Performance evaluation and optimization of a suspension-type reactor for use in heterogeneous catalytic ozonation.

Packed fixed-bed reactors are traditionally used for heterogeneous catalytic ozonation. However, a high solid-to-liquid requirement, poor ozone dissolution, ineffective utilization of catalyst surface area, and production of large amounts of catalyst waste impede application of such reactors. In this study, we designed a suspension catalytic ozonation reactor and compared the performance of this reactor with that of a traditional fixed-bed catalytic ozonation reactor employing oxalic acid (OA) as the target contaminant. Our results showed that total O3 dissolved into the suspension reactor (117-134 mg.L-1) was much higher compared to that measured in the fixed-bed reactor (53 mg.L-1) due to a higher O3(g) interphase mass transfer rate in the suspension reactor. In accordance with the higher O3(g) interphase mass transfer, we observed a much higher proportional OA removal (32 %) compared to that achieved in the fixed-bed reactor (10%) employing an Fe-oxide catalyst supported on Al2O3 (Fe-oxide@Al2O3) in both reactors. Use of a double-layered Cu-Al hydroxide (Cu-Al LDHs) catalyst in the suspension reactor further enhanced the performance with nearly 90 % OA removal observed. Given the superior performance of the suspension reactor, we investigated the impact of operating conditions (catalyst dosage, hydraulic retention time and ozone dosage) employing Cu-Al LDHs as the catalyst. We also developed a mathematical kinetic model to describe the performance of the suspension reactor and, through use of the kinetic model, showed that O3(g) interphase transfer rate was the rate-limiting step in OA removal. Thus, improvement in ozone gas diffuser design is required to improve the performance of the suspension reactor. Overall, the present study demonstrated that suspension reactors were more effective than fixed-bed reactors for oxidation of surface-active organic compounds such as OA due to the higher ozone interphase mass transfer rate and effective utilization of the catalyst surface area that can be achieved. As such, further research on suspension reactor design and development of catalysts suitable for use in suspension reactors should facilitate large-scale application of catalytic ozonation processes by the wastewater treatment industry.

Facile approach for nanoconfinement of multilayer graphene oxide with polyether polyurethane sponge as biological carrier for the establishment of microalgal-bacterial bioreactor.

Physically precise and mechanically robust biocarrier is basic and urgent requirement of algal-bacterial wastewater treatment plants for homogenously biofilm growth. Herein, a highly efficient graphene oxide (GO) coordinated polyether polyurethane (PP) sponge was synthesized through GO incorporation into PP sponge to improve the GO coating, followed by UV-light treatment for industrial application. The resulted sponge showed remarkable physiochemical characteristics, excellent thermal (>0.02 Wm-1 K-1) and mechanical (>363.3 KPa) stability. To test the potential of sponge in real world scenarios, the activated sludge from real wastewater treatment plant was utilized. Interestingly, the GO-PP sponge enhanced the electron transfer between microorganisms and promoted the standardized microorganism's growth and biofilm formation (22.7 mg/d per gram sponge, 172.1 mg/g), providing the feasibility to accomplish a symbiotic system within specifically design upgraded algal-bacterial reactor. Furthermore, the continuous flow process by utilizing GO-PP sponge in algal-bacterial reactor demonstrated the effectiveness in treating low concentration antibiotic wastewater, presenting 86.7 % removal rate and >85 % after 20 cycles. Overall, this work illustrates an applicable strategy to develop a sophisticated modified pathway for the next-generation biological-based applications.

In situ investigation of acute exposure of graphene oxide on activated sludge: Biofilm characteristics, microbial activity and cytotoxicity.

Graphene Oxide (GO) has wide applications in many fields which has caused a large expected quantity of the graphene-based wastes. It is necessary to understand the toxic effects of the GO on the activated sludge (AS) considering its inevitable discharge to the wastewater treatment plants as the ultimate repositories for these wastes. In this study, the acute exposures of the multilayer Nano-graphene oxide (MNGO) at different dosages were conducted in order to investigate its integrated effects on the formation of the biofilm, mature biofilm and the microbial activity of the activated sludge. Raman spectroscopy and laser scanning confocal microscopy (LSCM) were adopted for the in-situ characterization of the biofilm with the exposure of the MNGO. The results showed that the activated sludge was tolerable to the acute exposure of the less than 100 mg/L of the MNGO, especially for the mature biofilm, and only a subtle decrease was found in the size and thickness during the formation of the biofilm, while the amount of 300 mg/L of the MNGO caused the sever deterioration on the activated sludge system. The microbial metabolic activity, viability, and the biological removal of the nutrients were significantly affected with the more than 100 mg/L of the MNGO. It was also demonstrated by the microbial cytotoxicity tests that the increase in the exposure of the MNGO was related to the increase in the reactive oxygen species (ROS) and the damaging degree of the cell membrane.

Biocompatibility and biodegradability of polyacrylate/ZnO nanocomposite during the activated sludge treatment process.

Polymer nanocomposites have been widely used in the preparation of coating agents in the leather industry. Considering the complex bio-effect and ecological risk of nanomaterial, research on the biodegradability and biocompatibility of polyacrylate/metal nanocomposites in activated sludge system is of specific significance. We investigated the change of the bacterial community and diversity of activated sludge fed with polyacrylate/ZnO nanocomposites in both low (500 mg COD /L) and high (1000 mg COD/L) doses. COD removal, dehydrogenase activity, and total protein of activated sludge system were monitored in all treatments over 30 days. The results demonstrated that the exposure to both polyacrylate/ ZnO nanocomposite and polyacrylate decreased the dehydrogenase activity at early stage comparing to the control, but had no significant influence on COD removal. Overall, the bacterial communities in activated sludge were resistant to polyacrylate/ZnO nanocomposites, and had higher levels of metabolic activity, protein accumulation and bioavailability when exposed to these chemicals comparing to the control especially at later stages of incubation (15-30 days), which indicated that these polyacrylate/ZnO nanocomposites of certain amount were biocompatible to activated sludge system.