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In this work, the humic acid (HA)-modified g-C3N4-supported hydrotalcite-like compounds (g-C3N4@HTLcs/HA) was successfully synthesized, characterized, and further applied to remove 2,4-dichlorophen...

Sludge treatment and disposal have become critical environmental issues in China. Electro-dewatering (ED) is an attractive technology for enhancing dewaterability and improving the sustainability of waste activated sludge (WAS) handling. However, electrically assisted mechanical dewatering processes consume more energy and the extracellular polymeric substance (EPS) dissolution caused by electrochemical reactions can lead to clogging of the filter cloth. Carbon-based materials (CBMs) such as activated carbon and graphite have electrical conductivity and well-developed pore structures which can adsorb the biopolymers. Therefore, addition of CBMs is expected to improve WAS electro-dewatering performance for fuel treatment by enhancing sludge conductivity and filterability. In this study, we evaluated the effects of the three carbon materials (AC-0, AC-5, and graphite) on sludge electro-dewatering behavior and the flammability of sludge cakes. The results showed that CBMs promote the performance of WAS electro-dewatering, and the promoting effect of the carbon materials on the sludge electro-dewatering is proportional to the electrical conductivity of the carbon material, and carbon materials can increase the electrophoretic mobility of sludge flocs and the electro-osmotic effect. Moreover, CBMs can adsorb the dissolved EPS, thus alleviate the plugging and filtration resistance of the filter medium. The addition of CBMs also decreases the energy consumption for water removal during the electro-dewatering process and improves the calorific value and sustainable combustion time of the sludge cake. Our approach can facilitate the resource utilization of the dewatered sludge cake in electro-dewatering processes.

Sludge pyrolysis carbonization has shown potential to convert sludge biomass into multifunctional carbon materials. However, ecological risks of dissolved organic matters (DOMs) with obscure molecular characteristics retaining in sludge-based carbons (SBCs) have received little attention. This study investigated the impact of pyrolysis temperatures on the molecular conversion and biotoxicity effects of DOMs in SBCs. The results revealed that DOMs in SBCs300–400 were mainly derived from depolymerization of biopolymers and the polycondensation and cyclization of small intermediate molecules, which mainly consisted of aromatic CHON compounds with 1–3 N atoms, featuring high unsaturation and molecular weights. High-temperature pyrolysis (500–800 °C) promoted the decomposition and ring-opening of aromatic CHON compounds into saturated aliphatic CHO compounds with 2–4 O atoms in SBCs500–800. Noteworthily, SBCs300–400-derived DOMs showed relatively strong biotoxicity on the growth and development of wild-type zebrafish embryos, pakchoi seeds, and Vibrio qinghaiensis Q67, which was significantly related to aromatic amines, phenols, and heterocyclic-N compounds in DOMs of SBCs300–400. SBCs500–800-derived DOMs were mainly straight-chain fatty acids and showed no observable acute biotoxicity. This study highlights the negative impact of DOMs in SBCs on the ecological environment, and provides the theoretical basis for controlling toxic byproducts in sludge pyrolysis process.

Sludge contains large amounts of antibiotic resistance genes (ARGs), that reduce the efficacy of antibiotic therapies when transmitted to humans. However, conventional sludge treatment often fails to remove ARGs. Herein, critic acid chelated Fe(II) catalyzed peroxidation (CA-Fenton) was conducted to simultaneously improve sludge dewaterability and ARGs removal. As results, the CA-Fenton process exhibited significantly improved sludge dewatering performance and ARGs removal, in which the capillary suction time (CST), specific resistance to filtration (SRF) and cake moisture of sludge were reduced from 8.8 s·L/g, 5.8 × 1013 m/kg and 93.2% to 2.3 s·L/g, 5.8 × 1012 m/kg and 79.1%, respectively, and the removal efficiencies of 7 types-ARGs in sludge achieved over 90%. In addition, synergistic sludge dewatering and ARGs degradation mechanisms were elucidated with a suit of macro and spectroscopic evidence (high performance liquid chromatography-size exclusion chromatography (HPLC-SEC) and two-dimensional fourier-transform infrared correlation spectroscopy (2D-FTIR)). During CA-Fenton treatment, CA acidification enhanced permeability of the cell barrier in EPS, releasing intracellular ARGs into sludge bulk solution, which accelerated the ARGs degradation via CA chelated Fe(II) catalyzed H2O2 process. Meanwhile, destruction of secondary structure represented β-turn in proteins enhanced the hydrophobicity of EPS, which contributed the improvement of sludge dewaterability. The study not only proposed an efficient method to improve traditional Fenton oxidation for sludge treatment, but also provided a mechanistic basis for better understanding of the CA-Fenton process, and enable the harmless disposal for sludge.

In this work, blast furnace slag was successfully used to prepare five kinds of polymeric titanium aluminium flocculant (PTAC) with different polymerization degrees by two-step acid leaching method, which were applied as the effective dredged sludge conditioners. The results indicated that PTAC can obviously improve the sludge dewaterability. Compared with other four types of PTAC, PTAC0.6 showed the best sludge conditioning efficiency under the optimum dosage of 4 mg Al + Ti/g TSS. It can reduce the capillary suction time of the sediment by 81.4%, the specific resistance to filtration by 65.1%, and the moisture content of the mud cake from 81.9% to 45.81%. PTAC can significantly increase the zeta potential of the dredged sludge, while it has no obvious effect on the floc size D0.5. The electric neutralization substantially contributed to the conditioning of PTAC on dredged sludge dewatering. The concentration of dissolved organic carbon, total phosphorus in the residual water was significantly reduced after PTAC conditioning. PTAC can also remove large molecular weight components in dissolved organic matter by flocculation, or hydrolyze large molecular components into small and medium molecular weight components, furthermore reduce the concentration of these organic components. 3D-EEM analysis results showed that PTAC can effectively remove fulvic acid-like substances and some protein-like substances by flocculation, especially the removal effect of fulvic acid-like substances was more prominent.

In this work, a novel carbon-based hydrotalcite-like compounds materials (LDO-SBCs) were prepared by coupling layered double hydroxides (LDHs) conditioning and pyrolytic carbonization, and characterized by X-ray diffraction (XRD), Thermogravimetric Analyzer (TGA), X-ray photoelectron spectroscopy (XPS) and Brunner-Emmet-Teller (BET) measurements. The synthesized LDO-SBCs composites were used in wastewater treatment for simultaneous removal of phosphate and dissolved organic matter (DOM). The adsorption of DOM and phosphate were well conformed to pseudo-second-order mode. Adsorption equilibrium was better fitted by Langmuir model for phosphate, while Freundlich model for DOM. Compared with the raw sludge carbon, the removal efficiency of DOM and phosphate by LDO-SBCs were increased by 8% and 13%, respectively. Based on the fluorescence spectrum and parallel factor analysis (PARAFAC), LDO-SBCs performed well in promoting the removal of protein substances (TPN and APN). Pore filling, hydrogen bonding, electrostatic adsorption and surface complexation might be dominant in the adsorption of DOM, while, surface complexation and ion exchange between the LDO layers were mainly responsible for the adsorption of phosphate. The difference of adsorption capacity of LDO-SBCs was related to the superior channel structure of composite materials and the composition of interlayer anions of LDO.