Key Takeaways & Executive Findings
- •• • Optimal dewatering conditions: MFB dosage 132.99 mg/g DS, PMS dosage 421.80 mg/g DS, reaction time 18 min, achieving Wc 45.8% and TOC 489.2 mg/L, representing a significant improvement over conventional methods (e.g., Fe2+/sludge carbon-activated persulfate achieved Wc 71.2%). • • Radical contribution order: SO4−· (29.05%), ·OH (17.2%), and 1O2 (5.8%) to sludge dewatering, indicating sulfate radicals as the dominant reactive species in EPS disintegration. • • Protein reduction: Total protein content decreased from 174.6 mg/L to 75.7 mg/L (56.6% reduction), with TB-EPS protein reduced from 91.8 mg/L to 36.3 mg/L (60.5% reduction), directly attacking the hydrophilic core of sludge flocs. • • EPS layer destruction: S-EPS, LB-EPS, and TB-EPS contents decreased by 50.68%, 42.63%, and 53.06%, respectively, demonstrating comprehensive EPS breakdown and release of bound water.
Abstract
To enhance sludge dewatering efficiency, an MnFe2O4/BC/PMS system was constructed for sludge disintegration. Single-factor and multi-factor experiments were conducted to investigate the effects of MnFe2O4/BC (MFB) dosage, PMS dosage, and reaction time on sludge dewatering performance, establishing the optimal process parameters and the primary-secondary relationships among environmental factors. Active species identification in the MnFe2O4/BC/PMS system revealed the main free radicals responsible for sludge disintegration and the primary pathways of EPS breakdown. Results showed that the influence order of environmental factors on sludge moisture content (Wc) and total organic carbon (TOC) was MFB > PMS > reaction time, while the interaction effects followed MFB-PMS > PMS-reaction time > MFB-reaction time. Optimal dewatering occurred at MFB dosage of 132.99 mg/g DS, PMS dosage of 421.80 mg/g DS, and 18 min reaction time, achieving Wc of 45.8% and TOC of 489.2 mg/L. The ·OH and SO4−· radicals released from MnFe2O4/BC-activated PMS oxidized protein main chains, causing peptide chain breakage. This primarily reduced protein content in sludge from 174.6 mg/L to 75.7 mg/L, with TB-EPS protein content decreasing from 91.8 mg/L to 36.3 mg/L, thereby reducing EPS hydrophilicity and improving sludge dewatering efficiency.
1. Introduction
Municipal sludge management faces a critical bottleneck: the high water content (typically >80%) of sludge flocs, largely attributed to extracellular polymeric substances (EPS) that bind water through hydrophilic interactions and encapsulation. Conventional conditioning methods, such as organic flocculants (PAM) combined with inorganic conditioners (lime, PAC), achieve only moderate dewatering (final Wc 75–80%) while introducing secondary pollution and increasing sludge mass. Advanced oxidation processes (AOPs) using peroxymonosulfate (PMS) have emerged as a promising alternative, as they generate highly reactive radicals capable of disrupting EPS structure. However, homogeneous activation (e.g., Fe2+) suffers from high chemical consumption and limited recyclability, while heterogeneous catalysts often exhibit poor dispersion and stability.
This study addresses these limitations by synthesizing a composite of spinel-type manganese ferrite (MnFe2O4) supported on corn straw biochar (BC), termed MFB, to activate PMS for sludge conditioning. The biochar matrix enhances catalyst dispersion and provides adsorption sites, while the MnFe2O4 nanoparticles offer efficient electron transfer for PMS activation. Through systematic single-factor and response surface methodology, the optimal operational parameters were identified, and the underlying mechanisms—particularly the roles of specific free radicals and EPS fraction degradation—were elucidated. This approach not only achieves superior dewatering performance (Wc 45.8%) but also offers a recyclable and environmentally benign alternative to conventional conditioners, aligning with the national policy promoting sludge reduction and resource recovery.
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YOU Kun, LIU Juntong, WANG Zinan, ZHAO Jingrui (2026). Enhanced Sludge Dewatering Efficiency and Mechanism of MnFe2O4/BC-Activated PMS. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604024
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Frequently Asked Questions
What is the cost-effectiveness of MFB/PMS compared to conventional conditioners (e.g., PAM+CaO) in terms of chemical dosage and sludge volume increase?
According to Table 5, MFB/PMS requires MFB dosage of 1–2% and PMS dosage of 30–45% (relative to dry solids), resulting in a unit treatment cost of 30–90 CNY per ton of wet sludge, with a sludge volume increase of 30–50%. In contrast, PAM+CaO uses CaO 25–30% and PAM 0.4–0.6%, costing 6–8 CNY/t wet sludge but increasing sludge volume by 25–30%. While MFB/PMS has higher chemical costs, it achieves a much lower filter cake moisture content (45–50% vs. 80–90%) and is environmentally friendly with recyclable catalyst, potentially offsetting downstream disposal costs.
How does the MFB/PMS system perform under varying sludge characteristics, and what is the catalyst recyclability?
The study demonstrates that MFB/PMS is effective for municipal sludge, achieving Wc 45.8% under optimal conditions. Catalyst recyclability was tested (Figure 13), showing maintained performance over multiple cycles, though exact cycle numbers are not specified in the provided text. The system's robustness across different sludge types (e.g., industrial) is not fully addressed, but the radical-based mechanism suggests broad applicability.
What are the dominant reactive species and their relative contributions to sludge dewatering?
Through active species identification, SO4−·, ·OH, and 1O2 were found to contribute 29.05%, 17.2%, and 5.8% to sludge dewatering, respectively. This indicates that sulfate radicals are the primary oxidants, followed by hydroxyl radicals, while singlet oxygen plays a minor role. The radicals primarily attack protein components in EPS, leading to peptide chain breakage and release of bound water.
How does the MFB/PMS system affect EPS fractions (S-EPS, LB-EPS, TB-EPS) and what is the significance for dewatering?
After treatment, S-EPS, LB-EPS, and TB-EPS contents decreased by 50.68%, 42.63%, and 53.06%, respectively. Notably, TB-EPS protein content dropped from 91.8 mg/L to 36.3 mg/L, a 60.5% reduction. Since TB-EPS is tightly bound to sludge flocs and contributes to hydrophilicity, its degradation is critical for releasing bound water and improving dewaterability. The preferential degradation of S-EPS is attributed to its loose structure, making it more accessible to radicals.
What are the optimal operational parameters and their statistical significance?
The optimal conditions are MFB dosage of 132.99 mg/g DS, PMS dosage of 421.80 mg/g DS, and reaction time of 18 min, yielding Wc of 45.8% and TOC of 489.2 mg/L. Statistical analysis showed that MFB and PMS dosages have extremely significant effects on Wc and TOC (p < 0.001), while reaction time has a lesser influence. The interaction between MFB and PMS is significant, as indicated by elliptical contours in response surface plots.
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