Synergistic effects of earthworm mucus and different biochars on heavy metal bioavailability in sludge composting

WANG Xingming; LU Haopeng; SHEN Lu; CHU Zhaoxia

doi:10.13205/j.hjgc.202607013

Volume 44 Issue 7

Jul. 2026

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WANG Xingming, LU Haopeng, SHEN Lu, CHU Zhaoxia. Synergistic effects of earthworm mucus and different biochars on heavy metal bioavailability in sludge composting[J]. ENVIRONMENTAL ENGINEERING , 2026, 44(7): 118-128. doi: 10.13205/j.hjgc.202607013

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WANG Xingming, LU Haopeng, SHEN Lu, CHU Zhaoxia. Synergistic effects of earthworm mucus and different biochars on heavy metal bioavailability in sludge composting[J]. ENVIRONMENTAL ENGINEERING , 2026, 44(7): 118-128. doi: 10.13205/j.hjgc.202607013

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Synergistic effects of earthworm mucus and different biochars on heavy metal bioavailability in sludge composting

doi: 10.13205/j.hjgc.202607013

1. Anhui Province Engineering Laboratory of Water and Soil Resources Comprehensive Utilization and Ecological Protection in High Groundwater Mining Area, School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China;
2. Ma'anshan Engineering Technology Research Center of Land Test Evaluation and Restoration, Wanjiang University of Technology, Ma'anshan 243031, China;
3. Key Laboratory of Bioresource and Environmental Biotechnology of Anhui Higher Education Institutes, School of Biological Engineering, Huainan Normal University, Huainan 232038, China

Received Date: 2025-07-29
Available Online: 2026-09-01

Abstract

Abstract

To investigate the synergistic effects of earthworm mucus and different biochars on the bioavailability of heavy metals in sludge， composting experiments were conducted by adding earthworm mucus and two distinct biochar types （rice husk biochar and straw biochar） to sludge. This study analyzed the impacts of earthworm mucus synergistically combined with different biochars on the physicochemical properties of sludge， as well as on the total heavy metal content， bioavailable fractions， and occurrence states. The results indicated that， compared with sludge composted alone， the addition of mucus increased sludge pH and electrical conductivity （EC）but reduced total nitrogen （TN） and total phosphorus （TP） contents. Synergistic mucus-biochar composting further elevated sludge pH and EC whilst lowering TN content， with the optimal treatment achieved by adding mucus together with 10% rice husk biochar. Mucus-only composting reduced the total contents of heavy metals （Cd， Cu， Ni， Zn， Pb） and their bioavailability in sludge. The addition of different proportions and types of biochar further significantly decreased total heavy metal contents and bioavailable fractions. Mucus-enhanced composting with rice husk biochar demonstrated superior Cd removal， with total and bioavailable Cd levels decreasing by 27.03% to 55.68% and 9.52% to 28.57%， respectively， compared with the control group （P < 0.05）. Synergistic composting with mucus and straw biochar showed superior removal of Ni， Zn， and Pb， reducing total levels by 3.81% to 5.72%， 7.93% to 34.62%， and 42.61% to 79.46%， respectively， while the bioavailable fractions decreased by 2.90% to 26.31%， 15.58% to 24.14%， and 32.30% to 36.88%， respectively， compared with the control group （P < 0.05）. Following composting with mucus addition， the carbonate-bound fractions of Cd， Ni， and Pb in the sludge gradually transformed into residual fractions. After composting with mucus and biochar， the exchangeable fractions of heavy metals in the sludge progressively shifted toward Fe-Mn oxide-bound fractions. Among all treatments， straw biochar addition demonstrated the most effective heavy metal passivation in sludge， with the residual fractions of Cd， Cu， Ni， Zn， and Pb increasing by 0.35% to 7.02%， 8.61% to 12.90%， 16.62% to 23.02%， 17.33% to 26.10%， and 16.12% to 27.20%， respectively， compared with the control group （P < 0.05）. In summary， synergistic composting with earthworm mucus and biochar effectively reduced and passivated heavy metal contents in sludge. Earthworm mucus combined with these two biochars has promising application prospects in sludge composting.
- earthworm mucus,
- sludge,
- rice husk biochar,
- straw biochar,
- heavy metals

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References(57)

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