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Influence of synthetic wastewater on the transport and transformation in irrigated soils

机译：合成废水对灌溉土壤中迁移和转化的影响

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Irrigation with wastewater can increase the available water supply and present a feasible alternative for increasing resources in water-scarce areas. Despite these benefits, some potential negative environmental effects among which degradation of the hydraulic soil properties and groundwater contamination may arise in association with the use of wastewater. Because of these concerns, a randomized complete block design under unsaturated, steady-state flux was performed with aerobic sand columns treated with synthetic wastewater. Water treatments included four irrigation, and different levels of chemical oxygen demand (COD). A time domain reflectometry (TDR) probe was used to measure water content and electrical conductivity at two depths of 20 and 60 cm from the top of columns. Water samples were taken using Rhizon extractors placed at 25 cm and 65 cm from the top. At each column two tensiometers for measuring hydraulic potentials were placed, at two different depths 20 and 60 cm. Four steady-state flux conditions (1 cm h(-1)) tracer tests were used to obtain transport parameters such as the dispersion coefficient and pore-water velocity by analyzed a transfer-function method. Estimating water and solute transport parameters was simulated by inverse modelling techniques. Statistical analysis shows that transport parameters under the unsaturated conditions were remained fairly constant in all treatments during the experiment time. In contrast, after exploring different possible shapes for a curve the experimental data were fitted in a simple model for evaluating the zero order and first order form of rate equations to evaluate the kinetics. It was found that first order rate expression is the best fit for the synthetic wastewater under different concentrations that gives a best fit shape constant (R-2 = 0.9714). Overall, the HYDRUS-1D model successfully simulated the water flow and Pulse-response experiments in the columns. If during primary stages of municipal wastewater treatment, some elements like solids, the toxics or pathogens be removed, which is essential for trickle irrigation, then the municipal wastewater can be similar to our artificial wastewater. The results show that the effluent of our synthetic wastewater without toxic or pathogen elements, was very clear and its quality exceeded the direct discharge standard, poses little risks for groundwater pollution. In addition, the experimental results also show that the removal efficiencies of COD was high, being more than 65% and 95%.
机译：废水灌溉可以增加可用的水供应，并为增加缺水地区的资源提供了可行的替代方案。尽管有这些好处，但与废水的使用有关，可能会产生一些潜在的负面环境影响，其中水硬土壤特性的退化和地下水污染可能会出现。由于这些问题，使用合成废水处理的好氧砂柱在不饱和稳态通量下进行了随机完整块设计。水处理包括四次灌溉，以及不同水平的化学需氧量（COD）。使用时域反射法（TDR）探针在距柱顶20和60 cm的两个深度处测量水含量和电导率。使用放置在距顶部25厘米和65厘米处的Rhizon提取器采集水样。在每列上，分别在两个不同的深度20和60 cm处放置两个用于测量水力潜力的张力计。通过分析传递函数法，使用四个稳态通量条件（1 cm h（-1））示踪剂测试来获得诸如分散系数和孔隙水速度等输运参数。通过逆建模技术模拟了估计水和溶质的运移参数。统计分析表明，在整个实验过程中，所有处理中非饱和条件下的输运参数均保持相当恒定。相反，在探索了曲线的不同可能形状之后，将实验数据拟合到一个简单模型中，以评估速率方程的零阶和一阶形式来评估动力学。发现一阶速率表达最适合不同浓度下的合成废水，并给出最佳拟合形状常数（R-2 = 0.9714）。总体而言，HYDRUS-1D模型成功地模拟了色谱柱中的水流和脉冲响应实验。如果在市政废水处理的初期阶段去除了点滴灌溉必不可少的某些元素（如固体，有毒物质或病原体），那么市政废水可能类似于我们的人工废水。结果表明，不含毒性或病原体成分​​的合成废水的排放非常清晰，其质量超过了直接排放标准，对地下水污染的风险很小。另外，实验结果还表明，COD的去除率较高，分别达到65％和95％以上。

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