城市污水管网中污染物冲刷与沉积规律

为探明城市污水管网中污染物的冲刷与沉积规律,对西安市污水管网进行实际调研,结果表明,污水支管和干管的沉积物厚度时变化较大,变化量分别为0~24 mm和0~12 mm,管道污水中颗粒态污染物发生沉积和冲刷的概率高;而污水主干管的沉积物厚度时变化较小,管道内颗粒物沉积与沉积物冲刷水平维持相对平衡.为进一步明确污水中污染物浓度变化与水流流速的关系,建立了污水管道冲刷与沉积模拟中试装置,研究了不同流速下管道中碳(有机)、氮、磷三类污染物含量和粒径分布的变化规律.结果表明,随着污水流速的增加,冲刷强度增大,管道中污染物浓度急剧升高,通过粒径分布监测结果可知,管道中有机污染物易存在于粒径较大的颗粒物上,氮、磷类污染物易吸附在粒径较小的颗粒物上;当流速小于0.6 m·s~(-1)时,污水中颗粒态污染物的沉积作用大于冲刷作用,发生物理沉积,造成污水中碳源不足,当流速大于0.6 m·s~(-1)时,水流冲刷强度增大,沉积物被水流大量携带,但污水中碳类有机污染物的增加比重大于氮和磷类污染物,使现有污水碳源不足得到改观,利于生物脱氮除磷工艺的碳源需求.

Law of Pollutant Erosion and Deposition in Urban Sewage Network

In order to investigate the scouring and deposition law of pollutants in urban sewer systems, the investigation of sewer systems was carried out in Xi''an. The results showed that the thickness of sediment in the branch pipe and the main pipe varied obviously. At the peak of the drainage, the velocity increased gradually, and the thickness of the pipeline sediment decreased. At the bottom of the drainage trough, the changes of the velocity and the thickness of the pipeline sediment were opposite, with variations of 0-24 mm and 0-12 mm, respectively. And the probability of granular contaminants sedimentation and scouring in sewer systems was high, while the thickness of sediment in sewage main pipe was less than the above mentioned pipes, the variation of which was 0-7 mm. In addition, the sedimentation and scouring in the main pipeline kept relatively balanced and the thickness of sediment remained stable. In order to clarify the relationship between the concentration of pollutants and the flow velocity, a pilot sewer system was established. The effects of different flow rates, which were 0.1, 0.3, 0.6, 0.9, 1.2 m·s^-1, respectively, on the contents of carbon (organic), nitrogen and phosphorus in the pipeline were studied. The results showed that with the increase of the flow velocity, the scour intensity increased and the concentration of pollutants in the pipeline also increased sharply. As shown by the monitoring results of the static light scattering particle size analyzer, the carbon organic pollutants in the pipeline were easily adsorbed on the larger particles, while nitrogen and phosphorus pollutants were easily adsorbed on the particles with smaller size. Analysis on the change of the urban sewage pipeline showed, when the flow rate was less than 0.6 m·s^-1, the sedimentation of granular pollutants in the sewage was greater than the scouring effect. When the flow velocity was higher than 0.6 m·s^-1, the water scouring intensity increased and the scouring action was greater than the sedimentation, meanwhile, the sediments were carried by the water and the thickness of the sediments was reduced. The increase of the organic pollutants in the sewage was bigger than the nitrogen and phosphorus pollutants, so that the existing sewage carbon source was improved.