P and nitrate removal efficiency rose from 39.0 % and 48.4 % to 92.8 % and 93.6 % after 136 days of operation, and the total P content in the biofilm (TPbiofilm) rose from 15.8 mg/g SS to 57.8 mg/g SS. Moreover, the increase of TPbiofilm changed the metabolic mode of denitrifying polyphosphate accumulating organisms (DPAOs), increasing the P concentration of the enriched stream to 172.5 mg/L. Furthermore, the acid/alkaline fermentation led to the rupture of the cell membrane, which released poly-phosphate and ortho-phosphate of cell/EPS in DPAOs and released metal­phosphorus (CaP and MgP). In addition, high-throughput sequencing analysis demonstrated that the relative abundance of DPAOs involved in P storage increased, wherein the abundance of Acinetobacter and Saprospiraceae rose from 8.0 % and 4.1 % to 16.1 % and 14.0 %. What's more, the highest P recovery efficiency (98.3 ± 1.1 %) could be obtained at optimal conditions for struvite precipitation (pH = 7.56 and P: N: Mg = 1.87:3.66:1) through the response surface method (RSM) simulation, and the precipitates test analysis indicated that P recovery from biofilm sludge was potentially operable. This research was of great essentiality for exploring the recovery of P from biofilm sludge.

Simultaneous phosphorus recovery from wastewater and sludge by a novel denitrifying phosphorus removal system.

A novel process was proposed for simultaneous denitrification and phosphorus (P) recovery. The increased nitrate concentration facilitated the activity of denitrifying P removal (DPR) in P enrichment, which stimulated P uptake and storage, making P more readily accessible for release into the recirculated stream. The total P content in the biofilm (TPbiofilm) rose to 54.6 ± 3.5 mg/g SS as the nitrate concentration increased from 15.0 to 25.0 mg/L, while the P concentration of the enriched stream reached 172.5 ± 3.5 mg/L. Moreover, the abundance of denitrifying polyphosphate accumulating organisms (DPAOs) increased from 5.6% to 28.0%, and the increased nitrate concentration facilitated the process of carbon, nitrogen, and P metabolism due to the rise in the genes involved in critical functions of metabolism. Acid/alkaline fermentation analysis indicated that the EPS release was the primary P-release pathway. Additionally, pure struvite crystals were obtained from the enriched stream and fermentation supernatant.