Nano silver oxide-modified activated carbon as a novel catalyst for efficient removal of bacteria and micropollutants in aquatic environment.

Heterogeneous Fenton process is a promising water treatment technology for sterilization and degradation of organic pollutants, due to the strong oxidation of hydroxyl radicals (OH˙) generated. However, the low H2O2 activation efficiency and the instability of catalyst leading to low OH˙ production restricted development of this technology. Herein, we synthesized a novel porous activated carbon-loaded nano silver oxide (nAg2O/AC) catalyst to enhance the activation of H2O2 for removing bacteria (E. coli) and micropollutants (Tetracycline, TC) from water. In the nAg2O/AC Fenton system, reductive hydroxyl groups on AC accelerated Ag(i)/Ag cycle through mediated electron transfer, which markedly increased H2O2 activation efficiency to 73.7% (About 2.9 times that of traditional Fenton). Hence, nAg2O/AC Fenton achieved up to 6.0 log and 100% removal efficiency for E. coli and TC, respectively. The OH˙ as the major oxidizing species in nAg2O/AC Fenton system was detected and verified by radical scavenging tests and electron spin resonance (ESR) measurement. After 4 and 5 cycles of experiments, the removal of E. coli and TC still reached 5.2 log and 96%, respectively, confirming good stability of nAg2O/AC for considerable application prospects. This study concluded that nAg2O/AC is a promising H2O2 catalyst for simultaneous removal of bacteria and micropollutants in aqueous environment.

A temperature-resilient anammox process for efficient treatment of rare earth element tailings wastewater via synergistic nitrite supply of partial nitritation and partial denitrification.

Rare earth elements result in substantial tailings wastewater with high ammonium and nitrate during extraction. In this study, a temperature-resilient Anammox process was employed for efficient treatment of rare earth element tailings wastewater through implementing synergistic nitrite supply by partial nitritation (PN) and partial denitrification (PD). Enhancing temperature resilience of Anammox process relies on dynamic management of DO and COD inputs to shift the dominant nitrite supplier from PN to PD, stable PD (NAR ≥ 90 %) can boost nitrogen removal by Anammox to 97.8 %. The nitrogen removal rate and nitrogen removal efficiency at 10.6 °C could maintain at 0.12 kgN/m3·d-1 and 92.5 %, respectively. Microbial analysis reveals that Nitrosomonas, Thauera, and Candidatus_Kuenenia are the predominant genera responsible for nitrite supply and nitrogen removal, localized within the gas channels of granules, flocs, and micro-granules, respectively. Keeping the influent C/NO3--N ratio below 1.7 is ideal to prevent overgrowth of Thauera and maintain system stability.

Effective enrichment of anaerobic ammonia oxidation sludge with feast-starvation strategy: activity, sedimentation, growth kinetics, and microbial community.

To address the issue of floating and loss of floc sludge caused by gas production in anaerobic ammonia oxidation (anammox) reactors, this study proposes a limited nitrite supply strategy to regulate gas production during the settling and enhance sludge retention. Results indicate that the effluent suspended solids in the anammox reactor can be reduced to as low as 0.11 g/L under specific feast-starvation conditions. Even under long-term intermittent nitrite-starvation stress, the maximum growth rate of Candidatus_Kuenenia can still reach 0.085d-1, with its abundance increasing from 0.47% to 8.83% within 69 days. Although the combined effects of starvation and sedimentation would lead to a temporary decrease in anammox activity, this reversible inhibition can be fully restored through substrate intervention. The limited nitrite supply strategy promotes the sedimentation of anammox sludge without significantly affecting its growth rate, and effective sludge retention is crucial for enriching anammox sludge during initial cultivation.

Flow-Through Electrochemical Membrane Reactor with a Self-Supported Carbon Membrane Electrode for Highly Efficient Synthesis of Hydrogen Peroxide.

In situ electroreduction of O2 to H2O2 by using electrons as reagents is known as a green process, which is highly desirable for environmental remediation and chemical industries. However, the development of a cost-effective electrode with superior H2O2 synthesis rate and stability is challenging. A self-supported carbon membrane (CM) was prepared in this study from activated carbon and phenolic resin by carbonization under a H2 atmosphere. It was employed as the cathode to build a flow-through electrochemical membrane reactor (FT-ECMR) for electrosynthesis of H2O2. The results showed that the CM had a small pore size (34 nm), a high porosity (42.3%), and a high surface area (450.7 m2 g-1). In contrast to most of the state-of-the-art self-supported carbon electrode reported in the previous works, the FT-ECMR exhibited a high concentration of continuous and stable H2O2 electrosynthesis (1042 mg L-1) as well as a H2O2 synthesis rate of 5.21 mg h-1 cm-2. It had also demonstrated a high oxygen conversion (0.37%) and current efficiency (88%). The outstanding performance of the FT-ECMR for H2O2 synthesis was attributed to the enhanced mass transfer of the reactor, the existence of a relatively high surface area of CM, and the abundant disordered carbon structures (sp3-C, defects, and edges). In conclusion, our work highlighted using the FT-ECMR with the CM to synthesize H2O2 efficiently and cost-effectively.

Resilience of anammox application from sidestream to mainstream: A combined system coupling denitrification, partial nitritation and partial denitrification with anammox.

Anaerobic ammonium oxidation (anammox) is a potential process to achieve the neutralization of energy and carbon. Due to the low temperature and variation of municipal sewage, the application of mainstream anammox is hard to be implemented. For spreading mainstream anammox in practice, several key issues and bottlenecks including the start-up, stable NO2--N supply, maintenance and dominance of AnAOB with high activity, prevention of NO3--N buildup, reduction of sludge loss, adaption to the seasonal temperature and alleviation of COD impacts on AnAOB are discussed and summarized in this review in order to improve its startup, stable operation and resilience of mainstream anammox. Hence a combined biological nitrogen removal (CBNR) system based on conventional denitrification, shortcut nitrification-denitrification, Partial Nitritation and partial Denitrification combined Anammox (PANDA) process through the management of organic matter and nitrate is proposed correspondingly aiming at adaptation to the variations of seasonal temperature and pollutants in influent.

Anaerobic co-digestion of thermo-alkaline pretreated microalgae and sewage sludge: Methane potential and microbial community.

To improve methane production from sewage sludge (SS), co-digestion of SS and microalgae (MA) was studied and the application of thermo-alkaline pretreatment to MA was evaluated. The results showed that thermo-alkaline pretreatment at 90°C for 120 min on MA was the optimum pretreatment condition. Furthermore, when the volatile solids (VS) ratio of SS and MA was 1:2, the methane yield reached maximum (368.94 mL/g VS). Fourier transform infrared (FT-IR) and thermogravimetric analysis confirmed the synergetic effects of thermo-alkaline pretreated MA on its co-digestion with SS. The analyses of microbial community indicated that Methanobacterium and Methanosarcina were the dominant methanogens during the co-digestion process. However, the relative abundance of Methanosarcina in thermo-alkaline pretreated groups was higher compared to unpretreated groups. The microbial community structure might be affected by thermo-alkaline pretreatment rather than by the MA dosage in the co-digestion.

[Diversity and PICRUSt2-based Predicted Functional Analysis of Bacterial Communities During the Start-up of ANAMMOX].

Bacterial communities are vital for efficient nitrogen removal in an anaerobic ammonium oxidation (ANAMMOX) system. However, the diversity and functional characteristics of a bacterial community during the start-up of ANAMMOX has not been reported. In this study, an up-flow anaerobic sludge bed reactor was used to start-up the ANAMMOX system, and 16S rRNA high-throughput gene sequencing, combined with PICRUSt2-based functional prediction analysis, was used to investigate the dynamic changes in diversity and function of the bacterial community at different times (d0, d30, d60, and d90) during the start-up. The results showed that 48 phyla, 111 classes, 269 orders, 457 families, 840 genera, and 1497 species were present during the start-up of ANAMMOX. Candidatus Brocadia and Candidatus_Kuenenia were the main detected ANAMMOX bacteria, and their relative abundance was significantly different at different times during the start-up of ANAMMOX (P<0.05). During the start-up, the alpha diversity indices of the bacterial community were significantly decreased (P<0.05), and the structure of the bacterial community exhibited significant spatial differentiation (R=0.846, P<0.01). Functional prediction analysis with PICRUSt2 revealed that the bacterial community was active in organic systems and metabolism at hierarchy level 1, implying abundant functional diversity. Further, the abundance of functional genes was significantly different at hierarchy level 2, during the start-up of ANAMMOX. Forty-nine functional genes involving metabolic nitrogen were detected. The abundance of functional genes, involved in nitrification, denitrification, ANAMMOX, and nitrate and nitrite assimilatory/dissimilatory reduction, changed significantly during the start-up of ANAMMOX.

[Microbial Community Structure and Diversity During the Enrichment of Anaerobic Ammonium Oxidation Bacteria].

To understand the changes in microbial community characteristics during the enrichment of anaerobic ammonium oxidation (ANAMMOX) bacteria, an ASBR reactor was used to culture the ANAMMOX bacteria. The composition, diversity, and species co-occurrence network of the microbial community were investigated under different cultivation times. The results showed that the ANAMMOX bacteria were enriched by gradually increasing the substrate concentration, with removal efficiencies for NH4+-N, NO2--N, and total nitrogen of 97.6%, 95.4%, and 84.9%, respectively. The high-throughput sequencing found that the dominant phyla (relative abundance>5%) were Proteobacteria, Bacteroidetes, Chloroflexi, Planctomycetes, Armatimonadetes, and Actinobacteria in the whole culture process. Candidatus Brocadia was the main ANAMMOX bacteria in the reactor, with its relative abundance increasing from 1.42% to 24.66%. During the cultivation process, the composition of the dominant microbial community did not change, while the relative abundance showed a significant difference (P<0.05). The alpha diversity of the microbial community significantly increased first and then decreased (P<0.05), and the beta diversity of the microbial community was significantly spatially differentiated (R=0.5672, P<0.01) during the culture process. Species network densities were 0.188, 0.068, 0.059, 0.18, and 0.0735 at different times during the culture process. Although the enrichment culture process resulted in weaker correlations between microorganisms, the related group of microorganisms in the phylum Aspergillus became the main node in the network. The enrichment process weakened the correlation between microorganisms; however, the microbial taxa related to the phylum Planctomycetes became the key node in the network.