Comparison of the Effectiveness of Phytoremediation of Yellow Velvetleaf (Limnocharis flava) and Water Hyacinth (Eichhornia crassipes) on Reducing BOD and COD of Liquid Waste from Home-Made Tofu Industry in Namorambe District

Abstract

The household tofu industry produces liquid waste with a high organic load as reflected in the Biochemical Oxygen Demand and Chemical Oxygen Demand values, thus potentially polluting water bodies if discharged without treatment. This study aims to compare the effectiveness of phytoremediation using Yellow Velvetleaf (Limnocharis flava) and Water Hyacinth (Eichhornia crassipes) plants in reducing Biochemical Oxygen Demand and Chemical Oxygen Demand in liquid waste from the home-based tofu industry in Namorambe District, Deli Serdang Regency. The study used a pretest and posttest design with 6 treatment reactors, consisting of 3 Yellow Velvetleaf reactors and 3 water hyacinth reactors, and 2 control reactors without plants. Each reactor contained 5 L of liquid waste and 500 g of fresh plant biomass. Measurements of Biochemical Oxygen Demand and Chemical Oxygen Demand were carried out before treatment and after a retention time of 2, 4, and 6 days. The initial levels of Biochemical Oxygen Demand and Chemical Oxygen Demand were 510 mg/L and 1,560 mg/L, respectively. The results showed that both plants were able to reduce Biochemical Oxygen Demand and Chemical Oxygen Demand levels with different patterns. Water hyacinth showed the highest reduction on day 2, with a decrease in Biochemical Oxygen Demand of 46% and Chemical Oxygen Demand of 44%, while Yellow Velvetleaf reached the optimal reduction on day 4 with a decrease in Biochemical Oxygen Demand of 35% and Chemical Oxygen Demand of 37%. The effectiveness of both plants decreased after day 4, which is thought to be related to pollutant absorption saturation and plant biomass decomposition. In general, water hyacinth was more effective at short residence times, while Yellow Velvetleaf showed more stable performance at medium residence times. Phytoremediation using local aquatic plants has the potential to be a simple and low-cost alternative for treating tofu industrial wastewater, with residence time management being a key factor in success.