沼液中全氮在非饱和均质土壤中的吸附特征试验

Experimental study on adsorption of total nitrogen from biogas slurry in unsaturated homogeneous soil

为探讨沼液中全氮在非饱和均质土壤中的吸附特征,在室内恒温条件下,对非饱和均质土柱采用一维沼液吸附试验,测定不同沼液浓度、土壤密度及沼液入渗水头条件下渗出液电导率及全氮含量,并应用对流弥散溶质运移模型和CXTFIT2.0软件对试验数据进行拟合,得到了不同试验方案下的全氮平均孔隙水流速和水动力弥散度。试验结果表明:不同试验方案下较大密度土壤的渗出液电导率峰值点均小于较小密度土壤的峰值点;峰值点后渗出液的电导率与峰值点差值随沼液浓度的增大而增大;相同土壤密度及入渗水头条件下,随沼液浓度的增大,吸附曲线逐渐向右偏移,全氮运移吸附转折点对应时间及被截获在土柱中的全氮量增加,而吸附转折点渗出液相对浓度、平均孔隙水流速及水动力弥散度均减小;相同沼液浓度及土壤密度条件下,随入渗水头增大,土壤对全氮吸附达到饱和所需时间减少,平均孔隙水流速及水动力弥散度增大;相同沼液浓度及入渗水头条件下,随土壤密度的增大,全氮吸附转折点对应时间增长,水动力弥散度增大,而平均孔隙水流速减小。

A one-dimensional experiment of adsorption of biogas slurry by unsaturated homogeneous soil at constant room temperature was conducted in order to investigate the adsorption characteristics of total nitrogen from biogas slurry. The conductivity and total nitrogen content of percolates were measured with different concentrations of biogas slurry, soil densities, and infiltration heads of biogas slurry. The average pore-water velocities and hydrodynamic dispersion coefficients under different experimental conditions were obtained through fitting of the experimental data using the convection-dispersion model of solute transport and CXTFIT2. 0 software. The experimental results showed that the peak values of the conductivity of percolates in experimental schemes with higher soil density was less than those in schemes with lower soil density;the differences between the peak conductivity of the percolates and the conductivity after the peak point increased with the concentration of the biogas slurry; with the increase of the biogas slurry concentration, the adsorption curves gradually moved towards the right, and the time corresponding to the turning point of adsorption curve and the total nitrogen content in soil increased, but the relative concentration of the percolate at the turning point, the average prove-water velocity, and the hydrodynamic dispersion coefficient decreased under the same soil density and head conditions; with the increase of the infiltration head, the time that the soil needed to reach saturation of the adsorbed total nitrogen decreased, and the average pore-water velocity and hydrodynamic dispersion coefficient increased under the same biogas slurry concentration and soil density conditions;and, with the increase of soil density, the time corresponding to the turning point of adsorption curves and the hydrodynamic dispersion coefficient increased, but the average pore-water velocity decreased under the same biogas slurry concentration and head conditions.