Hydrothermal-enhanced pyrolysis for efficient NOX reduction and biochar valorization from food waste digestate.

Pyrolysis has emerged as a promising technology for valorizing digestate resulting from the anaerobic digestion of food waste. However, the high NOX emissions during pyrolysis limit its application. This study proposed a hydrothermal coupled pyrolysis process to control the element transfer in digestate during biochar production. The efficient reduction of NOX emissions and the improvement of biochar adsorbability were realized. The hydrothermal process reduced the nitrogen content in solid digestate by 49.10 %-81.79 %, thus reducing the NOX precursors in syngas and the N-containing substances in bio-oil. Additionally, the specific surface area and the total pore volume of biochar were enhanced from 25 m2/g to 60-73 m2/g and 0.06 cm3/g to 0.12-0.14 cm3/g, respectively. More defects, oxygen-containing functional groups, and doped Ca on the biochar resulted in a high phosphate removal efficiency of 94 %. The proposed technology provides an efficient and environmentally friendly way to utilize the digestate.

Determination of key factors affecting biofilm formation on the aged Poly(ethylene terephthalate) during anaerobic digestion.

Biofilm formation on plastic surface is a growing concern because it can alter the plastic surface properties and exacerbate the ecological risk. Identifying key factors that affecting biofilm formation is critical for effective pollution control. In this study, the poly (ethylene terephthalate) (PET) was aged in water and air conditions with UV irradiation, then incubated in the digestate of food waste anaerobic digestion to allow biofilm formation. Surface analysis techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), were utilized to investigated the changes in the topography, roughness, hydrophily, and functional groups change of the PET surface during the aging process. Confocal laser scanning microscopy (CLSM) was used to determine the distribution of microorganisms on the PET surface after incubation in the digestate. This study focused on understanding the interactions between the PET surface and biofilm to identify critical surface factors that affect biofilm formation. Results showed that the four months aging process decreased the contact angle of the PET surface from 96.92° to 76.08° and 68.97° in water and air conditions, respectively, corresponding to an increase of 44% and 70% in the surface energy. Additionally, aging in air conditions led to a rougher surface compared to water conditions. The arithmetic roughness average (Ra) of the PET-Water was 11.0 nm, comparable to that of the pristine PET, while the value of PET-Air was much higher (43.9 nm). The results further indicated that biofilm formation during anaerobic digestion was more sensitive to roughness than hydrophily. The PET surface aged in air conditions provided a more suitable environment for microbial reproduction, leading to the aggradation of living cells.

Exploiting Cation Intercalating Chemistry to Catalyze Conversion-Type Reactions in Batteries.

Effective harvest of electrochemical energy from insulating compounds serves as the key to unlocking the potential capacity from many materials that otherwise could not be exploited for energy storage. Herein, an effective strategy is proposed by employing LiCoO2, a widely commercialized positive electrode material in Li-ion batteries, as an efficient redox mediator to catalyze the decomposition of Na2CO3 via an intercalating mechanism. Differing from traditional redox mediation processes where reactions occur on the limited surface sites of catalysts, the electrochemically delithiated Li1-xCoO2 forms NayLi1-xCoO2 crystals, which act as a cation intercalating catalyzer that directs Na+ insertion-extraction and activates the reaction of Na2CO3 with carbon. Through altering the route of the mass transport process, such redox centers are delocalized throughout the bulk of LiCoO2, which ensures maximum active reaction sites. The decomposition of Na2CO3 thus accelerated significantly reduces the charging overpotential in Na-CO2 batteries; meanwhile, Na compensation can also be achieved for various Na-deficient cathode materials. Such a surface-induced catalyzing mechanism for conversion-type reactions, realized via cation intercalation chemistry, expands the boundary for material discovery and makes those conventionally unfeasible a rich source to explore for efficient utilization of chemical energy.

Variation behavior of organic compounds in melamine-urea-formaldehyde impregnated bond paper in different pyrolysis stages.

Melamine-urea-formaldehyde impregnated bond paper (MUF) is widely used as panel coating and decorative raw paper. Inappropriate treatment of MUF may lead to environmental pollution. In this study, routine MUF and MUF treated with additional titanium (MUF-T) were subjected to fast pyrolysis, and the product properties at different temperatures were investigated. The pyrolysis temperature was selected considering the reaction stages determined by Gaussian curve-fitting on thermogravimetric analysis curves. It was found that the presence of additional titanium changed the decomposition order of the organic components at 220 °C. Urea-formaldehyde in MUF could be decomposed at 220 °C, which had little effect on other components (melamine and cellulose). However, in terms of MUF-T, the decomposition temperature of urea-formaldehyde was postponed to 244 °C, which means that the pyrolysis strategy needs to choose a temperature higher than 244 °C. The volatiles in MUF-T are more easily converted to bio-gas or bio-oil than those in MUF. However, only CH4 was observed in the bio-gas generated of MUF-T at 220 °C, indicating that titanium did not catalyze the fracture of oxygen-containing functional groups at low temperatures. Titanium condensed at 550 °C, and the utilization of bio-char may face a problem of titanium particle shedding.

Improvement in the physicochemical characteristics of biochar derived from solid digestate of food waste with different moisture contents.

The management of digestate from food waste (DFW) has become a worldwide challenge. Pyrolysis is a promising technology to generate biochar from the DFW. However, unlike other biomass, DFW usually has high salt and moisture content, which affects the properties of biochar generated from pyrolysis. The characteristics of biochar derived from DFW with different MCs (5%, 20%, 40%, and 60%) were investigated in the present study. It was found that more micropore and mesopore structures were generated in the biochar with the increase of MC from 5% to 60%, resulting in the Brunauer-Emmett-Teller surface area of the biochar increased from 89.23 m2 g-1 to 117.75 m2 g-1. The MC could also promote the variation of oxygen-containing functional groups and the generation of amorphous carbon structures, which are beneficial for the adsorption property of the biochar. Pyrolysis could stabilize the metals in the biochar, while MC has little effect on the metal speciations. These results provide fundamental information on the impact of MC on the properties of biochar derived from DFW and are important for the optimization of the pre-drying process.

Aging simulation of thin-film plastics in different environments to examine the formation of microplastic.

Microplastics have received considerable attention in recent years. Understanding the aging mechanism of plastics in different environments (land, fresh water, estuary, and ocean) is critical to control the microplastic formation. Therefore, the aging process of plastics, including polyethylene (PE) and polypropylene (PP), in different environments was simulated by analyzing their physical and chemical structures by using the Raman spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy techniques. After 23 weeks, micro-scale microplastics (size less than 100 µm) could be extracted from the plastic surface through smashing waves in all fresh water and seawater samples. However, complete fragmentation was observed only in the case of thin-film plastics (TFPs, thickness of approximately 10 µm). This phenomenon indicated that TFPs disintegrated to microplastics more easily in the water system than on land, and the water flow notably affected the production of micro-scale particles. Furthermore, ultraviolet radiation affected the chemical structure of plastics through a two-stage process in all environments. In the initial stage, chemical aging occurred in the amorphous regions of both PE and PP, leading to the generation of newly functional groups such as C=O at 1717 cm-1, and a reduced contact angle. In the later stage, PE exhibited additional crystals and increased contact angles, whereas PP demonstrated the tendency of producing oxygen-containing functional groups that could reduce the crystallinity. In addition, several inorganic salts (such as sulfate and phosphorus) in seawater likely combined with C-H-type stretches, thereby promoting the chemical aging of plastics.