Simultaneous recovery of phosphorus and fulvic acid from anaerobic digestate of sewage treatment plants with calcium phosphate （CaP） crystallization

ZHANG Shuang; DENG Zhihua; LI Yinan; WANG Zhengbo; NIE Xiaobao

doi:10.13205/j.hjgc.202512007

Volume 43 Issue 12

Dec. 2025

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ZHANG Shuang, DENG Zhihua, LI Yinan, WANG Zhengbo, NIE Xiaobao. Simultaneous recovery of phosphorus and fulvic acid from anaerobic digestate of sewage treatment plants with calcium phosphate （CaP） crystallization[J]. ENVIRONMENTAL ENGINEERING , 2025, 43(12): 56-62. doi: 10.13205/j.hjgc.202512007

Citation:

ZHANG Shuang, DENG Zhihua, LI Yinan, WANG Zhengbo, NIE Xiaobao. Simultaneous recovery of phosphorus and fulvic acid from anaerobic digestate of sewage treatment plants with calcium phosphate （CaP） crystallization[J]. ENVIRONMENTAL ENGINEERING , 2025, 43(12): 56-62. doi: 10.13205/j.hjgc.202512007

Citation:

ZHANG Shuang, DENG Zhihua, LI Yinan, WANG Zhengbo, NIE Xiaobao. Simultaneous recovery of phosphorus and fulvic acid from anaerobic digestate of sewage treatment plants with calcium phosphate （CaP） crystallization[J]. ENVIRONMENTAL ENGINEERING , 2025, 43(12): 56-62. doi: 10.13205/j.hjgc.202512007

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Simultaneous recovery of phosphorus and fulvic acid from anaerobic digestate of sewage treatment plants with calcium phosphate （CaP） crystallization

doi: 10.13205/j.hjgc.202512007

1. Power China Northwest Engineering Corporation Limited, Xi'an 710065, China;
2. Hunan Chenzhou Hydrology and Water Resources Survey Center, Chenzhou 424108, China;
3. School of Hydraulic and Environmental Engineering, Changsha University of Science & Technology, Changsha 410114, China

Received Date: 2023-09-27
Accepted Date: 2023-12-10
Rev Recd Date: 2023-11-09

Available Online: 2026-01-09

Abstract

Abstract

Despite the presence of humic substances in the digestate of sewage treatment plants deteriorates the phosphorus （P） recovery efficiency of calcium phosphate （CaP） crystallization， it dose improve the phytoavailability of CaP when used as P fertilizer. To overcome the inhibitory effect of humic substances on CaP crystallization， phosphorus and humic substances were co-recovered efficiently using a fluidized-bed reactor through optimization of Ca/P molar ratio and stirring intensity. The results showed that recovery efficiencies of 73% for P， and 53% for fulvic acid （FA）， were achieved at an initial P concentration of 30 mg/L， an FA concentration of 25 mg/L， a stirring speed of 100 r/min， and a Ca/P molar ratio of 5. FA was proved to delay the crystallization process of CaP via hydrogen bonding and carboxyl surface complexation. Stirring promoted the nucleation of CaP and facilitated the aggregation of nuclei， thereby enhancing P recovery efficiency. Meanwhile， high FA recovery efficiency was obtained by the co-precipitation of FA and CaP and FA adsorption on the CaP surface. FA recovery efficiency can be further enhanced through Ca²⁺ bridging between FA in the liquid phase and FA adsorbed on the CaP surface. Within the tested pH range of 7 to 10， P recovery efficiency increased with the increasing of pH value， while FA recovery efficiency initially increased and then decreased， peaking at 53% at pH 9. In this case， CaP crystallization products contain hydroxyapatite （HAP） and its precursors.
- phosphorus recovery,
- humic substances,
- CaP crystallization,
- Ca/P molar ratio,
- stirring

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References(36)

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