Ammonia-Nitrogen Recovery from Synthetic Solution using Agricultural Waste Fibers

1Department of Chemical Engineering, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia; zahrim@ums.edu.my, rickylns@hotmail.com 2Centre for Water Advanced Technologies and Environmental Research (CWATER), College of Engineering, Swansea University, Swansea SA2 8PP, UK; n.hilal@swansea.ac.uk 3Department of Mechanical and Manufacturing Engineering, Faculty of Engineering Universiti Malaysia Sarawak (UNIMAS) Kota Samarahan, Malaysia; k.f.tamrin@outlook.com


Introduction
Industrial nitrogen can be discharged in large volume from pulp and paper, fertilizer, and mining industry 1 .Highest nitrogen discharges in pulp and paper industry is due to pulping and bleaching process 2 .Besides that, agricultural drainage and municipal waste are also among the main sources of polluter 1 .Ammonia nitrogen concentration greater than 10 mg/L causes intensifying of genotoxicity 3 .In addition, nitrogen pollution in waterways results in the eutrophication and fouling of rivers, lakes, water reservoirs and oceans.Recovering ammonia nitrogen from polluted water could be an option in treating the contaminated water and simultaneously recycle the nutrient back for agricultural purposes.Of numerous techniques investigated for ammonia nitrogen recovery 4 , a considerable amount of approaches seem to concentrate on developing cheaper and effective agricultural waste adsorbents 5 .This method is considered eco-friendly, economical, and practically simple to operate 6 .
In Malaysia, Empty Fruit Bunch (EFB) fibers are abundantly available waste with about 91.2 million tons were produced annually 7 .Previously, EFB fibers compost has shown potential in removing ammonia nitrogen from synthetic solution 8 .Degraded fibers could enhance the sorption of ammonia nitrogen due to increasing in negatively charge surface site.However, EFB biodegradation take a long time to biodegrade.To reduce the modification time, chemical modification is suggested in this study.Modification of pine cone powder using sodium hydroxide was found to increase the ammonia nitrogen sorption capacity to 6.15 mg/g 6 .In another study, adsorption capacity of banana peels treated with sodium hydroxide was found to increase from 8.6 to 20.0 mg/g 9 .However, the common purpose for EFB modification studies reported so far is mainly for the productions of sugar 10 and bioethanol 11 .Nevertheless, we find that there are limited studies focusing on modification of EFBs fiber for the recovery of ammonia nitrogen.In this study, adsorption-desorption studies of ammonia nitrogen into the modified EFB fiber were investigated and the biosorption isotherm was also determined.

Materials and Methods
Ammonium chloride salt (NH 4 Cl) (QRëC™) and distilled water were used for the preparation of a solution of 50 mg L -1 ammonia nitrogen solutions.The shredded EFB fibers were collected from Tawau, Sabah.The fibers were subjected to treatment using 10 mM of sodium hydroxide (NaOH) for 12 hours in room temperature.Batch adsorption experiments were conducted using fixed amount 15.71 g of EFB fibers.The effects of pH on adsorption were investigated at various pH values, ranging from 3 to 10. Desorption study was carried out by using 0.1 M HCl and NaOH solutions.The ammonia nitrogen concentration was measured according to volumetric method, known as Nessler Method 12 , using UV-vis spectrophotometer (Jasco UV-vis 650) at maximum wavelength of 425 nm.

Sorption Studies
Figure 1 shows ammonia nitrogen removal by various initial concentrations of ammonia nitrogen (0.5, 5, 50, 200, 1500, 4000 mg/L) at 40 minutes contact time.It clearly shows that the amount of ammonia nitrogen being removed increases with initial concentration.This trend is consistent with previous study 13 .According to Figure 1, the highest sorption capacity is 10.893 mg/g at ammonia nitrogen initial concentration of 4000 mg/L.Similarly, higher removal of ammonia nitrogen waste found at high initial ammonia nitrogen concentration using low-cost adsorbents 13,14 .The reason for these finding could be due to high probability of collision between ammonium ions with the surface of fibers especially at high concentration 14 .
The effects of temperature on the sorption of ammonia nitrogen onto modified EFB fibers at different contact time are shown in Figure 2. The sorption capacity of ions increases as the temperature increase in Figure 2 since at higher temperature, the diffusion rate of ions will increase.The effects of ammonia nitrogen sorption at different pH ranges are presented in Figure 3.The minimum equilibrium sorption capacity was achieved at lowest pH (pH 2, 0.400 mg/g).It gradually increases until it reaches optimum sorption at pH 7 (0.828 mg/g).Afterwards, one may notice a trend of decreasing in sorption capacity as the pH increases from 8 to 10.
At lower pH values (pH 2 to 4), H + ions in the aqueous solution and ions are both attracted to the fibers which causes a decrease in the amount of ammonia nitrogen being adsorbed.On the contrary, lignin and cellulose chains in the fibres are negatively charged between pH 5 to 7.This promotes sorption with the positively-charged ions through electrostatic attraction forces 13 .As pH increases beyond neutral (i.e.pH 7), the state of equilibrium sorption shifts rapidly towards the non-ionised form, making it less favourable for ammonia nitrogen removal 15 .The FTIR analysis Figure 4 is used to identify the functional groups involved in ammonia nitrogen sorption onto EFB fibers.As shown in Figure 4, the modified EFB shows peaks shift of C-H methyl and methylene groups from 2918 (unmodified EFB) to 2889 cm -1 , and -OCH 3 from 1029 to 984 cm -1 .It is noted that hydroxyl group at 3289 cm -1 was no lon-ger detected in the modified EFB.In addition, peak for triple bond stretching was observed at 2324 cm -1 .These functional groups (-OH, amine and -OCH 3 ) suggest that EFB fibers were structurally modified.Based on FTIR analysis, ammonia nitrogen sorption onto the modified EFB fiber might be due to ion exchanging of with Na + (during the modification of EFB fibers), and followed by chemisorptions between ammonium ions and some functional groups (e.g., O-H, -COOH and -SO 3 stretching) 16 .

Desorption Studies
In order to study the reusability of the adsorbed ammonia nitrogen by EFB fibers, the desorption study was carried out by changing the solution pH.The effect of solution pH on the desorption of ammonia nitrogen is displayed in Figure 5.The adsorbed ammonia nitrogen can be desorbed using water due to weak bonding between the fiber and ammonium ion.The maximum ammonia nitrogen recovery from adsorbed EFB fiber was found at pH 2 (0.0999 mg/g) and it gradually decreased to pH 10 (0.0271 mg/g) shown in Figure 5.As the pH increases from 2 to 6, the total ammonia nitrogen desorbed from the EFB surface decreases and it remains nearly constant from pH 6 to 10.The adsorbed ammonium ( ) ions onto the carboxyl group (-RCOO-) of the fibers might be replaced with the hydrogen (H + ) ions by ion exchange during the desorption of ammonium at lower pH 17 .The recovered ammonia nitrogen has immense reusability potential which includes soil conditioning 18 .

Conclusions
This study demonstrates the application of modified EFB fibers as adsorbent for the recovery of ammonia nitrogen from aqueous solutions.The ammonia nitrogen from the EFB fiber can be desorbed using an acid solution with maximum desorption capacity of 0.0999 mg/g.

Figure 1 .
Figure 1.Effect of ammonia nitrogen initial concentrations during sorption onto modified EFB (Weight of modified EFB: 15.71 grams, volume of ammonia nitrogen: 1000 mL, contact time: 40 min, room temperature: 27 ± 0.2 0 C and pH: 7.0).The FTIR analysis Figure4is used to identify the functional groups involved in ammonia nitrogen sorption onto EFB fibers.As shown in Figure4, the modified EFB shows peaks shift of C-H methyl and methylene groups from 2918 (unmodified EFB) to 2889 cm -1 , and -OCH 3 from 1029 to 984 cm -1 .It is noted that hydroxyl group at 3289 cm -1 was no lon-

Figure 2 .
Figure 2. Effect of contact time on temperature dependent on sorption capacity of ammonia nitrogen onto the modified empty fruit bunch (Weight of modified EFB: 15.71 grams, ammonia nitrogen concentration: 50 mg/L, and pH: 7.0).