Removal of nutrients and heavy metals from urban wastewater using aeration, alum and kaolin ore

REMOVAL OF NUTRIENTS AND HEAVY METALS FROM URBAN WASTEWATER USING AERATION, ALUM AND KAOLIN ORE
M.N. Rashed and M.E. Soltan
Chemistry Department, Faculty of Science, 81528 Aswan, Egypt.

E-mail: [e-mail]-

ABSTRACT

Some urban wastewater resulted from domestic and industrial wastewater and needs special treatments before discharge to surface water or used for irrigation. This study is target to use kaolin (from south Egypt) as adsorbent for the removal of heavy metals as well as aeration and alum for the removal of nutrients from Kima drain wastewater .The experiment proceeds through 3 steps, the first step applied the aeration method for 24,48,120 and 192 hr and obtained the suitable time to remove or reduce the nutrients. Second step includes treatment with alum [KAl(SO₄)₂.12H₂O] using different alum doses (50,100 &150 mg/l) at the obvious times to remove or reduce the nutrients , while the third one includes treatment with kaolin ore size <63 µm at different doses, pH and times to remove heavy metals. The results revealed that aeration method removed CO₃ ,OH and Mn ions , and reduced pH, Ca,Cl, NO₂, SiO₂, PO₄, Na and Fe concentrations. Treatment with alum was effective for the removal of CO₃,OH, NO₃,PO₄ ions and reduced Cl, F, Na, Cd, Cu, Cr, Sr, and Zn . Kaolin ore was very effective as adsorbent for reduced and removal of the heavy metals Cd, Cr, Cu, Ni, Pb, Sr and Zn from the wastewater. Using the three consecutive treatment processes ,we obtained wastewater in the range of standardized limits for discharge into surface water or used in irrigation as cited by Egyptian Authorities.

KEYWORDS
Heavy metals- kaolin - pollution- treatment- urban water- wastewater.
INTRODUCTION
Water pollution is responsible for the death of some 25 million people each year (Niemczynowicz, 1999) and cause a destroy of aquatic environment. The major point of water pollution was wastewater, especially urban wastewater, these urban wastewater come from varied sources include domestic wastewater from houses, hospitals and commercial uses as well as agricultural and industrial wastewater. These wastewater contains inorganic pollutants such as nutrient and heavy metals and causes pollution to the surface water. So, many studies were run to eliminate or reduce these pollutants before its discharge or reuse for irrigation. Wild and Stefist (1999) studied the simulation of nutrient fluxes in wastewater treatment plant with EBPR. Alum was used with ferric chloride as coagulators for the wastewater treatment (Ngtez et al, 1999). Many alkalis were currently being used for environmental control purposes particularly in wastewater treatments (Estefan, 1992), the most commonly used were lime and sodium carbonate. Natural ores were also used for wastewater treatment, zeolites were used for removal of heavy metals from wastewater (Yuan et al,1999). Ajmal (1995) was used naturally occurring pyrolusite for adsorption of Pb , Zn and Mg from industrial wastewater.

This study is target to apply a continuos three treatment processes on urban wastewater collected from Kima drain (canal received wastewater from fertilizer factory, houses and hospital uses) which consider as a source of pollution in river Nile water. These processes are:

1. 
   Treatment for reduce or removal of nutrients using aeration process.
   
2. 
   Treatment for the removal or reduce of both remain nutrients and heavy metals using alum (potassium aluminum sulfate) [KAl(SO₄)₂.12H₂O].
   
3. 
   Treatment for the removal of heavy metals using kaolin ore which found in a large quantity at Aswan (south of Egypt) .
   

Moreover, this study is target also to obtain treated wastewater in the range of ruse for irrigation or discharge on surface water as cited by Egyptian Authorities.

EXPERIMENTAL

Sample collection
Wastewater samples .The wastewater samples were taken from Kima drain. Wastewater samples were collected by dipping pre-cleaned glass jars into the drain stream and collected in 20-L plastic container. Samples were placed in coolers and transported to the laboratory.

Kaolin ore samples. Kaolin ore samples (5 Kg of each) were collected from Kalabsha ^{area (80 km south of Aswan city ,Egypt ). The ore was crushed using a mechanical crusher and ball mill. Then grinding by using an electric agate mortar. The powdered ore was sieved in sieve <63 m.}
Treatment experiment using aeration and alum
Twenty liters of wastewater samples were inserted in two glass jars (40x40x40 cm). 50 mg/l of alum (potassium aluminum sulfate) was added to the one jar every 24 hr till 192 hr , while the air was pumped in the another jar for 192 hr. The samples were analyzed after every addendum in the jar of alum and every known times 24,48,120 and 192 in the aeration jar.
Treatment experiment using kaolin ore

<sup>Adsorption studies. To choose the desired size of high adsorption capacity, one gram sample of the operating size <63 m was washed with 50 ml bidistilled water three times,then treated with 50 ml of solution containing 10 ppm mixture standard of Cd,Cr,Cu, Mn, Pb and Zn in a conical flask. Constant stirring of the solution was maintained for 24 h. After attainment of equilibrium,the content of the flask was filtered through Whatman 0.45m cellulose nitrate membrane filter and susequently analysed for residual concentrations of the metal ions using atomic absorption spectrophotometer (SP1900 Pye Unicam)The concentration of adsorbed metal ions were calculated from the known total amount of adsorbate added .

Effect of concentration. After choosing the ore size that had maximum adsorption capacity,the kaolin was treated with 50 ml mixture heavy metals standards (10,8,4,2 &1 ppm) in a conical flask for 24 h. After attainment of equilibrium,the content of the flask was filtered through Whatman 0.45m cellulose nitrate membrane filter, and metal ions were analysed using atomic absorption spectrophotometer. The adsorption capacity was calculated.

Effect of pH on adsorption.One gram of the kaolin sample was treated with 50 ml of 10 ppm standard mixture, then the pH of the adsorption mixture was adjusted to various pH values (3, 5 ,7& 9) by using 0.5 M NaOH or 0.5 M HCl.The final concentration of the metals were determined after 24 h and the adsorption capacity was calculated.</sup>

Effect of ore dosage. 0.25, 0.5,1 and 2 gm of kaolin was treated with 50 ml of 10 ppm standard mixture. The final concentration of the metals after 24 h were determined using AAS, and the adsorption capacity was calculated. After determined the suitable dose and time of alum, as well as, the optimum aeration time, kaolin (<63µm) experiment was applied on wastewater sample to obtain the ideal pH, dose and time for treatment.
^{Standard solutions:
Certified atomic absorption spectroscopic standard solution as Cd,Cr,Cu, Mn, Pb and Zn (1000 ppm) was purchased from BDH Company,UK. Working standard solutions 10,8,4,2 & 1 ppm were prepared by diluting the stock one.}
Analytical measurements:
The original wastewater sample and the samples resulted from each treatment were analyzed for pH, conductivity, ions CO₃,OH, Cl, SO₄,PO₄,NO₃,SiO₂, F, Na, Ca, Mg, and Fe according to standard methods . Heavy metals Cd, Cr, Co, Cu, Sr , Mn , Pb and Zn were analyzed using Atomic absorption spectrophotometer, SP1900 Pye Unicum.

RESULTS AND DISCUSSION

Wastewater treatment using aeration method:

The results of wastewater treatment experiments (Table 1) show that aeration method exhibited high efficiency (100%) after 120 hr for complete removal of CO₃, OH and Mn ions, while it reduced the concentrations of pH, Ca, Cl, NO₃, SiO₂, PO₄, Na and Fe at different times; Ca 44.8-42.4 mg/l and NO₃ 42-34 mg/l after 48 hr, SiO₂ 17-8.5 mg/l and Cl 76.5-6.3 mg/l after 120 hr . The chloride removal was as the result of the adsorption of some metal chlorides on the precipitate. Nitrate removal efficiency was decreased after 48 hr then increases as the time increased; this increase may be due to oxidation of free ammonia to nitrite that oxidized to nitrate (Wakeel&Wahby, 1970). Nitrate ground water was reduced by the addition of 315-mish iron and buffered at pH 8.8 (Cheng et al, 1997). PO₄ was removed after 192 hr (100% removal efficiency) , this was due to either precipitation of Ca and Al phosphate or adsorption of phosphate on the hydrous iron oxide ( Furumal & Ohgakl , 1989). Maximum reduction of SiO₂ observed after 120 hr . Sodium removal efficiency increased up to 24 hr and decreased as the time forward, this decrease was as the result of the adsorption of Na ions on the negative precipitated charge. pH decreased from 9.14 (initial wastewater concentration) to 6.89 after aeration time 120 hr ,as the results of acidic effect of the air CO₂ (Soltan,1991). Heavy metals Fe, Cd, Cr, Cu , Sr and Zn have not regular trends in the treatment efficiency with aeration , but nearly all reached maximum efficiency in the time range 48-120 hr.

Table 1: Treatment efficiency (%) of the study items in the wastewater.

Time. Methods.	24 hr A B C	48hr A B C	120hr A B	129hr A B
Ions
PH CO3 OH Cl PO4 NO3 SiO2 Ca Na Fe Cd Cr Cu Sr Mn Zn	3.51 5.04 - 27.7 44.45 - 100 - 83.6 - 62.7 - 100 - 58.8 - 96.4 - 64.1 - 5.75 92 20 100 33.3 100 200 100 66.6 94 100 100 75 87.5 88	9.09 - 86.1 - 100 - 91.6 - 75.8 - 100 - 18.2 - 96.4 - 66.3 - 21.8 93 20 100 66 33.3 100 0.0 100 73.3 92 100 100 100 87.5 37.5 87	12.9 100 100 91.6 100 100 48.2 104 59.9 69.9 46.6 33.3 50 73.3 100 62.5 25	23.7 100 100 91.6 100 111 32.9 128 58.7 56.3 66.6 66.6 150 93 75 25 50

A: Treatment with aeration. B: Treatment with Alum. C: Treatment with kaolin

These metals may be adsorbed on the colloidal precipitate formed in the solution. Constructed wetlands was used to treat some toxic wastewater under tropical conditions, which remove more than 99% of Cr and Ni concentrations ( Polprasert et al,1996). Single and two stage aerated system was used for the removal of nitrogen from wastewater (% N₂ efficiency removal 95%)(Andreadakis et al, 1995).

Wastewater treatment using alum method:
Effect of time. The effect of time in wastewater treatment with alum is shown in Table 1. The results revealed complete removal of OH, NO₃, Mn and Cu after 24 hr , while CO₃ and NO₃ after 120 hr. The method reduced the concentrations of SiO₂ and Zn after 24 hr, while it reduced Na after 48 hr, and Cl, F, Cd, Sr and Cr after 192 hr. Initial phosphate concentration in the sample was 3.7 mg/l which exhibited fast removal in alum method (after 120 hr) than those aeration (192 hr) (Table 2).This decrease was due to either precipitation of Ca and Al phosphate or adsorption of phosphate on hydrous aluminum oxide ( Ngtez et al,1999). Hydroxyl ion OH initial concentration was completely removed after 24 hr, this remove resulted when the addition of alum ,it furnishes Al⁺³ ion in solution which discharge the hydroxyl OH negative ion . Remove of Mn was as the result of it's consume in oxidation process by microorganisms. The decrease of Co, Cu, Cr, Cd, Fe, Pb and Zn were as the result of redissolved of the suspended or colloidal dehydrated oxide as a result of pH decreases (Ajmal et al, 1992).
Table 2: Nutrient levels ( ppm )in original and treated samples and Egyptian standard .

Sample	pH CO3 OH Cl NO3 PO4 SiO2 Ca Na F
Original sample Aeration treatment Alum treatment Egyptian Standard	9.14 144 768 76.5 42 3.7 17 44.8 46 0.3 6.08 0.0 0.0 63 34 0.0 8.5 42.4 17 0.42 6.92 0.0 0.0 63 0.0 0.00 8.8 43.2 15.5 0.06 6-9 -- --- 1 30 1 --- -- --- 1.0

Effect of alum dose. Figures 1 and 2 show the effect of alum dose (50,100 & 150 mg/l) on removal efficiency of ions. For CO₃, OH, Cl, PO₄,NO₃, SiO₂ , Na and Ca ions the suitable alum dose observed was 100 mg/l , while for heavy metals, the suitable alum dose was 50 mg/l . Alum dose of 100 mg/l for 120 hr was sufficient for complete removal of CO₃, OH and Mn, and reduce the concentrations of Cl , PO₄, SiO₂, Na and Ca. The obvious heavy metals were less reduced by alum method (30-50% efficiency removal), but more effective than aeration method. Possible component of the (SPM) suspended particle matter, such as Al, Fi, Fe and Mn oxides or hydroxides, were known to have substantially different binding affinities for metals (Ferreira et al, 1997). The effects of size and geochemical properties on the binding of trace metals to natural colloids and particles have been investigated in which Cd was more strongly bound to the smallest fraction than Cu (Lead et al, 1999).





Treatment using kaolin method
Effect of initial metal concentrations. From Table 3 ,it was shown that Cr , Cd , Cu and Pb undergo complete adsorption (100%) at kaolin surface for all the initial element standards. For remaining elements, Mn maximum adsorption observed with Mn initial concentration 10 ppm, while for Sr, Fe and Zn, maximum adsorption was observed from 8 ppm Sr , Fe and Zn standards. Parkman et al (1998) reported that per cent uptake of Sr on kaolinite was greatest at the highest initial Sr concentration.
Effect of pH. The adsorption of the heavy metals on kaolin at different pH was performed using 10 ppm standard mixture elements. The results (Fig.3) show that the adsorption of the studied heavy metals increased as pH increase from 3 -6.5, the maximum adsorption of the metals observed at pH < 7. After pH 7 the metals adsorption decrease as the result of precipitation of these metals.
Table 3: Effect of initial heavy metals concentration on adsorption efficiency

Element initial Concentration(ppm)	Mn Sr Fe Cr Pb Cd Zn Cu % Adsorption
1 2 4 8 10	94 98 99 100 100 100 99 100 95.5 95 100 100 100 100 100 100 91.7 93 98.7 100 100 100 98.7 100 95.5 99 100 100 100 100 100 100 97 91 99.5 100 100 100 99.5 100

Other study on the adsorption of heavy metals on the biomass of Phormidium sp was suitable at pH 5 for Pb, Cu, Cd, Zn and Ni (Wang et al, 1998), the maximum adsorption was 13,600 mg/kg for Pb; 10,100 mg/kg for Cu; 9,600 mg/kg for Cd ; 9,400 mg/kg for Zn and 5,700 mg/kg for Ni. Ajmal et al (1995) reported the maximum adsorption of Pb ,Zn and Cd on pyrolusite under pH 7. The optimum pH for removal of Cd, Cu and Mo using carbonaceous material, developed from the waste slurry generated from fertilizer plant, was about pH 6, for Cr and Hg was at pH 2, while for Pb it was almost in the range 6-7 (Srivestava et al, 1989).

Effect of kaolin dose. Using different dose of kaolin (0.5, 1, 1.5 and 2 gram) for the adsorption technique, suitable kaolin dose for the maximum adsorption of the studied heavy metals was obtained (Fig.4). It shown that the adsorption of Fe, Cd, Cr, Co, Cu, Sr, Mn and Pb increased as the kaolin dose increase and reach maximum at 2g.



Langmiur adsorption isotherm. Langmuir equation was used as the model for adsorption, the adjusted Langmuir equation in its linear form being (Bohn et al, 1985)

1/(x/m)= 1/c b + 1/a (1)

where c (mg/kg) , is the concentration of adsorbate left in solution at equilibrium,

x/m(mg/kg) ,is the amount of adsorbate adsorbed per unit mass of adsorbent,

a ,is Langmuir binding energy coefficient, and

b (mg/kg) , is the adsorption maximum.

Parameters (a ) and ( b ) can be obtained from the equation (Table 4 ). it was shown that the adsorption maximum parameter using kaolin (a) was the highest for Fe, while the lowest was for Mn .Zinc adsorption maximum was less than of Fe and Sr. Kaolin binding energy (b) was nearly the same for Fe, Zn and Sr ,while binding energy for Mn was the lowest . This mean that Fe and Zn was higher bounded to kaolin than Mn and Sr. Correlation coefficient (R²) ,obtained from Langmuir isotherms, were positive
Table 4: Langmuir parameters for the adsorption of heavy metal on kaolin

Ions	Adsorption maximum a (mg/kg)	Binding energy b (mg/kg)	R^2 for Langmuir equation
Mn Fe Zn Sr	2.62 1666 1000 90.9	0.557 1.007 1.006 1.003	0.224 0.999 0.999 0.999

and highly significant. Other study (Wang et al, 1998) on the heavy metals binding and removal by Phormidium sp biomass reported the highly maximum adsorption, calculated from Langmuir isotherm, was for Pb (13,600 mg/kg) and Cu (10,100 mg/kg), while it was nearly the same for Cd (9,600 mg/kg) and Zn (9,400 mg/kg ).
Wastewater treatment using kaolin. After concluded the suitable conditions for the adsorption of heavy metals Fe, Cd, Cr, Co, Cu, Sr, Mn and Pb on kaolin using standard solution, Kima drain wastewater was applied for the removal of heavy metals using kaolin. Treatment with kaolin ore size <63 µm exhibited the high efficiency for the complete removal of heavy metals. The adsorption per cent (Table 5) was 100% for Cd, Cu, Cr, Mn and Pb. Kaolin reduce the concentration of Fe, Sr and Zn (adsorption per cent 92%, 94 % and 88 % respectively). Kaolin treatment method was very effective for the removal of heavy metals Fe, Cd, Cr, Co, Cu, Sr, Mn and Pb than aeration and alum methods (Table 5). Various low cost adsorbents reported to be effective for the removal of heavy metals from wastewater,

Fe(III)hydroxide was used for the removal of Cr ,Ni ,Cu , Cd and Zn from electroplating wastewater (Ajmal et al,1992).

The results of the wastewater treatment processes (Table 5) were in the limits cited by Egyptian Authority for discharge into surface water or reuse for irrigation.
Table 5: Heavy metals levels (ppb) in Alum treatment samples and Egyptian standard.

Sample	Fe Cd Cu Cr Sr Mn Pb Zn
Original sample Alum treatment Kaolin treatment Egyptian Standard*	430 30 22 32 150 40 32 80 30 0.0 0.0 0.0 10 0.0 0.0 10 1 0.0 0.0 0.0 0.80 0.0 0.0 0.9 1000 ppb

*Egyptian limits for treated wastewater discharge to surface water ,law 48 of the year 1982 for the protection of the river Nile.

CONCLUSION

Continuous treatment processes, aeration, addition of alum and adsorption at kaolin surface, were developed for removal of nutrients and heavy metals. Aeration and alum processes were effective for the removal or reduce of nutrients, while kaolin process was very effective for removal of Cd, Cu, Cr , Mn and Pb and reduced the concentrations of Fe , Sr and Zn. The results of the wastewater treatment processes were in the limits cited by Egyptian Authority for discharge into surface water or reuse for irrigation.

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