Key Takeaways & Executive Findings
- •• • Cotton thread immobilization outperformed PVA, wood chips, and sodium alginate, yielding earlier and more sustained enzyme activity, higher biomass, and minimal loss, leading to a 10.09% TCOD removal from ADS. • • WRF treatment selectively degraded soluble EPS, reducing total protein and polysaccharide content by 8.9 mg·L−1, and decreased capillary suction time by 27.33%, significantly enhancing sludge dewaterability. • • Periodic replacement of half the carrier every 4 days maintained fungal activity over a 16-day treatment, achieving 12.7% TCOD removal, 16.5% ammonia nitrogen removal, and 59.4% UV254 reduction. • • The dual action of WRF—organic matter degradation and physical conditioning—promoted sludge floc aggregation and particle homogenization, addressing both recalcitrant organics and dewatering bottlenecks.
Abstract
Anaerobic digestion sludge (ADS) contains recalcitrant organic matter and exhibits poor dewaterability, posing challenges for disposal. This study evaluated the immobilization of white rot fungi (WRF) on four carriers—polyvinyl alcohol, cotton thread, wood chips, and sodium alginate—for ADS treatment. Cotton thread immobilization yielded the earliest and most sustained enzyme activity, highest biomass retention, and minimal biomass loss. WRF treatment achieved a 10.09% removal of total chemical oxygen demand (TCOD) and significantly disrupted extracellular polymeric substances (EPS), selectively degrading soluble EPS. To maintain fungal activity, periodic carrier replacement was required. Compared to the control, the experimental group showed an 8.9 mg·L−1 reduction in total protein and polysaccharide content in soluble EPS, a 27.33% decrease in capillary suction time (CST), and improved sludge dewaterability. These results demonstrate the potential of WRF for ADS treatment.
1. Introduction
Anaerobic digestion sludge (ADS) is a byproduct of wastewater treatment that accumulates persistent organic pollutants, heavy metals, and microplastics, posing significant environmental and health risks if improperly managed. Conventional sludge treatment methods often struggle with the recalcitrant organic fraction and poor dewaterability, which increase disposal costs and environmental footprint. White rot fungi (WRF) are known for their extracellular enzyme systems (laccase, lignin peroxidase, manganese peroxidase) capable of degrading a wide range of recalcitrant pollutants. However, direct application of free WRF to sludge is hampered by complex sludge matrices that inhibit fungal activity and cause biomass loss, limiting long-term efficacy.
This study addresses these bottlenecks by employing immobilization techniques to enhance WRF stability and performance. Four carriers—polyvinyl alcohol, cotton thread, wood chips, and sodium alginate—were compared for their ability to support WRF growth and enzymatic activity. Cotton thread emerged as the superior carrier, providing a conducive environment for fungal attachment and enzyme production. The study also introduced a periodic carrier replacement strategy to counteract fungal aging and activity decline, ensuring sustained treatment over 16 days. This approach not only improved TCOD removal and EPS disruption but also significantly enhanced sludge dewaterability, offering a promising solution for ADS management.
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LIU Wang, ZHU Xuefeng, WANG Ziyi, CHENG Shicai, FANG Zexian, XU Wenjing, TONG Wanzi, LIU Hongbo (2026). Application of Immobilized White Rot Fungi in the Treatment of Anaerobic Digestion Sludge. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202507059
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Frequently Asked Questions
What are the failure mechanisms of immobilized WRF under long-term operation, and how does the carrier replacement strategy mitigate them?
Under long-term operation, immobilized WRF may suffer from carrier aging and fungal detachment, leading to reduced enzyme activity and treatment efficiency. The study found that replacing half of the carrier every 4 days maintained fungal activity over a 16-day period, achieving 12.7% TCOD removal and 16.5% ammonia nitrogen removal, indicating that periodic replacement effectively counters activity decline.
How does cotton thread immobilization compare to other carriers in terms of enzyme production and biomass retention?
Cotton thread immobilization resulted in earlier and more sustained enzyme activity, higher biomass, and minimal biomass loss compared to PVA, wood chips, and sodium alginate. This translated to a 10.09% TCOD removal from ADS, demonstrating superior performance in supporting WRF viability and treatment efficacy.
What is the impact of WRF treatment on EPS composition and sludge dewaterability?
WRF treatment selectively degraded soluble EPS, reducing total protein and polysaccharide content by 8.9 mg·L−1. This disruption of EPS led to a 27.33% decrease in capillary suction time (CST), indicating significantly improved sludge dewaterability.
What are the scalability bottlenecks for this immobilized WRF process in industrial sludge treatment?
Scalability challenges include the cost and logistics of carrier replacement every 4 days, the need for consistent fungal cultivation, and potential variability in sludge characteristics. However, the study demonstrates that cotton thread is an inexpensive and effective carrier, and the periodic replacement strategy can be automated, making the process potentially viable for pilot-scale applications.
How does the performance of immobilized WRF compare to free WRF in terms of pollutant removal?
The study did not directly compare immobilized and free WRF, but prior literature indicates that immobilization significantly enhances WRF performance. For example, immobilized Trametes versicolor achieved 80% decolorization and 40 U·L−1 laccase activity compared to 10% and 5 U·L−1 for free fungi, highlighting the benefits of immobilization in complex matrices like sludge.
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