ABSTRACT
Deposition particles can lead to blockage, odor, and corrosion of pipes, and the deposition process of suspended particles is particularly complicated. In order to quantify the deposition process of suspended particles and mastered the critical conditions for the deposition in storm drainage, the process was simulated experimentally, and the deposition states of suspended particles under the different roughness of pipe wall, particle size, and density were analyzed. Two mathematical models of deposition critical velocity and easy deposition velocity were established. Results showed that with the increase of particle size and density, the gravity of particles increased and deposition was more likely to occur. In the rough pipeline, the kinetic energy consumption of water flow increased, the ability to carry particles was weakened, and the deposition rate would increase accordingly. The higher the flow velocity, the lower the deposition rate. The deposition states of particles in the pipeline could be divided into three types according to the deposition rates: "no deposition," "minor deposition," and "bulk deposition." Verification showed that the difference rates between the calculated values and measured values of the deposition critical velocity ranged from - 3.23 to 2.86%, and the difference rates of the easy deposition velocity were - 4.14-4.72%, showing good consistency.
Subject(s)
Models, Theoretical , Particle Size , CorrosionABSTRACT
In the sediment-water system of storm sewers (e.g., sediments, interstitial water, and the water column), the migration of nitrogen and its biological transformation with different dissolved oxygen conditions were investigated. Results showed that in an aerobic segment, γ-proteobacteria, α-proteobacteria, and nitrospira, which are aerobic, grew actively in water column and interstitial water through ammonification and nitrification. In anoxic segment, ammonification depended mainly on clostridia, whereas nitrification was inhibited. Thus, after 20 days, the concentration of NH4+-N in the aerobic segment became noticeably lower (5.97 mg/L) than that in the anoxic segment (18.09 mg/L). In sediments, the biological transformation of organic nitrogen in the anoxic environment was more complete, resulting in elevating amino acid nitrogen and NH4+-N in the anoxic segment compared to the aerobic segment. Furthermore, the concentration gradient of NH4+-N between interstitial water and water column in aerobic and anoxic segments, thereby causing NH4+-N to migrate from interstitial water to the water column. In the sediment-water system, the different forms of nitrogen changes were the common result of biological transformation and material migration.
