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Application of water extract of brown coal fly ash to phosphate precipitation from polluted waters
Water Research Vol. 14, pp. 1289 to 1293 Pergamon Press Ltd 1980. Primed in Great Britain
0043-1354/S0/0901-1289502.00/0
APPLICATION OF WATER EXTRACT OF BROWN COAL FLY ASH TO PHOSPHATE PRECIPITATION FROM POLLUTED WATERS I. KUZ~MSr~ Institute of Hydroengineering of the Polish Academy of Sciences, 80-953 Gdansk-Oliwa, uL. Cystersow, Palac Opat6w, Poland (Received December 1979) Abstract--A method is discussed of phosphate precipitation from municipal wastes and from the strongly polluted waters using water extract of brown coal fly ash from the Konin power plant. It is shown, that phosphate precipitation occurs immediately after introduction of the coagulant and after a short and intensive mixing. Precipitation intensity depends mainly on the v coefficient(ratio of mass of a alkalinity in the extract to that in the water to be treated) and on the alkalinity of the treated water. Using a mathematical model of regression curve, described and applied in this paper, the degree of influence of each parameter on the process of phosphate precipitation has been determined.
INTRODUCTION
chemical oxygen demand COD, (Chru~ieL 1973) an
The increasing eutrophication of water reservoirs is a problem of constant interest. This eutrophication is caused by biogenic matter surplus and it demands constant checking of quality of discharged poliuted water. Therefore an easy effective and cheap method is necessary,
increase of transparency to about 98% accompanied by precipitation of phosphates, iron salts and partially by ammonia nitrogen removal (Chru~iel & Kuziemska, 1974). It has been also shown, that the addition of water extracts of fly ash decreases the total amount of bacteria and increases the Coli index
Looking for cheap and effective phosphate absorbents, attention has been paid to fly ash extracts, e.g. to waters'from hydraulic ash removal, These water extracts are excellent coagulants of waters from briquetting plants (Chru~ciel, 1964); they
in waters Results of research on biological regeneration of strongly eutrophicated lakes with the application of fly ash were also published earlier. In field experiments there were used only fly ashes in the form of a screen of a few cm thickness which covered the lake sediments rich in nutritive substances (Higgins et al., 1976).
are also good reactants in sealing process of water reservoirs by chemical coagulation method (Chru~ciel, 1971a,b). During research of the influence of chemical additions on the microbenthos in laboratory tanks, attention has been paid to a pronounced decrease of the quantity of green benthonic microflora while the quantitative-qualitative equilibrium of animal microbenthos forms remained unchanged. An analysis of nutritive salt concentration in experimental tanks subject to chemical addition indicate a pronounced decrease of phosphate level (Kuziemska 1973a,b). Water extracts of fly ash contain soluble ash components such as: hydroxides and sulphates of calcium, sodium, potassium, iron and aluminium, Concentrations of these components in ash extracts depend on the burned coal quality, on the technology of burning, and ash removal and also on the method of ash storage. Waters from hydraulic removal of ash from power plants gave excellent results when used for treatment of municipal wastes, of food industry wastes (meat, diary, fish) and of tannery wastes. As the result of reaction of the waters from hydraulic ash removal with the above mentioned wastes there occurred a significant decrease (45-90~) of biochemical oxygen demand from BOD, a decrease 9 2 ~ of
MATERIALS AND RESEARCH METHOD The process consits in the reaction of the water extracts of fly ash with wastes, indicating carbonate hardness and alkalinity and pH of 6.0-8.0. Suspended solids precipitate in this reaction, the grain size and the sedimentation time being dependent on the value of the coetficient v, which expressesthe ratio of volumes and alkalinities of reacting solutions, VI Z1 V2 Z~-~= v where: V~ = volume of water extract (l) Zt = alkalinity of water extract (meal l-1) v : -- volume of tested water (I) Z: = alkalinity of tested water (meal l- t). There were studied biologically treated municipal wastes and polluted waters in which PO4a- concentration ranged between2.3 and 22.5 mg PO~- l- ~, and the total alkalinity was 4.4-8.4 meal I-1. The water extract of fly ash has been used as coagulant. It was prepared by leaching I00 g of brown coal ashes with 1 I. of tap water. Leaching time being 24 h. The alkalinity' of extract varied from 40 to 53 meal 1-1 pH was about 12,
1289 W,R. 14D--H
1290
f.
KUZIEMSKA
sulphate content was 1259.7mg 1-1, calcium content was 1252.0 mg I- t, magnesium content was 36.0 mg 1- ~. Phosphates removal has been carried out at coefficients v ranging from 0.2 to 1.2. Coagulant was mixed with water by a mechanical stirrer at 50 rpm and the mixture was poured into Imhoff funnels. Measurements of residual PO~- concentrations have been made after 2 h sedimentation, assuming this period to be enough for efficient sedimentation process. Phosphate deammoniumterminati°molybdatehaS n been carried(PolishStandards).°ut photometrically, using
RESULTS
o~o~ !: ii t., tl~/~'""'~""----"-°-----------~o" ~oo ~ ...~k
i ~
Measurements of residual concentrations of PO 3were carried out on water--coagulant mixtures which were either centrifugated immediately after stirring or centrifugated 2 h after stirrin& Results were identical (Fig. 1). These data indicate, that for a given v a characteristic amount of PO~- is removed from the solution during precipitation of suspended solids, In conditions of natural sedimentation the minimum PO3, - residual concentration for a given v depends on the sedimentation time (Fig. 2). Waters with a high v coefficient indicate quick sedimentation of large floccules (Table 1). In case of waters, in which precipitation occurs at a low coefficient, very finegrained suspension is formed, which remains suspended for a long time. Therefore at low coefficient v the residual concentration of PO~- depends on sedimentation time and it varies from 75.0% of initial concentration after 2 h to 22.0°/0 of initial concerttration after 6 h. For higher coefficients v the values are 3.0°/0 after 2 h and 2,0% after 6 h.
l
" ' -
.
....
o
~v=O 6
,c ~.._:_ ~| i o,i°
-- _ .~,_
L ~Io
_~. ~=oo __t. ~o~o __~.12
~o ' ~o ' do ' s!o ' ~o - - "
Time s e d i m e r ~ (rain}
Fig. 2. The kinetics of phosphate precipitation.
These observations are substantiated also by measurements of residual level of PO3, - in mixed waters decanted after 2-h sedimentation (Fig. 3), Factors controlling the quantity of removed phosphate ions Tests have been carried out with the following variable parameters of the process: 1. Coefficient v, 2. I~fi-ai-i/O~ - concentration, 3. Total alkalinity of the coagulant 4. Total alkalinity of the tested water
t ,co
and they have shown, that each of these parameters has a significant influence on the amount of PO3, removed from the tested water.
%-
Influence of coeOicient v .~,o(
~
,
~
8
~
h
Tests performed for coefficients v varying from 0.2 to 1.2 have shown, that the amount of precipitated phosphates depends on the applied v value. Three typical ranges of process intensity have been found (Fig 4). Ist range up to 0.3 v---weak intensity of the process. The degree of phosphate precipitation is maintained at + 30*/0 of the initial concentration. lind range 0.3-0.8 v-very intense phosphate precipitation (80-90%). IIIrd range, above 0.8v--maximum precipitation (90-96%)
O~
o'2
da
d6 ba Coefficient
,'o
~z
Fig. 1. Residual concentration of PO~- in centrifugated waters. H immediately after precipitation, and after 2 h of contact with the reactant A A.
Influence of alkalinity of the treated water The alkalinity of tested waters, i.e. the amount of available acid calcium carbonates Ca(HCO3h which can react with hydroxide ions of the coagulant, is a
Water extract of brown coal fly ash to phosphate precipitation
1291
Table I. Volume of precipitate in ml I- ~ at various values of coefficient v Time (min)
v = 0.2
v = 0.4
v = 0.6
~. = 0.8
v = 1.0
v = 1.2
l0 20 30 60 90 120
990 980 960 900 790 600
800 70 42 29 21 19
150 60 39 20 17 16
84 35 26 19 16 15
76 34 23 16 15 14
66 25 20 15 14 13
factor, that influences the amount of precipitated phosphates. The water alkalinity determines the intensity of the process. At low alkalinity, maximum precipitation occurs at higher values of coefficient v in (Fig. 4) limits of range II shift towards higher v values. At
with biologically treated waste water with initial P O ~ - concentration of 22.5 mg I- 1 and of alkalinity 8 reval l - i resulted in identical values of residual PO~-concentration. For all tested v coefficients the same degree of precipitation was obtained (Fig. 6).
higher alkalinity intense precipitation occurs even at lower coefficient v. For instance for a constant coefficient v, in waters with the same initial P O ~ - concentration, a larger percentage of phosphate precipitation occurs in water with a higher total alkalinity (Fig. 5). The above observations have been confirmed also by tests carried out on nine waters differing in alkalinity and initial phosphate concentration.
Influence of initial P O ~ - concentration Tests carried out at constant coefficient v and constant water alkalinity, but at variable initial POa4 concentrations, have shown slight increase in values of residual phosphate concentrations with increase in initial P O ~ - concentrations (Fig. 7).
Regression model as a method of determination of relations between tested variables in the phosphate
It was observed, that the value of coefficient v at which the given decrease of initial POa4- c o n c e n tration occurs, e.g. by 50~o, depends on alkalinity of the treated water. This is the reason why even at low initial P O ~ - concentrations, precipitation of 5 0 ~ of phosphate may occur at high coefficient v, on the condition that the tested water shows a low total alkalinity (Table 2).
Basing on the analysis of stochastic structure parameters of the regression model, a power function was found: X2 ~ X4 y = =0"X~" =~" 3. =, which described the empirical data. The parameters of
Influence of reactant
investigated function assume the following values:
It was found that the tested range of total alkalinity (40-53 mval 1-1) of the reactant does not influence the amount of precipitated POa4-. Three water extracts of brown coal fly ash indicating the alkalinity of 53 mval 1-1, 45 mval 1-1 and 40 mval 1- ~ reacting
80 70
x
precipitation process
Correlation coefficient
R2 =
Standard error Variation of coefficient
S= = 0.4661 V,= = 23.0600
The investigated function explains in 8 6 ~ phosphate precipitation for the given conditions of experiments.
8o
,
70
I
I
60~
I
I
50
"6 4 0
40
.,~ 3 0
"6 3o
E 2o
I
0
Coefficient, v
Fig. 3. Residual concentration of PO~- after 2 h of sedimentation in centrifugated water H and in decantated water x x.
0.8558
OI
02
03 04 05 06
07 08
09
I0
II
12
Fig. 4. The influence of coefficient v on the intensity of phosphates precipitation in waters of different alkalinities H 8.2mvall-~; x x 7.8m; A A 7.4 reval I- ~; 4.4 mval 1- ~ n ~.
1292
I KUZIEMSKA
,
9(5~
"6
,:~C,i
4o
t t
0~ 30
7//
....
o, o~ 03 04 as oeoz oa o9 ,o,~ ~Coefficient, v
Fig. 5. The influence of water alkalinity on the intensity of POa,- precipitation, The remaining 14% is the influence of other factors not taken into account in the model. On the basis of analysis of the regression function parameters (Table 3). It is stated, that three of the tested parameters, i.e. coefficient v (XI), initial P O , concentration (X2) and alkalinity of tested water (X,) have a significant influence on the degree of phosphate precipitation. The increase of the first (X0 and fourth (X,) parameter by one percent increases phosphate precipitation by 1.25 and 1.10% of the initial concentration. On the other hand the increase of initial PO~- concentration by 1% decreases mean phosphate precipitation by 0.97%. Influence of parameter X3 (reactant alkalinity) is found to be insignificant. After elimination of variable X3 as an insignificant variable, a repeated estimation of regression function parameters has shown, that the fit of the regression model to empirical data does not change significantly, Table 2. Relation between the total water alkalinity and coefficient v for 50% precipitation the of initial phosphate concentration Initial Expected concentration Alkalinity coefficient (mg PO~- 1- 1 ) (mval 1-') (v) 7.75 22.50 19.00 30.00 19.00 7.50 6.80 2.30
8.4 8.0 7.8 7.4
5.8
5.2 4.8 4.4
0.26 0.32 0.38 0.42 0.48 0.50 0.54 0.57
Table 3. Values of the regression function parameters Variable
Parameter
Parameter evaluation
--
~to ~l ~z ~q ~,~
- 2.33561
1.24709 -0.96616 -0.08662 1.13429
Fig. 6. Dependence between the initial and residual PO~ concentration at constant coefficient (v = 0.8) and constant alkalinity of water (6.4 reval I- 1). On the other hand, standard deviation becomes smaller. From the point of view of utilization of these results in practice, it is important to determine the explicit influence of the coefficient v and of water alkalinity on the amount of precipitated phosphate. Thus, the following function parameters have been evaluated .
:tt,
~4
Y = ~0 Xt X4 Calculated parameters of the regression model R 2 = 0.7430 S, = 0.6219 S,, = 32.10 have shown a worse fit of the regression function to empirical data. The investigated function describes only 74.3% of phosphate precipitation found. Estimated parameters (Table 4) of the regression function indicate, that the variable X, has a greater influence on PO~- precipitation than the variable X1. Increase by 1% in water alkalinity increases average phosphate precipitation by 3.7%. The influence of coefficient v on phosphate precipitation remains unchanged. Taking into account these two parameters, the precipitation
! i
~ i~
/~oSr,.._.,.--,~
2>,
:~7:;f ~ 4o~
]
~t
/
Significance Yes Yes No Yes
"
mq PO~" I-Iof inim:ll c o o e e n t r ~
IOL
Xl X2 X3 X4
_ _ _ - - . - - -
o ~ ~, & S 6 e ~4-~'6 ,'8~o
~
,53 mmot I :
x 45 m too) t
/
oL.' ' " o*
a 4 0 m rnol I i
i
L
i
6z ~3 04 05 ba ~7 c~V'~oo9,o ~, ~
........
Co~ic~t, u Fig. 7. The influence of different alkalinities of water extract of fly ash on the amount of the precipitated PO~-.
Water extract of brown coal fly ash to phosphate precipitation
Table 4. Values of regression equation parameters
Variable
Parameter ao
X~
:t I
X4
:t4
Parameter evaluation
Significance
-4.69352 1.05148 3.70954
Yes Yes
of a determined amount of phosphate may be preclicted with about 75~o accuracy. CONCLUSION The described method of phosphate removal from waste water is one of the cheapest methods presently known. Fly ash is a waste product of the power industry. Basic difficulties in its utilizing for waste treatments may be caused only by the distance between the storage area and the treated object, since ash transportation demands special protections, Therefore it may be best applied in the vicinity of brown coal open mines, where usually also power plants are situated, As it has been shown, the water extract of brown coal ash contains large amounts of hydroxide, calcium, magnesium and aluminium ions. Each of these ions can react with phosphate ions e.g. to precipitate calcium phosphate, magnesium phosphate or aluminium phosphate. In general water extract of brown coal ash contains those coagulants, which in the form of expensive commercial substances are used for phosphate precipitation in waste waters. Water extract of brown coal ash has a very high total alkalinity, Investigations and the regression model of statistical analysis have shown that fluctuations of reactant concentration of about a dozen mval !-1 have no practical influence on the intended effect. In the process of phosphate precipitation by water extract of brown coal ash the ratio of volume and alkalinity of reacting solutions is of importance (it is the general case in water treatment). For removing phosphate, which are especially susceptible to the water extract of fly ash, the optimal coefficient v is lower i.e. in the range 0.4-0.8. Very favourable is also the fact, that the alkalinity of the treated water is the activator of the process. Investigations and regression model of statistical analysis, have shown that the increase in alkalinity increases pronouncedly the amount of precipitated phosphates. The use of low v coefficients for phosphate removal is especially advantageous, since a temporary increase in pH is maintained within the limits of pH 9.0. At higher coefficient v the increase may reach the value 10. Investigation results described above indicate that the initial increase in PO 3- concentration is a factor restraining to a certain degree the intensity of the precipitation process. Nevertheless, basing on regres-
1293
sion model of statistical analysis, it is proved that the influence of this factor on the process is smaller than that of the alkalinity of the tested water and that of coefficient v. Taking into account the last two parameters only, it is possible to predict in 75~g the precipitation of a PO~- from water.
SUMMARY
A method of application of water extract of brown coal fly ash as a coagulant of phosphates from POlluted waters has been described. Reactivity of calcium, sodium, potassium, iron and aluminium hydroxides and sulphates with waters having temporary hardness, carbonate alkalinity and pH of 6-8 is utilized. Solid and suspension precipitate sediment easily, and water above the sediments shows a significant improvement of sanitary indicators (BODs and COD), and also removal of a substantial amount of phosphate ions occurs. It was observed, that phosphates precipitate immediately after introduction of the coagulant and after a short, intensive mixing of the solution. In the investigated process, the influence of some parameters on the degree of phosphate precipitation has been analysed. It has been determined on the basis of the results obtained and of a mathematical multiple regression model used in the investigations, {hat two parameters have the most significant influence, i.e. the coefficient v expressing the alkalinity and volume ratio of reacting waters, and the total alkalinity of the tested water. It has been shown, that only these two parameters enable 75% reliability of prediction of the precipitation of phosphate ions from any water indicating total hardness and alkalinity. Reactant alkalinity in the tested range of 40 mval53 reval 1-1 has no significant influence on the process. Higher initial PO~- ions concentration increase slightly residual PO~-. REFERENCES
Chrugciel J. (1964) Investigation on Konin brown coal mine wasters treatment. Rozpr. hydrotech. 15, 39-74. Chruk'iel J. (1971a) Some aspects of chemical coimatation in laboratory tests. Rozpr. hydroteeh. 25, 139-152. Chru~'iel J. (1971b)The method of water reservoir seating. Patent No. 67427. Chru~,-ielJ. (1973) The new method of water and waste water treatment using ash removal waters from thermal power stations. From the Problems Institute of Hyd° rocngin~ring PAS GdafisL Chru~iel J. & Kuziemska I. (1974) The method of waste water treatment. Patent No. 91010. Higgins B. B. et al. (1976) Lake treatment with fly ash, lime and gypsum. J. Wat. Pollut. Control Fed. 9, 2153-2167. Kuziemska I. (1973) The influence of chemical colmatation on the population of organisms living on the bottom and near the bottom of the water reservoir. Rozpr. hydrotech. 32, 317-327. Kuziemska I. (1973b) The infltlence of fly ash water extract over the precipitation of biogenic substances and the growth of plants in water reservoir. Archwm Hydrotech. 20, 363-378.
0043-1354/S0/0901-1289502.00/0
APPLICATION OF WATER EXTRACT OF BROWN COAL FLY ASH TO PHOSPHATE PRECIPITATION FROM POLLUTED WATERS I. KUZ~MSr~ Institute of Hydroengineering of the Polish Academy of Sciences, 80-953 Gdansk-Oliwa, uL. Cystersow, Palac Opat6w, Poland (Received December 1979) Abstract--A method is discussed of phosphate precipitation from municipal wastes and from the strongly polluted waters using water extract of brown coal fly ash from the Konin power plant. It is shown, that phosphate precipitation occurs immediately after introduction of the coagulant and after a short and intensive mixing. Precipitation intensity depends mainly on the v coefficient(ratio of mass of a alkalinity in the extract to that in the water to be treated) and on the alkalinity of the treated water. Using a mathematical model of regression curve, described and applied in this paper, the degree of influence of each parameter on the process of phosphate precipitation has been determined.
INTRODUCTION
chemical oxygen demand COD, (Chru~ieL 1973) an
The increasing eutrophication of water reservoirs is a problem of constant interest. This eutrophication is caused by biogenic matter surplus and it demands constant checking of quality of discharged poliuted water. Therefore an easy effective and cheap method is necessary,
increase of transparency to about 98% accompanied by precipitation of phosphates, iron salts and partially by ammonia nitrogen removal (Chru~iel & Kuziemska, 1974). It has been also shown, that the addition of water extracts of fly ash decreases the total amount of bacteria and increases the Coli index
Looking for cheap and effective phosphate absorbents, attention has been paid to fly ash extracts, e.g. to waters'from hydraulic ash removal, These water extracts are excellent coagulants of waters from briquetting plants (Chru~ciel, 1964); they
in waters Results of research on biological regeneration of strongly eutrophicated lakes with the application of fly ash were also published earlier. In field experiments there were used only fly ashes in the form of a screen of a few cm thickness which covered the lake sediments rich in nutritive substances (Higgins et al., 1976).
are also good reactants in sealing process of water reservoirs by chemical coagulation method (Chru~ciel, 1971a,b). During research of the influence of chemical additions on the microbenthos in laboratory tanks, attention has been paid to a pronounced decrease of the quantity of green benthonic microflora while the quantitative-qualitative equilibrium of animal microbenthos forms remained unchanged. An analysis of nutritive salt concentration in experimental tanks subject to chemical addition indicate a pronounced decrease of phosphate level (Kuziemska 1973a,b). Water extracts of fly ash contain soluble ash components such as: hydroxides and sulphates of calcium, sodium, potassium, iron and aluminium, Concentrations of these components in ash extracts depend on the burned coal quality, on the technology of burning, and ash removal and also on the method of ash storage. Waters from hydraulic removal of ash from power plants gave excellent results when used for treatment of municipal wastes, of food industry wastes (meat, diary, fish) and of tannery wastes. As the result of reaction of the waters from hydraulic ash removal with the above mentioned wastes there occurred a significant decrease (45-90~) of biochemical oxygen demand from BOD, a decrease 9 2 ~ of
MATERIALS AND RESEARCH METHOD The process consits in the reaction of the water extracts of fly ash with wastes, indicating carbonate hardness and alkalinity and pH of 6.0-8.0. Suspended solids precipitate in this reaction, the grain size and the sedimentation time being dependent on the value of the coetficient v, which expressesthe ratio of volumes and alkalinities of reacting solutions, VI Z1 V2 Z~-~= v where: V~ = volume of water extract (l) Zt = alkalinity of water extract (meal l-1) v : -- volume of tested water (I) Z: = alkalinity of tested water (meal l- t). There were studied biologically treated municipal wastes and polluted waters in which PO4a- concentration ranged between2.3 and 22.5 mg PO~- l- ~, and the total alkalinity was 4.4-8.4 meal I-1. The water extract of fly ash has been used as coagulant. It was prepared by leaching I00 g of brown coal ashes with 1 I. of tap water. Leaching time being 24 h. The alkalinity' of extract varied from 40 to 53 meal 1-1 pH was about 12,
1289 W,R. 14D--H
1290
f.
KUZIEMSKA
sulphate content was 1259.7mg 1-1, calcium content was 1252.0 mg I- t, magnesium content was 36.0 mg 1- ~. Phosphates removal has been carried out at coefficients v ranging from 0.2 to 1.2. Coagulant was mixed with water by a mechanical stirrer at 50 rpm and the mixture was poured into Imhoff funnels. Measurements of residual PO~- concentrations have been made after 2 h sedimentation, assuming this period to be enough for efficient sedimentation process. Phosphate deammoniumterminati°molybdatehaS n been carried(PolishStandards).°ut photometrically, using
RESULTS
o~o~ !: ii t., tl~/~'""'~""----"-°-----------~o" ~oo ~ ...~k
i ~
Measurements of residual concentrations of PO 3were carried out on water--coagulant mixtures which were either centrifugated immediately after stirring or centrifugated 2 h after stirrin& Results were identical (Fig. 1). These data indicate, that for a given v a characteristic amount of PO~- is removed from the solution during precipitation of suspended solids, In conditions of natural sedimentation the minimum PO3, - residual concentration for a given v depends on the sedimentation time (Fig. 2). Waters with a high v coefficient indicate quick sedimentation of large floccules (Table 1). In case of waters, in which precipitation occurs at a low coefficient, very finegrained suspension is formed, which remains suspended for a long time. Therefore at low coefficient v the residual concentration of PO~- depends on sedimentation time and it varies from 75.0% of initial concentration after 2 h to 22.0°/0 of initial concerttration after 6 h. For higher coefficients v the values are 3.0°/0 after 2 h and 2,0% after 6 h.
l
" ' -
.
....
o
~v=O 6
,c ~.._:_ ~| i o,i°
-- _ .~,_
L ~Io
_~. ~=oo __t. ~o~o __~.12
~o ' ~o ' do ' s!o ' ~o - - "
Time s e d i m e r ~ (rain}
Fig. 2. The kinetics of phosphate precipitation.
These observations are substantiated also by measurements of residual level of PO3, - in mixed waters decanted after 2-h sedimentation (Fig. 3), Factors controlling the quantity of removed phosphate ions Tests have been carried out with the following variable parameters of the process: 1. Coefficient v, 2. I~fi-ai-i/O~ - concentration, 3. Total alkalinity of the coagulant 4. Total alkalinity of the tested water
t ,co
and they have shown, that each of these parameters has a significant influence on the amount of PO3, removed from the tested water.
%-
Influence of coeOicient v .~,o(
~
,
~
8
~
h
Tests performed for coefficients v varying from 0.2 to 1.2 have shown, that the amount of precipitated phosphates depends on the applied v value. Three typical ranges of process intensity have been found (Fig 4). Ist range up to 0.3 v---weak intensity of the process. The degree of phosphate precipitation is maintained at + 30*/0 of the initial concentration. lind range 0.3-0.8 v-very intense phosphate precipitation (80-90%). IIIrd range, above 0.8v--maximum precipitation (90-96%)
O~
o'2
da
d6 ba Coefficient
,'o
~z
Fig. 1. Residual concentration of PO~- in centrifugated waters. H immediately after precipitation, and after 2 h of contact with the reactant A A.
Influence of alkalinity of the treated water The alkalinity of tested waters, i.e. the amount of available acid calcium carbonates Ca(HCO3h which can react with hydroxide ions of the coagulant, is a
Water extract of brown coal fly ash to phosphate precipitation
1291
Table I. Volume of precipitate in ml I- ~ at various values of coefficient v Time (min)
v = 0.2
v = 0.4
v = 0.6
~. = 0.8
v = 1.0
v = 1.2
l0 20 30 60 90 120
990 980 960 900 790 600
800 70 42 29 21 19
150 60 39 20 17 16
84 35 26 19 16 15
76 34 23 16 15 14
66 25 20 15 14 13
factor, that influences the amount of precipitated phosphates. The water alkalinity determines the intensity of the process. At low alkalinity, maximum precipitation occurs at higher values of coefficient v in (Fig. 4) limits of range II shift towards higher v values. At
with biologically treated waste water with initial P O ~ - concentration of 22.5 mg I- 1 and of alkalinity 8 reval l - i resulted in identical values of residual PO~-concentration. For all tested v coefficients the same degree of precipitation was obtained (Fig. 6).
higher alkalinity intense precipitation occurs even at lower coefficient v. For instance for a constant coefficient v, in waters with the same initial P O ~ - concentration, a larger percentage of phosphate precipitation occurs in water with a higher total alkalinity (Fig. 5). The above observations have been confirmed also by tests carried out on nine waters differing in alkalinity and initial phosphate concentration.
Influence of initial P O ~ - concentration Tests carried out at constant coefficient v and constant water alkalinity, but at variable initial POa4 concentrations, have shown slight increase in values of residual phosphate concentrations with increase in initial P O ~ - concentrations (Fig. 7).
Regression model as a method of determination of relations between tested variables in the phosphate
It was observed, that the value of coefficient v at which the given decrease of initial POa4- c o n c e n tration occurs, e.g. by 50~o, depends on alkalinity of the treated water. This is the reason why even at low initial P O ~ - concentrations, precipitation of 5 0 ~ of phosphate may occur at high coefficient v, on the condition that the tested water shows a low total alkalinity (Table 2).
Basing on the analysis of stochastic structure parameters of the regression model, a power function was found: X2 ~ X4 y = =0"X~" =~" 3. =, which described the empirical data. The parameters of
Influence of reactant
investigated function assume the following values:
It was found that the tested range of total alkalinity (40-53 mval 1-1) of the reactant does not influence the amount of precipitated POa4-. Three water extracts of brown coal fly ash indicating the alkalinity of 53 mval 1-1, 45 mval 1-1 and 40 mval 1- ~ reacting
80 70
x
precipitation process
Correlation coefficient
R2 =
Standard error Variation of coefficient
S= = 0.4661 V,= = 23.0600
The investigated function explains in 8 6 ~ phosphate precipitation for the given conditions of experiments.
8o
,
70
I
I
60~
I
I
50
"6 4 0
40
.,~ 3 0
"6 3o
E 2o
I
0
Coefficient, v
Fig. 3. Residual concentration of PO~- after 2 h of sedimentation in centrifugated water H and in decantated water x x.
0.8558
OI
02
03 04 05 06
07 08
09
I0
II
12
Fig. 4. The influence of coefficient v on the intensity of phosphates precipitation in waters of different alkalinities H 8.2mvall-~; x x 7.8m; A A 7.4 reval I- ~; 4.4 mval 1- ~ n ~.
1292
I KUZIEMSKA
,
9(5~
"6
,:~C,i
4o
t t
0~ 30
7//
....
o, o~ 03 04 as oeoz oa o9 ,o,~ ~Coefficient, v
Fig. 5. The influence of water alkalinity on the intensity of POa,- precipitation, The remaining 14% is the influence of other factors not taken into account in the model. On the basis of analysis of the regression function parameters (Table 3). It is stated, that three of the tested parameters, i.e. coefficient v (XI), initial P O , concentration (X2) and alkalinity of tested water (X,) have a significant influence on the degree of phosphate precipitation. The increase of the first (X0 and fourth (X,) parameter by one percent increases phosphate precipitation by 1.25 and 1.10% of the initial concentration. On the other hand the increase of initial PO~- concentration by 1% decreases mean phosphate precipitation by 0.97%. Influence of parameter X3 (reactant alkalinity) is found to be insignificant. After elimination of variable X3 as an insignificant variable, a repeated estimation of regression function parameters has shown, that the fit of the regression model to empirical data does not change significantly, Table 2. Relation between the total water alkalinity and coefficient v for 50% precipitation the of initial phosphate concentration Initial Expected concentration Alkalinity coefficient (mg PO~- 1- 1 ) (mval 1-') (v) 7.75 22.50 19.00 30.00 19.00 7.50 6.80 2.30
8.4 8.0 7.8 7.4
5.8
5.2 4.8 4.4
0.26 0.32 0.38 0.42 0.48 0.50 0.54 0.57
Table 3. Values of the regression function parameters Variable
Parameter
Parameter evaluation
--
~to ~l ~z ~q ~,~
- 2.33561
1.24709 -0.96616 -0.08662 1.13429
Fig. 6. Dependence between the initial and residual PO~ concentration at constant coefficient (v = 0.8) and constant alkalinity of water (6.4 reval I- 1). On the other hand, standard deviation becomes smaller. From the point of view of utilization of these results in practice, it is important to determine the explicit influence of the coefficient v and of water alkalinity on the amount of precipitated phosphate. Thus, the following function parameters have been evaluated .
:tt,
~4
Y = ~0 Xt X4 Calculated parameters of the regression model R 2 = 0.7430 S, = 0.6219 S,, = 32.10 have shown a worse fit of the regression function to empirical data. The investigated function describes only 74.3% of phosphate precipitation found. Estimated parameters (Table 4) of the regression function indicate, that the variable X, has a greater influence on PO~- precipitation than the variable X1. Increase by 1% in water alkalinity increases average phosphate precipitation by 3.7%. The influence of coefficient v on phosphate precipitation remains unchanged. Taking into account these two parameters, the precipitation
! i
~ i~
/~oSr,.._.,.--,~
2>,
:~7:;f ~ 4o~
]
~t
/
Significance Yes Yes No Yes
"
mq PO~" I-Iof inim:ll c o o e e n t r ~
IOL
Xl X2 X3 X4
_ _ _ - - . - - -
o ~ ~, & S 6 e ~4-~'6 ,'8~o
~
,53 mmot I :
x 45 m too) t
/
oL.' ' " o*
a 4 0 m rnol I i
i
L
i
6z ~3 04 05 ba ~7 c~V'~oo9,o ~, ~
........
Co~ic~t, u Fig. 7. The influence of different alkalinities of water extract of fly ash on the amount of the precipitated PO~-.
Water extract of brown coal fly ash to phosphate precipitation
Table 4. Values of regression equation parameters
Variable
Parameter ao
X~
:t I
X4
:t4
Parameter evaluation
Significance
-4.69352 1.05148 3.70954
Yes Yes
of a determined amount of phosphate may be preclicted with about 75~o accuracy. CONCLUSION The described method of phosphate removal from waste water is one of the cheapest methods presently known. Fly ash is a waste product of the power industry. Basic difficulties in its utilizing for waste treatments may be caused only by the distance between the storage area and the treated object, since ash transportation demands special protections, Therefore it may be best applied in the vicinity of brown coal open mines, where usually also power plants are situated, As it has been shown, the water extract of brown coal ash contains large amounts of hydroxide, calcium, magnesium and aluminium ions. Each of these ions can react with phosphate ions e.g. to precipitate calcium phosphate, magnesium phosphate or aluminium phosphate. In general water extract of brown coal ash contains those coagulants, which in the form of expensive commercial substances are used for phosphate precipitation in waste waters. Water extract of brown coal ash has a very high total alkalinity, Investigations and the regression model of statistical analysis have shown that fluctuations of reactant concentration of about a dozen mval !-1 have no practical influence on the intended effect. In the process of phosphate precipitation by water extract of brown coal ash the ratio of volume and alkalinity of reacting solutions is of importance (it is the general case in water treatment). For removing phosphate, which are especially susceptible to the water extract of fly ash, the optimal coefficient v is lower i.e. in the range 0.4-0.8. Very favourable is also the fact, that the alkalinity of the treated water is the activator of the process. Investigations and regression model of statistical analysis, have shown that the increase in alkalinity increases pronouncedly the amount of precipitated phosphates. The use of low v coefficients for phosphate removal is especially advantageous, since a temporary increase in pH is maintained within the limits of pH 9.0. At higher coefficient v the increase may reach the value 10. Investigation results described above indicate that the initial increase in PO 3- concentration is a factor restraining to a certain degree the intensity of the precipitation process. Nevertheless, basing on regres-
1293
sion model of statistical analysis, it is proved that the influence of this factor on the process is smaller than that of the alkalinity of the tested water and that of coefficient v. Taking into account the last two parameters only, it is possible to predict in 75~g the precipitation of a PO~- from water.
SUMMARY
A method of application of water extract of brown coal fly ash as a coagulant of phosphates from POlluted waters has been described. Reactivity of calcium, sodium, potassium, iron and aluminium hydroxides and sulphates with waters having temporary hardness, carbonate alkalinity and pH of 6-8 is utilized. Solid and suspension precipitate sediment easily, and water above the sediments shows a significant improvement of sanitary indicators (BODs and COD), and also removal of a substantial amount of phosphate ions occurs. It was observed, that phosphates precipitate immediately after introduction of the coagulant and after a short, intensive mixing of the solution. In the investigated process, the influence of some parameters on the degree of phosphate precipitation has been analysed. It has been determined on the basis of the results obtained and of a mathematical multiple regression model used in the investigations, {hat two parameters have the most significant influence, i.e. the coefficient v expressing the alkalinity and volume ratio of reacting waters, and the total alkalinity of the tested water. It has been shown, that only these two parameters enable 75% reliability of prediction of the precipitation of phosphate ions from any water indicating total hardness and alkalinity. Reactant alkalinity in the tested range of 40 mval53 reval 1-1 has no significant influence on the process. Higher initial PO~- ions concentration increase slightly residual PO~-. REFERENCES
Chrugciel J. (1964) Investigation on Konin brown coal mine wasters treatment. Rozpr. hydrotech. 15, 39-74. Chruk'iel J. (1971a) Some aspects of chemical coimatation in laboratory tests. Rozpr. hydroteeh. 25, 139-152. Chru~'iel J. (1971b)The method of water reservoir seating. Patent No. 67427. Chru~,-ielJ. (1973) The new method of water and waste water treatment using ash removal waters from thermal power stations. From the Problems Institute of Hyd° rocngin~ring PAS GdafisL Chru~iel J. & Kuziemska I. (1974) The method of waste water treatment. Patent No. 91010. Higgins B. B. et al. (1976) Lake treatment with fly ash, lime and gypsum. J. Wat. Pollut. Control Fed. 9, 2153-2167. Kuziemska I. (1973) The influence of chemical colmatation on the population of organisms living on the bottom and near the bottom of the water reservoir. Rozpr. hydrotech. 32, 317-327. Kuziemska I. (1973b) The infltlence of fly ash water extract over the precipitation of biogenic substances and the growth of plants in water reservoir. Archwm Hydrotech. 20, 363-378.