phosphorus removal by activated alumina

Environmental Pollution (Series B) 2 (1981 ) 327-343

PHOSPHORUS REMOVAL BY ACTIVATED ALUMINA

NAVA NARKIS

Environmental and Water Resources Engineering, Technion, Israel

&

MORDEHAI MEIRI

Institute of Technology, Technion City, Haifa, Israel

ABSTRACT

Activated alumina effectively removed orthophosphates from effluent of biological sewage treatment plant and from synthetic aqueous solutions in continuous flow and batch systems. Acidic and basic treatment of the activated alumina significantly improved the sorption capacity for phosphorus removal. The sorption capacity o f an activated alumina columnar packed bed was found to be 30mg P04 3 per gram alumina, up to the breakthrough of 1000 bed volumes. Langmuir adsorption isotherms from biological treatment effluent showed that AIcoa F-1 acidic and basic activated alumina have a very high orthophosphate adsorption capacity of 179 meq PO £ 3/100 g alumina.

The mechanism of orthophosphate removal on activated alumina is mainly ion exchange accompanied by chemical reactions, precipitation and formation of complexes.

INTRODUCTION

It is now recognised that discharge of incompletely treated wastewater, containing algal nutrients, will hasten the natural processes of eutrophication or ageing of lakes and other water bodies (US Environmental Protection Agency, 1976; Wuhrman, 1968). Phosphorus compounds are considered inter alia as essential elements, responsible for excess fertilisation of surface waters which can be prevented by limiting the concentration of phosphorus in receiving waters. Physico-chemical treatment processes of precipitation with lime or flocculation with aluminium or iron salts are most commonly used for removal of phosphorus compounds from raw

327 Environ. Pollut. Set. B. 0143-148X/81/0002-0327/$02.50 ~ Applied Science Publishers Ltd, England, 1981 Printed in Great Britain

328 NAVA NARKIS, MORDEHAI MEIRI

sewage or sewage treatment plant effluents (Nesbitt, 1973; Narkis et al., 1975). The main disadvantages of chemical precipitation and flocculation are the high sensitivity to pH of operation and chemical characteristics of the wastewater, the increase of electrolyte concentration in effluent, and the need for ultimate disposal of sludge. The sludge produced requires further treatment and handling such as thickening, dewatering, filtration and incineration. When recycling of chemicals is attempted complicated treatment facilities must be added, including addition of chemicals, pH adjustment and skilled separation techniques, and even then recovery of chemicals is not satisfactory.

The strong phosphorus fixation by mineral clays in soils (Muljadi et al., 1966; Kafkafi et al., 1967; Kafkafi, 1968) suggested using alumina for phosphorus removal from synthetic aqueous solutions (Yee, 1966; Neufeld & Rhodos, 1969; Ames & Dean, 1970; Chen et al., 1973a,b; US Environmental Protection Agency, 1976). Ames & Dean (1970) showed that increasing the surface area of the alumina increased phosphorus capacity and over-shadowed any effects due to differences in crystalline structure of the alumina. Activated aluminas are obtained from various hydrated forms by controlled heating to eliminate most of the water of hydration (Papee & Tertian, 1970). The activated aluminas are very widely used in adsorption, where their properties of large surface area and very fine pores play an important part.

Activated alumina is a phosphorus-selective adsorbent which can be used in continuous flow in columns and can be regenerated easily.

The aim of this research was the investigation of activated alumina for removal of phosphorus from sewage treatment plant effluents and from synthetic aqueous solutions.

EXPERIMENTAL PROCEDURES

Analysis of various phosphorus compounds in biological treatment effluents showed that 99.4 ~o of the totalphosphorus is soluble, of which 98 ~o is present as inorganic orthophosphates. Actually there are a number of forms of orthophosphates in equilibrium with the predominant form changing as pH changes. At the usual pH of municipal wastewater the predominant form is HPO 4 2. Since the main fraction of the phosphorus in effluents is present as orthophosphates, it was decided to study the removal of the inorganic orthophosphates by activated alumina, from aqueous solutions and from effluents of biological treatment plants. All results are expressed as pO~3 without regard to the actual form present.

Synthetic aqueous solutions of orthophosphates were prepared in distilled water, in the range of concentration 25 to 40 mg/litre PO~ 3, typical for sewage treatment plant effluents. The effect of Ca + ÷ and Mg ÷ ÷ ions on phosphorus removal was studied in aqueous solutions containing a total of 10 meq/litre CaCI 2 or MgC12.

PHOSPHORUS REMOVAL BY ACTIVATED ALUMINA 329

Effluents from an extended aeration sewage treatment plant, located at the Technion Neve Shaanan, were used. Total hardness in effluent was 510mg/litre as CaCO 3 of which there were 6-2 meq/litre Ca ++ and 4meq/li tre Mg ++

Activated alumina Activated aluminas manufactured by Merck and Alcoa were used. Merck 90." Commercially prepared acidic, basic and neutral activated aluminas

were used as received, with grain size of 100 325 mesh, specific surface area of 100 to 130 m2/g and pore diameter of 90 A.

Alcoa F-I: Neutral activated alumina with grain size of 28~48 mesh, specific surface area 210 m 2/g and pore diameter of 45 A. The neutral activated alumina was treated to become an acidic or basic form in a column, with a flow rate of 5 bed volumes (BV) per hour. Ten BV of2N N a O H solution, followed by 50 BV of distilled water were passed through to prepare the basic activated alumina. The pH of the column effluent at the end of the washing was 8.5. The column was drained off and the basic activated alumina was dried in an oven, at 120°C for 24h.

Acidic activated alumina was prepared by passing through 10 BV of 1N N a O H solution, followed by 50 BV of distilled water, and then 10 BV of 1S H N 0 3 followed by 50 BV of distilled water. The pH at the end of washing was 6.5. The acidic activated alumina was also dried in an oven, as above.

Adsorption experiments Removal of phosphorus by activated alumina was studied in batch and in

continuous flow through columnar packed bed reactors. The batch experiments were carried out in 500 ml samples, shaken for 24 or 48 h at 25 _+ 1 °C. At the end of the experiment the supernatant was filtered. In the preliminary experiments pH was adjusted at the beginning and measured at the end. Since pH changes were observed special care was taken to achieve the desired pH, by adjusting that of the activated alumina suspension an hour before the orthophosphates were added. Ten minutes after addition of phosphates the pH was readjusted and again after 24 h, when the adsorption studies continued for 48 h.

The biological treatment effluents were filtered through Whatman GF-A filter paper. The down flow adsorption studies were carried out in two glass columns 2.0cm in diameter and 64cm high, filled with 200ml (194g) of acidic or basic activated alumina. The flow rate was maintained at 5 BV/h and at a frontal velocity of 3.2m/h. Orthophosphates were determined as a phosphomolybdate complex (Ramanthan, 1968; Sheiner, 1974).

RESULTS

The main purpose of this research was to study the possibility of phosphorus removal from effluents using activated aluminas, manufactured by Merck and


Alcoa. The neutral activated alumina was changed to acidic and basic forms, and a comparison among the various forms was carried out in batch and in continuous systems.

Batch experiments Effect of time: Figure 1 shows the rate of orthophosphates removal from extended

aeration biological treatment effluents, containing 36.4mg/litre POg a, using 1.5 g/litre of Merck acidic activated alumina. The pH was held constant at 5.7 and the temperature was 26°C. Equilibrium was reached after 6.5 h. All experiments were carried out for 24 or 48 h, ensuring complete equilibrium.

Fig. 1.

2 o

10

Oo 2 0 0 ,400 d O 0

~ u e - m Z v . u / ¢ 5

Rate of orthophosphate removal from extended aeration effluent by Merck's acidic activated alumina. Initial concentration, 36.4 mg/litre PO2 3.

Effect of pH: Orthophosphates removal capacity by activated alumina was studied under various pH conditions. Figure 2 shows the effect of pH on orthophosphate removal from distilled water solutions using 2 g/litre acidic and basic Merck activated alumina.

The ratio (C O - C)/W represents the amount of PO 2 3, in milligrams, removed by a unit mass, in grams, of activated alumina. C O and C are the initial and final PO2 3 concentrations in mg/litre and W is the activated alumina concentration in g/litre.

Maximum phosphate removal capacity from distilled water solution was at pH range of 4-5 in both acidic and basic activated aluminas. The acidic activated

Fig. 2.

2O

10

0 0

9

2. 4 6 8 f o 12.

Fina~ p H Effect o fpH on orthopbosphate removal from distilled water solution by acidic and basic Merck activated alumina. Temperature, 24°C and initial concentration, 37 mg/litre PO 23.

Fig. 3.

7

3 0

ZO

10

%

o.--.,,-,__._._______

/

7 B 9 1o ~ pN

Effect of pH on orthophosphate removal from biologicaJ sewage treatment effluent by Merck acidic, basic and neutral activated alumina. Initial concentration, 34.4mg/litre POg 3.


alumina showed somewhat higher removal capacities and a wider range of pH for an effective reaction.

Figure 3 presents the effect of pH on the orthophosphate removal capacity from biological sewage treatment plant effluent. Although the initial pH was adjusted to the pH range 4.5 to 9.5, the pH changed during the experiment; and since the values were not readjusted the results are shown in terms of the final pH, which covers a narrower range, from 6.4 to 9.2. Acidic Merck activated alumina showed a better removal capacity than the basic alumina. The neutral alumina had the lowest removal capacity. In the alkaline range the phosphate removal capacity from effluent increased sharply, and was equal for all types of activated aluminas examined. At pH 9 Ca + + and Mg + + ions present in effluent are responsible for the precipitation of calcium hydroxyapatite, and formation of phosphate salts and complexes of Ca ÷ + and Mg + +, overcoming the differences among the various types of aluminas.

The efficiency of removal from a solution of 29.3mg/litre PO~ -3 by 1-0g/litre alumina was studied in distilled water solutions, in a pH range from 6.0 to 8.0, typical for effluents. Figure 4 shows that at this narrow pH range no significant

30

Fig. 4.

2O

tO

0 5

®

-~'3,o o

6 7 8

Orthophosphate removal from distilled water solution at pH range of 6 to 8 by acidic, basic and neutral Merck activated alumina. Initial concentration, 29.3 mg/litre PO23.


difference was observed between acidic and basic treated activated alumina, while the neutral alumina was markedly less efficient.

The effect of Ca ÷÷ and Mg ÷÷ ions on phosphorus removal was studied by addition of 10 meq/litre CaC12 or MgCI 2 to a phosphate solution containing 26 to 32.6 mg/litre PO47 a. Figure 5 shows the orthophosphate removal capacity in the presence and absence of Ca ÷ ÷ and Mg ÷ ÷. The correlation coefficient, r, of the

Ken zo

:Po

"-... ,

6.o 7 . 0 8 . 0

• " ( n ~ t pH Fig. 5. Effect of Ca + + and Mg + + ions on orthophosphate removal from distilled water solution by Merck acidic activated alumina. C), 5 meq/litre Ca + + + 5 meq/litre Mg + ÷ ; Q, 10meq/litre Ca+ ÷ ; ~),

l0 meq/litre Mg ÷ *; ®, distilled water.

straight lines at pH range 6.0 to 8.0 is also given. At pH 8.0 the orthophosphate removal capacity of Merck acidic activated alumina was 13.4 mg PO£ 3 per gram from distilled water solution, increasing to 26 mg PO 4 a per gram in the presence of 10 meq/litre CaC12 or 5 meq/litre CaC12 plus 5 meq/litre MgC12, and to 21 mg PO 4 3 per gram in the presence of 10meq/litre MgC12. The effect of Ca ÷÷ was more pronounced than that of Mg *÷. Thus, Ca ÷÷ and Mg *÷ present in sewage treatment plant effluent play an important role in increasing alumina capacity for phosphate removal at pH 8-0, typical for effluents.

?

k~ I

Fig. 6.

/

B a S i c *

0 10 2 0 .30

C ~P04 ~ ?

Adsorption isotherms of Merck activated alumina (100 + 325 mesh) from biological treatment effluents. Initial concentration, 34.0mg/litre PO,~ 3.

Fig. 7.

. / /

10 2o

C ~ PO~ "~ 1

Adsorption isotherms of Alcoa F-1 activated alumina (28 + 48 mesh) from biological treatment effluents. Initial concentration, 24.4 mg/litre PO~ ~.


Fig. 8.

Z5

1 - O

0.5

J ~ bg, P

10 2 0 J O

c rngP~/ /

Linear form of Langmuir adsorption isotherms for Merck activated aluminas from biological treatment effluents. Initial concentration, 34-0meq/litre PO4 3.

0.50

o.25

Fig. 9.

f

0 0 5 to 15

C ~ Po4 -~ /

Linear form of Langmuir adsorption isotherm for Alcoa F-1 activated a |umina from biological t reatment effluents.

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Adsorption isotherms The adsorption isotherms of Merck and Alcoa F-1 activated aluminas for

orthophosphate adsorption from extended aeration effluents were studied and are shown in Figs 6 and 7. Their Langmuir linear forms are shown in Figs 8 and 9.

Table 1 summarises the Langmuir and Freundlich adsorption isotherms coefficients of Merck and Alcoa F-I, variously treated, activated aluminas from effluents. Ky and 1/n are Freundlich isotherm constants, Qmax is the maximum amount of orthophosphate adsorbed per unit weight of adsorbent in forming a complete monolayer on the surface and b is a constant related to the energy of adsorption.

Amongst the Merck activated aluminas the maximum amount of phosphates adsorbed is the highest with acid treated alumina (37mgPO~-3/galumina), followed by basic alumina (28.3 mg po£3/ga lumina) and neutral alumina is the lowest with 23.8 mg POg 3/g alumina. In the Alcoa F-1 activated alumina, the acidic and basic treated forms show almost the same maximum amount of phosphates adsorbed: 57.2 mg PO 4 3/g alumina and 57.5 mg PO~-3/g alumina. The acidic and basic Alcoa F-1 activated aluminas have higher sorption capacities of orthophosphates than the Merck activated alumina.

Continuous flow Orthophosphate removal from biological treatment effluent was examined in a

down flow packed bed of Alcoa F-1 acidic and basic activated aluminas. The breakthrough curves are shown in Fig. 10. The average concentration of

O.5

/ 5 0 0 1000 1500

B e d u,olumea Breakthrough curves for Alcoa F- 1 acidic and basic activated alumina oforthophosphate from

biological treatment effluents.

o o

Fig. 10.


orthophosphates in the feed to column was 30mg/litre pO~3. Both aluminas adsorbed most of the phosphates with a residual less than 1-0 mg/litre PO 4 3 up to around 1000 bed volumes (BV). Breakthrough of the basic treated activated alumina occurred after 970 BV (194 h) and of the acidic activated alumina after 1005 BV (201 h). Integration of the breakthrough sorption curves, up to the appearance of phosphate concentration higher than 1.0 mg/litre PO 2 3 (C/C ° = 0-033) gives 5-9 g PO£ 3 adsorbed on the basic activated alumina, and 6.9 g PO~ 3 up to saturation (1400BV), which means 85~o column efficiency. The acidic activated alumina adsorbed 5-9 g PO2 3 up to the breakthrough and 7-1 g PO 4 3 up to saturation (1500BV), which means 83-5 ~o column efficiency. No significant difference was observed between acidic and basic activated alumina in terms of removal efficiencies and sorption capacities.

pH changes were observed during the first hours of operation. In the effluent from the basic treated activated alumina the pH was 9.8 during the first 5 h of running, then it decreased sharply to 8.3 and remained stable at 8-0. In the acid treated activated alumina column effluent the pH was 4.2, increased to 5.6 after running 250 BV and stayed stable at 7.5 after running 285 BV, up to the breakthrough at which the pH was 8-0, the same as that of the influent.

DISCUSSION

Activated alumina was examined as a phosphorus selective adsorbent for the removal of orthophosphates from aqueous solutions and effluents of biological treatment of domestic sewage.

The use of conventional ion exchange resins for phosphorus removal from effluents would not be practical for the removal of phosphates alone, because of the extensive removal of nearly all other anions, which reduces the efficiency and capacity of the resins to remove phosphates (Ames & Dean, 1970; Nesbitt, 1973).

The activated aluminas examined were treated to form acidic, basic and neutral types and their orthophosphate removal capacities were studied, in batch and in continuous flow systems. No significant difference was observed between acidic and basic activated aluminas, although the acidic was somewhat better; the neutral activated alumina was always less efficient. The breakthrough curves of orthophosphate sorption from biological treatment effluent in columnar beds of Alcoa F-I activated alumina showed that the appearance of more than 1.0 mg/litre p o 2 3 in column effluent occurred at 1000 BV, which is consistent with the results reported by Yee (1966), for synthetic orthophosphate solutions. The adsorption capacity up to the breakthrough was 30.4 mg PO 2 3/g alumina for Alcoa F- 1 acidic and basic activated aluminas. Up to column saturation the adsorption capacity of the basic activated alumina was 35.5 mg PO 2 3/g alumina and for the acidic form

P H O S P H O R U S REMOVAL BY ACTIVATED A L U M I N A 339

36.6mgPO~3/galumina. Alcoa F-1 activated alumina proved to have higher sorption capacities than that of Merck. Even though the Alcoa F-1 has a bigger particle size, it has higher specific surface area (210mZ/g), which increases the available sorption sites.

Langmuir and Freundlich adsorption isotherms coefficients from effluents measured in batch experiments (Table 1) show that the basic and acidic pre- treatment has an important role. It increases the active sites for sorption and improves the selective phosphate removal by activated alumina.

Mechan&m of orthophosphate removal Previous investigations (Muljadi et al., 1966; Ames & Dean, 1970; Chen et al.,

1973a,b) on adsorption by alumina and mineral clays have considered that phosphorus adsorption consists of both ion exchange and chemical reaction. At around pH 8-0 of biological treatment effluent, the adsorption is mainly by a mechanism of ion exchange, while other factors such as crystallisation and formation of complexes with polyvalent cations, such as A13 +, Ca + + and Mg + +, also have an effect. The pH affects the importance of the secondary reactions in addition to ion exchange.

The structure of alumina is of aluminium atoms co-ordinated with six oxygen atoms or hydroxyl groups, which are located around the aluminium atom (Van Olphen, 1963), with their centres on the six corners of a regular octahedron. The sharing of oxygen atoms by neighbouring octahedrons results in a sheet in which the oxygen atoms and hydroxyl groups lie in two parallel planes with aluminium atoms between these planes. At the edges of the plates the octahedral alumina sheets are disrupted and primary bonds are broken. On such surfaces an electric double layer is created by the adsorption of potential determining ions. The surface of an alumina particle carries a positive double layer in acid solution, with A13 + ions acting as potential determining ions, and a negative double layer in alkaline solution with hydroxyl ions acting as potential determining ions. The positive double layer may become more positive with decreasing pH and its sign may be reversed with increasing pH.

The isoelectric point is known to vary with the crystal structure of the alumina particle.

The positive edge double layer is responsible for the adsorption of anions acting as counter ions. The acidic and basic activated aluminas examined in this research proved to have a very high anion adsorption capacity, in comparison with cation exchange capacities of mineral clays. 179 meq PO,~ 3/100 g alumina were adsorbed on acidic and basic Alcoa F-1 activated alumina, from biological treatment effluents, while Merck acidic activated alumina adsorbed l 1 5 m e q P O 4 3 / 100 g alumina, and the basic form adsorbed 87meqPO43/100galumina cor- responding to a very high anion adsorption capacity.

Van Olphen (1963) has suggested several reasons why the anions are specifically

340 NAVA NARK1S, MORDEHAI MEIRI

adsorbed at the edges of the clay plates or of the alumina. In the first place, the anions would be attracted by the positive edge surface, and must be adsorbed in excess. Phosphates appear to have a specific reactivity with aluminium with which they form either complex anions or insoluble salts. Hence, these anions will be chemisorbed at the edges by reacting with the exposed aluminium. Chen et al.

(1973a) showed that, in the acid region, the driving force for the establishment of aluminium phosphate bonds is quite large and its extent depends on the concentration of the solutions and the periods of time for adsorption; they also showed that chemical precipitation formed a monolayer of aluminium phosphate on the surface of ~-alumina or kaolinite particles, in relatively concentrated solutions over long periods of time, and surface adsorption occurred at low concentrations on a short time scale.

According to Van Olphen (1963) when an insoluble neutral alumina salt is the reaction product it seems likely that the additional anions will be preferentially adsorbed on the aluminium salt, which is attached to the edge surface.

The form of orthophosphate anions reacting with the positive edges depends upon the form predominating in solution at the pH of adsorption. Figure 2 shows the adsorption capacity of orthophosphates from distilled water solution at various pH levels. Maximum adsorption capacity was obtained between pH values of 4.5 and 5-0 which corresponds with the isoelectric point of basic aluminium phosphate (Chen et al., 1973a). The adsorption capacity decreased at lower pH. The affinity of the H2PO £ species for aluminium on the surface, although large, is less than the affinity of H2PO 4- for protons (Chen et al., 1973a).

The lower adsorption capacities at the alkaline range can be explained by increased repulsive forces between the negatively charged alumina and HPO~ -2 anions. As the alkaline pH increases the repulsive force increases too, due to the formation of the more negatively charged trivalent anion, POZ 3.

The behaviour of the sorption capacities of phosphate was different in the alkaline range in effluents and in the presence of Ca + + and Mg + + ions (Fig. 5). At pH range 6-0 to 8.0 the presence of Ca ++ and Mg ++ cations improved the phosphates sorption capacity as a result of an electrical double layer compression, which lowered the potential repulsive energies. At pH higher than 8.5 (Fig. 3) phosphorus removal is increased due to the precipitation of calcium hydroxyapatite, Cas(PO4)3OH, and magnesium phosphate salts. At least part of the phosphorus is bonded to the alumina surface by a complex involving Ca + + and Mg + + (Ames & Dean, 1970).

At pH 8.0 (Figs 3 and 5), in the presence of 10 meq/litre Ca + + or Ca + + + Mg + + orthophosphates, sorption capacities of acidic Merck activated alumina, from distilled water solutions and from biological treatment effluents were similar, although it might be expected that the presence of dissolved soluble organics, measured as COD and TOC, could interfere with phosphates adsorption. Chen et al. (1973a) showed that anions of chelating agents strongly reduced the sorption


capacity of alumina at a pH of 4-0, with a less pronounced effect at pH 8.0. This investigation has shown that at pH 8.0, typical for effluents, the negatively charged soluble organic anions present in the effluents do not affect the capability of activated alumina to remove phosphates from effluents.

Regeneration and environmental protection After the phosphate-removing capacity of the activated alumina has been

exhausted it can be regenerated with a solution of sodium hydroxide, followed by washing with distilled water and neutralisation of the excess alkali with an acid solution of nitric acid (Ames & Dean, 1970). The results of the research reported here have shown no significant difference in phosphate removal capacities between acidic and basic treated activated aluminas. Thus the acid rinse is not essential from the economic and ecological points of view.

If nitric acid is used for regeneration, instead of protecting the environment against eutrophication, nitrogenous compounds will increase the burden of nutrients. Ames & Dean (1970) recommended basic elutions, because they are more efficient and do not reduce the later step of phosphorus reloading, and they reduce alumina losses.

Kubli (1947) found the anion alumina adsorption series in order of decreasing preference to be: OH , PO4 3, C2042, F- , SO~, SO2 z, CrO4 -2, NO~-, CI-, NO 3 and MnO 4.

Kubli's series explains why sodium hydroxide is a good regenerant. Hydroxyl anions displace orthophosphate anions and convert the alumina to the hydroxide form. It should be remembered that Kubli's series was found for the specific conditions prevailing in his systems, and it may be different for other systems.

From the theory of ion exchanges (Weber, 1972) it is known that the selectivity of certain ions is dependent upon concentration of the solution phase. The preference for counter ions of highest charge increases with dilution of the external solution. Thus, for a dilute solution of HPO2 z, as in the biological treatment effluents, the uptake of phosphates by activated alumina is very efficient. Conversely, for regeneration of cation exchangers in water softening with a very concentrated sodium salt solution, the elution of the Ca ++ ions is readily accomplished. A relatively concentrated sodium hydroxide solution is used to elute the orthophosphate anions, and so regenerate the exhausted alumina.

Kubli's series also suggests an explanation of why the NO~ acidic form of the activated alumina is somewhat more efficient than the OH- form for the removal of HPO2 z. The NO 3 acidic alumina is formed by the addition of relatively concentrated nitric acid solution to a well washed hydroxide-activated alumina, so that anion exchange occurs between NO~ ions in solution and OH- ions attached to the fixed, basic, activated alumina matrix. The NO 3 anions are furthermore, readily exchanged by orthophosphate anions, present in a relatively very dilute phosphate solution, as the biological treatment effluent.

342 NAVA NARK1S, MORDEHAI MEIRI

ADVANTAGES AND CONCLUSIONS

Acidic and basic activated a luminas effectively remove or thophosphates f rom

biological t rea tment plant effluent and synthetic aqueous solutions at pH 8.0, as is typical for effluent. It neither adds salts to the treated water, nor produces a nuisance

of sludge handl ing and t rea tment before ul t imate disposal. The activated a lumina can be easily regenerated with sodium hydroxide solution. The spent regenerant solut ion can be treated for re-use of sodium hydroxide (Ames & Dean, 1970), or can be evaporated to a small volume of solid wastes. This process is applicable to phosphorus removal f rom waste t rea tment effluent and clear wastewaters con ta in ing or thophosphates and polyphosphates ( P u r u s h o t h a m a n & Yue, 1970), with an efficiency higher than that obta inable by chemical precipi tat ion or flocculation. A co lumnar activated a lumina packed bed adsorpt ion can be used for polishing the removal of residual phosphorus remain ing after chemical t reatment , and from clear drainage water f rom agricul tural soils, for the protect ion of surface waters f rom eutrophicat ion.

ACKNOWLEDGEMENT

This research is partially based on the MSc thesis of M. Meiri.

REFERENCES

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CHEN, Y. R., BUTLER, J. N. 8¢. STUMM, W. (1973a). Adsorption of phosphate on alumina and kaolinite from dilute aqueous solutions. J. Colloid and Interface Sci., 43, 421 36.

CHEN, Y. R., BUTLER, J. N. & STUMM, W. (1973b). Kinetic study of phosphate reaction with aluminium oxide and kaolinite. Environ. Sci. & Technol., 7, 327-32.

KAFKAFI, U. (1968). Hydrogen consumption and silica release during initial stages of phosphate adsorption on kaolinite at a constant pH. Israel J. Chem., 6, Mokady Memorial Issue, 367 73.

KAFKAFI, U., POSNER, A. M. • QUIRK, J. P. (1967). Desorption of phosphate from kaolinite. Proc. Soil Sci. Soc. Am., 31,348-53.

KUBLI, H. (1947). Zur Kenntnis von Anionentrennungen mittels Adsorption an Tonerde. Heir. Chim. Acta., 3, 453-63.

MULJADI,[ D., POSNER, A. M. & QUIRK, J. P. (1966). The mechanism of phosphate adsorption by kaolinite gibsite and pseudobohemite, Part I: The isotherms and effect of pH on adsorption. J. Soil Sci., 17, 212-47.

NARKIS, N., REBHUN, M. &. OFFER, R. (1975). Ferric chloride or lime for chemical treatment. War. Sewage Wks, 122, 43-5.

NESBITT, J. B. (1973). Phosphorus in wastewater treatment. In Environmentalphosphorous handbook, ed. by E.J. Griflith, A. Beeton, J. M. Spencer and D.T. Mitchell, 649-68. New York, John Wiley.

NEUFELD, R. D. ~/. RnODOS, G. (1969). Removal of orthophosphates from aqueous solutions with activated alumina. Environ. Sci. & Technol., 3, 661-7.

PAPEE, D. & TERTIAN, R. (1970). Aluminium oxide (alumina). In Kirck Othmer Encyclopedia of Chemical Technology, ed. by H. F. Mark, J.J. McKetta and D. F. Othmer, 41-58, New York, John Wiley.


PURUSHOTHAMAN, K. & YUE, C. M. (1970). Removal o f phosphates by adsorption on activated alumina. Missouri Water Resources Research Center PB 196 872, Dec., 1 79.

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phosphorus removal by activated alumina

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