Soil Science Institute, National Agricultural Research Foundation, 57001 Thessaloniki, Greece.
J Environ Manage. 2011 Dec;92(12):3130-5. doi: 10.1016/j.jenvman.2011.08.008. Epub 2011 Aug 26.
Performance of a full-scale duckweed-covered treatment system in removing faecal bacteria is presented. The system consisted of three ponds in series and received septage from holding tanks. Inflow averaged between 36 m(3) d(-1) in the cold season and 60 m(3) d(-1) in the warm season, resulting in a total hydraulic retention time of 88 and 58 days, respectively. Duckweed (Lemna minor) colonized the ponds in the summer and continued to grow in the cold season. Due to the difficult harvesting process of the duckweed biomass, the investigation of the treatment efficiency was carried out without plant harvesting. The system was monitored for temperature, pH, oxygen, chlorophyll-a, Escherichia coli and Enterococci. Duckweed growth resulted in chlorophyll-a concentration reduction from 924 to 13 μg L(-1), causing neutral and anoxic conditions in the pond water. A temperature effect was noticed on the E. coli decay coefficient with a decreasing trend along the treatment system. Enterococci always decayed less than E. coli. Differences on decay coefficients and removal efficiencies were not observed between the three ponds for both bacterial types. Effluent quality in terms of E. coli was 489 and 1377 cfu/100 mL, in the warm and the cold seasons, respectively, with average removals of 99.65 ± 1.46% and 99.33 ± 3.03%. Total Enterococci removal was 88.91 ± 23.1% in the warm season and 94.43 ± 24.45% in the cold season, resulting in mean effluent values of 1058 and 1404 cfu/100 mL, respectively. The seasonal differences in total removal efficiencies were insignificant for both bacterial types.
展示了一个大型浮萍覆盖处理系统去除粪便细菌的性能。该系统由三个串联的池塘组成，接收来自储存罐的粪水。冷季的平均入流量为 36 m³/d，暖季为 60 m³/d，分别导致水力停留时间总计为 88 天和 58 天。浮萍（Lemna minor）在夏季在池塘中繁殖，并在冬季继续生长。由于浮萍生物量的收获过程困难，因此在没有植物收获的情况下进行了处理效率的调查。该系统监测了温度、pH 值、氧气、叶绿素-a、大肠杆菌和肠球菌。浮萍的生长导致叶绿素-a 浓度从 924μg/L 降低到 13μg/L，导致池塘水中呈中性和缺氧状态。发现温度对大肠杆菌衰减系数有影响，随着处理系统的进行呈下降趋势。肠球菌的衰减总是小于大肠杆菌。对于两种细菌类型，三个池塘之间均未观察到衰减系数和去除效率的差异。在温暖和寒冷季节，大肠杆菌的出水质量分别为 489 和 1377 cfu/100mL，平均去除率分别为 99.65±1.46%和 99.33±3.03%。温暖季节肠球菌的总去除率为 88.91±23.1%，寒冷季节为 94.43±24.45%，导致平均出水值分别为 1058 和 1404 cfu/100mL。对于两种细菌类型，总去除效率的季节性差异不显著。
