Department of Sustainable Development, Environmental Science & Engineering, Division of Water and Environmental Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
Department of Sustainable Development, Environmental Science & Engineering, Division of Water and Environmental Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
Sci Total Environ. 2022 Aug 10;833:155254. doi: 10.1016/j.scitotenv.2022.155254. Epub 2022 Apr 13.
The sorption capacities of sand filters used for onsite wastewater treatment and their associated risks of phosphorus (P) leaching on contact with rainwater were investigated in column experiments and with modelling tool for over 300 days. Columns packed with sand were exposed to real domestic wastewater of different characteristics and hydraulic loading modes. The wastewater fed into the columns was effluent collected from three different treatment units in the field: a septic tank (ST), biofiltration tank (BF) and Polonite® filter bag (PO). The risk of P leaching to groundwater and surface water was also assessed, by exposing the same sand columns to natural rainwater. Overall results indicated that sand soils can exhibit different adsorption and desorption capacities for electrical conductivity (EC), Total-P, phosphate-P and total suspended solids, depending on the characteristics of influent wastewater, loading rate and total operation time. The removal efficiencies of the sand columns increased in the order ST (98.16%) > PO (93.36%) > BF (81.57%) for PO4-P and slightly decreased ST (97.11%) > PO (92.06%) > BF (76.76%) for Total-P columns. All sand columns loaded with actual wastewater solutions from septic tanks and biofiltration tank have demonstrated high risks of phosphorus leaching (>99.99%) to the groundwater. The modelling was successful captured behavior of EC tracer and adsorption of PO-P with acceptable prediction uncertainty in the PO < 8% columns. The modelling results indicated that the decrease of loading rate from 83.3 mL d-1 to 20.83 mL d-1 led to an average increase of removal efficiency and prolong operational lifetime and mass of adsorbed Total-P in the sand soil. This study concludes that sand is a valuable filter medium at low loading rate for phosphorus removal in full-scale operations of onsite treatment systems, however very vulnerable for leaching P when in contact with rainwater.
采用柱实验和模拟工具对用于现场污水处理的砂滤器的吸附能力及其与雨水接触时磷（P）浸出的相关风险进行了研究，研究时间超过 300 天。用砂填充的柱子暴露于不同特性和水力负荷模式的实际家庭废水中。将废水注入柱子中，该废水是从现场的三个不同处理单元收集的：化粪池（ST）、生物过滤池（BF）和 Polonite®过滤袋（PO）。还通过暴露相同的砂柱于天然雨水来评估 P 对地下水和地表水的浸出风险。总体结果表明，砂土壤可能表现出不同的吸附和解吸电导率（EC）、总磷（Total-P）、磷酸盐-P 和总悬浮固体的能力，这取决于进水废水的特性、加载速率和总运行时间。砂柱的去除效率按 ST（98.16%）>PO（93.36%）>BF（81.57%）的顺序增加PO4-P，而按 ST（97.11%）>PO（92.06%）>BF（76.76%）的顺序略微降低了总磷（Total-P）。所有用实际来自化粪池和生物过滤池的废水溶液加载的砂柱均显示出对地下水磷浸出的高风险（>99.99%）。该模型成功地捕获了 EC 示踪剂的行为以及 PO-P 的吸附，在 PO <8%的柱子中具有可接受的预测不确定性。模拟结果表明，从 83.3 mL d-1 降低至 20.83 mL d-1 的加载速率导致在砂土壤中的去除效率、操作寿命和吸附的总磷（Total-P）质量的平均增加。本研究得出结论，在现场处理系统的全规模运行中，砂是一种有价值的低负荷率磷去除过滤介质，但在与雨水接触时，磷浸出的风险非常大。
