Metagenomic insights into mixotrophic denitrification facilitated nitrogen removal in a full-scale A2/O wastewater treatment plant.

Wastewater treatment plants (WWTPs) are important for pollutant removal from wastewater, elimination of point discharges of nutrients into the environment and water resource protection. The anaerobic/anoxic/oxic (A2/O) process is widely used in WWTPs for nitrogen removal, but the requirement for additional organics to ensure a suitable nitrogen removal efficiency makes this process costly and energy consuming. In this study, we report mixotrophic denitrification at a low COD (chemical oxygen demand)/TN (total nitrogen) ratio in a full-scale A2/O WWTP with relatively high sulfate in the inlet. Nitrogen and sulfur species analysis in different units of this A2/O WWTP showed that the internal sulfur cycle of sulfate reduction and reoxidation occurred and that the reduced sulfur species might contribute to denitrification. Microbial community analysis revealed that Thiobacillus, an autotrophic sulfur-oxidizing denitrifier, dominated the activated sludge bacterial community. Metagenomics data also supported the potential of sulfur-based denitrification when high levels of denitrification occurred, and sulfur oxidation and sulfate reduction genes coexisted in the activated sludge. Although most of the denitrification genes were affiliated with heterotrophic denitrifiers with high abundance, the narG and napA genes were mainly associated with autotrophic sulfur-oxidizing denitrifiers. The functional genes related to nitrogen removal were actively expressed even in the unit containing relatively highly reduced sulfur species, indicating that the mixotrophic denitrification process in A2/O could overcome not only a shortage of carbon sources but also the inhibition by reduced sulfur of nitrification and denitrification. Our results indicate that a mixotrophic denitrification process could be developed in full-scale WWTPs and reduce the requirement for additional carbon sources, which could endow WWTPs with more flexible and adaptable nitrogen removal.

Scaling responses of leaf nutrient stoichiometry to the lakeshore flooding duration gradient across different organizational levels.

Most wetlands have been subject to changes in flooding regimes by climate change and human activities, resulting in widespread alteration of wetland plants at different organizational levels. However, scaling the responses of wetland plants to changes in flooding regimes is still challenging, because flooding could indirectly affect wetland plants through affecting environment factors (e.g. soil properties). During the non-flooding period, we investigated leaf N and P stoichiometry at three organizational levels (intra-species, inter-species, inter-community) along a flooding duration gradient in a lakeshore meadow of Poyang Lake floodplain, China. At the intra-species level, leaf N and P stoichiometry showed species-specific responses to flooding duration. At the inter-species level, leaf N or P contents or N:P ratio showed no significant response to flooding duration. At the inter-community level, leaf N and P contents significantly increased with flooding duration, while leaf N:P ratio decreased. At each organizational level, leaf N and P stoichiometry showed poor correlation with soil N and P stoichiometry. Moreover, intra-specific responses of leaf N and P contents to flooding duration and soil nutrient content increased with mean flooding duration of species distribution, which was the index of species hydrological niche. Intraspecific variation had lower contribution than species turnover to variations in community leaf nutrient stoichiometry. In all, flooding duration affected leaf N and P stoichiometry mainly through direct pathway at the intra-species and inter-community level, rather than the indirect pathway via soil nutrient stoichiometry. Therefore, our results have implications for scaling up from environmental conditions to ecosystem processes via wetland plant communities.

Design and Optimization of Flexible Polypyrrole/Bacterial Cellulose Conductive Nanocomposites Using Response Surface Methodology.

Flexible conductive materials have greatly promoted the rapid development of intelligent and wearable textiles. This article reports the design of flexible polypyrrole/bacterial cellulose (PPy/BC) conductive nanocomposites by in situ chemical polymerization. Box-Behnken response surface methodology has been applied to optimize the process. The effects of the pyrrole amount, the molar ratio of HCl to pyrrole and polymerization time on conductivity were investigated. A flexible PPy/BC nanocomposite was obtained with an outstanding electrical conductivity as high as 7.34 S cm-1. Morphological, thermal stability and electrochemical properties of the nanocomposite were also studied. The flexible PPy/BC composite with a core-sheath structure exhibited higher thermal stability than pure cellulose, possessed a high areal capacitance of 1001.26 mF cm-2 at the discharge current density of 1 mA cm-2, but its cycling stability could be further improved. The findings of this research demonstrate that the response surface methodology is one of the most effective approaches for optimizing the conditions of synthesis. It also indicates that the PPy/BC composite is a promising material for applications in intelligent and wearable textiles.

Rapid and efficient activated sludge treatment by electro-Fenton oxidation.

Advanced oxidation process is one of the important process to improve the efficiency of activated sludge dewatering and digestion. In this study, electro-Fenton (EF) was investigated as a pretreatment method for improving activated sludge dewatering and disintegration in terms of specific resistance to filtration, volatile suspended solids removal and release of soluble organics. The morphology of sludge flocs and properties of extracellular polymeric substance (EPS) were investigated to understand the involved mechanisms. The results showed that EF could increase the dewaterability of activated sludge effectively in 40-60 min. The size of sludge flocs decreased after EF treatment, but zeta potential was elevated to near zero and floc structure became coarser with bigger holes. EF could enhance the sludge floc disintegration, released protein and polysaccharide to soluble EPS fraction, and promote the humification process. The kinetic analysis further indicated that EF increased the pseudo first-order EPS solubilization rate. EF had high operational stability by retaining over 90% initial activity even after five repeated use of dewatering filtrate. This study provides a rapid and efficient solution for improving sludge dewaterability by electro-Fenton.

Performance of a full-scale modified anaerobic/anoxic/oxic process: High-throughput sequence analysis of its microbial structures and their community functions.

The average COD, TN, TP, and NH4(+)-N elimination rates in a new wastewater treatment plant (WWTP) based on a modified A2/O process were 83%, 72.4%, 93.5%, and 98.6%, respectively, even under conditions of a low C/N ratio and low temperature. Among the four potential denitrifying units, the post-anoxic unit was the least efficient with respect to the removal efficiency. However, the structures of the bacterial community among samples obtained from the treatment units were similar, as demonstrated using Illumina Miseq high-throughput sequencing. Genera with nitrifying, denitrifying, hydrolyzing, and glycogen-accumulating activities were identified in all units, indicating that functional groups were highly enriched in the active sludges and thus enabled nitrogen removal. The key functional microorganisms responsible for nitrification-denitrification in the WWTP were species belonging to the genera Nitrospira, Hydrogenophilaceae, Comamonas, Dechloromonas, Thauera, Haliangium, and Halomonas.