This study evaluated the potential of biochar impregnated with Fe3+ or Ca2+, or mixed with Polonite®, as a filter material for removal of phosphate (PO4-P) from wastewater in onsite wastewater treatment systems (OWTS). Four treatments with biochar were investigated: unimpregnated biochar (UBC), biochar impregnated with iron Fe3+ (FBC), biochar impregnated with calcium oxide (CBC), and biochar mixed with Polonite® (PBC). In a batch experiment using phosphate solution at concentrations 0.5, 3.3, 6.5, 13, and 26 mg PO4-P L–1, adsorption of PO4-P in the different treatments was modeled using Langmuir and Freundlich isotherms. Column filters (5 diameter × 55 cm height) packed with UBC, FBC, CBC, and PBC were then furnished with raw wastewater over 148 weeks. During this experiment, adsorption of PO4-P was investigated in response to increasing hydraulic loading rate (HLR; 56, 74, and 112 L m–2 day–1) and increasing phosphate loading rate (PLR; 195, 324, 653, and 1715 mg PO4-P m–2 day–1). Among the materials, FBC had the highest maximum adsorption capacity (Qm) based on Langmuir isotherms (3.21 ± 0.01 mg g–1). FBC and CBC showed robust performance with increasing HLR, while increasing PLR increased the amount of PO4-P retained in all filters. After 148 weeks of operation, removal of PO4-P (averaged over the last 18 weeks of operation) was 13 ± 16% for UBC, 40 ± 20% for CBC, 88 ± 12% for FBC, and 30 ± 18% for PBC. The PO4-P amount retained in filters over the 148 weeks was 84.75, 221.75, 358.38, and 152.36 g m–2 in UBC, CBC, FBC, and PBC, respectively. The adsorption capacity of the filters after 148 weeks was 1.50, 4.02, 6.41, and 2.75 mg g–1 for UBC, CBC, FBC, and PBC, respectively. The adsorption capacity values and breakthrough curves showed that low concentrations (i.e., <2.6 mg L–1) of PO4-P in wastewater would allow the FBC filter to remain active for 58 months and the CBC filter for 15 months, before PO4-P removal declined to <70%. In conclusion, biochar impregnated with iron and calcium is a promising solution for removal of PO4-P from wastewater in OWTS.

中文翻译：

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铁和钙浸渍生物炭在现场废水处理系统中从废水中吸附磷酸盐的效率

本研究评估了用 Fe3+ 或 Ca2+ 浸渍或与 Polonite® 混合的生物炭作为过滤材料从现场废水处理系统 (OWTS) 中去除废水中的磷酸盐 (PO4-P) 的潜力。研究了四种生物炭处理方法：未浸渍生物炭 (UBC)、浸渍铁 Fe3+ (FBC) 的生物炭、浸渍氧化钙 (CBC) 的生物炭和与 Polonite® (PBC) 混合的生物炭。在使用浓度为 0.5、3.3、6.5、13 和 26 mg PO4-P L-1 的磷酸盐溶液的批量实验中，使用 Langmuir 和 Freundlich 等温线模拟了不同处理中 PO4-P 的吸附。然后在 148 周内向装有 UBC、FBC、CBC 和 PBC 的柱式过滤器（5 个直径 × 55 厘米高）提供原废水。在这个实验过程中，研究了 PO4-P 的吸附响应增加的水力加载率（HLR；56、74 和 112 L m–2 day–1）和增加的磷酸盐加载率（PLR；195、324、653 和 1715 mg PO4-下午-2 天-1)。在这些材料中，基于朗缪尔等温线 (3.21 ± 0.01 mg g-1)，FBC 具有最高的最大吸附容量 (Qm)。FBC 和 CBC 随着 HLR 的增加表现出稳健的性能，而 PLR 的增加会增加所有过滤器中保留的 PO4-P 量。手术 148 周后，PO4-P 的去除率（手术最后 18 周的平均值）为 UBC 13 ± 16%、CBC 40 ± 20%、FBC 88 ± 12% 和 PBC 30 ± 18% . 在 UBC、CBC、FBC 和 PBC 中，148 周内过滤器中保留的 PO4-P 量分别为 84.75、221.75、358.38 和 152.36 gm-2。148 周后过滤器的吸附容量分别为 1.50、4.02、6。UBC、CBC、FBC 和 PBC 分别为 41 和 2.75 mg g-1。吸附容量值和穿透曲线表明，在 PO4-P 之前，废水中低浓度（即 <2.6 mg L-1）的 PO4-P 将使 FBC 过滤器保持活性 58 个月，CBC 过滤器保持活性 15 个月去除率下降到 <70%。总之，用铁和钙浸渍的生物炭是去除 OWTS 废水中 PO4-P 的有前途的解决方案。