Biochar-Assisted Catalytic Pyrolysis of Oily Sludge to Attain Harmless Disposal and Residue Utilization for Soil Reclamation.

Pyrolysis of oily sludge (OS) is a feasible technology to match the principle of reduction and recycling; however, it is difficult to confirm the feasible environmental destination and meet the corresponding requirements. Therefore, an integrated strategy of biochar-assisted catalytic pyrolysis (BCP) of OS and residue utilization for soil reclamation is investigated in this study. During the catalytic pyrolysis process, biochar as a catalyst intensifies the removal of recalcitrant petroleum hydrocarbons at the expense of liquid product yield. Concurrently, biochar as an adsorbent can inhibit the release of micromolecular gaseous pollutants (e.g. HCN, H2S, and HCl) and stabilize heavy metals. Due to the assistance of biochar, pyrolysis reactions of OS are more likely to occur and require a lower temperature to achieve the same situation. During the soil reclamation process, the obtained residue as a soil amendment can not only provide a carbon source and mineral nutrients but can also improve the abundance and diversity of microbial communities. Thus, it facilitates the plant germination and the secondary removal of petroleum hydrocarbons. The integrated strategy of BCP of OS and residue utilization for soil reclamation is a promising management strategy, which is expected to realize the coordinated and benign disposal of more than one waste.

Pyrolysis Behaviors and Residue Properties of Iron-Rich Rolling Sludge from Steel Smelting.

Iron-rich rolling sludge (FeRS) represents a kind of typical solid waste produced in the iron and steel industry, containing a certain amount of oil and large amounts of iron-dominant minerals. Pyrolysis under anaerobic environment can effectively eliminate organics at high temperatures without oxidation of Fe. This paper firstly investigated comprehensively the pyrolysis characteristics of FeRS. The degradation of organics in FeRS mainly occurred before 400 °C. The activation energy for pyrolysis of FeRS was extremely low, ca. 5.44 kJ/mol. The effects of pyrolytic temperature, atmosphere, heating rate, and stirring on pyrolysis characteristics were conducted. Commonly, the yield of solid residues maintained around 85 wt.%, with approximately 13 wt.% oil and 2 wt.% gas. Due to the low yield of oil and gas, their further utilization remains difficult despite CO2 introduction which could upgrade their quality. The solid residues after pyrolysis exhibited porous properties with co-existence of micropores and mesopores. Combined with the high content of zero-valent iron, magnetic property, hydrophobic characteristic, and low density, the solid residues could be further utilized for water pollution control and soil remediation. Moreover, the solid residues were suitable for sintering to recover valuable iron resources. However, the solid residues also contained certain heavy metals, such as Cd, Cr, Cu, Ni, Pb, and Zn, which might cause secondary pollution during their utilization. In particular, the toxic Cr possessed high content, which should be treated with detoxification and removal. This paper provides fundamental information for pyrolysis of FeRS and utilization of solid residues.

Utilizing waste duckweed from phytoremediation to synthesize highly efficient FeNxC catalysts for oxygen reduction reaction electrocatalysis.

Duckweed is a universal aquatic plant to remove nitrogen source pollutants in the field of phytoremediation. Due to the naturally abundant nitrogen, synthesis of carbon materials from duckweed would be a high-value approach. In oxygen reduction reaction (ORR) of metal-air batteries and fuel cells, non-noble metals and heteroatoms co-doped electrocatalysts with excellent catalytic activity and remarkable stability are promising substitutes for Pt-based catalysts. The first-class ORR performance is determined by appropriate pore structure and active sites, which are strongly associated with the feasible synthesis methods. Herein, a facile one-step synthesis strategy for the transition metals- and nitrogen-codoped carbon (MNxC) based catalysts with hierarchically porous structure was developed. The MNxC (M = Fe, Co, Ni, and Mn) active sites were constructed and FeNxC (D-ZB-Fe) was the best electrocatalyst with excellent ORR performance. Results showed that D-ZB-Fe exhibited an obvious honeycomb porous structure with specific surface area of 1342.91 m2·g-1 and total pore volume of 1.085 cm3·g-1. It also possessed considerable active atoms and sites, where the proportion of pyridine N and graphite N was up to 72.9%. The above feature made for a superior ORR electrocatalytic activity. In specific, the onset and half-wave potential were 0.974 V and 0.857 V vs. RHE (Reversible Hydrogen Electrode), respectively. When compared with performances of commercial Pt/C, the four-electron pathway and relatively low peroxide yield, ca. 5%, were almost equivalent. Furthermore, D-ZB-Fe showed an excellent stability and remarkably methanol tolerance by the durability test. In conclusion, this research provides a new synthesis strategy of electrocatalysts with porous structures and active sites.

Triple combination of natural microbial action, etching, and gas foaming to synthesize hierarchical porous carbon for efficient adsorption of VOCs.

Fungi residue, vinasse, and biogas residue differ from general biomass waste due to natural microbial action. Microbial fermentation helps create natural channels for the permeation of activators and produces proteins for natural nitrogen doping. Inspired by these advantages on porous carbon synthesis, this study adopted dual activators of KOH and KHCO3 to synthesize porous carbon with different pore ratios for efficient adsorption of volatile organic compounds (VOCs). The fungi residue possessed the least lignin due to the most severe microbial action, contributing to the best pore structures after activation. The etching effect from potassium compounds and gas foaming from the carbonate decomposition contributed to creating hierarchical porous carbon with ultra-high surface area, ca. 1536.8-2326.5 m2/g. However, KHCO3 addition also caused nitrogen erosion, such that lower adsorption capacity was attained even with a higher surface area when the mass ratio of KOH/KHCO3 decreased from 2.5:0.5 to 2:1. The maximum adsorption capacities of chlorobenzene (CB) and benzene (PhH) reached 594.0 and 394.3 mg/g, respectively. Pore structure variations after adsorption were evaluated by freeze treatment to discover the adsorption mechanism. The surface area after CB and PhH adsorption decreased 40.3% and 34.5%, respectively. Most of the mesopores might transform into micropores due to the mono/multilayer stacking of adsorbates. The VOC adsorption kinetics were simulated by the Pseudo-first- and -second-order models and Y-N model. This paper provides a new approach for high-value biomass waste utilization after microbial action to synthesize efficient adsorbents for VOCs.

Insoluble matrix proteins from shell waste for synthesis of visible-light response photocatalyst to mineralize indoor gaseous formaldehyde.

HCHO is the most concerned indoor air pollutant that photocatalytic degradation is a feasible approach. To achieve efficient and complete degradation of HCHO under visible light irradiation, heteroatoms are usually doped in TiO2. But using natural materials as a dopant instead of expensive and toxic chemicals to fertilize TiO2 remains challenging. This paper proposes a sustainable and green approach to synthesize an efficient N, Ca co-doped TiO2 photocatalyst (TIMP) by using the insoluble matrix proteins (IMPs) extracted from abalone shell. TIMP-0.8 achieves near completely degradation HCHO within 45 min under visible light at ambient temperature and exhibits superior stability after 7 cycles. TIMP-0.8 has monodispersity with smaller diameter, high porosity, abundant defects and high adsorption affinity for surface hydroxyls compared with pure TiO2. With the assistance of IMPs, the rate-determining step of HCHO degradation changes from -COOH oxidation to spontaneous decomposition of HCO3-, significantly facilitating the elimination and mineralization of HCHO. Overall, IMPs from abalone shell are natural surfactant, bio-templet, and dopant for TiO2 modification, contributing to desirable visible-light photocatalytic performance for HCHO degradation. This paper provides new insight for high-value utilization of waste shell and photocatalytic indoor purification.

Utilization of edible fungi residues towards synthesis of high-performance porous carbon for effective sorption of Cl-VOCs.

Edible fungi residues are natural fungi etching feedstock that provide loose structure with multidimensional framework. These advantages help KOH to penetrate rigid cytoderm into innermost space and attain porous carbon with high porosity. Utilization of edible fungi residue not only avoids artificial operation of fungal inoculation and culture steps, but also provides new method for waste disposal. As expected, carbon derived from three fungi residues attains excellent porosity. The highest surface area reaches 3463.3 m2/g, which is approximately 2 and 6 times higher than original biomass (1630.7 m2/g) and commercial carbon (691.1 m2/g), respectively. Filiform structures derived from hyphae growth contribute to pores formation. Coprinus comatus fungi residue as optimal raw material obtains hierarchical pore channel with dominant micropores (76%) and natural nitrogen doping (1.28 at.%). The highest DCM and CB adsorption capacities attain 716.9 and 641.7 mg/g, respectively, which are 13 and 6 times higher than that of commercial carbon. The positive effects from fungi growth improve DCM adsorption particularly. DCM adsorption over fungi residues derived carbon is twice higher than original biomass carbon. Competitive adsorption, recyclability, surface variations and desorption components after saturated adsorption are fully investigated for practical application. The present study provides a new insight for developing high-value technology for synthesizing Cl-VOCs adsorbents using edible fungi residues.

Comparative investigation on catalytic ozonation of VOCs in different types over supported MnOx catalysts.

This paper conducted catalytic ozonation of CB (chlorobenzene) over a series of MnOx based catalysts with different supports (Al2O3, TiO2, SiO2, CeO2, and ZrO2) at 120 °C. Mn/Al2O3 exhibited highest CB conversion efficiency, ca. 82.92 %, due to its excellent textual properties, O2 desorption, redox ability, and desirable surface adsorbed oxygen species and acidity. O3 conversion all approached nearly 100.0%, with residual <10 ppm. Mn/Al2O3 was further employed to investigate effect of temperature, O3/CB, and space velocity on CB conversion. Hereafter, catalytic ozonation of single and binary VOCs in different types was performed, i.e., CB, DCE (dichloroethane), DCM (dichloromethane), and PhH (Benzene). Conversion results demonstrated aromatics degraded easier than alkanes and more carbon atoms decreased difficulty, as CB∼PhH > DCE∼DCM, and DCE > DCM; but chlorinated substitution increased difficulty, as PhH > CB. Catalytic co-ozonation of CB/DCE indicated that DCE significantly improved CB conversion to reach totally degradation at low O3 input, but inhibited DCE conversion, especially at higher ratio of DCE/CB. Co-ozonation improved ozone utilization efficiency, and maintained the original property of catalyst. By contrast, CB/PhH co-ozonation displayed very mild effects. Finally, critical intermediates during catalytic CB ozonation, i.e., DCM, carboxyl and formic acid, were detected from mass spectrum results.