Treatment efficiency of residual sludge anaerobic digestate by immobilized <i>Chlorella vulgaris</i>

WANG Hui; LIU Bo; DU Dandan; ZHU Hongni; ZHAI Pengxiang; MA Jianghang; ZHANG Zhuo; XU Zhiqiang

doi:10.13205/j.hjgc.202506007

Volume 43 Issue 6

Jun. 2025

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Article Navigation > ENVIRONMENTAL ENGINEERING > 2025 > 43(6): 65-76

WANG Hui, LIU Bo, DU Dandan, ZHU Hongni, ZHAI Pengxiang, MA Jianghang, ZHANG Zhuo, XU Zhiqiang. Treatment efficiency of residual sludge anaerobic digestate by immobilized Chlorella vulgaris[J]. ENVIRONMENTAL ENGINEERING , 2025, 43(6): 65-76. doi: 10.13205/j.hjgc.202506007

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WANG Hui, LIU Bo, DU Dandan, ZHU Hongni, ZHAI Pengxiang, MA Jianghang, ZHANG Zhuo, XU Zhiqiang. Treatment efficiency of residual sludge anaerobic digestate by immobilized Chlorella vulgaris[J]. ENVIRONMENTAL ENGINEERING , 2025, 43(6): 65-76. doi: 10.13205/j.hjgc.202506007

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Treatment efficiency of residual sludge anaerobic digestate by immobilized Chlorella vulgaris

doi: 10.13205/j.hjgc.202506007

1. State Key Laboratory of Water Engineering Ecology and Environment in Arid Area, Xi'an University of Technology, Xi'an 710048, China;
2. School of Water Resources and Hydro-Electric Engineering, Xi'an University of Technology, Xi'an 710048, China;
3. Yangling Vocational & Technical College, Yangling 712100, China

Received Date: 2024-01-24
Accepted Date: 2024-08-06
Rev Recd Date: 2024-07-09

Abstract

Abstract

The residual sludge anaerobic digestate is characterized by high nitrogen and phosphorus content and a low C/N ratio， which is not suitable for direct biological treatment. Microalgae can be used as a pre-treatment technology for residual sludge anaerobic digestate as a fast-growing， renewable source of biomass energy. The immobilized Chlorella vulgaris has a good performance in nitrogen and phosphorus removal in residual sludge anaerobic digestate. In this study， sodium alginate （SA） was used as a carrier， powdered activated carbon （PAC） as an adsorbent and calcium chloride （CaCl₂） as a cross-linking agent， and the effects of the proportional concentrations of the three additives on the properties of immobilized Chlorella vulgaris， such as mass transfer， stability and specific growth rate were analyzed. The immobilization conditions were optimized through orthogonal test to investigate the optimal proportions and effectiveness in nitrogen and phosphorus removal from residual sludge anaerobic digestate. The results showed that when the concentration of SA， PAC， and CaCl₂ was 2.5%， 4.5%， and 0.2%， the specific growth rate， material mass transfer， and mechanical properties of the immobilized Chlorella vulgaris were optimal. The removal efficiencies of NH₄⁺-N， TP， and COD by immobilized Chlorella vulgaris in the residual sludge anaerobic digestate were 96.70%， 51.30%， and 52.92%， which were 3.13%， 17.05%， and 8.53% higher than those of the suspension Chlorella vulgaris group， respectively. While the removal efficiencies of NH₄⁺-N， TP， and COD were only 22.93%， 14.89%， and 8.12% by the adsorption of PAC and SA without Chlorella vulgaris. As the reuse times increased， the specific growth rate of immobilized Chlorella vulgaris and the removal efficiencies of NH₄⁺-N， COD， and TP decreased. In addition， the removal efficiencies of TN and TP in the residual sludge anaerobic digestate by immobilized Chlorella vulgaris were affected by N/P ratio， and the concentration of Ca²⁺ and COD. When N/P ratio was 14：1， the removal efficiencies of TN and TP were the highest （91.23%， 86.54%）. With an increasing Ca²⁺ concentration， the algal density of immobilized Chlorella vulgaris showed an increasing-decreasing trend. When Ca²⁺ concentration was 0 to 20 mg/L， it had little effect on TN removal efficiency， while that of TP was positively correlated with Ca²⁺ concentration， and the best removal efficiency of TP was 90.0% when the Ca²⁺ concentration was 40 mg/L. When the COD concentration was 600 mg/L， the removal efficiencies of TN and TP were 84.39 % and 83.50 %， respectively， which were 46.24 and 11.75 percentage points higher than those of the 1200 mg/L COD group. The results can provide theoretical and technical support for the treatment of residual sludge anaerobic digestate.
- sodium alginate,
- powdered activated carbon,
- immobilized Chlorella vulgaris,
- residual sludge anaerobic digestate,
- nitrogen and phosphorus removal

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References(31)

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