Performance of Reactive Nitrogen in Leachate Treatment in Constructed Wetlands

Reactive Nitrogen (Nr) is produced from natural and human activity, the use of fuel, the activities of industry, and agriculture. The Nr from agriculture is used to produce food crops, but excess Nr has an impact on the surrounding land. Landfills also generate Nr from the decomposition of waste which then releases the leachate containing Nr. This study aimed to determine the value of Nr generated by landfills, the effect of Nr on the environment, and the performance of Nr when used in Constructed Wetlands (CW). Review papers were collected from several studies and publications. Nr commonly found in leachate landfills include: NH4, NH3, NO2, and NO3. The Nr present in landfill leachate at CW can be used for proper plant development and growth, which significantly increases and enhances its quality and yield by playing an important role in the biochemical and physiological functions of plants. In addition, the content of hazardous substances in landfill leachate can also be processed using CW. This review paper discusses the effects of Nr from human activities ending up in landfills. The landfill leachate with Nr content can be used in CW for plant growth.


INTRODUCTION
All nitrogen compounds except N 2 , are Reactive Nitrogen (Nr). Naturally available, Nr is generated primarily by and Biological N 2 Fixation (BNF), lightning, and forest fires. Nitrogen is an essential constituent for all life, and is part of protein and many other compounds (Bach et al., 2020). In order to increase agricultural production, humans have developed the technology to produce synthetic Nr fertilizers (Schlesinger, 2009). In addition, humans also generate Nr by accident. Gases such as CO 2 and sulfur dioxide, but also NOx produced from fossil fuels combustion by industry, transportation and the energy sector emit not only emissions . Reactive nitrogen is an indispensable nutrient for agricultural production. The largest contributor to Nr pollution which causes severe damage to human health and ecosystem is the agricultural sector. Globally, about 425 TgNr are generated through natural processes in the oceans, land, and by human activities (Sutton et al., 2011). The outcomes of all human activities finally enter the landfill which produces Nr in leachate. The resulting landfill leachate contains NH 3 about 6.83 mg/L (Kahar, 2017), NH 4 166.07 mg/L (Yalçuk and Ugurlu, 2020), NO 2 about 2,497 mg/L, and NO 3 with a value 12.5 mg/L (Silvestrini et al., 2019). From year to year, the human activities that produce Nr are increasing 15 TgNyr −1 to 140 TgNyr −1 from 1890-1990 (Raza et al., 2018).
The excess Nr can cause environmental pollution problems, such as radiation emission, air and water quality pollution (Ibrahim et al., 2020;Ravishankara et al., 2009). The reactive nitrogen generated can enter the groundwater, rivers, and estuaries, causing eutrophication (Braun, 2007). Eutrophication can negatively impact biodiversity and fish stocks (United Nations Environment Programme (UNEP), 2014). The increased release of Nr into the environment has a negative Performance of Reactive Nitrogen in Leachate Treatment in Constructed Wetlands impact on living things and ecosystems (Lassaletta et al., 2014; Leach et al., 2012). When released from soil, reactive nitrogen can make surface water and groundwater unfit for human consumption. After the Nr molecules are produced, they can remain in the environment for quite a long time because they are highly mobile and can contribute to several environmental effects as they flow through soil and water (Erisman et al., 2011). Excessive Nr release to the environment has led to many problems, including the loss of marine and terrestrial biodiversity, the formation of greenhouse gases, air pollution, and increased levels of nitrates in groundwater and marine ecosystems. The limit for nitrogen has been exceeded so that reducing the nitrogen emissions should be a key objective of environmental policy (Bach et al., 2020).
The mechanisms involved in Nr removal in Constructed Wetland (CW) include evaporation and adsorption (Kadlec and Wallace, 2009). The performance of Nr mechanism in CW depends on the microbial and vegetation processes (Gupta et al., 2016;Kadlec and Wallace, 2009). These organisms contribute to Nr uses such as microbial interactions and uptake by vegetation. Abiotic mechanisms include sedimentation, filtration, chemical precipitation, and adsorption (Dordio et al., 2009). Organic matter is excreted in SSF built up in wetlands by aerobic bacteria that adhere to porous media and plant roots. Plant roots not only provide the necessary surface for bacterial growth, but also oxygen. The performance of Nr in CW is basically achieved by microbial interaction and adsorption (Gupta et al., 2016;Mangkoedihardjo & Samudro, 2014).
Reactive nitrogen is an important plant nutrient and some can fertilize agricultural areas (Sutton et al., 2011). As it passes through the agricultural supply chain, the Nr from these sources is then lost as waste (Bodirsky et al., 2014). The average total nitrogen removal efficiency was 98.5%, 68.9% and 79.6% using CW (Wojciechowska, 2017). Biological assimilation of CW can recover Nr in 83-87% (Sengupta et al., 2015). The P increased deposition of N improves plant growth (Y. Wang et al., 2019;Xu et al., 2014). Some data show that Nr in plants has a function in overcoming aging in plant seeds, as a factor that has the potential to improve seed vitality, thereby increasing the rate of germination (Ciacka et al., 2020). Nitrogen can contribute to improved vegetation restoration and soil fertility (Samudro and Mangkoedihardjo, 2020;Wang et al., 2010Wang et al., , 2011. The objectives of this literature review were to determine the origin of Nr generated from landfills, to analyze the effect of leachates containing Nr, and to analyze the reactive performance of nitrogen in landfill leachate by plants in CW.

SOURCE OF REACTIVE NITROGEN
The natural sources Nr include, for example, the process of nitrification while anthropogenic sources, comprise, for example, the application of nitrogen fertilizers and the burning of fossil fuels ( In order to reduce agricultural Nr pollution, mitigation measures including fertilizer, livestock management, waste recycling, and community consumption, are implemented. However, these measures have not been assessed quantitatively as to how much they reduce the Nr pollution on a global scale. The previous analyses of the global agricultural nitrogen cycle focused largely on the estimates of current and past Nr flows, references to future Nr flows, and nitrogen fixation (X. Liu Table 1.
Landfill leachate is defined as liquid waste resulting from the percolation of rainwater through solid waste discharged into landfills, as well as moisture present in waste and waste degradation products (Costa et

REACTIVE NITROGEN EFFECTS
The anthropogenic intervention into the biogeochemical cycles of nitrogen has substantially been increasing the global levels of Nr, thus causing damage to the environment on a local, regional and global level. Such increases could exacerbate the impact on climate balance either through changes in atmospheric constituents, or feedback in terrestrial ecosystems. Reactive nitrogen has an indirect or direct effect on the GHG sources and Reactive nitrogen is highly soluble in water, so that if it is released into the environment it can contaminate surface water and groundwater. As a result, the Nr that enters the surface of the water will flow and affect the aquatic ecosystem. The presence of Nr in aquatic ecosystems encourages algal growth. Algal blooms produce eutrophication that blocks sunlight from entering the water. The absence of sunlight entering the waters will disrupt the productivity of the aquatic ecosystem. The drinking water treatment process can also produce Nr. The content of Nr in drinking water can cause methemoglobinemia. Nitrates in the body are converted into nitrites in the digestive system by binding to oxygen which can irritate the respiratory system (Holmes et al., 2019).

MECHANISM AND PERFORMANCE NR FROM LANDFILL LEACHATE IN CW
In CWs, the mechanism of ammonia nitrogen utilization is caused by adsorption, nitrification, plant uptake and volatilization (Cui et  Changes in time (∆t), changes in water volume (∆V) can be neglected (Kadlec and Wallace, 2009;Lavrnić et al., 2018). The measurement of infiltration and evapotranspiration rates cannot be carried out separately, so that the water balance for hydrological flow equilibrium is calculated as: In equation (2) (I + (ET × A)) as overall water loss in the constructed wetland (Lavrnić et al., 2018). The effect of capacity and discharge vary depending on time differences (Johannesson et al., 2017; Reinhardt et al., 2005). Water is stored in the constructed wetland system and is partially lost due to infiltration and evapotranspiration (Lavrnić et al., 2018). The influent will enter the constructed wetland system; microbes in the soil convert organic nitrogen into ammonium, which is then available for adsorption and absorption by plants to be reduced to nitrate (Samudro & Mangkoedihardjo, 2020). The available of nitrate to plants is reduced to nitrogen gas (N 2 ). The input of oxygen from root transport and gas is vital for the BOD and ammonium removal. Anoxic conditions are needed to reduce nitrates. The carbon source for denitrification in Carbon BOD (CBOD) is needed to increase the BOD and nitrogen removal (Fuchs, 2011). The mechanism and performance Nr in CW can be seen in Figure 1.
The process of using Nr is 3549 g with an average load of 36 g TKN/m 2 /d in CW which is adsorbed by 32%, the nitrification-denitrification process is 59%, and the rest is released into the environment. During the rest period, the amount of adsorbed ammonium is drastically reduced to 186 g (5%) and converted to nitrate, increasing the mass of nitrified nitrogen to 2,543 g (72%) ammonium and involving high concentrations of nitrate in the waste (Morvannou et al., 2014). The performance of Nr in plants in CW can be seen in Table 2.
The form of Nr that is absorbed by plants at CW is different. For example, the NH 4 preference is common in macrophytes that live in limited nitrifying environments, where NH 4 is abundant (Garnett et al., 2001). The rate of absorption and storage of nutrients by plants depends on the concentration of nutrients in their tissues. The desirable traits of a plant used for storage and nutrient assimilation include rapid growth, the ability to obtain an upright plant, and high tissue nutrient content. Conversely, plants that have large biomass accumulations during fall and winter can release a lot of nitrogen accumulated back into the water during winter (Lee et al., 2009;Vymazal, 2007).
Reactive nitrogen is a molecule that regulates various physiological processes in plants, including germination, seed formation, dormancy, and maturation. Aging causes a decline in seed quality, which limits not only agricultural production, but also the preservation of global biodiversity. NO and other compounds belonging to the Nr family appear to reduce the negative effects of seed aging (Ciacka et al., 2020). Nitrogen occupies a prominent place in the metabolic system of plants. All important processes in plants are related to protein, of which nitrogen is an essential constituent. As a result, to achieve greater crop production, nitrogen application is indispensable and unavoidable (Massignam et al., 2009). Nitrogen plays a key role in agriculture by not only increasing yields, but also improves the food quality (Ullah et al., 2010). The optimal amount of N can increase the photosynthesis process, the production of leaf area, the duration of the leaf area and the net assimilation rate (Ahmad et al., 2009). Maximum leaf area and total plant leaf biomass are determinants of higher yields (Rafiq et al., 2010). All crops, including cereals, vegetable oils, fiber, and sugar and horticulture, require a balanced amount of nitrogen for a vigorous plant growth and development processes (Leghari et al., 2016).

CONCLUSIONS
Human activities can produce by-products, some of which can be harmful to the environment and humans themselves. Activities such as industry, agriculture, transportation, and other daily activities produce waste. The waste that cannot be reused is placed in landfills, some of which are separated, such as landfills for organic, nonorganic and medical waste. Some landfill sites are not separated, so that they contain many hazardous materials, one of which is the presence of 2. NO 2 Plants exposed to soil nitrogen with NO 2 gas can increase nutrient uptake, photosynthesis, and nutrient metabolism so that shoot biomass, total leaf area, and content of C, N, P, K, Ca, Mg, per shoot, and S (or Fe), free amino acids and crude protein were roughly double that of the control plants. The uptake of ammonia and nitrate by macrofites changes the form of inorganic nitrogen to organic compounds, as building blocks for cells and tissues (Lewin, 1999). Nr. The Nr of landfill leachate found in the literature review was NH 4 , NH 3 , NO 2 , and NO 3 . The Nr content in landfill leachate which is directly removed to the environment will cause negative effects. However, Nr is needed by plants as nutrition. Therefore, it was found that Nr had a good performance when used in CW for the growth of plant metabolism and photosynthesis, thereby releasing a non-reactive form of N. N which is not reactive in the form of N 2 can be accepted by the environment. Besides changing Nr to be unreactive, CW can also change other hazardous content in the leachate landfill.