Removal of Ammonia Nitrogen NHN and Hexavalent Chromium ( VI ) From Wastewater Using Agricultural Waste Activated Carbon

Highly porosity characterized activated carbon (AC) was achieved using agricultural waste as raw material used as adsorbent to treat wastewater through removal of ammonia nitrogen (NH-N) and hexavalent chromium (Cr (VI). The preparation method of AC included using zinc chloride as activation agent. Characterizations of the porosities of AC preparations were performed using N2 adsorption-desorption to ascertain surface area and pore volume. Existing groups on the AC surfaces were resolved using Fourier Transform Infrared Spectroscopy (FTIR) analyses. Scanning electron microscopic (SEM) was used to asses AC morphologies. Maximal surface areas of AC preparations were discovered to be 1190.41 m2/g at activation temperatures of 700 oC. Adsorption isotherm was analyzed using two models Langmuir and Freundlich. The kinetic study was represented through Pseudo first order and pseudo second order.


INTRODUCTION
Environmental conservation protection takes a great consideration over the years in all all over world, especially the protection of water from pollution.One of the most toxic pollutants in wastewater which affect human healthy is the high concentration of hexavalent chromium and ammonia nitrogen.Previous studies showed that high concentration of ammonia nitrogen is inhibit the biological degradation by the microorganis 1,2 .Hexavalent form of chromium is toxic and is suspected to be carcinogenic.It affects the kidney and liver and causes dermatitis, diarrhea 3 .For these reasons, its important to treat wastewater effluent before discharging it to environmental.
Various technologies have been investigated for treatment of wastewater including physical and chemical methods, ion exchange, electrochemical treatment (Erabee et al., 2017a).Membrane separation and AC adsorption 4 .Adsorption onto AC has several advantages over other water treatment methods, primarily as a very simple technology and more efficient in removing high molecular weight compounds from aqueous matrix (Erabee et al.,  2017b).Nowadays, good source for AC preparation is agricultural material because of low cost and availability 5 (Erabee et al., 2017c).The most widely used precursor for production of AC is jute and coconut fibre 6 , apricot stone 7 , coconut husk 8 , and rice husk 9 .This study aimed to treat sample of wastewater by producing low cost adsorbent with high porosity for removal of ammonia nitrogen and hexavalent chromium.Also, to study the equilibrium and kinetic mechanism of NH-N and Cr (VI) adsorption onto the prepared activated carbon, and to identify characteristics of prepared activated carbon including functional groups and surface area.

Analysis of Sample Solution
The waste water that used in this study was collected from Mini STP (Sewage Treatment Plant) at faculty of engineering in University Putra Malaysia (UPM) which is located at Selangor state in Malaysia.The sample of wastewater is followed by laboratory testing in order to evaluate levels of organic and inorganic contaminates based on the Examination of Water and Wastewater methods.Table (1) shows the parameters limits of sample and effluent of Standard B which stated in the Sewage and Industrial Effluents Regulations 1979 by Department of Environmental Malaysia.
The measuring of PH, TDS, salinity and electrical conductivity were made using Tracer Pocket tester (Code:1766, LaMotte, Taiwan).TSS of the sample was determined by pouring a well-mixed sample (20 ml) through a pre weighted filter paper that was mounted on a vacuum filtration apparatus.A standard laboratory procedure was used to measure COD and BOD of sample.In testing the turbidity a multi-detector optical turbid meter was used.For measuring NH-N and heavy metals a multi-detector optical colorimeter (Hach DR/890 Colorimeter).

Preparation of AC
Garden waste, which is the small branching of trees, collected from the agricultural waste of UPM gardens.These garden waste is used as a raw material for the AC preparation.Washed and cleaned raw materials were crushed and grinded to small particles (0.3-0.6 mm) and dried in at 100 °C for 24 h 10 g of the dried sample was carbonized at 300 °C for 4 h using electric tubular furnace at a rate of 10 °C/min.and under continuous 100 ml/min.N 2 flow.After carbonization, the sample was mixed with chemical activation agent of ZnCl 2 at impregnation ratio of 1.5/1 (weight of ZnCl 2 / weight of precursor, w/w) for 12 h, then dried heated at activation temperatures of 700 °C.Holding time at final temperature was 1 hours.Hot distilled water was used for washing the resulted sample after cooling until neutral PH.The sample was dried at 100 °C for 24 h and stored in desiccator.

Characterization of activated carbon
SEM analysis was used to indicate textural morphology of prepared AC.Chemical functional groups of activated carbon were identify using Fourier transform infrared spectroscopy (FTIR) in the scanning range of 400-4000 cm -1 .The surface properties was characterized with Micrometrics ASAP 2020, using adsorption of N at 77 k.
The following formula is used to evaluate the removal efficiencies 10 .
Where C0 initial concentration, Ce concentration at time t.
Ascertainment of AC's sorption capacity was done by calculating using following equation.
Where m adsorbent mass and V volume of leachate sample.

Adsorption Equilibrium Isotherms
Equilibrium adsorption study was analysed using two models Langmuir and Freundlich as follows.
Where KL (L/mg) and qm (mg/g) are represent energy of adsorption and adsorption capacity, respectively.The constant qm and KL are characteristics of the Langmuir equation which can be determined from the slope and intercept of the plot Ce/qe against Ce.The equilibrium parameter R L can be found from the following equation: Unfavourable adsorption was assumed when R L >1, while linear adsorption at R L =1, favourable (0< R L <1), and irreversible when R L = 0.

Adsorption Kinetic Study
Pseudo first order and pseudo second order models were used to represent kinetic study, as follows.

Pseudo first order Model
Integral form of pseudo first order equation was indicated in the following equation 11 .
Where qe (mg/g) is the amount of adsorbate at the equilibrium, qt(mg/g) is the amount of adsorbate at time t (min.), respectively and k1(L/min.) is the rate constant.The adsorption rate constant, K1, can be calculated by plotting Log (qe -qt) versus t.

Pseudo-Second Order Model
Linearized integral form of pseudo second order kinetic model is represented as where qe and qt(mg/g) are the amount of adsorbate at the equilibrium and at time t (min.), respectively k is the pseudo-second order rate constant of adsorption (g/mg.min).K 2 and qe can be obtained from the intercept and slope by plotting t/qt versus t.

AC Characterizations
The nitrogen adsorption isotherms are used to obtain the surface physical parameters which were indicated in Table 1.The surface area, pore volume, micropore surface area and micropore volume of AC-GW was 1190.41 m²/g, 0.43 cm³/g, 568.752 m²/g and 0.299 cm³/g, respectively.Fig. 1 presents the surface chemistry of the prepared AC with ZnCl 2 activation.The FTIR of AC illustrated simple surface chemistry, the band at 3361 cm -1 is due to the presence of N-H stretching.The shorted peak at 2314 cm -1 was attributed to presence of C-N stretching.The broad peak between 1673 cm -1 to 1544 cm -1 is a result of the N-H bond.
SEM test used to perform surface morphology of AC-GW as shown in Fig. 2. Its clear from the figure that well-developed porous in the surface of prepared AC which were considered as channels to microporous network.As a result, the removal efficiencies of NH-N and Cr (VI) increased with increasing of contact time due to the active sites abundance on the surface of adsorbent 12,13 .The slow removal capacity with the subsequent time may be due to the diffusion of heavy metal ions onto the surface of AC and fewer binding sites 14 .The same results were conducted by Kyzas 15 who concluded that the end of adsorption was at 180 minutes.Babel and Kurniawan 16 observed that removal efficiency increased with an increase in contact time.The adsorbent dose is strongly effected removal percentage in adsorption process 17 .From Fig. 3 and 4, it can be observed that removal efficiencies of NH-N and Cr(VI) improved with increasing adsorbent doses due to availability of more adsorption sites 18 .
Maximum removal percentages were obtained at 5 mg/L adsorbent dose and 180 min. of contact time for all different dosages of parameters.These results were noted as optimum conditions for subsequent studies.

Equilibrium Adsorption Models
The adsorption Langmuir isotherm for NH-N is represented in Fig. 5.The Langmuir constants and their correlation coefficients R 2 for adsorption of NH-N and Cr (VI) via AC-GW, are listed in Table 2.For NH-N, the value of R L is 0.0015 which indicates favorable adsorption of NH-N using AC-GW.Fig. 6 shows Freundlich isotherm for NH-N removal by AC-GW at 3 h of contact time.The Feundlich isotherm constant (KF and n) and their correlation coefficients R 2 are summarized in Table 2.The value of n for Freundlich isotherm for NH-N is equal to 1.883, represent moderately good adsorption between 1-2 19 .The results showed that the Freundlich isotherm model better fits the experimental data.
The Langmuir adsorption isotherm for Cr (VI) by AC-GW was shown in Fig. 7. Value of R L equal to 0.001 as determined in Table 2 and correlation coefficient is equal to 0.870.

While Freundlich adsorption isotherm for
Cr (VI), as in Fig. 8, showed that high correlation coefficient (0.992) with value of n (1.137) between 1 and 2, and represented good adsorption.From the results, the Freundlich isotherm of Cr (VI) better fits to experimental data than Langmuir isotherm.3 and 4 show Pseud first order and pseudo second order parameters of NH-N and Cr (VI), respectively, on AC-GW.The correlation coefficients (R2) values of pseudo first order were found to be 0.858 and 0.719, respectively, for NH-N and Cr (VI), respectively.While pseudo second order model demonstrated much linearity

CONCLUSION
The treatment of wastewater was examined using agricultural waste collected from garden waste activated carbon assisted adsorption process.The porosity characterizations of prepared activated carbon indicated that garden waste is good adsorbent due to its highly surface porosity and effective precursor for adsorption of pollutants from wastewater such as NH-N and Cr(VI).The results illustrated that the Freundlich isotherm of NH-N and Cr(VI) better fits to experimental data.Kinetic adsorption study shows pseudo second order model was suitable to describe the kinetic adsorption process of NH-N and Cr(VI) onto AC-GW.The removal efficiencies of NH-N and Cr (VI) using AC-GW were found to be equal 92 and 93%, respectively.

Fig. 3 .Fig. 4 .
Fig. 3. Effect of adsorbent dose and contact time on removal efficiency of Zn using AC-SPB

Fig. 10 .
Fig. 10.Pseudo first order of Cr(VI) adsorption Figures 11 and 12 show the plots of the second order models for adsorption of NH-N and Cr (VI), respectively.

Table 2 : Langmuir and Freundlich isotherms parameters
Figures 9 and 10 show the plots of the first order model of NH-N and Cr (VI) adsorption, respectively.