Hexavalent Chromium Migration Characteristics By Permeable Fine-grained Sand Barrier Filters

It’s significant to use reasonable and efficient wastewater irrigation to solve the shortage of water resources. Research shows that it’s effective to apply pre-dam treatment technology to purify wastewater in agriculture. The permeable barrier filter is the first part of pre-dam, which is composed of serial fine-grained sands. With the advantages of the physical and chemical properties of soil and seepage characteristics of groundwater, this filter wall can break down, prevent, control, purify and remove the contaminants in order to meet the agricultural irrigation water quality standards. The research of permeable barrier filter is carried to provide the theories basis and technical support.This paper selected hexavalent chromium, one of the most dangerous pollutants, as research subject and analyzed migration features through theoretical analysis, indoor experimental and numerical simulation. The research was carried out with the following main aspects:(1) A mathematical model was built to couple seepage field and concentration field. With the governing equation of contaminants transport and definite conditions, analytic expression was given and fundamental theory was analyzed.(2) Indoor physical experiment was performed in single fine-grained filter wall, which is filled with0.5mm,0.2mm,0.1mm and0.075mm sand. The results showed that hexavalent chromium migration was caused by the interactions of convection, mechanical dispersion, molecular diffusion and adsorption. The influence factors of migration include concentration, groundwater flow velocity, PH, HRT and soil properties, of which groundwater flow velocity and soil properties are main factors.(3) The modules of SEEP and CTRAN of the rock engineering software GeoStudio were applied to verify corresponding conditions of the experiment and analyze the remove rate of hexavalent chromium. The results showed that hydrodynamic dispersion coefficient was an important variable for solute transport. Under the same compact degree, the smaller sand size is, the smaller coefficient is, the longer HRT takes.(4) Serial filter wall was established to further analyze the hexavalent chromium migration. The structure size and hydraulic conditions were given under high remove rate, and coupling rule of seepage and concentration was revealed as well.