The impact of temperature and dissolved oxygen (DO) on the partial nitrification of immobilized fillers, and application in municipal wastewater

Water Quality Characteristics and Seasonal Changes in Wastewater Treatment in the Southern Hebei Region by Branch

This study analyzed three years of data (2021-2024) from three wastewater treatment plants (WWTPs), namely D, X, and T, in the main urban area of Handan, a typical city in the southern Hebei region, and investigated the influent characteristics and impact of temperature on these wastewater treatment facilities. With 90% assurance, the overall influent conditions of the three WWTPs in this region were normal. However, Plant T operated more effectively with slightly lower BOD5/CODCr (B/C), organic carbon/total phosphorus (C/TP), and organic carbon/total nitrogen (C/TN) ratios in the influent. Plant D consistently met the Level A standard, Plant X essentially reached the Level A standard, while Plant T attained the Level 2 standard prior to its upgrade. Following the upgrade, Plant T also steadily met the Level A standard. The effluent from all plants was relatively stable, primarily influenced by the influent characteristics and slightly influenced by temperature, but without having a noticeable impact on the effluent quality.

High efficiency and stable partial nitration achieved via gel immobilization

Long-term high efficiency and stable partial nitrification (PN) performance was achieved using gel-immobilized partial nitrifying bacteria. The PN characteristics of the filler under high and low ammonia nitrogen concentrations and low temperature were comprehensively studied and the rapid reactivation was achieved after reactor breakdown or long stagnation period. The results showed that the maximum ammonia oxidation rate was 66.8 mg•(L•h)-1 and the nitrite accumulation rate was above 95 % for the filler. Efficient and stable PN performance depends on the high abundance of ammonia-oxidizing bacteria (AOB) inside the filler and dynamically microbial community. In addition, the oxygen-limited zone and competition between the microorganisms inside the filler effectively inhibited the growth of nitrite oxidizing bacteria, and the sludge outside the filler assisted in this process, which supported the dominant position of AOB in fillers. This study provides a reliable technology for the practical application of the PN nitrogen removal process.

Numerical modelling of nitrate transport in fractured porous media under non-isothermal conditions

Subsurface contamination is a frequent occurrence in fractured porous systems, posing a potential threat for the groundwater contamination. Tracking the movement of these contaminants is an inherent aspect of effective remediation strategy. The non-isothermal conditions prevailing in the subsurface environment further add to the complexity of the existing scenario. The current study focuses on simulating the concentration profiles of nitrogen species in a fracture-matrix system under non-isothermal conditions. The kinetics and biochemical thermodynamics of nitrogen transformation reactions were explicitly modelled in this study by adopting a finite differential numerical scheme. The numerical results clearly depicted the spatial-temporal profiles of the concentration of all the species in response to the observed peak values. Considering the sensitivity of the model parameters, an increase in flow velocity triggered the migration of all nitrogen species in the fracture, while an increase in matrix porosity reduced the concentration by enhancing the chemical reactions. An increase in fracture aperture also could trigger the denitrification process in the fracture to reduce the nitrate-nitrogen contamination in the fracture. The temperature variation between 25 °C and 45 °C in the fracture and the matrix essentially reduced the availability of nitrate-nitrogen and nitrogen gas in the fracture under non-isothermal conditions. Hence, an increase in the temperature coefficient can reduce the spike of nitrate-nitrogen and nitrogen gas in fracture by minimizing such transformation rates.