Search Results (4)

The anaerobic-multistage anoxic/aerobic (A-MAO) process has shown good potential for advanced nitrogen removal in recent years, but its greenhouse gas emissions still need to be fully explored. The effects of the influent distribution and external carbon source sodium acetate on nutrient removal, greenhouse gas emissions, and the microbial community structure in a continuous plug-flow A-MAO reactor fed with real low C/N ratio domestic sewage were investigated. The results showed that altering the allocation of carbon source resulted in average chemical oxygen demand (COD) and total nitrogen (TN) concentration in effluent reduced to 26.10 ± 4.86 and 6.65 ± 1.73 mg/L, respectively. Both operations reduced the emission rate of greenhouse gas. While the addition of external car-bon sources leaded to lower N₂O emission rates and higher CO₂ and CH₄ emission rates. The addition of sodium acetate facilitated nitrification and denitrification processes, thereby leading to a reduction in N₂O production. Meanwhile, it spurred the growth of methanogenic bacteria and heterotrophic microorganisms, thus boosting the production of CO₂ and CH₄. Influent distribution promoted the increase of Bacteroidota, Chloroflexi and Acidobacteriota of the reactor. The enrichment of typical hydrolytic bacteria and glycogen accumulating organisms (GAOs) increased the utilization efficiency of carbon sources in the system after the addition of sodium acetate. The significant increase of typical denitrifying bacteria (DNBs) Azospira reduced the N₂O emission during heterotrophic denitrification process, which was considered to be an important functional genus for increasing nitrogen loss in this system. The rational utilization of carbon source makes the difference in metabolism function. The study provides a valuable strategy for comprehensively evaluating the pollutant removal and greenhouse gas emission reduction from the A-MAO process. Full article

Low air pressure is a feature of high-altitude regions. Domestic wastewater from such regions typically has a low carbon-to-nitrogen ratio (C/N ratio). These factors combine to make traditional biological nitrogen removal in high-altitude regions inefficient and more energy-intensive. The partial denitrification-anaerobic ammonium oxidation (PD/A) process was reported to remove ammonia nitrogen from municipal sewage, consuming fewer carbon sources and requiring no aeration supply. In this study, we set up laboratory-scale reactors in simulated high-altitude environmental conditions, and studied the effect of air pressure on the PD/A process. We found that low pressure promotes nitrogen removal efficiency (NRE), achieving 93.0 ± 0.3% at 65 kPa, and the contribution rate of anaerobic ammonium oxidation (anammox) to nitrogen removal increased to 77.7%. Lower dissolved oxygen (DO) concentrations caused by lower air pressure were the reason for higher nitrite accumulation efficiency (NAE) in a partial denitrification (PD) system, with measured values of 78.4 ± 2.8% at 65 kPa. The anammox process was promoted by low air pressure, mainly because the low air pressure resulted in higher anaerobic ammonia-oxidizing bacteria activity, with specific anammox activity (SAA) reaching 26.3 mg·N/(g·VSS·d). Although the relative abundance of partial-denitrifying bacteria declined slightly, at 65 kPa compared with 96 kPa, they were still the dominant genus of the PD/A sludge, and continued to generate nitrite nitrogen steadily, even at low air pressures. The anaerobic ammonia-oxidizing bacterial abundance remained relatively stable, but their activity was increased, which aided the PD/A process. This study demonstrates how low pressure promotes the PD/A process, indicating the possibility of sustainable improved nitrogen removal in high-altitude regions. Full article

Low C/N wastewater results from a wide range of factors that significantly harm the environment. They include insufficient carbon sources, low denitrification efficiency, and ${\mathrm{NH}}_4^{+}$-N concentrations in low C/N wastewater that are too high to be treated. In this research, the membrane biofilm reactor and hydrogen-based membrane biofilm reactor (MBR-MBfR) were optimized and regulated under different operating parameters: the simulated domestic sewage with low C/N was domesticated and the domestic sewage was then denitrified. The results of the MBR-MBfR experiments indicated that a C/N ratio of two was suitable for ${\mathrm{NH}}_4^{+}$-N, ${\mathrm{NO}}_2^{-}$-N, ${\mathrm{NO}}_3^{-}$-N, and chemical oxygen demand (COD) removal in partial nitrification-denitrification (PN-D) and hydrogen autotrophic denitrification for further treatment. The steady state for domestic wastewater was reached when the MBR-MBfR in the experimental conditions of HRT = 15 h, SRT = 20 d, 0.04 Mpa for H₂ pressure in MBfR, 0.4–0.8 mg/L DO in MBR, MLSS = 2500 mg/L(MBR) and 2800 mg/L(MBfR), and effluent concentrations of ${\mathrm{NH}}_4^{+}$-N, ${\mathrm{NO}}_3^{-}$-N, and ${\mathrm{NO}}_2^{-}$-N were 4.3 ± 0.5, 1.95 ± 0.04, and 2.05 ± 0.15 mg/L, respectively. High-throughput sequencing results revealed the following: (1) The genus Nitrosomonas as the ammonia oxidizing bacteria (AOB) and Denitratisoma as potential denitrifiers were simultaneously enriched in the MBR; (2) at the genus level, Meiothermus,Lentimicrobium, Thauera,Hydrogenophaga, and Desulfotomaculum played a dominant role in leading to ${\mathrm{NO}}_3^{-}$-N and ${\mathrm{NO}}_2^{-}$-N removal in the MBfR. Full article

The aim of the study was to assess the possibility of using polyurethane foams (PUF) as a filling of a foam-sand filter to directly treat domestic sewage with increased content of ammonium nitrogen and low organic carbon to nitrogen ratio (C/N). The study compared performance of two types of flexible foams: new, cylinder-shaped material (Novel Foams, NF) and waste, scrap foams (Waste Foams, WF). The foams serving as a filling of two segments of a foam-sand filter were assessed for their hydrophobic and physical properties and were tested for their cell structure, i.e., cell diameter, cell size distribution, porosity, and specific surface area. The study accounted also for selected application-related properties, such as hydrophobicity, water absorption, apparent density, dimensional stability, amount of adsorbed biomass, and the possibility of regeneration. Cell morphology was compared in reference foams, foams after 14 months of the filter operation, and regenerated foams. The experimental outcomes indicated WF as an innovative type of biomass carrier for treating domestic sewage with low C/N ratio. SEM images showed that immobilization of microorganisms in NF and WF matrices involved the formation of multi-cellular structures attached to the inner surface of the polyurethane and attachment of single bacterial cells to the foam surface. The amount of adsorbed biomass confirmed that the foam-sand filter made up of two upper layers of waste foams (with diameters and pore content of 0.50–1.53 mm and 53.0–63.5% respectively) provided highly favorable conditions for the development of active microorganisms. Full article