The Key Laboratory of Water and Sediment Sciences, Ministry of Education; College of Environmental Sciences and Engineering, Peking University, Beijing 100871, PR China.
Department of Environmental Science, Zhejiang University, Key Laboratory of Environmental Pollution and Ecological Health of Ministry of Education; Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou 310058, PR China.
Water Res. 2022 Aug 1;221:118783. doi: 10.1016/j.watres.2022.118783. Epub 2022 Jun 19.
The release of microplastics (MPs) especially those with sizes less than 10 μm from effluent of wastewater treatment plants (WWTPs) is one of the major sources of plastics into aquatic environment. To reduce the discharge of MPs into environment, it is essential to further enhance their removal efficiencies in WWTPs. In present study, to boost the removal performance of MPs in sand filtration systems (units that commonly employed in WWTPs to remove colloidal pollutants), six types of biochar fabricated from three raw biomass materials (i.e. lignin, cellulose, and woodchips) at two pyrolysis temperatures (400 °C and 700 °C) was respectively amended into sand columns as thin permeable layer. We found that adding all six types of biochar into sand columns as thin permeable layer could greatly improve the retention of MPs with the diameter of 1 μm under either slow (4 m/d) or fast flow rates (160 m/d) due to the high adsorption capability of biochar. Woodchip-derived biochar exhibited the highest MPs retention performance, which was followed by cellulose-derived biochar and then lignin-derived biochar. Moreover, for biochar derived from three raw biomasses, increasing pyrolysis temperature could improve MPs retention performance. The direct observation of real-time plastics retention processes on different types of biochar via a visible flow chamber showed that woodchip-derived biochar especially that fabricated at 700 °C exhibited more MPs trapping processes relative to lignin and cellulose-derived biochar due to their more complex surface morphology. Thus, the highest MPs retention performance was achieved in sand columns with amendment by 1 wt% woodchip-derived biochar fabricated at 700 °C. More importantly, we found that for these modified sand filtration column systems, complete MPs removal could be achieved in real river water and actual sewage water, in multiple filtration cycles, longtime filtration process (100 pore volumes injection) as well as with interval flow conditions. Moreover, biochar could be regenerated and reused as thin permeable layer to effectively remove MPs. The results of this study clearly showed that biochar especially woodchip-derived biochar fabricated at 700 °C had the potential to immobilize MPs especially those with small sizes in WWTPs.
微塑料（MPs）特别是那些小于 10μm 的尺寸从废水处理厂（WWTPs）的污水中释放出来，是塑料进入水生环境的主要来源之一。为了减少 MPs 排放到环境中，必须进一步提高 WWTPs 中 MPs 的去除效率。在本研究中，为了提高砂滤系统（ WWTPs 中通常用于去除胶体污染物的单元）中 MPs 的去除性能，分别将三种生物质原料（木质素、纤维素和木屑）在两种热解温度（400°C 和 700°C）下制成的六种生物炭添加到砂柱中作为薄的渗透层。我们发现，由于生物炭具有高吸附能力，将所有六种类型的生物炭添加到砂柱作为薄的渗透层，可以大大提高直径为 1μm 的 MPs 的保留率，无论是在慢速（4m/d）还是快速流速（160m/d）下。木屑衍生的生物炭表现出最高的 MPs 保留性能，其次是纤维素衍生的生物炭，然后是木质素衍生的生物炭。此外，对于三种原始生物量衍生的生物炭，提高热解温度可以提高 MPs 的保留性能。通过可见流室对不同类型生物炭上实时塑料保留过程的直接观察表明，木屑衍生的生物炭，特别是在 700°C 下制备的生物炭，与木质素和纤维素衍生的生物炭相比，具有更多的 MPs 捕集过程，这是由于其更复杂的表面形态。因此，在添加 1wt%的由 700°C 制备的木屑衍生生物炭的砂柱中实现了最高的 MPs 保留性能。更重要的是，我们发现对于这些改性砂滤柱系统，在多次过滤循环、长时间过滤过程（100 个孔隙体积注入）以及间歇流动条件下，在实际河流水中和实际污水中可以实现 MPs 的完全去除。此外，生物炭可以被再生和再用作薄的渗透层，以有效地去除 MPs。本研究的结果清楚地表明，生物炭，特别是在 700°C 下制备的木屑衍生生物炭，具有在 WWTPs 中固定 MPs 的潜力，特别是那些尺寸较小的 MPs。
