Adsorption Performance of Four Substrates in Constructed Wetlands for Nitrogen and Phosphorus Removal

In this research, nitrogen and phosphorus adsorption characteristics of four substrates, including lava, activated carbon, furnace slag and spongy iron, were studied through basic experiments. Meanwhile, adsorption kinetics, effects of different pH on adsorption performance, sequencing batch adsorption isotherm experiments and saturation analysis of substrates experiments were analysed. Moreover, the possible secondary pollution risks after four substrates saturation adsorption were discussed. The results showed that Freundich and Langmuir models were favourably fit for the variance on nitrogen and phosphorus adsorption characteristics of substrates. The order of ammonia nitrogen adsorption capacity for four substrates was activated carbon>furnace slag>lava>spongy iron. In addition, judging from ammonia nitrogen desorption rates, the capacity of releasing ammonia nitrogen for four substrates increased as an order of spongy iron>lava>furnace slag>activated carbon. Besides, the order of phosphorus adsorption capacity for four substrates was activated carbon>spongy iron>furnace slag>lava. And the capacity of releasing phosphorus after phosphorus desorption for four substrates increased as an order of lava>spongy iron>furnace slag>activated carbon. In summary, after adsorption and desorption properties of four substrates were analysed, it could be concluded that activated carbon was a more favourable filler for constructed wetlands.