Different pollutant removal efficiencies of artificial aquatic plants in black-odor rivers

Responses of composition and metabolism of microbial communities during the remediation of black and odorous water using bioaugmentation and aeration

This study elucidated the effect patterns of aeration and bioaugmentation on indigenous microbial communities, metabolites, and metabolic pathways in the remediation of black and odorous water. This is crucial for the precise formulation and targeted development of effective microbial consortia, as well as for tracking and forecasting the bioremediation of black and odorous water. The results confirmed that combining bioaugmentation with aeration markedly enhanced the degradation of COD, NH4+-N, and TN and the conversion of Fe and Mn. Aeration significantly increased the relative abundance of Flavobacterium and Diaphorobacter, and the positive interbacterial interaction in the effective microbial consortia EM31 gave the constituent strain Klebsiella and Bacillus a dominant niche in the bioaugmentation. Furthermore, bioaugmentation improved the capacity of the indigenous microbial consortia to utilize basic carbon source, particularly the utilization of L-glycerol, I-erythritol, glucose-1-phosphate, and the catabolism of cysteine and methionine. Moreover, during the remediation of black and odorous water by aeration and bioaugmentation, Glucosinolate biosynthesis (map00966), Steroid hormone biosynthesis (map00140), Folate biosynthesis (map00790), One carbon pool by folate (map00670), and Tyrosine metabolism (map00350) were identified as key functional metabolic pathways in microbial communities.

Purification of aquaculture wastewater by macrophytes and biofilm systems: Efficient removal of trace antibiotics and enrichment of antibiotic resistance genes

The purification performance of aquaculture wastewater and the risk of antibiotic resistance genes (ARGs) dissemination in wetlands dominated by macrophytes remain unclear. Here, the purification effects of different macrophytes and biofilm systems on real aquaculture wastewater were investigated, as well as the distribution and abundance of ARGs. Compared to the submerged macrophytes, artificial macrophytes exhibited higher removal rates of TOC (58.80 ± 5.04 %), TN (74.50 ± 2.50 %), and TP (77.33 ± 11.66 %), and achieved approximately 79.92 % removal of accumulated trace antibiotics in the surrounding water. Additionally, the biofilm microbial communities on the surface of artificial macrophytes exhibited higher microbial diversity with fewer antibiotic-resistant bacteria (ARB) enrichment from the surrounding water. The absolute abundance of ARGs (sul1, sul2, and intI1) in the mature biofilm to be one to two orders of magnitude higher than that in the water. Although biofilms could decrease ARGs in the surrounding water by enriching ARB, the intricate network structure of biofilms further facilitated the proliferation of ARB and the dissemination of ARGs in water. Network analysis suggested that Proteobacteria and Firmicutes phyla were dominant and potential carriers of ARGs, contributing 69.00 % and 16.70 %, respectively. Our findings highlight that macrophytes and biofilm systems have great performance on aquaculture wastewater purification, but with high risk of ARGs.

Effects of chemical oxygen demand/nitrogen on electrochemical performances and denitrification efficiency in single-chamber microbial fuel cells: Insights from electron transfer and bacterial communities

The electrochemical performances and denitrification efficiency of microbial fuel cells (MFCs) are often limited by chemical oxygen demand/nitrogen (COD/N) of wastewater. To overcome this limitation, single-chamber air cathode MFCs with varying COD/N (16/1, 8/1, and 4/1) were established to investigate their electrochemical performances, denitrification efficiency, and bacterial communities. The optimal COD/N for maximizing electricity generation and denitrification efficiency was 8/1, as supported by the greatest corrected coulomb efficiency (13.6%) and electron transfer rate (2.36 C/h for electricity generation, 39.77 C/h for denitrification). As COD/N decreased, the electrochemically active genus Geobacter was replaced by the denitrifying genera Un._f_Burkholderiaceae, Dechlorosoma, and Petrimonas. These results indicated that the efficiency of electricity generation and denitrification was not solely determined by the abundance of electrochemically active and denitrifying bacteria. The presence of a faster electron transfer pathway, possibly direct interspecies electron transfer, enhanced simultaneous electricity generation and denitrification in MFCs with COD/N of 8/1.

Effects of magnetite on microbially driven nitrate reduction processes in groundwater

Nitrate is a common pollutant in the aquatic environment. Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are the main reduction processes of nitrate. In the relatively closed sediment environment, the competitive interaction of these two nitrate reduction determines whether the ecosystem removes or retains nitrogen. In the process of NO₃^--N bioreduction, Magnetite, which is a common mineral present in soil and other sediments can play a crucial role. However, it is still not clear whether magnetite promotes or inhibits NO₃^--N bioreduction. In this paper, the effect of magnetite on NO₃^--N bioreduction was studied by batch experiments. The results show that magnetite can increase the NO₃^--N reduction rate by 1.48 %, and can inhibit the DNRA process at the beginning of the reaction and then promote the DNRA process. Magnetite changed the microbial community structure in our experiment systems. The relative abundance of Sphingomonas, which mainly exists in a high carbon and low nitrogen environment, increased under sufficient carbon source conditions. The relative abundance of Fe-oxidizing and NO₃^--N reducing bacteria, such as Flavobacterium, increased in the absence of carbon sources but in the presence of magnetite. In addition, magnetite can significantly increase activity of the microbial electron transport system (ETS). the added microbial electronic activity of magnetite increased nearly two-fold under the same experiment conditions. The acid produced by the metabolisms of Pseudomonas and Acinetobacter further promotes the dissolution of magnetite, thus increasing the concentration of Fe (II) in the system, which is beneficial to autotrophic denitrifying bacteria and promote the reduction of NO₃^--N. These findings can enhance our understanding of the interaction mechanism between iron minerals and nitrate reducing bacteria during nitrate reduction under natural conditions.

Effects of Vallisneria natans on H2S and S2- releases in black-odorous waterbody under additional nitrate: Comprehensive performance and microbial community structure

Releases of hydrogen sulphide (H₂S) and sulphur ions (S^2-) through sulphate reduction in black-odorous waterbody is a great environmental health concern. Aquatic planting for blackening and odour controls has received great attention in research and practice. Nitrate concentration in black-odorous waterbody can vary significantly but little is known about the responses of aquatic plants on H₂S and S^2- releases under different nitrate levels. This controlled laboratory study explored the changes of H₂S and S^2- releases in simulated black-odorous waterbody planted with Vallisneria natans and artificial plants (control). V. natans growth was stimulated by additional nitrate (6.6 mg/L NO₃^--N), resulting in an increase of dissolved oxygen (DO) and pH in overlying water and an 11.0% decrease in removal efficiency of chemical oxygen demand (COD). At relatively low nitrate level (i.e., 2.0 mg/L NO₃^--N in the absence of additional nitrate), V. natans after the 48th day inhibited H₂S and S^2- releases by 81.5% and 66.8%, respectively, and their inhibition efficiencies were improved to 95.7% and 98.8% by the presence of additional nitrate. Additional nitrate reduced the relative abundance of sulphate-reducing bacteria (SRB) in the sediments while increased the relative abundance of sulphur-oxidizing bacteria (SOB) and nitrate-reducing sulphur-oxidizing bacteria (NR-SOB) in the leaf biofilms of V. natans and artificial plants. Genus compositions in leaf biofilms showed host specificity. Pearson correlation analysis showed that DO, pH, and nitrate concentration had a positive correlation with the relative abundance of SOB (Aeromonas) and NR-SOB (Hydrogenophaga), while were negatively correlated with the relative abundance of SRB (MSBL7). These results indicated that V. natans under additional nitrate altered microbial community to be unfavourable for H₂S and S^2- releases. This study clarified the inhibition of H₂S and S^2- releases by aquatic planting under additional nitrate and provided theoretical basis for improving black-odorous waterbody restoration technology.

Increasing chemical oxygen demand and nitrogen removal efficiencies of surface-flow constructed wetlands in macrophyte-dominant seasons by adding artificial macrophytes

The objective was to test the effectiveness of a new strategy, i.e., adding artificial macrophytes (AMs) to surface-flow constructed wetlands (SFCWs) planted with emergent macrophytes (EMs), to improve COD and N removal efficiencies (REs) at the pilot scale. During EM-dominant periods, the SFCWs with only EMs had REs of 78.2%, 59.8%, 50.8% and -54.2% for NH₄⁺-N, NO₃^--N, TN, and COD, respectively, while the SFCWs with both AMs and EMs increased the REs to 85.1%, 72.2%, 73.8%, and 2.0%. The addition of AMs to SFCWs had no significant effect on EM growth (biomass or root activity). Mutual benefit was found between EMs and AMs, i.e., AMs reduced the secondary pollution caused by withered EMs, while EMs improved AM-attached biofilm functions of chemoheterotrophy, nitrate_reduction, and nitrification. Therefore, AM addition is a useful strategy to improve COD and N REs during EM-dominant periods when pollutant removal is a challenge for SFCWs.

Mutual promotion of submerged macrophytes and biofilms on artificial macrophytes for nitrogen and COD removal improvement in eutrophic water

Both submerged macrophytes (SMs) and artificial macrophytes (AMs) have been widely used to improve water quality in eutrophic water. However, in heavily eutrophic aquatic ecosystems, the purification function of SMs is often restricted by the poor growth state due to competition from algae, while the purification function of AMs is often restricted by the limited carbon source supply for biofilm microbes attached to the AM surface. The objective of this study was to develop a new strategy to increase pollutant removal efficiency (RE) by combining the use of SMs and AMs. Pilot-scale microcosms, including treatments with both SMs and AMs (S&A), only SMs (SO) and only AMs (AO), were established to identify the performance of the new strategy. The results suggest that treatment S&A obtained REs of 88.9% for total nitrogen (TN) and 48.1% for chemical oxygen demand (COD); as comparison, treatments SO and AO obtained REs of 77.4% and 81.2% for TN and REs of -13.7% and 39.0% for COD, respectively. Compared with SO, the S&A treatment benefited SM growth in biomass, leaf chlorophyll concentration and root activity by inhibiting algae growth. In addition, compared with treatment AO, S&A increased the biofilm microbial biomass and the relative abundance of nitrifiers of families Nitrosomonadaceae and Nitrospira attached to AM surfaces. Therefore, by the mutual promotion of SMs and biofilms on AMs, the synergic application of SMs and AMs is a useful strategy for improving TN and COD REs in eutrophic water bodies such as rivers and constructed wetlands. A strategy was developed to increase nitrogen and COD removal in eutrophic water by the mutual promotion of submerged macrophytes and biofilms on artificial macrophytes.

A novel magnesium-based oxygen releasing compound for eutrophic water remediation

Eutrophication of surface water bodies is a global problem in recent years. Dosing polluted water with oxygen releasing compounds (ORCs), especially those that can remove excessive nutrients simultaneously is regarded as one of the most economical and eco-friendly methods of treating eutrophic waters. In this study, a novel Mg-based ORC was synthesized and characterized as a magnesium hydroxide and hydrogen peroxide complex (MHHPC) with Mg to H₂O₂ ratio of 2:1. Oxygen-releasing, pH-adjusting and nutrient-removal potentials of MHHPC were evaluated in nano-pure and eutrophic water. The overall performance of MHHPC in preventing the eutrophic water from turning black and odorous was compared with the performance of other ORCs namely, MgO₂, CaO₂ and the combination of MgCl₂ and H₂O₂. The results showed that MHHPC was capable of constantly releasing oxygen to aqueous phase over a period of one week. Phosphate and ammonia nitrogen in synthetic buffered water can were removed as struvite and other precipitates from the aqueous phase. In the synthetic eutrophic water, all the ORCs tested were able to reduce aqueous ammonia nitrogen below 0.5 mM, while only CaO₂ and MHHPC successfully removed the aqueous phosphate. However, CaO₂ and MgCl₂+H₂O₂ significantly inhibited microbial activity.