Reduction of Ammonia Nitrogen and Chemical Oxygen Demand of Fertilizer Industry Liquid Waste by Coconut Shell Activated Carbon in Batch and Continuous Systems

The fertilizer industry laboratory produces urea and ammonia nitrogen waste that can harm living things in the surrounding water bodies. Urea, nitrogen, and ammonia can be reduced by adsorption using activated carbon. This research reduced urea nitrogen and ammonia through activated carbon adsorption with a batch and continuous system. Percentage indicator of urea and ammonia nitrogen removal through Ammonia Nitrogen ( NH 3 -N) and Chemical Oxygen Demand (COD) NH 3 -N and COD analysis was determined. This study aimed to obtain: 1) the percentage of NH 3 -N and COD reduction in stem batch; 2) the percentage of NH 3 -N and COD reduction in the continuous system; 3) the Freundlich and Langmuir isotherm adsorption equation against NH 3 -N wastewater. They are testing the adsorption power of activated carbon in a batch system using variable levels of activated carbon: 40 g/L, 55 g/L, 70 g/L, 85 g/L, and 100 g/L and testing the adsorption power of activated carbon in a continuous system using the variable frequency of wastewater in contact with activated carbon filter cartridges, namely 2, 3, 4, 5, and 6 times. The results showed: 1) in the batch system NH 3 -N reduction of 98.26–98.82% and COD reduction of 92.53–97.05%; 2) in continuous system reduction of NH 3 -N of 86.05–88.07% and COD reduction of 93.91–97.05%; 3) Freundlich isotherm adsorption equation yields constant R 2 0.9464, n 0.4482, K F 0.0616 mg/g; while Langmuir’s isotherm adsorption equation yields constant R 2 0.8684, b -0.1046 L/mg, and q m 7.9872 mg/g.


INTRODUCTION
Indonesia is an agrarian country where agriculture is booming throughout the archipelago. This thriving farm requires much fertilizer to optimize its yields. Some industries that produce fertilizers in Indonesia include PT Petrokimia Gresik, PT Pupuk Kujang Cikampek, PT Pupuk Kalimantan Timur, PT Pupuk Iskandar Muda, and PT Pupuk Sriwijaya Palembang. Production of urea fertilizer in Indonesia in 2021 reached 6.5 million tons per year. The quality of fertilizers on the market is controlled by analyzing packaging samples on the market and for production purposes. Laboratory operations in the fertilizer industry produce nitrogen waste from urea and its derivatives. Waste with the ammonia content that exceeds quality standards causes ecosystem inequality in water bodies.
Several treatment methods reduce the nitrogen content of urea and ammonia, and organic substances contained in wastewater, including filtration, adsorption, exchange ions, and wetland use. Sulfur-based wetlands and traditional artificial wetlands reduced total nitrogen and nitrates in wastewater by 69% and 82% (Wang et al., 2022). The removal of various types of nitrogen in wastewater can also be done using microorganisms of the Klebsiella oxytoca (EN-B2) strain, namely ammonium 51%, nitrite 32%, and nitrate 47% (He et al., 2023). In addition, ZrO 2 (DWS500@ZrO 2 ) sludge can also remove nitrates from contaminated water up to 31 mg/g at pH of 2 and temperature of 500 °C (Quang et al., 2022). Nitrogen removal can also be done by neutralization and coagulation methods (Nurhayati, 2018). The studies that have been carried out can reduce the content of nitrogen and organic substances in wastewater but require considerable operational costs and quite complicated methods. Research is still needed by applying the adsorption methods that are cheap and easy to operate.
Adsorbers that can be used to adsorb pollutants include activated carbon (Chansa et You et al., 2020). The research related to activated carbon adsorption power resulted in findings of activated carbon adsorption capacity; however, the adsorption process has not been maximized, because the process uses a batch system and even causes an increase in TSS. The research on reducing the levels of dissolved nitrogen compounds in waste by maximizing contact between wastewater and activated carbon, namely using a continuous system and circulating (repeated contact) between activated carbon and wastewater, may solve the problem experienced.

Materials and tools
The materials used in this study are liquid waste from the fertilizer industry laboratory containing urea and its derivatives, coconut shell activated carbon, concentrated sulfuric acid (H 2

Testing of the ability of activated carbon remove NH 3 -N, and COD
The ability of activated carbon to remove NH 3 -N and COD in wastewater is expressed in % removal of total nitrogen (NH 3 -N) (Equation 1) and % removal of total COD (Equation 2).

Freundlich and Langmuir isotherm adsorption equation test
Freunlich assumed heterogeneous surfaces with different adsorption energies. According to Equation 3, K F and n are also Freundlich constants, which determine the adsorption capacity and intensity, respectively. This constant can be obtained from the intercept and slope of the log diagram q e versus C e (Nowruzi et al., 2020). (3) where: q e -the equilibrium capacity of NH 3 -N, i.e., the amount of NH 3 -N adsorbed per unit mass of activated carbon (mg/g), is the equilibrium concentration of NH 3  . (4) Plotting data using the Freundlich Equation obtained data on constants K F and n, may be used to form an adsorption equation of activated carbon isotherm to NH 3 -N contained in artificial waste.
The Langmuir isothermal adsorption equation is presented in Equation 5. (5) where: C e (mg/L) -the equilibrium concentration of NH 3 -N; q e -the equilibrium capacity of NH 3 -N.
The capacity of adsorption of activated carbon is the weight of NH 3 -N adsorbed per unit weight of activated carbon (mg/g); b (l/mg) and q m (mg/g) are the Langmuir constant a constant relating to the adsorption energy, and maximum adsorption capacity of the adsorption is determined from the intercept and slope of the diagram, respectively.

Initial laboratory waste parameters
The results of the analysis of laboratory waste samples of the fertilizer industry before processing are presented in Table 1. The parameters are focused on TSS, NH₃-N, COD, and pH. Table 1 shows the TSS, NH₃-N, COD, and pH levels from fertilizer industry laboratory waste. From the table, it appears that the level of NH₃-N 752 mg/l is more than 750% of the standard, COD 1592 mg/l is much higher than the standard of 200 mg/l, as well as the pH is still very low, i.e. 1.05, even though the quality standard is only between 6-9. The initial condition of the fertilizer industry's laboratory waste is processed to achieve standard quality conditions.

Waste parameters after processing
Fertilizer industry laboratory waste processed by batch and continuous processes is analyzed. The sample analysis results of industrial waste after processing are shown in Figure 1-4. Figure 1 shows the concentration of activated carbon as an adsorbent in fertilizer laboratory waste. The figure shows that increased activated carbon can remove TSS but increases TSS levels at higher concentrations. This condition happens because the type and size of activated carbon used are not appropriate and increase the TSS of the waste. Activated carbon with a large surface and microscopic pores can capture organic molecules and solid particles residing in water. When water flows through the activated carbon medium, solid particles suspended in the water stick to the surface of the activated carbon and become trapped inside the pores. The content of solid particles trapped in activated carbon increases, in addition to greater TSS in water and desorption. Therefore, it is crucial to carry out periodic maintenance and replacement of activated carbon to ensure the effectiveness of the adsorption process and prevent an excessive increase of TSS in the water produced (Zhang et al., 2019). Figure 2 shows the effect of activated carbon concentration added as an adsorbent on fertilizer industry laboratory waste. It was seen that increasing the concentration of activated carbon from 40 g/l tar to 100 g/l can reduce NH 3 -N levels from 13.1 and 8.9 mg/l. The percent of NH 3 -N removal reached 98.3% to 98.7% with activated carbon. This data shows that a 250% increase in activated carbon from 40 g/l to 100 g/l has little effect on percent removal. This condition is likely because, at a small concentration of NH 3 -N, 13.1-8.9 mg/l is an area that is not sensitive for activated carbon to absorb NH 3 -N.  Figure 3 shows the effect of activated carbon concentration used to treat fertilizer industry waste with an initial COD of 1592 mg/l on COD and % COD removal. The picture shows that COD decreased with 92.5-97.0% removal due to absorption by activated carbon. The increase in activated carbon levels from 40 g/l to 100 g/l only increased the percentage of COD removal to 4.5% from 92.5%. This condition shows that the working area of activated carbon against this  Figure 4 is the TSS value and % TSS removal of lime water after treatment using adsorption filtration and cation exchanger with various recycle variants. The figure shows that TSS has experienced a sharp decrease in cycles. The highest TSS removal % reached 91.5%. These removal results are almost identical to the TSS removal from biodiesel wastewater (24). This result is different only if using activated carbon, as an adsorbent causes an increase in the TSS value. Figure 5 shows the effect of the number of process cycles on the concentration of NH 3 -N and NH 3 -N removal in waste. The figure shows that the NH 3 -N levels drop with the number of cycles, indicating that repeatability of the process can decrease NH 3 -N levels, but this decrease is small relative to the number of cycles cycle. The decrease in the NH 3 -N levels occurs due to NH 3 -N   Figure 6 shows COD concentration and COD removal from fertilizer waste in the adsorption process at various cycles. The increasing number of cycles decreases the COD value and increases COD removal. Increasing the number of cycles increases the contact time between the waste and activated carbon. Increasing the contact time raises the amount of chemical adsorbed by activated carbon. The increased adsorbed chemicals by activated carbon decrease the concentration of dissolved and suspended chemicals. The reduction of these chemicals causes a decrease in COD values.

Freundlich and Langmuir isotherm adsorption to NH 3 -N
Isotherm studies describe the behavior of adsorbents and state the relationship between the amount of adsorbate absorbed by adsorbents. Test of the adsorption behavior of activated carbon  Table 2. Figure 7 shows a test graph of the Freudlich Equation against the adsorption data of NH 3   7.98722 + 1 −5.09165 (7) Or in other words, qm = 7.98722 and value b = -0.1046. Comparison of the isothermic adsorption results using Freundlich and Langmuir isotherms can be seen in Table 2. Table 2 shows that the adsorption of NH 3 -N by activated carbon in fertilizer waste is more

CONCLUSIONS
Activated carbon can reduce the content of NH 3 -N and COD in the liquid waste of the urea and ammonia fertilizer industry to meet waste quality standards. The waste quality standard is based on East Java Governor Regulation Number 72 of 2013. The percentage of NH 3 N removal in the adsorption process by coconut shell activated carbon using the batch process is 98.26-98.82%. The use of continuous adsorption with multiple filtrations produces NH 3 -N removal of 86.05-88.07%. COD in the batch system is 92.53-97.05%, while in the continuous system, it is 93.91-97.05%. NH 3 -N adsorption in the batch system is better than in the continuous system. Adsorption of TSS by activated carbon in a batch system achieves COD removal of -56.6-17.5%, while using a continuous system it achieves COD removal of 93.9-97.0%. The Freundlich adsorption isotherm equation for NH 3 -N yielded constants R 2 , n, and K F of 0.9464, 0.4482, and 0.0616 mg/g. The Freundlich adsorption isotherm equation is more representative than the Langmuir equation.