Active Removal Of Ammonia Through Three Potted Plants

Ammonia has a serious adverse effect on the ecological environment.It enhances the formation of atmospheric secondary particles.After deposition,ammonia may lead to soil acidification,water eutrophication and biodiversity destruction.As an important source of ammonia,animal husbandry also poses a serious threat to human body and livestock health.Therefore,it is necessary to continuously develop ammonia purification technology.Physical,biochemical,and phytoremediation techniques have been studied and applied for ammonia removal.Among them,phytoremediation is a nature-based solution,being environmental friendly,of low cost,and free of secondary pollution.The existing research on phytoremediation of ammonia focused mainly on leaf fumigation,which is lack of utilization of cultivation substrate.In this study,at three ammonia concentrations of 6.8mg/m³,12.1 mg/m³,and 18.9 mg/m³,collaborative removal potential of plants and cultivation substrates for ammonia were investigated and compared with the performance of leaf fumigation.Three plants,including Radermachera sinica,Podocarpus macrophyllus,and Murraya exotica were considered and their physiological resistances to ammonia were explored.In addition,the transformation of nitrogen during the ammonia purification was preliminarily analyzed,and the duration for plants to maintain effective purification was identified.The conclusions are as follows:（1）The 72-hour purification experiment showed that the three plants had the ability to remove ammonia.Among them,the efficiency of fumigation purification（passive diffusion of gas to the surface of leaves and substrate）was low,ranging from 20%-60%.The synergistic purification of plants and substrate（forcing gas actively to pass through the cultivation substrate）could improve the efficiency to 70%-90%.The effect of different plants and the influence of ammonia concentration were different.Under ammonia fumigation,the purification efficiency of Radermachera sinica was the highest at 6.8mg/m³.On the other hand,Podocarpus macrophyllus exhibited better performance at ammonia concentrations of 12.1 mg/m³ and 18.9 mg/m³.In terms of synergistic purification,the efficiency of Radermachera sinica was the highest.Slightly lower efficiency was observed for Podocarpus macrophyllus and Murraya exotica.For the three ammonia concentrations investigated,the overall purification efficiency of plants for ammonia increased first and then decreased with the increase of ammonia concentration.In addition,the presence of plants could improve the purification efficiency of substrates.（2）The comprehensive physiological resistance of three plants to ammonia pollution was as follows:Radermachera sinica>Podocarpus macrophyllus>Murraya exotica.The malondialdehyde content,POD activity,and cell membrane permeability of plant leaves increased with the increase of ammonia concentration,while the chlorophyll content of plant leaves rised first and then declined.The variation rates of physiological and biochemical indexes of different plants were significantly different under ammonia fumigation.Due to the retain of ammonia by the cultivation substrates,the influence of plant species on the variation rate of physiological and biochemical indexes in synergistic purification was reduced,and the influence of ammonia concentration on the variation rate of these indexes was enhanced.（3）When the inlet ammonia concentration was 6.8 mg/m³,12.1 mg/m³,and 18.9mg/m³,under ammonia fumigation,Radermachera sinica could maintain the effective purification time of more than 9 days,6 days and 4 days,respectively.Due to the purification of substrates,the effective purification time of Radermachera sinica increased to more than 15 days,11 days and 6 days in synergistic purification.（4）From the change of total nitrogen content in plant leaves,the utilization rate of Murraya exotica for ammonia below 6.8 mg/m³ was not high.Rather,it had better utilization effect for ammonia of 12.1 mg/m³ and 18.9 mg/m³.The ammonia utilization of leaves of Radermachera sinica and Podocarpus macrophyllus was better than that of Murraya exotica.The total nitrogen increment of leaves of Radermachera sinica and Podocarpus macrophyllus was about 19 mg N/（g·DW）when reaching nitrogen saturation.Under leave fumigation and synergistic purification,saturation of leaf nitrogen did not affect the ammonia purification capacity.Radermachera sinica still exhibited purification ability when the nitrogen content in leaves saturated.However,purification efficiency dropped rapidly when the leaves showed symptoms of damage.From the change of nitrogen content in cultivation substrates,the purified ammonia mainly existed in the form of ammonium nitrogen.The proportion of NH₄⁺-N increment in total nitrogen increment was positively correlated with ammonia concentration,and the proportion of NO₃^--N increment in total nitrogen increment was positively correlated with purification time.（5）Compared with ammonia fumigation,synergistic purification of plants and substrates could significantly improve the ammonia purification efficiency and increase the upper limit of ammonia concentration that the plants can purify.In addition,synergistic purification could effectively reduce the negative impact of ammonia on plants,prolong the survival time of plants with the presence of ammonia,thus leading to the longer purification time.However,the resistance of cultivation substrates to the gas flow needs to be overcome.