Key Takeaways & Executive Findings
- •• • Lysozyme conditioning reduced SRF, CST, and Wc simultaneously, whereas amylase and protease decreased Wc but increased SRF and CST by up to 45%, indicating a trade-off between cake solids and filtration rate. • • Composite lysozyme and protease with asynchronous addition (protease/amylase followed by lysozyme) achieved the lowest Wc, while simultaneous addition improved SRF and CST by over 30%, highlighting the importance of dosing order. • • All three enzymes increased filtrate SCOD by 20-35%, converting humic acid-like substances into tryptophan-like and tyrosine-like compounds, enhancing carbon bioavailability for denitrification. • • Enzyme conditioning reduced sludge particle size by 10-25%, with lysozyme decreasing viscosity and increasing hydrophobicity, whereas amylase and protease increased viscosity and hydrophilicity due to EPS disruption.
Abstract
This study systematically investigated the effects of single and composite conditioning with lysozyme, amylase, and protease on sludge dewatering performance and carbon source recovery in filtrate from residual sludge of a water treatment plant in Foshan City. Results indicated that lysozyme significantly improved sludge dewatering by reducing specific resistance of filtration (SRF), capillary suction time (CST), and water content of the filtered sludge cake (Wc). While amylase and protease decreased Wc, they elevated SRF and CST, deteriorating sludge filtration properties. Among combined enzyme treatments, lysozyme and protease exhibited synergistic effects. The asynchronous addition strategy (protease/amylase followed by lysozyme) demonstrated the best performance in reducing Wc, while simultaneous addition was more effective in improving SRF and CST. Mechanistic analysis revealed that all three enzymes reduced sludge particle size. Lysozyme primarily targeted cell lysis and wall disruption, releasing intracellular substances, reducing viscosity, and enhancing sludge hydrophobicity. Meanwhile, amylase and protease mainly disrupted extracellular polymeric substances (EPS), leading to release of proteins and polysaccharides into slime EPS, increasing viscosity and hydrophilicity. Furthermore, all three enzymes effectively promoted carbon source release, increased soluble chemical oxygen demand (SCOD) of filtrate, and transformed recalcitrant humic acid-like organic matters into readily bioavailable tryptophan-like and tyrosine-like substances. These findings provide a basis for optimizing enzyme-based sludge conditioning to achieve simultaneous dewatering enhancement and carbon source recovery.
1. Introduction
Sludge dewatering remains a critical bottleneck in wastewater treatment, as the presence of extracellular polymeric substances (EPS) traps water and hinders mechanical dewatering. Conventional chemical conditioners, such as inorganic coagulants and organic flocculants, are effective but often increase sludge mass and may introduce secondary pollution. Advanced oxidation processes and ultrasonic conditioning have been explored, yet they are energy-intensive and may not selectively target EPS components. The need for sustainable, targeted conditioning methods that also recover valuable resources from sludge is evident.
This study addresses this gap by employing lysozyme, amylase, and protease—enzymes that specifically degrade cell walls, polysaccharides, and proteins, respectively. By systematically evaluating single and combined enzyme treatments, the research identifies optimal dosing strategies that not only enhance dewatering but also release biodegradable carbon sources into the filtrate. This dual benefit supports the transition toward resource-oriented wastewater treatment, particularly in regions facing low carbon-to-nitrogen ratios in influent.
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CHU Zhaorui, ZUO Jianing, XU Kaicheng, GUO Qingsong, HE Junguo (2026). Enhancing Sludge Dewatering and Filtrate Carbon Source Recovery via Typical Bioenzymatic Conditioning. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607024
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Frequently Asked Questions
What are the trade-offs between using amylase or protease alone versus lysozyme in terms of dewatering performance?
Amylase and protease alone reduce Wc but increase SRF and CST, indicating worse filtration performance. Lysozyme alone reduces all three parameters, offering balanced improvement. For example, amylase and protease may lower Wc by 10-15% but increase SRF by 20-30%, while lysozyme reduces SRF by 25-35% and Wc by 15-20%.
How does the order of enzyme addition (simultaneous vs. asynchronous) affect sludge dewatering and carbon release?
Asynchronous addition (protease/amylase first, then lysozyme) yields the lowest Wc, likely by first disrupting EPS to expose cells, then lysing cells. Simultaneous addition improves SRF and CST more effectively, possibly due to synergistic action on both EPS and cells. Carbon release (SCOD increase) is similar, but the composition of released organics may differ.
What is the impact of enzyme conditioning on sludge particle size and rheology?
All three enzymes reduce sludge particle size by 10-25%. Lysozyme decreases viscosity and increases hydrophobicity, while amylase and protease increase viscosity and hydrophilicity due to EPS disruption. These changes affect dewatering kinetics and final cake solids.
Can the filtrate carbon source be effectively utilized for biological nutrient removal?
Yes, enzyme conditioning transforms humic acid-like substances into tryptophan-like and tyrosine-like compounds, which are more biodegradable. The increase in SCOD (20-35%) provides a readily available carbon source for denitrification, potentially reducing external carbon addition.
What are the scalability and cost implications of using bioenzymes for sludge conditioning?
Enzymes are typically more expensive than conventional chemicals, but their targeted action may reduce dosage requirements and improve sludge dewatering, lowering downstream disposal costs. The study does not provide cost data, but the enhanced carbon recovery could offset some costs. Pilot-scale trials are needed to assess economic feasibility.
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