Dissolved oxygen drives heterotrophic microorganism succession to regulate low carbon source wastewater treatment enhanced by slurry.

The limited availability of carbon sources in low carbon source wastewater has always hindered nitrogen removal efficiency. The residual slurry liquid after anaerobic digestion has the potential to be used as a carbon source. This study investigated the optimal parameters of dissolved oxygen (DO) for enhancing the treatment of low carbon source wastewater using slurry, and revealed the characteristics of carbon metabolism gene enrichment and carbon fixation potential driven by DO. The results indicated that treating wastewater under high DO concentrations (3-4 mg/L) conditions could meet the emission standards set by wastewater treatment plants in China. However, the lower-cost DO concentration of 3 mg/L is considered a more cost-effective parameter, effectively removing 85.68% of chemical oxygen demand and 91.56% of total nitrogen. Mechanistic analysis suggested that reducing DO concentration increased the diversity of microbial communities. Regulating DO concentration reshaped the co-metabolic network of microorganisms with different DO sensitivities by influencing Hydrogenophaga and Chlorobium. This ultimately led to the reconstruction of heterotrophic microbial communities dominated by Sphaerotilus and Acidovorax under high DO conditions, and heterotrophic-autotrophic co-enriched microbial communities dominated by Chlorobium under low DO conditions (1-2 mg/L). Additionally, under high DO conditions, high microbial mass transfer efficiency and the enrichment of functional genes were crucial for achieving high nitrogen removal performance. Further, the microbial carbon fixation potential was relatively high under the DO 3 mg/L condition, helping to reduce the consumption of additional carbon sources. This study provided innovative ideas for the sustainable and low-carbon development of wastewater treatment technology.

Comparative insight into the effects of different carbon source supplement on antibiotic resistance genes during whole-run and short-cut nitrification-denitrification processes.

Mature landfill leachate is known for nitrogen-removal challenging and meantime was considered as an important sink of antibiotic resistance genes (ARGs). The added external carbon sources, enabling the short-cut nitrification and denitrification, may facilitate the proliferation of bacteria that possibly carry ARGs. However, this speculation has yet to be studied. Here, we explored the effects of glucose, sodium acetate, and methanol supplements on ARGs during whole-run and short-cut treatment processes. The results showed that sodium acetate supplement during short-cut process efficiently reduced the abundances of total ARGs (0.84-1.99 copies/16S rRNA) and integrons (0.59-1.20 copies/16S rRNA), which were highly enhanced by methanol addition during whole-run treatment process (total ARGs: 3.60-11.01 copies/16S rRNA, integrons: 1.20-4.69 copies/16S rRNA). Indirect gradient analysis showed that the variation of ARGs was not correlated with the supplement of different external carbon source. Correlation analysis indicated that dominant intl1 (55.99 ± 17.61% of integrons) showed positively significant correlations with all detected ARGs expect for sul2 and ermB (p < 0.05), suggesting the significant role on ARGs dissemination. Redundancy analysis illustrated that the potential hosts of intl1, intl2, sul1, tetQ, tetM, mefA, and mexF were dominant Bacteroidetes and Actinobacteria. Interestingly, the numbers and significant extent of correlations under the supplement of sodium acetate during short-cut denitrification process were obviously declined, and it was in accordance with ARGs reduced by sodium acetate supplement, suggesting sodium acetate displayed the efficient ARGs reduction during short-cut process. In summary, this study provides a comparative understanding of the effects on ARGs by different carbon source supplements during nitrification-denitrification processes of leachate; sodium acetate is the optimal carbon source.

Efficient biodegradation of 1,4-dioxane commingled with additional organic compound: Role of interspecies interactions within consortia.

Microbial consortia-mediated biodegradation of 1,4-dioxane (1,4-D), an emerging water contaminant, is always a superior choice over axenic cultures. Thus, better understanding of the functions of coexisting microbes and their interspecies interactions within the consortia is crucial for predicting biodegradation efficiency and designing efficient 1,4-D-degrading microbial consortia. This study evaluated how microbial community compositions and interspecies interactions govern the microbial consortia-mediated 1,4-D biodegradation by investigating the biodegradability and microbial community dynamics of both enriched (N112) and synthetic (SCDs and SCDNs) microbial consortia in the absence or presence of additional organic compound (AOC). In the absence of AOC, N112 exhibited 100% 1,4-D biodegradation efficiency at a rate of 12.5 mg/L/d, whereas the co-occurrence of AOC resulted in substrate-dependent biodegradation inhibition and thereby reduced the biodegradation efficiency and activity (2.0-10.0 mg/L/d). The coexistence and negative influence of certain low-abundant non-degraders on both 1,4-D-degraders and key non-degraders in N112 was identified as the prime cause behind such biodegradation inhibition. Comparing with N112, SCDN-1 composed of 1,4-D-degraders and key non-degraders significantly improved the 1,4-D biodegradation efficiency in the presence of AOC, confirming the absence of negative influence of low-abundant non-degraders and cooperative interactions between 1,4-D-degraders and key non-degraders in SCDN-1. On the contrary, both two-species and three-species SCDs comprised of only 1,4-D-degraders resulted in lower 1,4-D biodegradation efficiency as compared to SCDN-1 under all treatment conditions, while max. 91% 1,4-D biodegradation occurred by SCDs in the absence of AOC. These results were attributed to the negative interaction among 1,4-D-degraders and the absence of complementary roles of key non-degraders in SCDs. The findings improve our understanding of how interspecies interactions can regulate the intrinsic abilities and functions of coexisting microbes during biodegradation in complex environments and provide valuable guidelines for designing highly efficient and robust microbial consortia for practical bioremediation of 1,4-D like emerging organic contaminants.

Research on the enhanced biological nitrogen removal of wastewater by the ultrasound-hydrolysis acidification of excess sludge.

To simultaneously improve the removal of nitrogen and phosphorus from wastewater with a low C/N ratio and reduce excess sludge production, in this paper, excess sludge ultrasound-hydrolysis acidification (UHA) pretreatment was coupled with the anaerobic-anoxic-oxic (AAO) process to provide carbon source and enhance biological nitrogen removal performance, and the experimental results can be summarized as follows. First, the total nitrogen (TN) concentrations in the effluent of the system decreased from 16.94 mg/L to 5.74 mg/L, and the removal rate of TN increased by 25.5%. In addition, the concentrations for ammonia nitrogen (NH3 -N) in the system decreased 12.59 mg/L, and the removal rate of this index increased by 29.0%. Furthermore, the specific oxygen uptake rate (SOUR) in the anoxic zone increased significantly because the application of UHA products enhanced the microbial activity, and the addition of UHA products had an effect on the microbial community structure in the system. The amounts of denitrifying bacteria such as Betaproteobacteria and Alphaproteobacteria also increased, which enhanced the nitrogen removal efficiency of wastewater biological treatment. PRACTITIONER POINTS: Treatment of excess sludge in UHA device as an additional carbon source. Nitrogen removal efficiency was greatly improved after adding UHA products. Input of UHA products enhanced microbial activity in AAO system. Denitrifying bacteria increased with the addition of UHA products.

A pilot-scale deep bed denitrification filter for secondary effluent treatment using sodium acetate as external carbon.

A pilot-scale quartz sand deep bed denitrification filter (DBDF) using sodium acetate as the additional carbon source was implemented to treat secondary effluent, with a high nitrate nitrogen (NO3 -N) concentration and low C/N ratio, from an urban municipal water resource recovery facility. By the 18th day, results showed that the removal efficiency of NO3 -N and the chemical oxygen demand (COD) were stable at above 85% and 70%, respectively. When the filter layer depth was set to 1,600 mm and the concentration of additional sodium acetate was maintained at 51 mg/L, the total nitrogen and COD concentrations of the DBDF effluent were stabilized below 5 and 30 mg/L, respectively. The quartz sand DBDF had a good effect on the removal of dissolved organic matter, especially for aromatic protein-like and tryptophan protein-like substances. Bacteria with denitrification function, such as Cloacibacterium and Zoogloea, became increasingly dominant with increasing filling layer depth. PRACTITIONER POINTS: The denitrification filter had a good effect on the removal of aromatic protein-like and tryptophan protein-like substances. Cloacibacterium and Zoogloea became increasingly dominant with increasing filling layer depth.

Non-additional carbon source one-step synthesis of Bi2O2CO3-based ternary composite for efficient Z-scheme photocatalysis.

Bi2O2CO3-based ternary composite materials are generally synthesized by two- or multi-step method and special precursor of CO32- is usually utilized in synthesis of Bi2O2CO3, which are time-consuming, laborious and relatively costly. In this paper, for the first time, a facile one-step solvothermal method is used to fabricate Z-scheme Bi2O2CO3/Bi/Bi2WO6 ternary composites. Interestingly, ethylene glycol not only acts as solvent for the reaction system, but also reduced Bi3+ into metallic Bi and itself is oxidized to CO32-, which could construct Bi2O2CO3. On this occasion, Bi2O2CO3/Bi/Bi2WO6 ternary composites are obtained after one-step method. High resolution transmission electron microscopy clearly reveals each component in composites. The as-prepared samples could be applied in various photocatalytic activities. Under solar light irradiation, Bi2O2CO3/Bi/Bi2WO6 composites exhibited prominent photodegradation performances for both ciprofloxacin and bisphenol A. Meanwhile, these composites could also be used in efficient photoreduction of CO2. The efficient photocatalytic activity could be mainly ascribed to Z-scheme electron transfer mechanism in ternary composites, which is determined by surface redox reactions, active species trapping experiment, electron spin resonance spectrum.