Catalytic pyrolysis is a promising chemical recycling technology to supplement mechanical recycling since plastics can be broken down into monomers or converted to the required fuels and chemicals. In this study, a microwave (MW) -responsive SiC foam@zeoltie core-shell structured catalyst was proposed for the catalytic pyrolysis of polyolefins. Under microwave irradiation, the SiC foam core works as both microwave adsorber and catalyst support, thus concentrating the generated heat energy on the ZSM-5 zeolite shell, where the catalytic reaction takes place. SiC foam with an open cellular structure can also improve the global transport of mass and heat during plastics pyrolysis. In this work, the effects of the SiO₂/Al₂O₃ ratio and alkaline treatment of ZSM-5 zeolite coated SiC foam under MW irradiation on the variations in product distribution from low-density polyethylene (LDPE) pyrolysis were investigated at 450 °C. The results indicated that the appropriate acidity and pore structure were crucial to upgrading gas and liquid products. Particularly, the creation of a mesoporous structure in ZSM-5 zeolite via alkaline treatment could improve the diffusion of large molecules and products, thus significantly increasing the selectivity of high-valued light olefins and aromatics while inhibiting the formation of unwanted alkanes, which are expected in the chemical industry. Concretely, the concentration of olefins in gas increased to 51.0 vol% for ZSM-5(50)-0.25AT, and 65.6 vol% for ZSM-5 (50)-0.50AT, compared with 45.2 vol% for the parent ZSM-5(50). The relative concentration of aromatics in liquid decreased from 96.6% for ZSM-5(50) to 75.9% for ZSM-5(50)-0.25AT, and 71.1% for ZSM-5(50)-0.50AT. Given the respective yield of gas and liquid, the total selectivity of C2–C4 olefins and aromatics for mesoporous ZSM-5 zeolites could reach 58.6–64.9% during LDPE pyrolysis, which were higher than that for the parent ZSM-5 zeolite.

Aquatic plant biomass like Iris pseudacorus can be used as electron donor to improve denitrification performance in subsurface constructed wetlands. However, the phenomenon that the nitrogen removal rate declined in the terminal stage restricted the utilization of litters. In terms of this problem, this study investigated the performance of the used biomass through alkali treatment on nitrogen removal and analyzed the effect of alkali treatment on the component and structure of biomass and microbial community. The results showed that the alkali-treated biomass could further enhance the nitrogen removal by nearly 15% compared with used ones. The significant damage of cell walls and compact fibers containing cellulose and lignin through alkali treatment mainly resulted in the improvement of carbon release and nitrogen removal. With the addition of alkali-treated biomass, the richness index of microbes was higher compared with other biomass materials. Furthermore, the abundance of denitrification related genera increased and the abundance of genera for nitrification was maintained. Based on these finds, a mode of a more efficient Iris pseudacorus self-consumed subsurface flow constructed wetlands was designed. In this mode, the effluent total nitrogen could be stabilized below 5 mg L⁻¹ for nine months and the weight of litters could be further cut down by 75%. These findings would contribute to efficient utilization of plant biomass for nitrogen removal enhancement and final residue reduction in the wetlands.

Phosphatization of ZnO nanoparticles (ZNPs) at various pHs and its influence on subsequent lead sorption were investigated. Results showed that, in presence of phosphate, both the chemical speciation and crystalline phase of ZNPs were pH dependent that most of them were converted to crystalline Zn3(PO4)2 at acidic pHs, but only little amorphous hopeites can be formed under alkaline condition. Phosphatization process significantly enhanced subsequent lead sorption with the order of acidic process > alkaline > pristine ZNPs. Spectroscopic analysis including ATR-FTIR and XPS revealed main mechanisms of lead phosphate precipitation and inner-sphere complexes for lead sorption on acidic and alkaline treatment products, respectively. The potential toxicity of ZNPs and heavy metals in eutrophic aquatic ecosystems would thus be reduced due to the ubiquitous phosphatization process. This study highlights the importance of environmental variables in exploring the environmental behavior and fate of heavy metals as well as nanoparticles in natural waters.

Iron-incorporated silica (Fe/SiO₂) with different Fe/Si molar ratio was successfully prepared from rice husk pyrolytic residues (RHR) through alkali pretreatment, co-precipitation, and calcination. Various characterization methods indicated that the Fe/SiO₂ samples possessed mesoporous structure with Fe species incorporated into the framework of silica. The obtained materials were applied in the treatment of hazardous banknote printing wastewater, and under the optimal conditions, colored pollutants, humic acid-like and soluble microbial by-product-like organics were removed significantly. It was found that Fe/SiO₂ acted as both flocculant and catalyst, and the framework iron species catalyzed the oxidative degradation of refractory organics in the presence of H₂O₂. A heterogeneous Fenton-like system was formed in the wastewater treatment process.

Alkaline pretreatment (APT) is the promising disintegration pretreatment for the anaerobic digestion (AD) of sewage sludge (SS) to improve digestion efficiency and methane yields. In this study, the heavy metals (HMs) were observed to be leached from SS in the APT process, which could lower the HMs secondary pollution risk of the residual biosolids after AD in land application. The sequential chemical extraction (SCE) experiment was performed to determine the variation in HMs’ distribution prior to and after the APT. The alkaline extracts were characterized in order to elucidate the HMs’ release mechanism. The APT could cause significant release of Zn and Cu with a maximum release efficiency of 96.6% ± 4.6% and 62.7% ± 8.4% under the condition of 1.5 mol/L NaOH and 25 ℃, respectively. The release efficiency of Zn and Cu was reduced by 63.0% and 21.7%, respectively, due to the extra addition of 0.25 mol/L NaCl at a NaOH concentration of 1.25 mol/L in the APT process. The release of Zn and Cu may be attributed to a complex process including disruption of microbial cells in SS, solubilization of organic matters bounded with metals, and the chemical leaching reaction of minerals. This study demonstrates the possibility to remove the Zn and Cu from the SS in the APT process before the AD disposal.

This study prepared a biosorbent from the agricultural waste of atemoya peels, which was then used to remove the methylene blue dye. The atemoya peels were used in natura, and some were subjected to an alkaline treatment. The pH values obtained for the points of zero charge were 6.0 and 8.0 for the untreated and alkaline-treated materials, respectively. For neutral and/or alkaline pH values, the untreated and treated materials achieved average removals of approximately 80% and 90%, respectively. A kinetic study of the model dye removal profile showed a higher removal ratio over a shorter period for the alkaline-treated material. This profile is described by the pseudo-second-order model, which was the best fit for the D-R isotherm in both biosorbents. The maximum biosorption capacities were 190.18 mg g⁻¹ (untreated) and 264.50 mg g⁻¹ (treated) at 45 °C, and the alkaline-treated materials were shown to be reusable for at least 5 cycles. The results show that these biosorbents are efficient and cost-effective to remove the studied model molecules.

This study investigated the biogas production and dewaterability of sewage sludge with alkaline pretreatment at mesophilic and thermophilic temperatures. The total suspended solids (TSS) and volatile suspended solids (VSS) of raw sludges were 21.1 ± 2.3 and 16.2 ± 1.5 g L⁻¹, respectively. Raw sludges were pretreated at uncontrolled, pH 8, pH 10, and pH 12 under mesophilic (Mu, M8, M10, and M12) and thermophilic (Tu, T8, T10, and T12) conditions, respectively. All the pretreatments last 6 days. The pH of pretreated sludges was adjusted to the pH 7.0 prior to inoculating with mesophilic anaerobic digested sludge and undergoing 60 days of anaerobic digestion. The ultimate biogas yield of Mu, M8, M10, M12, Tu, T8, T10, and T12 was 296.8, 384.8, 339.9, 323.1, 376.6, 322.4, 271.5, and 258.1 mL g⁻¹-VSₐddₑd, respectively. Both the pH of alkali treatment and temperature of thermal treatment affect the performance of anaerobic digestion. High hydrolysis pH (pH 10 and pH 12) resulted in high Na⁺ concentration (over 4000 mg L⁻¹), and Na⁺ inhibitory effect reduced the ultimate biogas yield. The normalized capillary suction time (NCST) found in the treatments of M8 and Tu were 11.8 ± 1.1 to 23.4 ± 1.7 and 27.9 ± 5.4 to 111.8 ± 1.7 s g⁻¹-TSS, respectively. The results suggest that both the pH of alkali treatment and temperatures of mild thermal treatment affect the performance of anaerobic digestion and sludge pretreated at pH 8.0 under mesophilic conditions could achieve high biogas yield and adequate dewaterability of digested sludge.

Sewage sludge, a common by-product of wastewater treatment plants, is one important repository of antibiotic resistance genes (ARGs). The growing demands of sewage sludge reclamation, such as land application, increase the possibility of introducing ARGs into the environment and even the further dissemination of antibiotic resistance. Previous studies have paid much attention to the removal efficiencies of conventional pollutants such as heavy metals and pathogenic microorganisms during the sludge treatment processes. However, the effects on the abundance and diversity of ARGs got great concerns only recently. This paper mainly focuses on the enrichment and transmission modes of ARGs in sludge and the effects of representative sludge treatment technologies on ARG distributions in sludge. It seems that most physical and chemical techniques such as microwave, alkali treatment, and coagulation are ineffective in ARG reduction. The impacts of biological sludge treatment technologies on ARGs are varied, probably because of the diverse microbial community structures, operational parameters, and even environmental factors such as rainwater. Therefore, the sensitivities of potential hosts of specific ARG to the sludge treatments should determine the abundance of ARG before and after treatment. In addition, a reasonable combination of different sludge process techniques is usually a better choice than the single one for ARGs’ removal due to its better ability to efficiently damage the embedded cells and directly degrade the released ARGs. In summary, the appropriate treatment techniques should be applied on the excess sewage sludge to help mitigate the release of ARGs to the environment.

The present study investigated the effect of thermo-chemical pretreatment on the enhancement of enzymatic digestibility of olive mill stones (OMS), as well as its possible valorisation via bioconversion of the generated free sugars to alcohols. Specifically, the influence of parameters such as reaction time, temperature, type and concentration of dilute acids and/or bases, was assessed during the thermo-chemical pretreatment. The hydrolysates and the solids remaining after pretreatment, as well as the whole pretreated slurries, were further evaluated as potential substrates for the simultaneous production of ethanol and xylitol via fermentation with the yeast Pachysolen tannophilus. The digestibility and overall saccharification of OMS were considerably enhanced in all cases, with the maximum enzymatic digestibility observed for dilute sodium hydroxide (almost 4-fold) which also yielded the highest total saccharification yield (91% of the total OMS carbohydrates). Ethanol and xylitol yields from the untreated OMS were 28 g/kg OMS and 25 g/kg OMS, respectively, and were both significantly enhanced by pretreatment. The highest ethanol yield was 79 g/kg OMS and was achieved by the alkali pretreatment and separate fermentation of hydrolysates and solids, whereas the highest xylitol yield was 49 g/kg OMS and was obtained by pretreatment with sulphuric acid and separate fermentation of hydrolysates and solids.

Lignocellulosic biomass is considered as a recalcitrant substrate for anaerobic digestion due to its complex nature that limits its biological degradation. Therefore, suitable preprocessing for the improvement of the performance of conventional anaerobic digestion remains a challenge in the development of anaerobic digestion technology. The physical and chemical characteristics of wheat straw (WS), as a representative lignocellulosic biomass, have a significant impact on the anaerobic digestion process in terms of quantity and quality of the produced biogas. This study aimed at investigating the enzymatic saccharification and detoxification of straw prior to anaerobic digestion with the final objective of enhancing the performance of conventional anaerobic systems of recalcitrant fractions of agricultural waste. The experimental activity was performed in lab and pilot scale treating WS. Alkaline delignification of straw using sodium hydroxide (NaOH) was studied prior to enzymatic hydrolysis for the production of easily biodegradable sugars. After defining the optimum conditions for the pretreatment scheme, the anaerobic digestability of the effluents produced was measured. Finally, the final liquid effluents were fed to a pilot scale anaerobic digester of 0.5 m³ volume, applying an increasing organic loading rate (OLR) regime (in terms of chemical oxygen demand (COD) from 0.2 to 15 kg COD/m³/day). The optimum conditions for the delignification and enzymatic hydrolysis of WS were defined as 0.5 M NaOH at 50 °C for 3–5 h and 15 μL Cellic CTec2/g pretreated straw at 50 °C. It was proven that the resulting liquid effluents could be fed to an anaerobic digester in the ratio that they are produced with satisfactory COD removal efficiencies (over 70%) for OLRs up to 10 kg COD/m³/day. This value is correspondent to a hydraulic retention time of around 7.5 days, much lower than the respective one for untreated straw (over 12 days).