Comparative performance of subsurface and free-surface planted beds for polishing real recycled paper effluent: Influence of biomass ratio to pollutant

A polishing technology through phytoremediation was performed to reduce COD and colour from real recycled paper effluent using Typha angustifolia. Subsurface (SS) and free surface (FS) systems were operated, with batches of 10 and 26 L of effluent treated, respectively. Various numbers of plants (4 (T4), 6 (T6) and 8 (T8) plants with mass of 54, 82 and 100 g, respectively) were vegetated in each system. All treatments were run with plant control and control contaminants. After 60 days of treatment, there was significant (p < 0.05) removal of contaminants, with the highest removals of colour were 71 % (T8) and 80 % (T4); and the highest COD removals were 97 % (T8) and 89 % (T8) for SS and FS, respectively. Additionally, COD and colour removal for the treatment with eight plants (T8) in the SS system (97 % and 71 %, respectively) was significantly higher than for the treatment with four plants (T4) (COD removal = 91 % and colour removal = 50 %). This is due to the high survival percentages of plants in T8, with 100 % tolerance in the SS system which represents healthy plants undergoing the phytoremediation process with no or less fewer toxicity symptoms. Overall, the SS system performed better since the FS system faced a higher pollutant loading. The mass ratio of plants to COD for the SS system with eight plants is 37 which means for every 1 g of COD, about 37 g of plants is required to facilitate the phytoremediation process with high removal efficiency and 100 % survival of plants.