Enhanced nitrogen removal of the anaerobic ammonia oxidation process by coupling with an efficient nitrate reducing bacterium (Bacillus velezensis M3-1).

Bacillus velezensis M3-1 strain isolated from the sediment of Myriophyllum aquatium constructed wetlands was found to efficiently convert NO3--N to NO2--N, and the requirements for carbon source addition were not very rigorous. This work demonstrates, for the first time, the feasibility of using the synergy of anammox and Bacillus velezensis M3-1 microorganisms for nitrogen removal. In this study, the possibility of M3-1 that converted NO3--N produced by anammox to NO2--N was verified in an anaerobic reactor. The NO3--N reduction ability of M3-1 and denitrifying bacteria in coupling system was investigated under different C/N conditions, and it was found that M3-1 used carbon sources preferentially over denitrifying bacteria. By adjusting the ratio of NH4+-N to NO2--N, it was found that the NO2--N converted from NO3--N by M3-1 participated in the original anammox.The nitrogen removal efficacy (NRE) of the coupled system was increased by 12.1%, compared to the control group anammox system at C/N = 2:1. Functional gene indicated that it might be a nitrate reducing bacterium.This study shows that the nitrate reduction rate achieved by the Bacillus velezensis M3-1 can be high enough for removing nitrate produced by anammox process, which would enable improve nitrogen removal from wastewater.

Fast start-up of anammox process: Effects of extracellular polymeric substances addition on performance, granule properties, and bacterial community structure.

The slow startup is the major obstacle to the application of anaerobic ammonium oxidation (anammox) process in mainstream wastewater treatment. Extracellular polymeric substances (EPS) are one potential resource for stable anammox reactor operation. Response surface analysis was used to optimize the specific anammox activity (SAA) with the addition of EPS; SAA was maximum at a temperature of 35 °C and the EPS concentration of 4 mg/L. By comparing the nitrogen removal of anammox reactors with no EPS (R0), immobilized EPS (EPS-alginate beads) (R1), and liquid EPS (R2), we found that EPS-alginate beads significantly speed up the startup of anammox process and enable the start time to be shortened from 31 to 19 days. As a result of the higher MLVSS content, higher zeta potential, and lower SVI30, anammox granules of R1 exhibited a stronger capacity to aggregate. Moreover, EPS extracted from R1 had higher flocculation efficiencies than EPS derived from R0 and R2. Phylogenetic analysis of 16S rRNA genes revealed that the main anammox species in R1 is Kuenenia taxon. To clarify the relative significance of stochastic vs deterministic processes in the anammox community, neutral model and network analysis are employed. In R1, community assembly became more deterministic and stable than in other cultures. Our results show that EPS might inhibit heterotrophic denitrification and thereby promote anammox activity. This study suggested a quick start-up strategy for the anammox process based on resource recovery, which is helpful for environmentally sustainable and energy-efficient wastewater treatment.

Transcriptomics Insights into Phosphorus Stress Response of Myriophyllum aquaticum.

Through excellent absorption and transformation, the macrophyte Myriophyllum (M.) aquaticum can considerably remove phosphorus from wastewater. The results of changes in growth rate, chlorophyll content, and roots number and length showed that M. aquaticum could cope better with high phosphorus stress compared with low phosphorus stress. Transcriptome and differentially expressed genes (DEGs) analyses revealed that, when exposed to phosphorus stresses at various concentrations, the roots were more active than the leaves, with more DEGs regulated. M. aquaticum also showed different gene expression and pathway regulatory patterns when exposed to low phosphorus and high phosphorus stresses. M. aquaticum's capacity to cope with phosphorus stress was maybe due to its improved ability to regulate metabolic pathways such as photosynthesis, oxidative stress reduction, phosphorus metabolism, signal transduction, secondary metabolites biosynthesis, and energy metabolism. In general, M. aquaticum has a complex and interconnected regulatory network that deals efficiently with phosphorus stress to varying degrees. This is the first time that the mechanisms of M. aquaticum in sustaining phosphorus stress have been fully examined at the transcriptome level using high-throughput sequencing analysis, which may indicate the direction of follow-up research and have some guiding value for its future applications.

Microbial community structure analyses and cultivable denitrifier isolation of Myriophyllum aquaticum constructed wetland under low C/N ratio.

With the rapid expansion of livestock production, the amount of livestock wastewater accumulated rapidly. Lack of biodegradable organic matter makes denitrification of livestock wastewater after anaerobic digestion more difficult. In this study, Myriophyllum aquaticum constructed wetlands (CWs) with efficient nitrogen removal performance were established under different carbon/nitrogen (C/N) ratios. Analysis of community composition reveals the change of M. aquaticum CWs in microbial community structure with C/N ratios. The proportion of Proteobacteria which is one of the dominant phyla among denitrifier communities increased significantly under low C/N ratio conditions. Besides, to obtain cultivable denitrifier that could be added into CWs in situ, 33 strains belonging to phylum Proteobacteria were isolated from efficient M. aquaticum CWs, while the best-performing denitrification strain M3-1 was identified as Bacillus velezensis JT3-1 (GenBank No. CP032506.1). Redundancy analysis and quadratic models showed that C/N ratio had significant effects on disposal of nitrate (NO3--N) and the strains isolated could perform well in denitrification when C/N ratio is relatively low. In addition, they have relatively wide ranges of carbon sources, temperature and a high NO3- removal rate of 9.12 mg/(L·hr) at elevated concentrations of 800 mg/L nitrate. Thus, strains isolated from M. aquaticum CWs with low C/N ratio have a practical application value in the treatment of nitrate-containing wastewater. These denitrifying bacteria could be added to CWs to enhance nitrogen removal efficiency of CWs for livestock wastewater with low C/N ratio in the future.

Partial nitrification in free nitrous acid-treated sediment planting Myriophyllum aquaticum constructed wetland strengthens the treatment of black-odor water.

Black-odor water pollution in rural areas, especially swine wastewater, can lead to the deterioration of water quality and thus seriously affect the daily life of people in the area. However, there is a lack of effective treatment measures with simultaneous attention to carbon, nitrogen and sulfur pollution in rural black-odor water bodies. This study evaluated the feasibility of an in-situ pilot-scale constructed wetland (CW) for the synchronous removal of COD, ammonium, and sulfur compounds in the swine wastewater. In this study, the operation strategy of CW sediment pretreated with free nitrous acid (FNA) and Myriophyllum aquaticum plantation was established. Throughout the 114-day operation, the total removal efficiencies of COD and ammonium nitrogen in experimental groups were 81.2 ± 4.2 % and 72.8 ± 1.8 %, respectively, which were significantly higher than CW without any treatment. Removal efficiencies of Sulfur compounds, i.e. sulfide, sulfate, thiosulfate, and sulfite, were 92.3 ± 1.9 % (61.2 % higher than the no-treatment group), 42.1 ± 3.8 %, 97.9 ± 1.7 %, and 42.7 ± 4.5 % respectively. High-throughput sequencing and qPCR revealed that experimental group significantly increased denitrification genes (nirK, nosZ) and sulfur oxidation genes (soxB, fccAB) and enriched the corresponding microbial taxa (Bacillus, Conexibacter and Clostridium sensu stricto). Moreover, metabolic pathways related to nitrogen and sulfur and the degradation of organic matter were up-regulated. These results indicated that partial nitrification in CW planted with M. aquaticum promoted sulfur oxidation denitrification and heterotrophic denitrification. Overall, the in-situ pilot-scale study revealed that the cultivation of M. aquaticum in FNA-treated CW can be a sustainable approach to treat black-odor water bodies.

Research on reinforcement learning-based safe decision-making methodology for multiple unmanned aerial vehicles.

A system with multiple cooperating unmanned aerial vehicles (multi-UAVs) can use its advantages to accomplish complicated tasks. Recent developments in deep reinforcement learning (DRL) offer good prospects for decision-making for multi-UAV systems. However, the safety and training efficiencies of DRL still need to be improved before practical use. This study presents a transfer-safe soft actor-critic (TSSAC) for multi-UAV decision-making. Decision-making by each UAV is modeled with a constrained Markov decision process (CMDP), in which safety is constrained to maximize the return. The soft actor-critic-Lagrangian (SAC-Lagrangian) algorithm is combined with a modified Lagrangian multiplier in the CMDP model. Moreover, parameter-based transfer learning is used to enable cooperative and efficient training of the tasks to the multi-UAVs. Simulation experiments indicate that the proposed method can improve the safety and training efficiencies and allow the UAVs to adapt to a dynamic scenario.

Mechanistic insights into the reactivity of Ferrate(VI) with phenolic compounds and the formation of coupling products.

In this paper, the removal of 2-benzylphenol (2-BP), phenol (Ph), chlorophene (CP), and 4-chlorophenol (4-CP) by Fe(VI) have been examined at pH 8.0. The second-order rate constant (k) for substrates degradation at a Fe(VI) concentration of 0.2 mM was in the order of kCP (353 M-1 s-1) > k4-CP (131 M-1 s-1) > k2-BP (102 M-1 s-1) > kPh (40 M-1 s-1), indicating that the presence of chlorine and benzyl groups in benzene ring can enhance the reactivity of the phenolic compounds with Fe(VI). Reaction products were identified by a liquid chromatography-quadrupole-time-of-flight-mass spectrometry (LC-Q-TOF-MS), and four reaction mechanisms, including hydroxylation of benzene ring, cleavage of C-C bridge bond, substitution of chlorine atom by hydroxyl group, and the single-electron coupling mechanism were proposed for phenols degradation by Fe(VI). The extracted peak areas of the degradation products showed that the single-electron coupling reaction is the main degradation mechanism in Fe(VI) oxidation processes. In addition to direct attack by Fe(VI), hydroxyl radical, as detected by electron paramagnetic resonance (EPR) spectra, also plays a role in phenols degradation. The •OH initiated reactions and single-electron coupling reactions were further explored by total charges distribution, transition state calculations and potential energy profiles. In addition, Fe(VI) could also work as a highly effective oxidant for substrates removal from real waters.

Understanding the ozonated degradation of sulfadimethoxine, exploration of reaction site, and classification of degradation products.

Ozonation has been demonstrated to be an efficient method of water treatment. In this study, the degradation of 20 mg/L of sulfadimethoxine (SDM) in different water matrices during ozonation was investigated. At pH 7.0, 100% removal of SDM was achieved by ozonation within 10 min. The degradation of SDM was more pronounced at acidic pH than under ambient environmental conditions, and was also dependent on different water matrices. Both direct and indirect oxidation of SDM by ozone were observed, and it was also shown that both ozone molecules and hydroxyl radicals were involved in the SDM degradation process, whereas it was found that the saturated ring of SDM made it O3-recalcitrant. Seven transformation products (TPs) were identified during SDM ozonation, allowing three degradation pathways to be proposed. Additionally, the main reaction sites, including N (7) and C (2) on the aniline ring, and the __S__N__ bond, were confirmed both experimentally and theoretically. The toxicity evolution during the degradation process was investigated, and the results showed no toxic intermediate products obtained during ozonation.