Nitrite produced during ammonia oxidation can inhibit the activity of microorganisms. To provide guidance for the optimization and design of a biofilter, a pilot-scale biofilter was established to investigate the influence of nitrite on organic matter and manganese removal and on the kinetics. The results demonstrated that COD_Mn, ammonia, and manganese in effluent were 2.77, 0.034, and 0.026 mg/L in the steady phase, respectively. Organic matter and manganese removal were affected by nitrite during the start-up process, as well as in the ammonia increasing process. When ammonia increased from about 0.5 to 1 and 2 mg/L, organic matter, and manganese removal were affected at 4 and 3 days and 6 and 5 days, respectively. When organic matter, ammonia, and manganese in the influent were 6.27, 2.07, and 1.19 mg/L, respectively, organic matter, ammonia, and manganese oxidation all followed a first-order kinetic rate. The k-value was 0.0268, 0.268, and 0.216 min⁻¹, and the half-life time was 24.236, 2.583, and 3.202 min, respectively. The influence of nitrite on the structure of microbial communities in the biofilter will be investigated in the future.

The underground space, also known as the "fourth dimension" of the city, reflects the efficient use of urban development intensive. Urban traffic link tunnel is a typical underground limited-length space. Due to the geographical location, the special structure of space and the curvature of the tunnel, high-temperature smoke can easily form the phenomenon of "smoke turning" and the fire risk is extremely high. This paper takes an urban traffic link tunnel as an example to focus on the relationship between curvature and the temperature near the fire source, and use the pyrosim built different curvature fire model to analyze the influence of curvature on the temperature of the fire, then using SPSS Multivariate regression analysis simulate curvature of the tunnel and fire temperature data. Finally, a prediction model of urban traffic link tunnel curvature on fire temperature was proposed. The regression model analysis and test show that the curvature is negatively correlated with the tunnel temperature. This model is feasible and can provide a theoretical reference for the urban traffic link tunnel fire protection design and the preparation of the evacuation plan. And also, it provides some reference for other related curved tunnel curvature design and smoke control measures.

As a modern city’s “fourth dimension space”, UTLT is a typical narrow and confined underground space. Due to the special structural position and the curvature of the tunnel, the hot smoke in the fire field can easily form a “smoke turning circle” phenomenon, which greatly reduces environmental visibility and threatens people escape quickly. This article takes a UTLT small radius tunnel as an example to investigate the relationship between the curvature of the tunnel and the visibility of the fire near the fire source. Firstly, using Pyrosim to simulate the change of visibility in different curvatures of fire field, and using SPSS to carry out multiple regression analysis on numerical simulation data, summarizing the prediction model of the impact of small radius UTLT tunnel curvature on the visibility near the fire source. Finally, regression model analysis and test show that the curvature is negatively correlated with the visibility of the tunnel and the prediction model is feasible. The research results can provide theoretical guidance for the design of UTLT-type small-radius circulation smoke evacuation and rapid evacuation of personnel, and provide a reference for similar curve tunnel curvature design and smoke control measures.