Selective renovation of eutrophic wastes—phosphate removal

s

SELECTIVE RENOVATION OF EUTROPHIC WASTES PHOSPHATE REMOVAL G. BoAal and L. LIBERTI IRSA-CNR, Via F, De Blasio Zona Industriale 70t23, Bari, Italy and R. PAssrxo IRSA-CNR, Via Reno, 1 00198 Rome, Italy (Receire d 29 July 19751

Al~tract--This is the first part of a basic investigation concerning the multicomponent chloride:sull:ate/ phosphate/nitrate equilibrium on anion resins. The study is to throw more light on the fundamentals of poly-anions, heterovalent equilibria on anion resins, and to develop a selective process to remove eutrophic species from sewage effluents. In this paper the chloride/phosphate equilibrium is described for a large selection of different anion resins and the selectivity dependence on several external (i.e. solution pH, concentration and compositiont or internal (i.e. resin basieity, porosity, matrix etc.) parameters evaluated. Large quantities of industrial cooling waters containing 5-10 ppm of phosphates (and/or chromates), used as corrosion inhibitors, are discharged daily. Appreciable amounts of inorganic forms of nitrogen and phosphorus are still present in conventionally treated domestic wastewaters. Both nitrogen and phosphorus compounds are commonly acknowledged as potential nutrients for algal growth in the receiving streams (Blomquist et al. 1971). On the other hand, the elimination of phosphates in detergent formulation would be an insufficient, though desirable decision, since human activity had been reported to be responsible for about 70% of their presence in domestic effluents in Italy (Bini, 1972) while severe eutrophication problems exist in low detergent consuming areas as Bangalore, India (Grinath and Pitlai, 1972). The need for post-treatments in order to reduce the eutrophic potentiality of domestic and industrial effluents thus becomes evident. Ion exchange has been repeatedly indicated in recent years as a challenging method to abate nutrient pollution. Full demineralization by conventional ion exchange has been proposed among others by Grantham and Robertson (1970); Midkiff and Weber (1969); Linstedt, Honek and O'Connor (1971); Jorgensen (1972) but the high cost makes such a process unattractive unless a high value could be attributed to the reclaimed water. Pilot plant experiments have been reported by Eliassen and Bennett (1967) and by Gregory and Dhond (1972a), who used strong anion resins in chloride cycle to remove nutrient components from secondary treated domestic effluents. Due to the poor selectivity of such resins and to the adverse influence of chlorides and sulfates on phosphate uptake, excessive regenerant levels and resin 421

consumptions were reported. Liquid ion exchange applications on a laboratory scale have been described by Ditsch, Swanson and Milum (1970). Softer, Lowell and Loran (1970) described a process based on the use of a strong cation resin in Fe form, regenerated by FeC13, to which lime was added to recover Fe and P. A somewhat similar process was proposed by Prober and Doughtery (1973). who used a strong anion resin in hydroxide form, supported by hydrous ferric oxide. A problem common to all these processes is the excessive cost with conventional ion exchangers or when special products are employed. In the first case, as long as phosphates have to be selectively removed by strong anion resins or by weak anion resins in full demineralization cycles, regeneration costs per equivalent of phosphate removed are unacceptable. Moreover, special ex(zhangers have too high a cost to be reasonably applied unless a wider market is developed for such products. Obviously, a possible use of the recovered phosphates as fertilizers could eventually pay, at least partially, for the removal process, as indicated, for instance, by Hummel and Smith (t970) and by Jorgensen (1973). On the other hand, the existence of very few data on the exchange equilibria of trophic components on anion resins has recently been pointed out by George and Zajicek (19681 and Gregory and Dhond (1972b) who made basic investigations into the chloride/phosphate equilibria on strong anion resins. It thus seemed useful to initiate a systematic study on the chloride/sulfate/phosphate/nitrate multicomponent system on different anion resins, with the dual aim of collecting more basic data about this system and to find experimental conditions where conventional ion exchangers, other than strong anion resins, could be economically used for selective renovation

""

G. BO;,RL L. LIBERTI and R P.~551.',o

of eutrophic wastes. In a previous work the chloride/ sulfate equilibria under different experimental conditions have been de~'ribed (Boari et el.. 1974a1. This paper refers to the bina~' chloride/pho~hate exchange in equilibrium conditions when different types of anion resins are used. In addition to the influence of several resin parameters (basicity. matrix, alkylation, etc.), the selectivity determinations have been referred to different solution conditions (,concentration, composition a n d pHI.

into chloride or phosphate form. using He1 or H3PO, at the same concentration and pH as the equilibrating solution, in order to make equilibrium approach independent of the initial form of the resin. A large excess of a known mixed chloride phosphate

EXPERIMENTAL Equilibrium determinations have been conducted at 1.0 × I0 -3 and 6'0 × 10 -3 st total solution concentration, with pH ranging from about 2.2-11-0, at room tempera-

for 2 weeks, with intermittent shaking, in 0-5 1, #ass stoppered Erlenmayer flasks containing 0-5 l. of 6 x I0-3M

solution was then passed through the resins until no difference between influent and effluent was detected. One more day's percolation was allowed tbr equilibrium. The c o l u m n s were drained under vacuum and the resins eluted v, ith 1 1. of warm 1 y N a O H solution. In some cases a batch procedure was also used. Al'~ut 0.5_e° of dr;. resin, previously, converted in chloride or phosphate form in the usual way, were allowed to stand

solution of known composition. The analysis of the super-

tltre.

The equilibrating solution was prepared by' mixing hydrochloric and phosphoric acids in known proportions.

diluting it to the required concentration and neutralizing with NaOH to the desired pH. The column procedure was preferably adopted, using a multicolumn apparatus which allows about 100 resins to be simultaneously operated under different conditions. Two samples (usually 1 g of dry resin each) for each resin, 20/30 U.S. mesh, were loaded in small jacketed glass columns. In each test the samples were initially converted

natant at equilibrium permitted the necessary equilibrium data to be easil? calculated by simple mass balance considerations, Moreover the resins were transferred to the columns and regenerated with sodium hydroxide in order to confirm the batch equilibrium data. Usually, a close a g e e m e n t was found between column and batch results,

with the latter being disregarded when the discrepancy was greater than lO°;. Though the phosphate average charge at different pH could be worked out from the dissociation constants of

phosphoric acid or. more accurately, by column dynamic balances, as described by George and Zajicek (t968), an

Table 1. Main physico-chemical properties of the investigated resins Resin

Matrix

Functional groups Porosity (,amlno-type)

Lewatit M 500 Lewatlt MP 500 Relite 3AS O u o l i t e SBR-P Wofatit SBW Amberlite IRA-400 Kaste! A 500 Kastel A 500 P Kastel A 510 Kaste[ A ~OL 0 O u o l i t e A 161 Asmit 259 N Lewatlt M 600 ~e[ite 3 AZ ~eilte 2 A ~ e t l t e 2 AS (astel A 300 (aste{ A 300 P lOuollte A 162 !Duolite ES 3 6 0 3 ) u o l l t e A 303 Duollte A 305 ) u o l i t e A 30~ Lewatlt MP 60 ~ e l i t e 4 MS ~mberlite IRA 93 (astel A 101 Lewetit Ca 9222 !Amberllte IRA 6S Kastel A 105 Ouollte A 6 )uollte A 7 iOuolite S 37 ~mbePIite IRA 47 ) u o l i t e A 308 (astel A IO0 I R e l l t e MS 170 !Dowex WGR ~ofetlt AK 40 Kaste[ A I02 R e l i t e NG I 3 u o l i t e A 366 tOuolite ES 3601 iOuolite ES 3602 O u o l i t e ES 3605 Kastel A 103/1 O u o l l t e S 2002 O u o l i t e A 57 Imac A 27 Amberlite IR 45

Styrenic Styrertic Styrenlc Styrenlc Styrenlc Styren~c Styrenic Styrenlc Styrenic Styrenlc Styrenic Styrenic Styrenic Styrenic Styrenlc S~yrenic Styrenlc Styrenic Styrenlc Acryllc Styren;c Styrenic Styrenlc Styrenic Styrenlc Styrenlc Styrenic Acrylic Acrylic Acrylic Phenolic Phenolic Phenolic Epoxy

|V dry (Lype [)

Styrenic

(&30~ [ I ~ y (&t0~ I I ~ y (& I I ary ) " (& II a r y ) I I aey (& I a r y ) m

Epoxy Styrenlcl Epoxy Styren;c Acrylic Acrylic Acrylic Acrylic Acrylic Styrenlc Styrenlc Styrenic Epoxy Epoxy Styrenlc

u

~

C,-o~l i n k l n 9 degree (~ DVB)

~el Macro Porous

"

po,.-ous

(6)

Gel "

Gel

(type { I )

Gel Porous Porous Porous Macro Porous Cel

7 5 4.5 7

Porou~

16

Gel Porous Gel

7

Porous

,, H I I larY(~o~ (&30% (&le~ (&tO~

,, IV ~'y IV cry IV ory IV a'y

M,acro Porous

Homo Mdcro Macro Porous Macro Porous Macro Gel

(& [l ary) (& I I ary) (& I I : ; y) (&

"

I

Y)

"

"

Mdcro

n larY

I

II

Gel Porous Gel Gel Porous Porous Gel-Porous Macro Macro

"

"

Porous Porous Macro

Itl

I I I l l IV III It I

IV

Gel Ii Macro I ~el-Porous Ge I

11

6 5+3

423

Selective renovation of eutrophic wastes-phosphate r e m m a l

Table 2. Phosphate selectivit~ dependence on total solution motarit), ( p H - 3-0: X - 0 " 5 : 2 5 Ci r'.l.;. l/P

Resin

-I

6 x t 0 " ° ~t Kastet A 500 K a s t e t A 500 P k a s t e l I 510 Kast¢l A 5 0 1 D A~nit A 259 N Rellte 3 aZ Kaste{ A 300 Kd~te[ A 300 P

7.70 5,67 5,41 5 . $ 2 ; 5.62 6 , 9 4 ; _5.36 5.33 5,94 4.73

4.00 3.01 3.'~7 3.79 3,6~ 3.79 3.41 "~.¢1

A 305 MP 60 S m b e r l [ t e IRA 93 L e ~ o t i t Ce 9222 i A m b e r l i t e IRA 6~ Kastel A I05/S14 ,~uolite A 6 ~uolite a 7 D u o l l t e S 37 Ambeelite IRA 47 3uotite A 30 8
2.3-'3 3.3l 5.02 2.26 2.07 0 . 9 0 ; 1.13 1.31 0.64 2.37 O. -g4 0.84 0.81; 0.70

t.54 1.71 2.43 O, "36 1.14 0.63 1.53 0.69 i .04 ,2.52 ?,70 0.58

0 . 8 2 ; 0,84 0.43; 0.43;0.44 0.4l; 0,40;0.43 0 , 5 9 ; 0.57 0.73 2.66; 2,00

1.07 0,27 0,27 0.40 0.36 2,07 t.3t 0,46 t .67 1.50

0uoli~e le~atit

i

Wofatit AK 40 A 102/812 R e l I t e MGI O ~ u l l t e A 366 D u o l l t e ES 3605 Kastel A 103/1 D u o l i t e ES 2002 Dowex WGR Duolite ES 3603 Amberlite IR 45

iKaste{

1.95

0.5l; 0.50 2 . 5 5 ; 2.47 t.72

N B. Phosphates preferred when xo i, (chloride to phosphate molar scparation factor) I.

appreciable degree of uncertainty is still associated with such determinations. It was therefore decided to refer all the concentration measurements to ion molarities. Chlorides and phosphates were automatically analyzed by the Mod. 11 Technicon Autonalyzer, The water content of the resins was determined according to Kinshofer et al. {1973) by the centrifugation method, from the curves obtained by plotting the weight of the resin sample vs the square of centrifugation speed.

Kosrel ASlO

Kastel ASOIO

Relite 3 A Z

30C

I0

2~C 5

10C C

3

Dowex WGR T

4OCF-

O.

20(:

Kastet AIO5

Duolite A7

---I0

30C

RESULTS AND DISCUSSION In Table l are listed the main physico-chemical properties of some of the investigated resins, selected as representative of the total anion exchanger production. Other experimental products have been used. expressly prepared by Montedison Co., Milan, Italy. The experimental results may be related to the different parameters as follows.

OC

9

¢

3

70C --Kosret A I 0 2 E

Relite~MGI

Duolite A366 --L~3

i

5OC

"

C

40(: 3OC

A. Influence of external parameters (referring to rite solution) A.I Solution comcentration. From the data in Table 2 it can be seen that the selectivity toward phosphates generally increases with solution dilution (see also Fig. 3). This phenomenon, usual in heterovalent exchanges, cannot be explained here bv the "electroselectivity effect" due to phosphate ions being prevailingly monovalent in the investigated conditions (pH-3"0). It seems more likely that, at lower ionic stren~hs of the external solution, a greater water con~' K [(1 5 I

IO

ZOC 5 IO£

C

;

I

0

pH

Fig. I. Phosphate uptake, q~,, [gPO,~ exchanged (kg dr.,, resin)- t], and relative selectivity, [- gPO, exchanged (kg dry resin)- [ -]

s,,~,,L~~~~c

•

vs pH for typical anion resins. (C = 6-9 x 10 -3 M: X = 0.4-0.6)

424

G. BoMtL L. LIBERTIand R. PARS[NO the "'dephosphation capacib", q'p {phosphates removed ~,- ~ of dr~ resinL and the "'relative ~electivitv"

2-5

O! y

~C

UR~IA47 Aml~erlite

i0

~S ~

, Dugli~'e/~. /

05 I

0 0

U 0.5

I0

05 x

iO

05

I0

Fig. 2. Chloride/phosphate equilibrium isotherms as a function of pH. (Y = phosphate molar fraction in the resin; X = phosphate molar fraction in solution: C = 6-10 x 10 . 3 M) pH ----7 (O), 3 (©) and I1 (A) tent within the resin phase exists, so that strongly hydrated oxyanions as phosphates can be more easily adsorbed. A.2 Solution pH. This parameter is partictflarly important, as far as both dissociations of the resin fixed charges and of phosphates depend on it. Fig. 1 gives

Sp o ('phosphates r e m o , j _ g - I dry resin) chlorides removed ~- t - d ~ ! as a function of solution pH for some typical resins. A great difference is immediately apparent between strong anion resins !Kastel A510 and A501. Relite 3AZ), relatively in~nsitive to pH, and the weak ones (Kastel A102. Relite MG1 and Duolite A366L for which both functions show a maximum. Let us now examine the pH influence separately. q'p rs pH. A continuous decrease of q'p with pH occurs for the ~eak resins, immediately after the first dissociation of phosphoric acid. In spite of the fact that higher phosphate setectivities could be expected with these resins at higher pH (electroselectivityt, this decrease can be explained by considering that two exchange sites are occupied by one HPO~.- ion (three be one PO 3-). so that smaller amounts of phosphates g - ~ of resin are effectively removed as pH increases. Moreover, as O H - concentration increases, fewer exchange sites become available for other anions, due to the selectivity sequence Ibr weak anion resins O H - > [H3_,PO,t]-" >, C1-.

This is not the case for strong anion resins, where the following sel~tivity is expected [H3_,PO.~]-" ~>CI- > O H - ,

. E ] o 6 x 10-3M IOfo

F'A*

I x 10-3M

I'

o~ O'~

Fig. 3. Separation factor vs predominant functional ~oup of the resins. ( C ~ 6 x 10-am (O) or l x 10-3M (O); X ~ 0.5; pH "= 3-01

(I)

(2)

Consequently, a (small) increase of q'p with pH occurs with strong resins. Sp/cz vs pH. The same considerations as for q'p apply. The continuous increase of selectivity with pH for strong resins is easily correlated with electroselectivity. A more complex situation exists with weak resins, where a maximum occurs. The latter may be explained considering the different equivalent weights of H:PO.7, HPO~.- and P O ] - ions ( S , o refers to g phosphate fixed g - t of chloride by 1 g of dry resin): at low pH, C1- and H,PO.7 ions exist: no electroselectivity, S~,,c~- 1: at neutral pH, CI- and HPO~ions exist: appreciable electroselectivity. Sect,> 1: at high pH, CI- and PO 3- ions exist: strong electroselectivity, but Spc,' - I, due to the small equivalent weight of PO,73 ion. A.3 Solution composition. The selectivity dependence on solution composition results from Fig. 2, where the equilibrium isotherms at different pH for some typical resins are reported. The pH influence is in agreement with previous considerations. It is interesting to note that selectivity reversal (inflection points) occurs with strong resins for phosphate molar fraction in solution X ~> 0-5. A possible explanation for this phenomenon, previously found also by Gregory and Dhond (1972b) and by George and Zajicek (1968) who gave no interpretation, may be the following. According to Eisenman's theory of ion exchange, (Eisenman, 1961) selectivity depends on the net difference between enerD' consumption required for (par-

Selective renovation of eutrophic wastes--phosphate removal

tiat) breakdown of the hydrated structure of the ion lea~ing the aqueous phase and the energy produced by the electrostatic interactions of this ion and the fixed charges within the resin. This difference is expected to be always favourabte to weak anion resins, due to the predominant role played by electrostatic interactions with these resins (Boari. 1974b) while hydrostatic interactions prevail with strong base resins. According to the increasing destruction of solration shells associated with phosphate ions penetrating the inner parts of the resin i Y > 0-5k an energy balance reversal is likely to occur with strong resins. From an application point of view, the influence of external parameters suggests the following considerations: with selectivity increasing with solution dilution, complete phosphate removal can be expected by fixed bed ion exchange, with negligeable leakages in the treated water. Furthermore. the selectivity of weak anion resins, which show the greatest affinity toward phosphates [see also the next paragraph), is at its maximum for pH between 6"5 and 7.5, which corresponds to the average pH range of conventionally treated sewage effluents. Lastly, values of X > 0.5 are likely to be encountered only during the regeneration of an anion exchange column used for selective phosphate removal. Any selectivity reversal would thus tRvour the regeneration of the resin.

The same sequence was previously found for C I - I S O ] - equilibrium. (Boari et al.. 19741 which led to the conclusion that a predominant role is played by electrostatic interactions among differently charged counterions. The data- in Fig. 3. however. refer to homovalent conditions (pH "- 3"0k where the equally charged C1- and H.,PO2 ions are expected to exhibit approximately the same coulombic electrostatic interactions, with the smaller C1- preferred (rct = 1'8t A, rH:pO / = 2"51A). Evidently, other electrostatic interactions have to be considered, particularly those (as van der Waals forces. London interactions, etc.) related to the higher polarizability of the polyatomic phosphate ion compared to the relatively non polar chloride ion. From a practical point of view it must be noted that the weakest anion resins (with prevalently primary amino groups) are substantially inactive at neutral pH. so that the selection of a resin to be used for domestic effluent renovation must necessarily be restricted to resins with secondary and tertiary amino groups. B.2 Alkylation degree. A series of similar experimental poly-acrilic products has been prepared, with different percentages of primary, secondary and tertiary amino functional groups, by controlling the alkylation reaction. --fC H--C'H z'J'-~

--(.C H - - - C H 2.F-~

t

I

C O

CH~CI

N H----C_,H,~--N H---C_,H4--N H: (secondary)

-

y(l-

-

(5)

C

,//\ O

CH 3

I

N H---C., H~--N----C2 Ha--N(CH 3),

(primary~

(tertiary)

B. h~uence of internal parameters Obviously, when varying a single resin parameter (porosity, for instance), it is hard to exclude that other modifications could be associated with that variation, so that care must be taken whenever a direct comparison between different resins is made. For this reason, grot~ps of resins with similar values of the investigated parameters have always been taken in this study. Accordingly. histograms will be used for such evaluation. B.I Resin basicity. In Fig. 3 are reported the molar separation factors, ~ct.,P, of different anion resins as a function of the type of amino functional groups. ~ p is calculated as ( 1 - Y)X :~cl P -

425

x)

IC

05

(3)

so that equilibrium is favourable toward phosphates when :t
Itertiary)

(4)

0

I

50 Alkylotion,

I00 %

Fig. 4. Separation factor vs alkylation degree of intermediately basic resins. (O = 70°,~porosity, 60%;water content; A = 50°;; porosity, 563-~ water content. C ---_6 x l0 -~ M; X ~ 0-5; pH ~ 2.35)

"26

G. I~)AR~,L. LIB£RTIand R. PA.istxo

The basicit~ of such products can thus be varied by controlling equation (51. As shown by the data in Fig. 4, phosphate selectivity decreases with the tertiary amino group percentage, in full ageement with expectations. B.3 Type ofalkyl-amine. In the preparation of potyacrylic resins, ethvlendiamine {EDAL diethylentriamine/DETA) or propslendiamine {PDA) are usually employed as copolymers of acrylic acid, yielding respectively one of the following products: --4CH--C H r,L-s, I

I

i C

r

C

J" ",

-4C H--CH,-~.

---{CH~CH 2)-s~

f O

As can be seen from the data in Table 4, remarkable selectivity differences are associated with the rnatrix hydrophilic nature of otherwise similar resins. tn some cases, a selectivity reversal has been found on going from hydrophobic (styrene) to hydrophilic (epoxy. polyamine-imine condensationt matrices. This is the most direct evidence that an important role in determining the phosphate affinity of anion resins is played by hydrostatic, other than by electrostatic, interactions within the resin phase.

C NH---C2H.t--NH:. O

S'\

NH--K23Hr--NH2, 0

(EDAt

NH--C2

(PDA)

Amberlite IRA 68 is a known example of PDA poly-acrylic resins, while standard Kastel A 102 and Kastel A t05 resins use DETA. In Table 3 the selectivity data of similar experimental products based on EDA or DETA are compared. Better results are always obtained with DETA in spite of the lower water content associated with it. In addition to stheric considerations, this may well be related to the longer distance of the - - N H 2 from the deactivating imido group ( - - C O N H ) B.4 Resin matrix. Polystyrenic resins are usually preferred in practical applications because of their good resistance to physical and chemical stresses. Nevertheless, due to the hydrophobic nature of the styrenic structure, strong osmotic shocks and low diffusional kinetics are associated with such matrices. In order to overcome these drawbacks, new hydrophilic resins with polyacrylic matrix have recently been developed, which combine faster kinetics and reduced osmotic pressures with acceptable physico-chemical stability. Other, more hydrophilic matrices (phenolic, epoxy, etc.) can be employed only in particular conditions (absence of oxidizing or reducing solution, of very low or vcry high pH, of mechanical stresses, etc.I.

H ~ - - N H - - - C 2H ~ - - N H

(DETA) B.5 Crosslinkiny deyree. In Fig. 5 the selectivities of two series of experimental products with different crosslinking degrees (expressed as percentage of divinylbenzene) are compared. No influence appears to correlate with this parameter, as expected, according to the negligible influence on homovalent exchanges (pH-3"0) of the Donnan potential variation known to be associated with different crosslinking. B.6 Porosity. Like matrix composition and DVB percentage, also the influence of resin porosity in systems at equilibrium is to be substantially related to the variation of water content of the resin (while the influence of the other three internal parameters can actually be related to the basic strength of the resin). A general, qualitative evaluation of the experimental results always confirms that better phosphate uptakes are obtained with porous resins (homoporous, macroporous, macroreticular) than with the corresponding gel products. This is intuitive since higher porosity is expected to be associated with higher water content, hence with easier diffusion of strongly hydrated oxyanions like phosphates, sulfates, etc. In order to obtain direct evidence to support this

Table 3. Phosphate selectivity dependence on the type of alkyl-amine. Tertiary amino resins Resin

.Monmme~s

(RA/AM)

5/117

5/95

~lkyl-amine Crosslinklng Porosity degree ec toluene ~ (~ DVB) I00 g mort. (~ H20) EDA 4 0 64.4

Water

content

5/121

"

56.1

5/128

"

58.4

5/124

"

47.1

5/I18 5/123 5/133

"

49.~

10/90

42.5 66.6

"

5/113

"

57.S

5/134

75/25

72.5

5/114

"

62.4

6

S

10

8

2.

70 4O

i%,/p

DETA

1.77 0.80

EDA

1.70

DETA

1.04

EDA

1.82

DETA EDA

1.14 2.11

OETA

0.92

EDA

1.96

DETA

O.S3

EDA = ethyten-diamine; DETA = diethylentriamine. NA = acrylonitrile, AM = metylacrylate.

Selective renovation of eutrophic wastes phosphate removal

-t2r

Table 4. Phosphate sdectivit? dependence on resin matrix ~mim3 F u n c t i o n a l group

Resin

Duolite J 305 lmberli~e

IRA 47

i

llla~}{i+|O~

4 MS

Kastel

I lOl

ller)

tltar~i&

Kastel A 105

0uollte

2.O/2.3~

0.~4

Epox~

la5

o.~1/0.7(

iStyrenic

leo

'

imlne

99

4.40

iAcry[iC

1;t

2.26

~crytic

I32

2.07

tAceylic

3tyreni¢

IRA 6S! ll°rYl

A 7

Oowe* WGR

)

c{c~ip

175

Poly

L e ~ a t l t Ca 0222 lmbertite

( contenl ( i'~"!

IV dr')') ~tyreni¢

Ka~gel A iO0

Relite

i

Natril

101

0,00

Phenolic

122

0,64

Epuxy

176

0.5i

(*) resins in chloride form (**} C - 6 x 10-3 M: X-0"5; pH - 2.5 statement, the selectivity of similar products prepared with different percentages of a porosity making agent (toluene) have been determined. As indicated by the data in Table 5, the experimental results fully confirmed the favourable influence of porosity on phosphate affinity. CONCLUSIONS

From a theoretical point of view, the experimental rcsuhs of this study seem to indicate that hydrostatic interactions have a great importance in determining resin selectivities in the chloride/phosphate system. The contrary was found when the chloride/sulfate equilibrium was studied. I5 & ..-...¢_.

,x iO

o.

6

0-5

In order to confirm the role of hydrostatic interactions, water transport isotherms will be determined to make a direct evaluation of water content associated with different ionic composition of the resins at equilibrium. On an applicative basis, the final characteristics of the preferred resin will appear from a general study of the multicomponent system, with special attention to sulfate affinities. Regarding the chloride/phosphate equilibrium, the experimental results would lead to the selection of a secondary and tertiary amino, porous, 8-10% crosslinked, poly-acrylic resin with DETA basic groups as the best suited for selective phosphate removal from secondary effluents, having 1-6 x 10 - s M total concentration, pH = 6.5--7.5 and low phosphate concentration (X ,< 0-1). In these conditions, equilibrium phosphate uptakes of up to 0'7kg. P O 4 k g - t of dry resin have been obtained. Resins with more hydrophilic matrices (phenolic. epoxydic) would require an adequate physico--chemical stabilization. Alternatively, a oncethrough utilization of chemically less resistant {hence cheaper) resins can be considered, with direct re-use of the resins in phosphate form as soil conditioners or fertilizers, provided an accurate balance of other organic and inorganic ingredients are supplied with it. Experimental evaluation of such combined utilization of anion resins is now being conducted.

Table 5. Phosphate selectivity dependence on resin porosity Resin

o

I

I

9

II

DVB,

Fig. 5. Separation factor vs crosslinking de~ee of intermediately basic resin. (O = secondary amino group resins; A = 80% tertiary + 207.0 secondary amino group resins. C ~ 6 x 10-s xl; X -~ 0-5: pH ~ 2-35).

t~i/p

(co t o l u e n e ) toe ~ monomer

13

%

Paro~ity

5/t23

0

1.14

5/116

40

0.90

5/I13

7O

0.92

a2S

G. P~}aRL L. LraEgrt and R. P:,ssryo

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Acknowledgements--Montedison Co., Milan (Italy) and Diaprosim, Vitry s.S. {France) are grate/;ally acknowledged for their assistance in the preparation of experimental products. Thanks are a l ~ due to Mr. N. Limoni and Mr. L. De Girotamo for their valuable contribution during the experimental part of this work.