New sustainable utilization approach of livestock manure: Conversion to dual-reaction-center Fenton-like catalyst for water purification

The study addresses the pressing issue of rural pollution driven by the accumulation and improper disposal of fecal waste (e.g., livestock and poultry manure), which contributes to environmental degradation, health risks, and substantial greenhouse gas emissions. Conventional treatments (biogasification, composting, fermentation) can be complex, slow, and risk releasing heavy metals, pathogens, odors, and GHGs. Chicken manure contains valuable organic and metallic constituents (e.g., Ca, Cu, Fe, Si, C, O) that could serve as raw components for functional materials such as MOFs/MOCPs, yet conventional syntheses of such materials are resource- and energy-intensive. Prior work by the authors on dual-reaction-center (DRC) catalysts showed that metal cation-π structures can create electron-rich/poor microregions that enable pollutants to donate electrons to reduce H₂O₂, greatly enhancing Fenton-like processes. However, catalyst synthesis in those systems remained energy-intensive. The research question is whether unprocessed livestock manure can be directly converted, in a sustainable manner, into an efficient, stable DRC Fenton-like catalyst that simultaneously addresses waste disposal and enables low-consumption water purification.

The paper situates the work within literature on rural sanitation and environmental health impacts, highlighting significant mortality associated with untreated fecal waste. It reviews existing manure treatment strategies and their environmental drawbacks. It notes the potential of chicken manure as a low-cost source of metals and carbon for advanced materials (MOFs/MOCPs), while emphasizing the high resource demands of conventional synthesis routes. The authors reference their prior DRC catalyst studies demonstrating cation-π interactions and electron-rich/poor microregions that facilitate pollutant-driven electron donation to H₂O₂ in Fenton-like reactions. The gap identified is the lack of a sustainable, low-energy synthesis route to such catalysts that also valorizes waste biomass.

Synthesis (resourcelized conversion): Unprocessed chicken manure (CM) was converted into a purified catalyst precursor (CM-precursor) via natural drying and purification. The precursor was heated (atmosphere containing 10–30% O₂) for 3–5 h at a set heating rate, then annealed. For Cu incorporation, hydrochloric acid solution was added to 3 g CM-precursor and stirred for 30 min; deionized water and a trace of Cu(NO₃)₂·3H₂O were added. The pH was adjusted to 11 with NH₃·H₂O. The mixture was stirred at 80 °C in a water bath to remove water, then evaporated at 140 °C in air to remove volatiles. The product was calcined at 550 °C in a muffle furnace (5 °C min⁻¹) for 3–5 h, washed with deionized water and ethanol, and dried at 100 °C for 4 h to yield Cu-decorated CM nanoparticles (CCM-Nps). A control (CM-Nps) was synthesized identically without Cu(NO₃)₂·3H₂O. The overall process is an in situ 2-stage calcination-annealing approach intended to order intrinsic metal-organic species and form DRCs with zero emissions and pollution. Characterization: Morphology and composition were analyzed by FE-SEM/EDX (JSM-6700F), HR-TEM (JEM-2100), and XRD (Philips X’Pert PRO). Surface chemistry was analyzed by XPS (VG Multilab 2000). Solid-state EPR (Bruker A300-10/12) was employed. Raman and FTIR spectra were recorded to identify carbon structures and bonding environments. Activity tests (Fenton-like degradation): Experiments were performed in 100 mL glass beakers with 50 mL pollutant solution (10 mg L⁻¹; natural pH ~7) at 35 °C. Unless noted, catalyst dosage was 0.2 g L⁻¹ (0.01 g in 50 mL) and H₂O₂ 10 mM. H₂O₂ was added under stirring; 2 mL aliquots were withdrawn over time and filtered (0.22 µm) for analysis. Pollutants included BPA, 2-CP, diphenhydramine (DP), and ciprofloxacin (CIP). H₂O₂ consumption was tracked. Effects of H₂O₂ concentration, initial pH (3.86–9.63 adjusted by NaOH/HNO₃), and anions (Cl⁻, SO₄²⁻, NO₃⁻, PO₄³⁻ at 1 mM) were tested. Practical wastewater tests: Kitchen wastewater samples from malls/restaurants were treated with the CCM-Nps/H₂O₂ system. Visual changes and 3D excitation-emission matrices (EEMs) tracked removal of protein-like fluorescence peaks. Stability: A packed-bed style reactor with CCM-Nps mixed with quartz sand (to minimize catalyst loss) was operated continuously; BPA removal was monitored for >900 h. A quartz-sand-only control was run. Reactive species and mechanism: EPR with spin-trapping (BMPO/TEMP) detected •OH, O₂•⁻/HO₂•, and ¹O₂ signals in systems with/without H₂O₂ and BPA. Radical quenching tests used tert-butanol (TBA, •OH quencher), p-benzoquinone (PBQ, O₂•⁻ quencher), and furfuryl alcohol (FFA, ¹O₂ quencher). LC-MS identified CIP degradation intermediates to elucidate pathways (hydroxylation and surface cleavage).

• Successful conversion of chicken manure into a DRC Fenton-like catalyst (CCM-Nps) featuring graphene-like carbon nanosheets decorated with Cu/O species; evidence includes TEM/HRTEM (0.65 nm graphene-like, ~0.272 nm Cu–O lattice), XRD (CaSO₄, SiO₂ matrix with CuO peaks at 2θ = 35.42°, 38.76°), Raman (D/G bands; Cu–O to Cu–O–C shifts), FTIR (C=O shift, emergence of Cu–O vibrations at 538 cm⁻¹), EPR/XPS (electron redistribution with Cu⁺ signal at 933.2 eV), indicating electron-rich/poor microregions and C–O–Cu bridges.
• High catalytic performance across multiple pollutants: complete degradation of BPA, 2-CP, DP, and CIP within 1 h at natural pH, 10 mg L⁻¹ pollutant, 0.2 g L⁻¹ catalyst, and 10 mM H₂O₂. Notably, DP achieved >90% removal within 1 min; BPA was rapidly degraded.
• CCM-Nps greatly outperformed CM-Nps: For BPA, CCM-Nps/H₂O₂ showed ~43× higher apparent rate than CM-Nps/H₂O₂; CM-Nps/H₂O₂ removed only ~20% in 60 min.
• Low H₂O₂ consumption: During BPA degradation, only ~20% of H₂O₂ was consumed in 60 min; even without BPA, H₂O₂ consumption was <40%.
• Effective over wide conditions: High activity from pH 3.86–9.63 (≥90% BPA removal within 30 min at both extremes). Common anions (1 mM Cl⁻, SO₄²⁻, NO₃⁻, PO₄³⁻) did not inhibit activity; NO₃⁻ and PO₄³⁻ notably enhanced performance (>90% BPA removal within 2 min).
• Practical wastewater treatment: Kitchen wastewater showed disappearance of protein-like fluorescence EEM peaks after 30 min, confirming efficient removal of organic matter; visual clarity improved.
• Durability: In a continuous reactor, CCM-Nps maintained ~60% BPA removal after >900 h; control (quartz sand only) remained <10%.
• Mechanistic insights: EPR detected •OH, O₂•⁻, and ¹O₂ even without H₂O₂ (•OH from water oxidation on DRCs; electrons transferred to O₂). With H₂O₂, •OH signal increased ~5×; adding BPA further increased •OH and O₂ signals while decreasing O₂•⁻, suggesting pollutant-supplied electrons and key roles of •OH and ¹O₂. Quenching reduced degradation by ~70% (TBA), ~10% (PBQ), and ~90% (FFA), indicating dominant roles of •OH and ¹O₂. LC-MS of CIP showed early hydroxylation products (m/z 308.2, 201, 279) and later surface-cleavage fragments (m/z 263, 223, 178), supporting dual pathways. H₂O₂ acts as a trigger requiring only trace amounts to initiate a chain reaction leveraging pollutant and dissolved oxygen energy.

The findings demonstrate that unprocessed chicken manure can be sustainably converted into a high-performance DRC Fenton-like catalyst through an in situ 2-stage calcination-annealing process that orders intrinsic metal-organic species and creates electron-rich/poor microregions. This architecture enables directional electron transfer: pollutants and water serve as electron donors via cation-π and π-π interactions with graphene-like carbon, while Cu-centered sites accept electrons to activate H₂O₂ and dissolved oxygen, forming ROS (•OH, ¹O₂, O₂•⁻) that drive pollutant degradation. The system achieves rapid, near-complete removal of diverse refractory organics with low H₂O₂ consumption, broad pH tolerance, salt compatibility, and exceptional long-term stability, addressing both waste valorization and efficient water purification. Compared to conventional heterogeneous Fenton-like catalysts, CCM-Nps achieves similar or superior performance using far lower dosages of both catalyst and H₂O₂, implying reduced resource and energy footprints for both synthesis and application, thereby advancing sustainable wastewater treatment and rural waste management goals.

The study pioneers a zero-emission, zero-pollution route to transform livestock manure (chicken manure) into a dual-reaction-center Fenton-like catalyst (CCM-Nps) that delivers rapid, efficient degradation of multiple refractory pollutants, robust performance across conditions, practical efficacy on real wastewater, and long-term operational stability with low H₂O₂ consumption. The work demonstrates a viable pathway for the resource utilization of rural solid waste while enhancing the sustainability of water treatment processes. The authors highlight that this approach can match or exceed conventional catalyst performance with significantly lower catalyst and oxidant dosages, underscoring its potential impact on sustainable development in environmental management.