Removal of Ammoniacal Nitrogen from Synthetic Wastewater Using Granular Activated Carbon and Limestone

Background: Discharging high concentrations of nitrogen compounds in industrial effluent such as those from fertilizer manufacturing plants can cause various environmental problems like eutrophication. Objective: to investigate the efficacy of the granular activated carbon (GAC) and limestone (LS) as low cost media in removing ammonium ions from aqueous solution. Methods: Batch experiments were conducted to evaluate the efficacy of GAC and different ratios of GAC and LS mixture in the removal of ammoniacal nitrogen. The investigated parameters included contact time, initial ammonium ion concentration, pH, and amount of adsorbent. The adsorption isotherm and adsorption kinetic of ammonium ions by a mixture of GAC and limestone (LS) was studied Results: The experiments showed that the efficacy of GAC alone on the adsorption of NH4-N was 95% at shaking time 150 min, agitation speed 210rpm, temperature 22oC and pH 9. The efficacy of a mixture ratio LS: GAC (30:20) on the removal of NH4-N was 75%. Conclusions: The study concluded that the removal percentage of ammoniacal nitrogen by a mixture of lime stone and GAC increase with the increase of agitation time and decrease with the increase of initial concentration while alkaline pH was more favorable for the adsorption of ammoniacal nitrogen.


INTRODUCTION
In human intestine, nitrate is also converted into nitrite under anaerobic conditions that may lead to methaemoglobinaemia in infants.
Moreover, cancers of the gastrointestinal tract system may be induced by formation of nitrosoamines from nitrite. (5) The removal ofNH 4 -N from wastewater is important in the alleviation of environmental problems including eutrophication, corrosion and fouling.
( The aim of the present study was to investigate the efficacy of the granular activated carbon (GAC) alone and its mixture with limestone (LS) as a low cost adsorbent in the removal of ammoniacal nitrogen from wastewater.

Study setting:
The

Batch adsorption studies
Batch adsorption experiments were conducted using total volume of media mixture (LS-GAC) 50 ml with 100 ml of    The Freundlich isotherm fits according to equation ( 5): Where q e is the amount sorbed per specified amount of adsorbent (mg g

Adsorption Kinetic
The pseudo-first-order kinetic model has been widely used to predict sorption kinetics.The model given by Langergren (25) is defined as in equation ( 6): dq= k 1 (q e − q) (equation 6) dt Integrating Eq. ( 6) with respect to boundary conditions q=0 at t = 0 and q = q e at t = t, Eq. ( 6) becomes as shown in equation (7): ln(q e − q t ) = lnq e − k 1 t (equation 7) Where q e and q t (mg/g) are the amounts of adsorbate adsorbed at equilibrium and at any time, t (h), respectively, and k ) is the adsorption rate constant.The plot of ln(q e −q t ) versus t gave the slope of k were 0.9, 0.963, 0.96 for ammonia initial concentration of 5, 10, 20 mg/l respectively.Furthermore, the experimental q e values did not agree with the calculated values obtained from the linear plots.

Effect of solution pH
The highest ammoniacal nitrogen removal (85%) was achieved at pH 11 with GAC at initial concentration of 5 mg/l (Figure 3).At pH 5 ammonia was largely in ionized (NH‫‬ + 4 ) form and was removed by adsorption but at pH ≥ 7 a substantial part of it was also in the molecular ammonia (NH 3 ) form, which was subject to gradual removal by ammonia stripping. (19,20)

Effect of initial concentration
The percentage removal for initial concentrations 5, 20, 30, 50 mg/l was 76%, 73%, 69% and 58% respectively (fig.4).The increase of initial concentration leaded to decrease the removal efficiency as pore sites were occupied by the molecule of ammoniacal nitrogen.These results agree with previous studies.

Effect of adsorbent dosage
The results of the present work showed that the increase in adsorbent dosage increased the percentage removal of NH 4 -N, due to the increase in adsorbent surface area, whereas the increase in the amount of GAC increased NH 4 -N removal. (15,16)The optimum dosage of the adsorbent reached 40 mL corresponding to 80 g of adsorbent mixture.The percentage removal of ammoniacal nitrogen by GAC (0:50) and a mixture ratio LS: GAC 30:20 was 90% and 84% respectively (fig.5).

Isotherm model:
The adsorption isotherm behaves species sorbed onto the surface of the solid with increasing concentrations of said species in the liquid phase. ( Adsorption mechanism: The intraparticle diffusion model proposed by Weber and Morris (26) is applied to study the adsorption process, as in equation ( 8): q t = k id t 1/2 + C i (equation 8) Where: k id is the intraparticle diffusion rate constant and is obtained from the slope of the straight line of q t versus t 1/2 (Fig. 8).C i , the intercept of stage i, gives an idea about the thickness of boundary layer, i.e., the larger the intercept, the greater the boundary layer effect. (27)The adsorption process of the adsorbate molecules from the bulk liquid phase onto the adsorbent surface is presumed to (3) adsorption at a site on the surface.(28)   The existence of an external layer diffusion process could be deduced by the fact that these plots do not pass through the origin.

CONCLUSION:
Adsorption of NH 4 N on a mixture of LS Equilibrium data were fitted to Freundlich present in industrial effluents such as those discharged from fertilizers manufacturing plants.These nitrogen compounds can end up onto rivers through effluent discharge, causing eutrophication which disrupt aquatic ecosystems in a severe manner.(1,2) The ammonium ion and ammonia can coexist in an aqueous solution according to equation(1) NH 4 + ↔NH 3 (aq) + H + (equation 1) The equilibrium presented in equation (1) depends on pH and temperature.The release of ammonia can promote the growth of algae and decrease the dissolved oxygen required for aquatic life if the concentration of NH 4 -N exceeds 0nitrate (NO 3 -) ions.However, these ions are removed by aquatic plants, algae and bacteria by assimilating them as a source of nitrogen. (4)Studies on the toxicity of nitrate on aquatic animals indicated that nitrate reacts with hemoglobin shortage of oxygen in their body (methaemoglobin) and finally death.
solutions of ammoniacal nitrogen of concentrations 5mg/l, in 250 ml stoppered conical flasks.The LS and GAC mixture (v/v)by volume(ml) were 40:10, 30:20, 20:30, 10:40 and 0:50 and by mass(g) 104:13, 78:26,52: 39,26:52,0:65 respectively .The glass-stoppered flasks were then placed in a water bath-shaker and shaken at agitation speed of 210 rpm at constant nitrogen adsorption on shaking time was examined in the initial study to determine the equilibrium time.The study was performed by concentration of ammoniacal nitrogen of 5mg/l with different mixture ratios of granular activated carbon and limestone for different intervals of time ranging from 30 min to 210 min.The effectiveness of ammoniacal nitrogen adsorption was examined by different concentrations of ammoniacal nitrogen of 5mg/l, 10mg/l, 15mg/l and 20mg/l with a desired mixture ratio of granular activated carbon and limestone for different intervals of time ranging from 30 min to 210 min.Samples were adjusted to pH 3, 5, 7, 9 and 11 (with 0.1 M HCl or 0.1MNaOH) to determine the effect of pH on NH 4 -N removal at different mixture ratios.The effect of adsorbent dosage by volume on the removal efficiency was studied .The effect of initial concentration of ammoniacal nitrogen on the removal efficiency was investigated by using different concentrations of NH 4 N i.e. 5, 10, 20, 30, 40 and 50 mg/L.The ammonium removal percentage was calculated by equation (2): initial concentrations were added, the pH was not adjusted, and the equilibrium time was set according to the preliminary experiments.The uptake of the adsorbate at equilibrium, q e (mg/g), was calculated by equation (3) : (7) q e = V (C 0 − C e ) (equation 3) m Where C 0 , C f and C e are the initial, final and equilibrium concentrations of the ammoniacal nitrogen (mg/L) in solution, respectively; V is the volume of the solution (L) and m is the weight of the adsorbent (g).The kinetic studies were performed following a similar procedure at 23 o C, the initial concentration was set as 20mg/L for ammoniacal nitrogen, and the samples were separated at predetermined time intervals.The uptake of the adsorbate at any time q t (mg/g) was calculated by equation (4) q t = V (C 0 − C t ) (equation 4) m Where C t (mg/l) is the concentration of ammonical nitrogen at any time t (min).Statistical study: Each run of the experiments of the studied parameters were performed three times and each sample was analysed in duplicates.The resulting data were represented as the average mean, and the percentages removal were calculated and were plotted on graphs.The R 2 The experiments were carried out with different LS: GA mixture ratios of 0:50, 10:40, 20:30, 30:20, 40:10 (v:v) of 100 ml solution of 5mg/l ammoniacal nitrogen at 20 • C solution temperature.The removal percentage of ammonia increased rapidly by increasing the time at the beginning Bull High Inst Public Health Vol.42 No.2 [2012] then followed by slight increase in the percentage removal of ammoniacal nitrogen (figure 1).It was observed that at time 150 min the percentage removal of ammoniacal nitrogen achieved was 90%,78%, 75% with adsorbent LS:GAC mixture of 0:50, 20:30, 30:20 respectively.The optimum mixture ratio was then determined to be30:20 to decrease the cost of GAC.

Figure 1 :Figure2:Figure 3 :
Figure 1: Effect of the shaking time on NH 4 N removal using different LS:GAC mixture ratios

Figure 4 :
Figure 4: Effect of various initial concentrations on the removal of NH 4 N

Figure 5 :
Figure 5: Effect of adsorbent dosages on the removal of NH 4 N n is the empirical parameter related to the intensity of sorption, which varies with the y = -0.0307x 2 + 3.0129x + 14.8 R² = Public Health Vol.42 No.2 [2012]heterogeneity of the material.The model parameters (K F and 1/n) can be determined from the linear plots of q e and C e .The K F was 0.004 and n was 1.4.The value of 0 < 1/n < 1 exhibits the favourability of adsorption onto activated carbons.

Freundlich model as shown
in figure (6).Freundlich model is an empirical equation based on sorption on a heterogeneous surfaces or surfaces supporting sites of varied affinities.It is assumed that the stronger binding sites are occupied first and that the binding strength decreases with the increasing degree of site occupation. (23)When 1/n values are in the range 0.1 < 1/n < 1, the sorption process is favourable.This model is valid for heterogeneous surfaces and predicts an increase in the concentration of the ionic Bull High Inst Public Health Vol.42 No.2 [2012] involve three stages:(1) mass transfer of the adsorbate molecules across the external boundary layer; (2) intraparticle diffusion within the pores of the adsorbent; and GAC was found to increase with increase of agitation time and decrease with the increase of initial concentration while alkaline pH was more favourable for the adsorption of NH 4 N.The experiments showed that the efficacy of GAC alone on the adsorption of NH 4 -N was 95% at shaking time 150 min, agitation speed 210 rpm, temperature 22ºC and pH 9. The results showed that the efficacy of LS: GAC mixture ratio (30:20) on the removal of NH 4 -N was 75%.The increase of