Effects of Longan Biochar as Filter Materials on Plant Responses and Wastewater Treatment by Typha angustifolia L.

Abstract This study investigated the effects of filter materials and Typha angustifolia L. (cattail) plantation on wastewater treatment efficiency and assessed the growth responses of cattail in the different filter materials. Five treatments of lab-scale experiment were set-up: unplanted and planted columns filled with either gravel or longan biochar, and columns without any filters and plants were used as a control. Without plantation, longan biochar filters removed 97% of biochemical oxygen demand (BOD5), 96% of total suspended solids (TSS), 86% of ammonium (NH4-N), 82% of total Kjeldahl nitrogen (TKN), and 75% of nitrate (NO3-N). Compared with the unplanted gravel-based system, 87% of BOD5 and 89% of TSS were removed but NH4-N, TKN, and NO3-N removal was only 27%, 37%, and 34%, respectively. However, the pollutant removal in gravel-based systems was as high as the removal in longan biochar-based systems when planted with cattail. It removed 84% and 81% of NH4-N and TKN, respectively, and removed 90% of total phosphorus (TP) whereas the TP removals in the other four treatments were only 13-25%. The study indicates that longan biochar is efficient for removing N and for filtering organic matters from wastewater. Hence, longan biochar may have promise for the use as a filter material in constructed wetlands (CWs). The biochar, however, may have adverse effects on the plants. Therefore, the proportion of biochar in the filter material must be optimized to obtain the most effective plant growth and water treatment before the system can be applied in real-life systems. Keywords: Cattail, Longan biochar, Gravel, Nutrient, Wastewater treatment