Ammonia Removal from Wastewater through ...

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obtain the process of ammonia removal through a combination of absorption in the membrane contactor and the advance oxidation process in the hybrid ...
Journal of Environmental Science and Engineering A 1 (2012) 1101-1107 Formerly part of Journal of Environmental Science and Engineering, ISSN 1934-8932

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Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor Sutrasno Kartohardjono, Puji Lestari Handayani, Seswila Deflin, Yuniar Nuraeni and Setijo Bismo Chemical Engineering Department, Universitas Indonesia, Depok 16424, Indonesia Received: August 29, 2012 / Accepted: September 9, 2012 / Published: September 20, 2012. Abstract: Wastewater containing high concentrations of ammonia can be harmful to aquatic life and degrade the water quality. Wastewater containing ammonia is usually removed by conventional methods such as aeration in towers, biological treatment and adsorption of the ammonium ion to the zeolite surface. However, these methods are less effective and relatively expensive. Therefore there is a need for alternative technologies that can improve the efficiency of ammonia removal from wastewater. This study aims to obtain the process of ammonia removal through a combination of absorption in the membrane contactor and the advance oxidation process in the hybrid plasma-ozone reactor. Wastewater containing ammonia used in the study was a synthetic wastewater with a concentration of about 800 ppm. In the experiment, the wastewater from the reservoir was firstly passed into the membrane contactor on the shell side, and then mixed with ozone from the ozonator before entering the plasma reactor, and finally was circulated back to the reservoir. Meanwhile, the absorbent solution was sent to the lumen fiber in membrane contactor. Experimental results showed that the ammonia removal efficiency increases with increasing in circulation rate and temperature of the wastewater. The highest efficiency of ammonia removal obtained from the experimental results was 77%. Key words: Ammonia, removal efficiency, membrane contactor, ozone, plasma reactor.

1. Introduction Ammonia even at low concentration can cause problem to aquatic life and degrade the water quality. Ammonia is usually removed through denitrification in the water treatment plant. There are several conventional methods to remove ammonia from wastewater such as aeration in pack tower, biological treatment [1] and adsorption as ammonium ion into the surface of zeolite [2]. However, these methods almost always depend on relatively high energy consumption [3]. Therefore there is need for alternative technologies that can improve the Corresponding author: Sutrasno Kartohardjono, Ph.D., professor, main research field: membrane gas-liquid contactor for gas absorption and desorption. E-mail: [email protected].

efficiency of ammonia removal from wastewater with less energy consumption. One technology that can be used for ammonia removal from wastewater is a membrane technology. Membrane contactor is a contactor device for mass transfer in liquid-liquid systems and gas-liquid without mixing of these phases [4]. Membrane contactor for such purposes are often used is a microporous hydrophobic hollow fiber membrane contactor. In the case of gas-liquid separation, the membrane will prevent water solution, which has a higher surface tension to penetrate the membrane pores thanks to the hydrophobic pores of the membrane. Volatile compounds will evaporate from the feed side, and then diffuses through the gas-filled membrane pores, and then be swept by a sweep gas,

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Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor

drawn by a vacuum pump, or reacting with the absorbing solution [5]. Several

studies

have

been

conducted

using

membrane contactors as a tool for the removal of ammonia from wastewater such as: the stripping of ammonia through the membrane contactor using sweep gas [3] and vacuum [6], and the removal of ammonia through the membrane distillation [7, 8] and vacuum membrane distillation [9]. Several studies have been performed using membrane contactors as a tool for the removal of ammonia from wastewater such as: the stripping of ammonia through the membrane contactor using sweep gas [3] and vacuum [5], and the removal of ammonia through the membrane distillation [6, 7] and membrane distillation vacuum [8]. This study aims to obtain ammonia removal process through a combination of absorption in the membrane contactor and the advance oxidation process in the hybrid plasma-ozone reactor.

2. Theory Ammonia in the wastewater stream present in two forms: volatile ammonia and ammonium ions. In the process of ammonia removal through the membrane contactor, the species of volatile ammonia in the equilibrium system is maximized. Therefore the amount of ammonia that can be separated from waste water depends on two factors: pH and temperature of waste water. It should also be aware that the solubility of ammonia in the water decrease as the temperature increases. For example, at 0 °C and atmospheric pressure, 1 volume of water able to dissolve 1,200 volumes of ammonia, while at 20 °C and atmospheric pressure, 1 volume of water can only dissolve 700 volumes of ammonia [9]. However, by simply raising the temperature, not all the ammonia present in the wastewater can be removed as part of this ammonia will dissociate again into the water to form ammonium ion, in accordance with the Eq. (1): K1 NH 3( g ) + H 2 O(l ) ←→ NH 4+( aq) + OH (−aq)

(1)

At 25 °C and atmospheric pressure, the equilibrium constant for this reaction are: K1 = 1.8 × 10-5 to the direction of formation of NH4+ and K2 = 5.6 × 10-10 to the direction of the ammonia formation [10]. Thus, the equilibrium reaction towards the formation of the ammonium ion is almost 32,000 times higher than in the direction of the ammonia formation. The increase in pH of the wastewater would also shift the equilibrium towards the formation of ammonia. Vapor pressure of a aqueous solution containing ammonia is higher than the vapor pressure of water so that the higher concentration of ammonia in the water will increase the vapor pressure of the solution. Thus, in the process of removal of ammonia through hydrophobic micro-porous membrane contactor, vapor formed will diffuse through the membrane pores and then will be swept by the sweep gas, pulled by vacuum, or react with the absorbent solution. The higher the amonia vapor formed in the wastewater solution, the more efficient ammonia removal process through the membrane contactor. Efficiency of ammonia removal process can be calculated using Eq. (2), R% =

C0 − Ct × 100% C0

(2)

where C0 and Ct are ammonia concentration at initial and time t, respectively. The use of hybrid reactor plasma-ozone in the experiment is expected can shift the ammonia equilibrium in Eq. (1) to the production of volatile ammonia.

3. Materials and Methodes Microporous hydrophobic membrane fiber of polyvynilchloride are used in the experiments sized of 0.8 mm inside diameter and 0.35 mm thickness. The contactor size are 3.0 cm, 2.4 cm and 40.0 cm in outside and inside diameter, and length, respectively. The number of fiber in the contactors are 40, 50 and 60, respectively. Figs. 1 and 2 show a schematic diagram of the ammonia removal process through the membrane and through the combination of membrane and hybrid reactor plasma-ozone.

Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor

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Fig. 1 Schematic diagram of the experimental of ammonia removal through the membrane contactor.

Fig. 2 Schematic diagram of the experimental of ammonia removal through combination of absorption process in the membrane contactor and advance oxydation process in the plasma-ozone reactor.

All chemicals used in the study were analytical grade from Merck. The water used for aqueous solutions and dilutions were prepared using distilled water. Wastewater containing ammonia were prepared through dillution of the measured mass of ammonium sulfate into distilled water. The wastewater were added with sodium hydroxide to maintain the prefered pH of the solution. The stripping solution was prepared through the addition of a given volumes of sulfuric acid to natural hot spring water. The ammonia concentration in the samples was measured using Ammonia Meter, Martini Mi405. In the membrane process, the wastewater solution with initial ammonia concentration of about 800 ppm is pumped into a membrane contactor in the shell side, while the absorbent solution was flowed to the fiber lumen in the contactor using a peristaltic pump. Meanwhile, for the combined process the wastewater solution was passed to the membrane and into the ozone plasma hybrid reactor, where ozone is also injected to the reactor. Samples of wastewater from the reservoir was taken 1 mL every 20 minutes during 2-hour circulation to measure its ammonia

concentration using ammonia Martini 405 Meter Instrument. Ammonia removal efficiencies were calculated using Eq. (2), whilst, overall mass transfer coefficient, KOV, is calculated using Eq. (3) [10, 11],

 (3)   where, V, A and t are wastewater volume in the reservoir, membrane area and time, respectively. K OV =

V  C0 ln  At  Ct

4. Results and Discussion In the ammonia removal process, the pH of the absorbent solutions, wastewater flowrates and temperatures are varied to see their effects on the ammonia removal performance. The mechanism of ammonia transfer through the membrane is shown in Fig. 3, where firstly ammonia in the vapor phase diffuses from the bulk wastewater solution to the membrane surface, then diffuses through the membrane pores containing gas, and finally react rapidly with sulfuric acid used as an absorbent solution. The effects of pH of absorbent solutions on ammonia removal efficiencies through the membrane process

Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor

Feed

Absorbent absorption

evaporation NH3(

NH4+ (aq)

liquid

gas

NH4+ (aq)

liquid

Fig. 3 The mechanism of ammonia absorption from wastewater through membrane [12].

and the combination of the membrane and the plasma-ozone reactor processes is shown in Figs. 4 and 5. The results showed that the lowest pH of the absorbent solution (0.7) gives the highest removal efficiency on both membrane and combination processes. This is due to more sulfuric acid that can absorb ammonia and based on Eq. (4), the ammonia removal efficiency is increased. The highest removal efficiency of the membrane process is 48%, while the combined process is 59%. An increase in efficiency is due to the amount of ammonia that has been broken down by the hydroxyl radicals to form other compounds. The hydroxyl radical is the result of the decomposition of ozone generated from the ozonator or the HPOR (hybrid plasma-ozone reactor). (4) 2 NH 3( g ) + H 2 SO 4 ( aq ) → ( NH 4 )2 SO 4 ( aq ) Experiments are also conducted for other ammonia removal processes such as ozonation process, HPOR (hybrid plasma-ozone reactor), combination membrane-ozone, combination of membrane and HPOR, and combination HPOR-ozone. All of the processes are using pH of absorbent solution 1.0. The removal efficiency of all processes is shown in Fig. 6. HPOR process has the smallest removal efficiency that is 13%. The similar phenomenon also found for the ozonation process and combination of ozonation-HPOR processes where its removal

efficiency values are not much different. However, after the processes is combined with membrane process there are significant increases in removal efficiency and reaches the highest value of 52% for the combination of membrane and HPOR processes. This phenomenon implies that the membrane plays a very important role in the ammonia removal process, while HPOR and ozonator helps reduce the membrane load on amonia removal. The effects of wastewater circulation rates on ammonia removal efficiencies through the membrane process is shown in Fig. 7, where the experiments were conducted at wastewater circulation rates 3, 4 and 5 LPM (litre per minute), and using contactor containing 60 fibers. It can be seen from Fig. 7 that, as the circulation rate of the wastewater increases, the removal efficiency of ammonia increases. The higher

R (%)

Macroporous hydrophobic membrane

pH = 0.7 pH = 1 pH = 2

t (s) Fig. 4 Variations of removal efficiency, R(%), versus time, t, at various of pH of absorbent solutions for membrane process.

R (%)

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pH = 0.7 pH = 1 pH = 2

t (s) Fig. 5 Variations of removal efficiency, R(%), versus time, t, at various of pH of absorbent solutions for membrane process and combined process of membrane and HPOR.

R (%)

Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor

t (s)

R (%)

Fig. 6 Variations of removal efficiency, R(%), versus time, t, for various processes using pH of absorbent solution 1.0.

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but the diffusivity also increase [8]. Fig. 9 shows the effects of temperature on the performance of ammonia removal for the combined of membrane-HPOR processes, and as it is expected the efficiency of ammonia removal increases with temperature. The highest removal efficiency achieved in this study is 77% at wastewater temperature 50 oC for the combined of membrane-HPOR processes. The effects of pH of the absorbent solutions, the circulation rate and temperature of wastewater on the performance of ammonia removal processes were also evaluated based on the overall mass transfer coefficients, which were calculated from Eq. (3). The effects these parameters on the overall mass transfer coefficients can be seen in Figs. 10-12, respectively. As shown in Fig. 10, the overall mass transfer coefficients decreased with increasing the pH of

the wastewater circulation rate, the more turbulent the flow and reduce the mass transfer resistance [13]. Therefore, the resistance in the wastewater boundary layer is not negligible in the range of flow rates studied [12]. Fig. 8 shows the effects of number of fibers in the membrane contactor on ammonia removal efficiencies through the combined processes of membrane-HPOR. The more the number of fibers in membrane contactors, the higher separation efficiency due to an increase in surface area contact. In order for ammonia removal process can take place efficiently, the ammonia in the wastewater should be in the volatile form. Increasing the temperature is one way to ensure the presence of free ammonia in solution due to an exponential increase in the vapor pressure of the feed solution, which will increase the trans-membrane vapor pressure and driving force. Not only the vapor pressure increases,

t (s)

Fig. 8 Variations of removal efficiency, R(%), versus time, t, for the combined membrane-HPOR processes using pH of absorbent solution 1.0.

R (%)

Fig. 7 Variations of removal efficiency, R(%), versus time, t, for membrane process using pH of absorbent solution 1.0.

R (%)

t (s)

t (s)

Fig. 9 Effects of wastewater temperature on the efficiency of ammonia removal for the combined membrane-HPOR processes using pH of absorbent solution 1.0.

Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor

Kov × 106 (m/s)

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pH

Kov × 106 (m/s)

Fig. 10 Variations of overall mass transfer coefficients, KOV, versus pH, for the membrane and combined processes using contactor containing 60 fibers.

QL (Lpm)

Kov × 106 (m/s)

Fig. 11 Variations of overall mass transfer coefficients, KOV, versus wastewater circulation rate, QL, for the membrane and combined processes using contactor containing 60 fibers.

T (oC)

Fig. 12 Variations of overall mass transfer coefficients, KOV, versus temperature, T, for the membrane and combined processes using contactor containing 60 fibers.

absorbent solution in the range 0.7-2.0 observed in this study. This fact indicated that interface between ammonia in the membrane’s outer surface and

absorbent solution was also act as the rate determining step in overall mass transfer coefficients. Increasing the pH of absorbent solutions will produce less sulfuric acid and based on Eq. (4) will decrease the absorption rate of ammonia. Fig. 11 showed that increasing the waste water circulation rate will increase the overall mass transfer coefficient. The increase in the overall mass transfer coefficient might be due to the fact that there is a transfer boundary layer near the wall of the membrane which becomes thinner as the wastewater circulation rate increases. As a result, the stripping rate of ammonia was enhanced as the wastewater circulation rate was increased due to a decrease in the liquid film resistance [5]. It is also observed that increasing the wastewater temperature will increase the overall mass transfer coefficient as shown in Fig. 12. Ammonia partial pressure in the wastewater increase with temperature and will create higher driving force in the membrane contactor for ammonia transfer from the wastewater to the absorption solution in the lumen fiber.

5. Conclusions The effectiveness of ammonia removal from wastewater through the combination of hybrid membrane with ozone plasma reactor and ozonator is better when compared with a single-membrane processes. Experimental results showed that Ammonia removal efficiency increase with an increase in the rate of circulation and temperature of the wastewater and the number of fibers in the contactor, but decrease with increasing pH of the absorbent solution. Ammonia removal efficiency in the combined process can reach 77%, while in the single membrane only 48%.

Acknowledgments The authors acknowledge financial supports for this work from the DGHE Ministry of National Education Republic of Indonesia through Penelitian Hibah

Ammonia Removal from Wastewater through Combination of Absorption Process in the Membrane Contactor and Advance Oxydation Process in Hybride Plasma-Ozone Reactor

Kompetensi 2012 Contract 3692/H2.R12/HKP.05.00/2012.

No.

References [1]

[2]

[3]

[4]

[5]

[6]

[7]

D.H. Belhateche, Choose appropriate wastewater treatment technologies, Chemical Engineering Progress 8 (1995) 32-38. Q. Du, S.J. Liu, Z.H. Cao, Y.Q. Wang, Ammonia removal from aqueous solution using natural Chinese clinoptilolite, Separation and Purification Technology 44 (3) (2005) 229-234. B. Norddahl, V.G. Horn, M. Larsson, J.H. du Preez, K. Christensen, A membrane contactor for ammonia stripping, pilot scale experience and modeling, Desalination 199 (1-3) (2006) 172-174. A. Gabelman, S.T. Hwang, Hollow fiber membrane contactors, Journal of Membrane Science 159 (1-2) (1999) 61-106. S.N. Ashrafizadeh, Z. Khorasani, Ammonia removal from aqueous solutions using hollow-fiber membrane contactors, Chemical Engineering Journal 162 (1) (2010) 242-249. A. Mandowara, P.K. Bhattacharya, Membrane contactor as degasser operated under vacuum for ammonia removal from water: A numerical simulation of mass transfer under laminar flow conditions, Computers & Chemical Engineering 33 (6) (2009) 1123-1131. Z. Ding, L.Y. Liu, Z.M. Li, R.Y. Ma, Z.R. Yang,

[8]

[9]

[10]

[11]

[12]

[13]

1107

Experimental study of ammonia removal from water by membrane distillation (MD): The comparison of three configurations, Journal of Membrane Science 286 (1-2) (2006) 93-103. Z. Xie, D. Tuan, H. Manh, N. Cuong, B. Brian, Ammonia removal by sweep gas membrane distillation, Water Research 43 (6) (2009) 1693-1699. M.S. El-Bourawi, M. Khayet, R. Ma, Z. Ding, Z. Li, X. Zhang, Application of vacuum membrane distillation for ammonia removal, Journal of Membrane Science 301 (1-2) (2007) 200-209. Z. Zhu, Z.L. Hao, Z.S. Shen, J. Chen, Modified modeling of the effect of pH and viscosity on the mass transfer in hydrophobic hollow fiber membrane contactors, Journal of Membrane Science 250 (1-2) (2005) 269-276. M. Khayet, T. Matsuura, Pervaporation and vacuum membrane distillation processes: Modeling and experiments, AIChE Journal 50 (8) (2004) 1697-1712. S. Kartohardjono, M.H. Putri, S. Fahmiati, E. Fitriasari, C. Ajeng, S. Bismo, Combination of ozonation process and absorption through membrane contactor using natural hot spring water as absorbent to remove ammonia from wastewater, Journal of Environmental Science and Engineering 1 (4) (2012) 428-433. A. Hasanoglu, J. Romero, B. Pérez, A. Plaza, Ammonia removal from wastewater streams through membrane contactors: Experimental and theoretical analysis of operation parameters and configuration, Chemical Engineering Journal 160 (2) (2010) 530-537.