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The effect of temperature on the growth of microbial film in a model trickling filter
Water Res. Vol. 17, No. 4, pp. 375-382, 1983 Printed in Great Britain. All rights reserved
0043-1354/83/040375-08503.00/0 Copyright © 1983 Pergamon Press Ltd
THE EFFECT OF TEMPERATURE ON THE GROWTH OF MICROBIAL FILM IN A MODEL TRICKLING FILTER Y. HONDA1 and J. MATSUMOTO2 ' Department of Civil Engineering, Ashikaga Institute of Technology, Ashikaga 326 and 2Department of Civil Engineering, Tohoku University, Sendai 980, Japan (Received M a y 1981)
Abstract--The daily weight change of a microbial film in a model filter after the start of synthetic feed application was observed and the effect of temperature on the growth of the film was studied. The rate of BOD removal, the rate at which SS was washed out, the yield coefficient and the autolysis coefficient were chosen as the factors related to the growth of the film and the effects of temperature on them were examined. The growth pattern of the film can be divided into the lag-phase, growth-phase and stationary-phase. The growth equation of the film in the growth-phase was obtained by assuming that the rates of BOD removal and SS washed out were constant. In order to evaluate the growth of the film at various temperatures, the growth capacity and the mean growth rate were defined. The growth capacity is the film weight at the stationary-phase and expresses the maximum weight to which the film can increase in a given filter. The growth capacity increased as the temperature fell. This is due to the autolysis coefficient which becomes lower at low temperatures. The period necessary to reach the stationary-phase was shorter at high temperatures. The mean growth rate, which was defined as the rate when the film has reached half the growth capacity, was at its maximum at 15°C.
NOMENCLATURE b = autolysis coefficient Of the film, day= SS concentration in the influent and the filter effluent, g 1- x C = rate at which SS is washed out, g dayC~ = mean rate at which SS is washed out in growthphase, g day- 1 E = BOD removal efficiency, % Gc = growth capacity, g Q = flow rate, 1 dayr = correlation coefficient S i, S e = BOD concentration in the influent and the filter effluent, g 1S = rate of BOD removal, g dayS , = mean rate of BOD removal in growth-phase, g day- 1 t = time, days t O = period of lag-phase, days wd= ratio of the dry to the wet weights of the film, g
Ci, Ce
g-2
film weight, g film weight accumulated within lag-phase, g AXm = mean growth rate of the film, g dayy = yield coefficient of the film, g film g- a BOD. X=
X o =
INTRODUCTION In a trickling filter, which is one of the biological wastewater treatment processes, removal of organic matter is performed by a microbial film which forms on the surface of the filter media. In order to examine the mechanism of purification or to design filters, it is necessary to investigate the growth characteristics of the film. It has been known that the amount of film accumulating in the filter fluctuates seasonally and that the amount of film increases in winter and de-
creases in summer. As it would seem that the growth of film is influenced significantly by temperature, it is important to investigate the relationship between the growth of the film and the temperature. The causes of the seasonal fluctuation in the amount of film have been considered as: change in microbiological activity with temperature (Holtje, 1943; Heukelekian, 1945; Cooke & Hirsch, 1958) and change in the grazing activity of macro-fauna with temperature (Reynoldson, 1939; Tomlinson, 1946; Hawkes, 1961, 1965; Williams & Taylor, 1968). Shephard & Hawkes (1976) reported that in the presence of macro-fauna the amount of film is kept at a lower level by grazing activity than when controlled microbiologically. Factors other than temperature control the growth of the film: the flow rate (Heukelekian, 1945; Tomlinson, 1946; Hawkes, 1961) and organic loading (Heukelekian, 1945; Hawkes, 1965). The flow rate exerts influence on the hydraulic shear of liquid to the film, that is, suspended Solids washed out from the filter. Tomlinson & Hall (1955) and Hawkes & Shephard (1972) reported that the accumulation of the film in winter is reduced by low-frequency dosing achieved by retarding the speed of rotation of the distributor. The organic loading influences the amount of organic matter removed by the filter and the growth rate of the film, because a part of the organic matter removed is converted into the film. This paper reports on the effect of temperature on the growth of the film in a model filter after feed application has started. First, the rate of B O D removal by the filter, the rate of SS washed out from the
375
376
ItOYl)A and J. MAISUMOFO
lilter, the yield coefficient and the autolysis coefficient were chosen as the factors which are related to the growth of the film, and the effects of temperature on them were examined. The rate of B O D removal, the rate of SS washed out and the film weight were observed with the experimental filter. The yield and the autolysis coefficients were calculated from the experimental data concerning the film weight, the rate of B O D removal and the rate at which SS was washed out. Next, the growth equation of the film was derived on the basis of the experimental result. Further, in order to evaluate the growth of the film at various temperatures, the growth capacity and the mean growth rate were defined and compared with respect to temperature.
:d tonk
liter " !S
n:
mortar sphere with of 2.6 cm
;
-onneet the spheres THE GROWTH MECHANISM OF THE FILM W h e n the organic matter applied to the filter is removed by the film, a part of the organic matter removed is converted into the film and increases the film weight. O n the other hand, the film weight is decreased by autolysis. The film also decreases, as part of it is sheared by liquid. The growth rate of the film in the filter can be summarized as follows: dX dt
Y'(sl -
Se)'Q - b.X
+ (cl - ce)'Q
(1)
detach series from ~ ]
Fig. 1. The experimental equipment. factor in film reduction. However, the existence of grazers on the filter was ignored in this study.
where
Ci,
Si~
EXPERIMENT
film weight, g Y = yield coefficient of the film, g film g - 1 B O D b = autolysis coefficient of the film, d a y SS concentration in the influent and the £e filter effluent, g 1Se ~- B O D concentration in the influent a n d the filter effluent, g 1Q ~__ flow rate, I d a y t---- time, days.
X
Final settling basin
~-
c e is SS which is washed out continuously and is
distinguished from sloughed SS which slides down irregularly from the media. (si se)'Q in equation (1) is the rate of B O D removal. The effect of hydraulic shear by liquid can be expressed by subtracting c i ' Q from c~.Q. Then, substituting S = (S i -- Se)" Q and C = (ce - cl).Q, equation (1) can be rearranged as follows: dX dt
-
Y.S-b.X-C
(2)
where S = rate of B O D removal, g d a y - 1 C = rate at which SS is washed out, g day ~. In this study, C became c e ' Q , for the synthetic waste used did not contain SS. In addition to autolysis a n d hydraulic shear, the grazing activity of macro-fauna is considered as a
The experiment was performed in a temperature-controlled room and temperature was kept constant throughout the experimental period. The temperature conditions were as follows: 5, 10, 15, 20, 25 and 30°C. There was no occurrence of macro-fauna grazers in the film through all experiments. Apparatus
Figure 1 shows the experimental equipment. Cementmortar spheres with diameters of about 2.6cm were used as the filter media. Cement-mortar spheres were provided in a wire-through hole in the central axis. The experimental filter consisted of three series in which 10 spheres were connected in a row with wire, i.e. 30 spheres. The substrate was applied by means of a micro-tube pump to the top of the filter through a tube. The liquid flowed onto the surface of the spheres. To weigh the film. each series could be detached. Procedure
The constituents of the synthetic waste used are presented in Table 1. The synthetic waste was diluted at the ratio of 2l. of solution A and 11. of solution B per 10001. of tap water. The BOD concentration of the substrate was 0.14g 1-t. The flow rate was 8.61 da} ~ in all experiments. The hydraulic loading was raised in comparison with that for a standard trickling filter in order to make the kinetics acting on BOD removal zero-order. The hydraulic reading employed can be estimated m terms of the flow rate per unit surface area of the filter by identifying the small filter as an upper part of the whole in a full-scale filter. Since about 1500 filters consisting of filter media with a diameter Of 2,6 can can be arranged in a rectangular lattice form in an area of 1 m 2, the flow rate per filter will be estimated at approx, 0.67 t day- ~ under the hydraulic loading of l m a m -2 day -1 Hence. 8.61
377
Temperature effect on microbial film growth Table 1. Composition of the synthetic waste used Solution A
Solution B Concentration (g 1- ~)
Constituents Glucose Monosodium glutamate Sodium chloride Calcium chloride Magnesium sulfate
Concentration (g 1- l)
Constituents
50.0 50.0 5.0 2.5 1.7
Potassium phosphate monobasic
14.3
Potassium phosphate dibasic
90.15
d a y - ' is equivalent to a flow rate of approx. 13 m a m -2 day-~. At 20°C, an experimental flow rate of 5.01 day-1 was also tried. The substrate was renewed once a day at 5, 10 and 15°C, and twice a day at 20, 25 and 30°C. The tube was replaced daily in all experiments.
time. SS in the filter effluent was determined by filtration through filter paper No. 5B.
RESULTS AND DISCUSSION
Analytical methods
Figure 2 shows the development over time of the film weight after the start of feed application at a flow rate of 8.61 day-1. Figure 3 shows the time charts of the rates of B O D removal a n d SS washed out at a flow rate of 8.61 day-1. Figure 4 shows the time charts of the film weight and the rates of B O D removal and SS washed out at 20°C and a flow rate of 5.01 d a y - 1.
For each experiment, the wet weight of the film, BOD in the influent and filter effluent and suspended solids in the filter effluent were measured periodically. Each series of spheres was detached from the filter and was allowed to drain for 10 rain before measurement of the wet weight of the film. The wet weight of the film was obtained by suspending the series from a balance and subtracting their original weight. The dry weight of the film each time after the start of feed application was determined by multiplying the wet weight at that time by the ratio of the dry to wet weights obtained at the end of the experimental period. It was assumed that the ratio of the dry to wet weights of the film is constant throughout the experimental period. In this paper, the film weight is hereafter expressed by its dry weight. Samples of the influent and the filter effluent were collected at the end of the feed tube and the bottom of the filter, respectively. Samples for BOD test were filtered through filter paper No. 5B (Japanese Industrial Standard, P3801). The rate of BOD removal was corrected as described later, due to the decrease in feed concentration over
18
The 9rowth pattern of the film The experiments, except those at 10 and 15°C, were considered to be finished when it was ascertained that the film weight reached a fixed value. The experimental period at 5°C was not long enough as will be discussed later. The experiments at 10 and 15°C were stopped due to sloughing of the film. The experimental results shown in Figs 2 and 4 indicate the tendency of film growth to increase
]
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@@ al'@'@'~Sloughing'~
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25*c ,.,-e = %'e"
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values /
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I 50
® 20"C
e 25"C
~ ~1~o 8"Z*- ' Z - 30"C ,e e i
---
0
J~Sloughing
=
I
Time,
days
i
-- Calculated i
I I00
o 30°C
by equation ( 5 ) i
, 130
Fig. 2. The development over time of the film weight after the start of feed application at a flow rate of 8.61 day- 1.
~Tx
Y. Hoxl)A [ 5°C ]
~
ESO°C]
7
r . ~ Growth - phase
~
Growth- phase
o.e, ~cI ~ u, s ~
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o.5
0.5
J
F, 0 [ IOoC] %, 0 8 c~
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and J. M~,rs[;Mo[()
,
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~
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IO0
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Time, r ' P Growth-phase
-
O 40 E25"C3 Time, days o 8 ~ Growth- phase
$ 0.5
0.5
o
C
g
0
r°
,
,
,
,
i
,
SO
,
,
.
,
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Time, days
.
120
O
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Time, days
eo
E20°Cl
[15°C3
OgP t " ~ Growth - phase
(3
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90
Time, days
a
|
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O
SO 60 Time,
days
Fig. 3. The time charts of the rate of BOD removal (S) and the rate at which SS was washed out (C) at a flow rate of 8.61 day- 1 rapidly after a slow beginning, reduce in growth rate with time and finally reach a fixed value. Film growth increased rapidly after stow growth at the beginning at a temperature of 15°C or below. The film finally reached a fixed value at temperatures above 15°C. Kuwahara & Momoi (1967) reported that film weight increases gradually at the beginning and finally reaches a fixed value. Tomlinson (t946) and Solbe et al. (1974) reported that the growth pattern of the film is divided into the lag-phase and the growth-phase and that the film weight increases at a constant rate in the growth-phase. The results of this experiment show, however, that the growth rate is not constant and decreases as the film weight increases. Furthermore, results suggest that the growth pattern of the
film can be divided into a lag-phase, a growth-phase and a stationary-phase. The film accumulated in the filter during the experimental period increased as the temperature fell except when at 5°C. The transition from lag-phase to growth-phase was determined to be the time when the growth rate increased suddenly. The period of the lag-phase (to) and the film weight accumulated within that period (Xo) obtained at each temperature are summarized in Table 2. The lower the temperature, the longer and the larger became the values of to and Xo, respectively. The ratio of the dry to wet weights of the film (Wd) which was collected from the filter at the end of the experiment, is summarized in Table 2. The higher the temperature, the higher this ratio became. The rate o[ BOD removal
I
~o oo o~Op-O-°O
~
.c
5
.o~5
"9
/
_E -(Y o 0 o
i
0 T ~ 0.7,
u~
~)#0 0 Experimentalvalue
o"o°
u_'-
0
-- -
l
- Calculated by equation (5) i
i
J
50
Time, days 0
,.-e, . G r5o w t hi - phase / ~ S ~
Time, days
'
60 ]
50
60
Fig. 4. The time charts of the film weight, the rate of BOD removal (S) and the rate at which SS was washedout (C) at 20~'C and a flow rate of 51 day 1.
When the synthetic sewage used in this experiment was allowed to stand, the BOD concentration decreased with time. This decrease was particularly remarkable at high temperature. Figure 5 shows the time chart of BOD concentration during a day at 30C. As samples for the periodical BOD test were collected at 1 p.m., the rate of BOD removal calculated by that data is represented by the quadrangle ABCD shown in Fig. 5. The actual rate of BOD removal is represented by the shadowed portion in Fig. 5. The ratio of the area of the shadowed portion to the quadrangle ABCD was calculated and the rate of BOD removal was corrected. The corrected rates of BOD removal (S) are plotted in Figs 3 and 4. The experimental results shown in Figs 3 and 4 indicate that S increases with formation of the film after the start of feed application, and that S decreases somewhat after reaching a maximum and subse-
379
Temperature effect on microbial film growth Table 2. The experimental results of the factors related to the growth of the film Flow rate
(1 day- 1)
to
(days)
X0
(°C)
(g)
(g g- 1)
(g day- t )
(g day- 1)
(g g- 1)
(day- 1)
5 10 15 20 25 30 20
8.6 8.6 8.6 8.6 8.6 8.6 5.0
52 26 19 6 5 3 8
3.36 2.97 2.35 2.20 1.06 0.65 1.40
0.022 0.025 0.022 0.026 0.028 0.028 0.022
0.532 0.605 0.747 0.691 0.677 0.638 0.534
0.224 0,214 0.228 0.241 0.275 0.281 0.135
0.800 0.869 0.807 0.842 0.867 0.926 0.814
0.009 0.015 0.025 0.043 0.064 0.076 0.040
Temp.
Wa
quently remains approximately constant. The rate of BOD removal is influenced by the contacting area between the film and liquid. On a spherical filter medium, the film increases its surface area with increases in its weight. On the filter used, however, the rate of increase in the contacting area is considered to become extremely slow once the film is accumulated to a certain extent. With an accumulation of film at the junction between the filter media, the film on the filter came to assume the form of a cylinder rather than that of a chain of spheres. Consequently, the streak line of liquid more appeared rectilinear rather than a chain of arcs. The length of flow of the liquid from the top to the bottom of the filter was assumed to be constant. As the film increased in Size, the liquid became unable to cover the entire surface of the film, flowing only over part of it. Since the wetted periphery on the film surface was assumed constant under the condition of such ribbon flowl S remained essentially constant regardless of increases in the film. The decrease of S after reaching the maximum is attributable to two factors: reduction in the flow length of liquid, and anaerobic decomposition at the bottom of the film. The weight of the film at the time S reached the maximum in Figs 3 and 4 was approx. 2 g as shown in Figs 2 and 4, except at the temperature of 10°C. As the film was accumulated to this extent, the flow length of liquid was presumably reduced by an accumulation of film between the filter Renewal
Renewal
I1.
.n.
Sm
Cm
Y
b
media. Also, the bottom of the film was blackened to show a sign of anaerobic decomposition. This anaerobic decomposition is assumed to have an ill effect on the effluent. Except at temperatures of 5 and 10°C, S reached a maximum immediately after the beginning of the growth-phase. Therefore, it is estimated that S is constant in the growth-phase. This can be explained by the following assumptions: anaerobic decomposition attains to equilibrium and the contacting area is constant with a narrow ribbon flow. The mean rate of BOD removal in the growthphase (Sin) is summarized in Table 2. Figure 6 shows the effect of temperature on the Sm value. The value of Sm'was at a maximum at 15°C. The actual BOD loading varied somewhat with the temperature condition, because the concentration of the influent decreased with time as shown in Fig. 5. The BOD removal efficiency was also at a maximum at 15°C, Referring to Fig. 2, the film weight in the growth phase, which remained virtually constant at temperatures up to 15°C, became lower at higher temperatures. It is considered that the decrease of Sm at temperatures above 15°C is due chiefly to differences in the amount of the active film. This phenomenon may also be attributable to anaerobic decomposition at the bottom of the film. At 20°C, the Sm value at 5.01 day-1 was 0.77 times higher than that at 8.61 day-1. The value of Sm was not proportional to the flow rate. 1.0
Influent
I
I
I
i
1'7 I00
+~ +s.o, aay-'~
T 1D Ot
so
~JEO.5 0
E
/ ~ o/
i 9
~ I 13
c, , ~ ~ , ~ , ~
' I
I 17
~
:
+ I I
I 21
I
I I
I
I 5
I
I 9
O'clock
Fig. 5. The time chart of BOD concentration during a day
at 30°C.
0
I
I
I0 20 Temperature, *C
,
I 30
0
Fig. 6. The effects of temperature on the mean rate of
BOD removal (Sin),the mean rate at which SS was washed out (Cm)and the BOD removal efficiency(E).
3~0
"1 H ( ) N I ) A
31]d,I.
\l()l(}
NIAISt
~.or-~-
'l he rate at which SS was washed out The rate at which SS was washed out (C) shown in Figs 3 and 4 was approximately constant ira the growth-phase except for the period from t i0 to 120 days at 5 C. The above result can be explained b~ assuming that the contacting area between the film and liquid is constant with a narrow ribbon flow. The mean rate at which SS was washed out in the growth-phase (C,,) is summarized in Table 2. The effect of temperature on the C,, wdue is shown in Fig. 6. The value of C,, increased slightly as the temperature rose. It is concluded that the film is sheared more easily by liquids at high temperatures. At 2ffC, the C,, value at 5.01 d a y - ~ was 0.56 times higher than that at 8.61 day- ~. The value of C,, was proportional to the flow rate. The yield and atttolysis coefficients By transforming equation (2), the following equation is obtained: (dX/dt) + C .......... X
S Y .... X
b
(3)
where SS washed out from the filter is considered to be a part of the film. When the relationship between [(dX/dt) + C]/X and S/X are plotted, the values of the yield coefficient (Y) and the autolysis coefficient (b) can be determined as the slope and the intercept of the straight line obtained, repectively. Figure 7 shows the result obtained at 20°C and a flow rate of 8.61 day ~. The values of Y and b were calculated by the method of least squares. The values of Yand b at each temperature are summarized in Table 2. The correlation coefficient (r) at each temperature was greater than 0.95. Figure 8 shows the effects of temperature on Y and b. The value of b became higher as the temperature rose. It is estimated that the autolysis of the film proceeds at high temperatures. The higher the temperature, the higher became the value of Y, except at a temperature of 10'~C. The following reports on the
y
I
~
T ------r~j-O. JO~-- ---o
X3-~.
c~
- - o .... 0-
/a
"
./
0.5
-
0. I 0
/I~
'
>.7
D,/
T
,
0.05
"
/
/
b e.----je'" I IO
..~ -I~5.0 1day-' ,n
I 20
Temperature,
~
I-
0
30 *C
Fig. 8. The effects of temperature on the yield coefficient (Y) and the autolysis coefficient (b).
yield coefficient of the activated sludge process have been made. The yield coefficient was maximum at 20~C (Friedman & Schroeder. 1972), slightly higher at 15 C and constant at temperatures except 15~C (Hashimoto & Toriyama. 1977J. and constant between 4 and 2 O C and tower at 31~C (Sayigh & Malina. 1978l, It is necessary to take into account the effect of anaerobic decomposition with respect to the higher values of Yat high temperatures. If the resulting product from anaerobic decomposition mcreases B O D in the effluent, the real rate of B O D removal by the film is greater than that measured. The value of Y at a high temperature becomes lower, because the value of S/X in equation /3) becomes larger and the slope of the straight line obtained becomes smaller, It seems to be probable that Yis constant with respect to temperature. At 20' Ck the values of Y and b were approximately constant with respect to the flow rate. It is predicted that in the same waste, the values of Y and b are constant at the same temperature regardless of the loading condition. CONSIDERATION
OF THE GROWTH
OF THE FILM
The ,qrowth equation ~?/ the.film 0.14
'
'
'
Correlation
Z7"
'
I
'
"
i
coefficient
tri'O.9~3
o.,o
'"
I
o/_
oO~O
In this experiment, the rate of BOD removal and the rate at which SS was washed out were approximately constant in the growth-phase. Assuming that the rate of B O D removal and the rate at which SS was washed out in the growth-phase are constant, equation (2) becomes as follows: dX
~1
0
X
~ --0.06
dt
• (Y) • 0.842
,
, S -~,
I 0.I0
,
g day-t
,
,
Y'Sm-b'X-Cm
(4)
where
Infercept(b) • 0.043 '
-
, 0.20
g-I
Fig, 7. Determination of the yield coefficient (Y) and the autolysis coefficient (b) at 20°C and a flow rate of 8~61 day- 2.
S m = mean rate of B O D removal in growth-phase, g day ~ C,, = mean rate at which SS was washed out in growth-phase, g d a y - ~. By integrating equation (4) by the initial condition of
Temperature effect on microbial film growth X = Xo at t = to, the growth equation of the film in the growth-phase is obtained. X -
Y' S~ - C,, [1 - e -b(t-t°)] + X0"e -b(t-t°) (5) b
25"C IO0 ~ 3 0 ° C
9e
20°C
?,
381 15°C
IO°C
5"C.
90
where 80
to = period of lag-phase, days Xo = film weight accumulated within lag-phase, g. To
The results calculated by equation (5) using the experimental values in Table 2 are shown in Figs 2 and 4. The values calculated approximately agree with the experimental values. It is concluded that the growth of the film in the growth-phase can be estimated by equation (5).
60
ooL 0
I00
200
Period, Growth capacity
When t becomes large in equation (5), e -b"-'°) approaches 0 and X approaches (Y. S,. - C,,)/b. That is, Go= lim X -
Y . S ~ - C,,
t-~
(6)
b
where G~ is given the name "growth capacity" and is equal to the film weight in the stationary-phase. When the loading, filter and temperature conditions are given, G~ expresses the maximum weight to which the film can increase in that filter. Figure 9 shows the effect of temperature on the G~ value. The value of G~ increased with the decrease of temperature. This is due to the fact that b becomes lower at low temperatures. At 20°C, the value of G~ at 5.01 day-~ was closer to that at 8.61 day-~. This is due to the f~ct that S,, was not proportional to the flow rate, although C,, was. Figure l0 shows the period taken until the film weight reaches G~. The higher the temperature, the shorter this period became. It is seen from Figs 9 and 10 that at low temperatures, the film reaches the stationary-phase slowly but that the amount finally accumulated is large, while at high temperatures, the
300
400
500
doys
Fig. 10. The period taken until film weight reaches the growth capacity. stationary-phase is reached rapidly but the final amount is small. At 5°C, the film weight at the time the experiment finished, was 55.7~o of G~. It takes more than 500 days at 5°C for the film weight to reach 99~ of Go. If the experiment at 5°C had not been stopped on the 126th day, the film weight would have increased further. The film at temperatures of 10 and 15°C sloughed after 113 and 89 days, respectively. Sloughing is when the film slides down irregularly from the surface of the media. In this study, sloughed SS is distinguished from the product of part of the film being continuously sheared by liquid. When the forces of adhesion between the film and the media are weakened by anaerobic decomposition (Heukelekian, 1945; Schulze, 1957) or macro-fauna grazing (Reynoldson, 1939; Holtje, 1943), the media can no longer support the film and the film sloughs. If the Gc value is larger than the amount of film which the media can support, the Gc value cannot be obtained practically, because the film sloughs before it reaches Go. Growth rate
24
I
I
I
0,~4
c~ 20
0.20
T
oJo ~: X <3
lo
AX
+ 5.0 1 day -I I
0
I
'10
z
I
20
,
I.
30
Temperature, =C
Fig. 9. The effects of temperature on the growth capacity (Go) and the mean growth rate (AX,,).
As seen from equation (4), as the film weight increases, the growth rate decreases and becomes 0 at X = Go. In order to evaluate the growth rate at various temperatures, the growth rate at X = Gel2 is examined. This rate is termed the "mean growth rate (AX,,)'. AX,, is obtained by substituting X = Gel2 for equation (4). AXr,=
X=~o/2
~
(7)
The value of AX,, is plotted in Fig. 9. The AX,, value was at a maximum at 15°C, because S,, became maximum at 15°C. The decrease of AX,. at temperatures above 15°C is also influenced by the increases of C,.. In the case of 20°C, the AX,. value at 5.0 1 day- 1 was closer to that at 8.61 day- 1.
3s2
H()NI)A and ,I. MAISt 'q()l() CON('I,USIONS
The following conclusions may be drawn as the results of this study : (1) The effects of temperature on the factors which control the growth of the film were examined by using a model filter. The rate of B O D removal was at a m a x i m u m at 15C. The rate at which SS was washed out increased as the temperature rose. The yield coefficient and the autolysis coefficient became higher as the temperature rose. The yield and autolysis coefficients were approximately constant regardless of the flow rate. {2) The growth pattern of the film after the start of feed application can be divided into the lag-phase, the growth-phase and the stationary-phase. The growth of the film in the growth-phase can be estimated by equation (5). (3) The growth capacity defined by equation (6) increased as the temperature decreased. This is due to the autolysis coefficient which becomes lower at low temperatures. O n the other hand, the period necessary to reach the stationary-phase was shorter at high temperatures. (4) The mean growth rate defined by equation (7) was at a m a x i m u m at 15°C. Acknowledqement--The authors wish to express their thanks to Mr T. Nakayama for his assistance in the accomplishment of the experimental program. REFERENCES
Cooke W. B. & Hirseh A. (1958) Continuous sampling of trickling filter populations. Sewaye Ind. Wastes 30. 138-156. Friedman A. A. & Schroeder E, D. (1972) Temperature effects on growth and yield of activated sludge. J. Wat. Pollut. Control Fed. 44, 1433 1442. Hashimoto S. & Toriyama A. (1977) Kinetic studies on the
influence of temperature upon the purification pertormante of activated sludge process {Part 2)..I. J,pan Sew. Wks ,Is.s. 14, (161), 26 36 iin Japanese). Hawkes H. A. {1961l An ecological approach to some bacteria bed problems..J. Inst. Sew. Puri£ No, 2. 105 127 Hawkes H. A. (1965) Factors inltuencing the seasonal incidence of fungal growths in sewage bacteria beds. I~g. ,l Air H/at. Pollut. 9, 693 714. Hawkes H. A. & Shephard M. R. N. 11972} The effect of dosing-frequency on the seasonal fluctuations and vertical distribution of solids and grazing fauna in sewage percolating filters. Water Res. 6, 721 730. Heukelekian H. (1945t The relationship between accumulation, biochemical and biological characteristics of film, and purification capacity of a biofilter and a standard filter. Sewage Wks J. 17, 23- 38. Holtje R. H. {I943) The biology of sewage sprinkling filters. Sewage l+~s J. 15, 14 29. Kuwahara R. & Momoi I. 11967) Biological studies on the trickling filter in a human waste disposal plant. Wat. Pur(ll Liquid Wastes Treat. 8, No. 3, 25 32 (in Japanese). Reynoldson T. B. (1939) The role of macro-organisms in bacteria beds. J. hist. Sew. Pur(ll No. 1, 158-168. Sayigh B. A. & Malina J. F. (1978) Temperature effects on the activated sludge process. J. Wat. Pollut. Control Fed. 50, 678 687. Schulze K. L. (1957) Experimental vertical screen trickling filter. Sewaye Ind. Wastes 29. 458-467. Shephard M. R. N. & Hawkes H. A. (1976) Laboratory studies on the effects of temperature on the accumulation of solids in biological filters. Wat. Pollut. Control 75, 58- 72. Solb6 J. F. de L. G., Ripley P. G. & Tomlinson T. G. {t974) The effects of temperature on the performance of experimental percolating filters with and without mixed macro-invertebrate populations. Water Res. 8, 557-573. Tomlinson T. G. (1946) Growth and distribution of film in percolating filters treating sewage by single and alternating double filtration, d. Inst. Sew. Pur(ll No. 1, 168- 178. Tomlinson T. G. & Hal1 H. (1955) The effect of periodicity of dosing on the efficiency of percolating filters. J. Inst. Sew. Purifi No. 1, 40 47. Williams N. V. & Taylor H. M. {1968} The effect of Psychoda alternata (Say.), (Diptera) and LumbrMllus ricatis (Levinsen) (Enchytraeidae) on the efficiency of sewage treatment in percolating filters. Wetter Res. 2, 139 150.
0043-1354/83/040375-08503.00/0 Copyright © 1983 Pergamon Press Ltd
THE EFFECT OF TEMPERATURE ON THE GROWTH OF MICROBIAL FILM IN A MODEL TRICKLING FILTER Y. HONDA1 and J. MATSUMOTO2 ' Department of Civil Engineering, Ashikaga Institute of Technology, Ashikaga 326 and 2Department of Civil Engineering, Tohoku University, Sendai 980, Japan (Received M a y 1981)
Abstract--The daily weight change of a microbial film in a model filter after the start of synthetic feed application was observed and the effect of temperature on the growth of the film was studied. The rate of BOD removal, the rate at which SS was washed out, the yield coefficient and the autolysis coefficient were chosen as the factors related to the growth of the film and the effects of temperature on them were examined. The growth pattern of the film can be divided into the lag-phase, growth-phase and stationary-phase. The growth equation of the film in the growth-phase was obtained by assuming that the rates of BOD removal and SS washed out were constant. In order to evaluate the growth of the film at various temperatures, the growth capacity and the mean growth rate were defined. The growth capacity is the film weight at the stationary-phase and expresses the maximum weight to which the film can increase in a given filter. The growth capacity increased as the temperature fell. This is due to the autolysis coefficient which becomes lower at low temperatures. The period necessary to reach the stationary-phase was shorter at high temperatures. The mean growth rate, which was defined as the rate when the film has reached half the growth capacity, was at its maximum at 15°C.
NOMENCLATURE b = autolysis coefficient Of the film, day= SS concentration in the influent and the filter effluent, g 1- x C = rate at which SS is washed out, g dayC~ = mean rate at which SS is washed out in growthphase, g day- 1 E = BOD removal efficiency, % Gc = growth capacity, g Q = flow rate, 1 dayr = correlation coefficient S i, S e = BOD concentration in the influent and the filter effluent, g 1S = rate of BOD removal, g dayS , = mean rate of BOD removal in growth-phase, g day- 1 t = time, days t O = period of lag-phase, days wd= ratio of the dry to the wet weights of the film, g
Ci, Ce
g-2
film weight, g film weight accumulated within lag-phase, g AXm = mean growth rate of the film, g dayy = yield coefficient of the film, g film g- a BOD. X=
X o =
INTRODUCTION In a trickling filter, which is one of the biological wastewater treatment processes, removal of organic matter is performed by a microbial film which forms on the surface of the filter media. In order to examine the mechanism of purification or to design filters, it is necessary to investigate the growth characteristics of the film. It has been known that the amount of film accumulating in the filter fluctuates seasonally and that the amount of film increases in winter and de-
creases in summer. As it would seem that the growth of film is influenced significantly by temperature, it is important to investigate the relationship between the growth of the film and the temperature. The causes of the seasonal fluctuation in the amount of film have been considered as: change in microbiological activity with temperature (Holtje, 1943; Heukelekian, 1945; Cooke & Hirsch, 1958) and change in the grazing activity of macro-fauna with temperature (Reynoldson, 1939; Tomlinson, 1946; Hawkes, 1961, 1965; Williams & Taylor, 1968). Shephard & Hawkes (1976) reported that in the presence of macro-fauna the amount of film is kept at a lower level by grazing activity than when controlled microbiologically. Factors other than temperature control the growth of the film: the flow rate (Heukelekian, 1945; Tomlinson, 1946; Hawkes, 1961) and organic loading (Heukelekian, 1945; Hawkes, 1965). The flow rate exerts influence on the hydraulic shear of liquid to the film, that is, suspended Solids washed out from the filter. Tomlinson & Hall (1955) and Hawkes & Shephard (1972) reported that the accumulation of the film in winter is reduced by low-frequency dosing achieved by retarding the speed of rotation of the distributor. The organic loading influences the amount of organic matter removed by the filter and the growth rate of the film, because a part of the organic matter removed is converted into the film. This paper reports on the effect of temperature on the growth of the film in a model filter after feed application has started. First, the rate of B O D removal by the filter, the rate of SS washed out from the
375
376
ItOYl)A and J. MAISUMOFO
lilter, the yield coefficient and the autolysis coefficient were chosen as the factors which are related to the growth of the film, and the effects of temperature on them were examined. The rate of B O D removal, the rate of SS washed out and the film weight were observed with the experimental filter. The yield and the autolysis coefficients were calculated from the experimental data concerning the film weight, the rate of B O D removal and the rate at which SS was washed out. Next, the growth equation of the film was derived on the basis of the experimental result. Further, in order to evaluate the growth of the film at various temperatures, the growth capacity and the mean growth rate were defined and compared with respect to temperature.
:d tonk
liter " !S
n:
mortar sphere with of 2.6 cm
;
-onneet the spheres THE GROWTH MECHANISM OF THE FILM W h e n the organic matter applied to the filter is removed by the film, a part of the organic matter removed is converted into the film and increases the film weight. O n the other hand, the film weight is decreased by autolysis. The film also decreases, as part of it is sheared by liquid. The growth rate of the film in the filter can be summarized as follows: dX dt
Y'(sl -
Se)'Q - b.X
+ (cl - ce)'Q
(1)
detach series from ~ ]
Fig. 1. The experimental equipment. factor in film reduction. However, the existence of grazers on the filter was ignored in this study.
where
Ci,
Si~
EXPERIMENT
film weight, g Y = yield coefficient of the film, g film g - 1 B O D b = autolysis coefficient of the film, d a y SS concentration in the influent and the £e filter effluent, g 1Se ~- B O D concentration in the influent a n d the filter effluent, g 1Q ~__ flow rate, I d a y t---- time, days.
X
Final settling basin
~-
c e is SS which is washed out continuously and is
distinguished from sloughed SS which slides down irregularly from the media. (si se)'Q in equation (1) is the rate of B O D removal. The effect of hydraulic shear by liquid can be expressed by subtracting c i ' Q from c~.Q. Then, substituting S = (S i -- Se)" Q and C = (ce - cl).Q, equation (1) can be rearranged as follows: dX dt
-
Y.S-b.X-C
(2)
where S = rate of B O D removal, g d a y - 1 C = rate at which SS is washed out, g day ~. In this study, C became c e ' Q , for the synthetic waste used did not contain SS. In addition to autolysis a n d hydraulic shear, the grazing activity of macro-fauna is considered as a
The experiment was performed in a temperature-controlled room and temperature was kept constant throughout the experimental period. The temperature conditions were as follows: 5, 10, 15, 20, 25 and 30°C. There was no occurrence of macro-fauna grazers in the film through all experiments. Apparatus
Figure 1 shows the experimental equipment. Cementmortar spheres with diameters of about 2.6cm were used as the filter media. Cement-mortar spheres were provided in a wire-through hole in the central axis. The experimental filter consisted of three series in which 10 spheres were connected in a row with wire, i.e. 30 spheres. The substrate was applied by means of a micro-tube pump to the top of the filter through a tube. The liquid flowed onto the surface of the spheres. To weigh the film. each series could be detached. Procedure
The constituents of the synthetic waste used are presented in Table 1. The synthetic waste was diluted at the ratio of 2l. of solution A and 11. of solution B per 10001. of tap water. The BOD concentration of the substrate was 0.14g 1-t. The flow rate was 8.61 da} ~ in all experiments. The hydraulic loading was raised in comparison with that for a standard trickling filter in order to make the kinetics acting on BOD removal zero-order. The hydraulic reading employed can be estimated m terms of the flow rate per unit surface area of the filter by identifying the small filter as an upper part of the whole in a full-scale filter. Since about 1500 filters consisting of filter media with a diameter Of 2,6 can can be arranged in a rectangular lattice form in an area of 1 m 2, the flow rate per filter will be estimated at approx, 0.67 t day- ~ under the hydraulic loading of l m a m -2 day -1 Hence. 8.61
377
Temperature effect on microbial film growth Table 1. Composition of the synthetic waste used Solution A
Solution B Concentration (g 1- ~)
Constituents Glucose Monosodium glutamate Sodium chloride Calcium chloride Magnesium sulfate
Concentration (g 1- l)
Constituents
50.0 50.0 5.0 2.5 1.7
Potassium phosphate monobasic
14.3
Potassium phosphate dibasic
90.15
d a y - ' is equivalent to a flow rate of approx. 13 m a m -2 day-~. At 20°C, an experimental flow rate of 5.01 day-1 was also tried. The substrate was renewed once a day at 5, 10 and 15°C, and twice a day at 20, 25 and 30°C. The tube was replaced daily in all experiments.
time. SS in the filter effluent was determined by filtration through filter paper No. 5B.
RESULTS AND DISCUSSION
Analytical methods
Figure 2 shows the development over time of the film weight after the start of feed application at a flow rate of 8.61 day-1. Figure 3 shows the time charts of the rates of B O D removal a n d SS washed out at a flow rate of 8.61 day-1. Figure 4 shows the time charts of the film weight and the rates of B O D removal and SS washed out at 20°C and a flow rate of 5.01 d a y - 1.
For each experiment, the wet weight of the film, BOD in the influent and filter effluent and suspended solids in the filter effluent were measured periodically. Each series of spheres was detached from the filter and was allowed to drain for 10 rain before measurement of the wet weight of the film. The wet weight of the film was obtained by suspending the series from a balance and subtracting their original weight. The dry weight of the film each time after the start of feed application was determined by multiplying the wet weight at that time by the ratio of the dry to wet weights obtained at the end of the experimental period. It was assumed that the ratio of the dry to wet weights of the film is constant throughout the experimental period. In this paper, the film weight is hereafter expressed by its dry weight. Samples of the influent and the filter effluent were collected at the end of the feed tube and the bottom of the filter, respectively. Samples for BOD test were filtered through filter paper No. 5B (Japanese Industrial Standard, P3801). The rate of BOD removal was corrected as described later, due to the decrease in feed concentration over
18
The 9rowth pattern of the film The experiments, except those at 10 and 15°C, were considered to be finished when it was ascertained that the film weight reached a fixed value. The experimental period at 5°C was not long enough as will be discussed later. The experiments at 10 and 15°C were stopped due to sloughing of the film. The experimental results shown in Figs 2 and 4 indicate the tendency of film growth to increase
]
I
f
I
~ iO°C"
@@ al'@'@'~Sloughing'~
15
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.z
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@@
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o
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E U_
/
•
20
@/¢,@
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~ @ 5"C
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_
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J @ IO*C
25*c ,.,-e = %'e"
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J @ 15"C
values /
t.
,
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I 50
® 20"C
e 25"C
~ ~1~o 8"Z*- ' Z - 30"C ,e e i
---
0
J~Sloughing
=
I
Time,
days
i
-- Calculated i
I I00
o 30°C
by equation ( 5 ) i
, 130
Fig. 2. The development over time of the film weight after the start of feed application at a flow rate of 8.61 day- 1.
~Tx
Y. Hoxl)A [ 5°C ]
~
ESO°C]
7
r . ~ Growth - phase
~
Growth- phase
o.e, ~cI ~ u, s ~
S
o.5
0.5
J
F, 0 [ IOoC] %, 0 8 c~
"~
~
and J. M~,rs[;Mo[()
,
a
,
J
l
J
~
n
50
J
~
i
130
IO0
doys
Time, r ' P Growth-phase
-
O 40 E25"C3 Time, days o 8 ~ Growth- phase
$ 0.5
0.5
o
C
g
0
r°
,
,
,
,
i
,
SO
,
,
.
,
lOO
Time, days
.
120
O
50
Time, days
eo
E20°Cl
[15°C3
OgP t " ~ Growth - phase
(3
(~
50
0
90
Time, days
a
|
|
•
O
SO 60 Time,
days
Fig. 3. The time charts of the rate of BOD removal (S) and the rate at which SS was washed out (C) at a flow rate of 8.61 day- 1 rapidly after a slow beginning, reduce in growth rate with time and finally reach a fixed value. Film growth increased rapidly after stow growth at the beginning at a temperature of 15°C or below. The film finally reached a fixed value at temperatures above 15°C. Kuwahara & Momoi (1967) reported that film weight increases gradually at the beginning and finally reaches a fixed value. Tomlinson (t946) and Solbe et al. (1974) reported that the growth pattern of the film is divided into the lag-phase and the growth-phase and that the film weight increases at a constant rate in the growth-phase. The results of this experiment show, however, that the growth rate is not constant and decreases as the film weight increases. Furthermore, results suggest that the growth pattern of the
film can be divided into a lag-phase, a growth-phase and a stationary-phase. The film accumulated in the filter during the experimental period increased as the temperature fell except when at 5°C. The transition from lag-phase to growth-phase was determined to be the time when the growth rate increased suddenly. The period of the lag-phase (to) and the film weight accumulated within that period (Xo) obtained at each temperature are summarized in Table 2. The lower the temperature, the longer and the larger became the values of to and Xo, respectively. The ratio of the dry to wet weights of the film (Wd) which was collected from the filter at the end of the experiment, is summarized in Table 2. The higher the temperature, the higher this ratio became. The rate o[ BOD removal
I
~o oo o~Op-O-°O
~
.c
5
.o~5
"9
/
_E -(Y o 0 o
i
0 T ~ 0.7,
u~
~)#0 0 Experimentalvalue
o"o°
u_'-
0
-- -
l
- Calculated by equation (5) i
i
J
50
Time, days 0
,.-e, . G r5o w t hi - phase / ~ S ~
Time, days
'
60 ]
50
60
Fig. 4. The time charts of the film weight, the rate of BOD removal (S) and the rate at which SS was washedout (C) at 20~'C and a flow rate of 51 day 1.
When the synthetic sewage used in this experiment was allowed to stand, the BOD concentration decreased with time. This decrease was particularly remarkable at high temperature. Figure 5 shows the time chart of BOD concentration during a day at 30C. As samples for the periodical BOD test were collected at 1 p.m., the rate of BOD removal calculated by that data is represented by the quadrangle ABCD shown in Fig. 5. The actual rate of BOD removal is represented by the shadowed portion in Fig. 5. The ratio of the area of the shadowed portion to the quadrangle ABCD was calculated and the rate of BOD removal was corrected. The corrected rates of BOD removal (S) are plotted in Figs 3 and 4. The experimental results shown in Figs 3 and 4 indicate that S increases with formation of the film after the start of feed application, and that S decreases somewhat after reaching a maximum and subse-
379
Temperature effect on microbial film growth Table 2. The experimental results of the factors related to the growth of the film Flow rate
(1 day- 1)
to
(days)
X0
(°C)
(g)
(g g- 1)
(g day- t )
(g day- 1)
(g g- 1)
(day- 1)
5 10 15 20 25 30 20
8.6 8.6 8.6 8.6 8.6 8.6 5.0
52 26 19 6 5 3 8
3.36 2.97 2.35 2.20 1.06 0.65 1.40
0.022 0.025 0.022 0.026 0.028 0.028 0.022
0.532 0.605 0.747 0.691 0.677 0.638 0.534
0.224 0,214 0.228 0.241 0.275 0.281 0.135
0.800 0.869 0.807 0.842 0.867 0.926 0.814
0.009 0.015 0.025 0.043 0.064 0.076 0.040
Temp.
Wa
quently remains approximately constant. The rate of BOD removal is influenced by the contacting area between the film and liquid. On a spherical filter medium, the film increases its surface area with increases in its weight. On the filter used, however, the rate of increase in the contacting area is considered to become extremely slow once the film is accumulated to a certain extent. With an accumulation of film at the junction between the filter media, the film on the filter came to assume the form of a cylinder rather than that of a chain of spheres. Consequently, the streak line of liquid more appeared rectilinear rather than a chain of arcs. The length of flow of the liquid from the top to the bottom of the filter was assumed to be constant. As the film increased in Size, the liquid became unable to cover the entire surface of the film, flowing only over part of it. Since the wetted periphery on the film surface was assumed constant under the condition of such ribbon flowl S remained essentially constant regardless of increases in the film. The decrease of S after reaching the maximum is attributable to two factors: reduction in the flow length of liquid, and anaerobic decomposition at the bottom of the film. The weight of the film at the time S reached the maximum in Figs 3 and 4 was approx. 2 g as shown in Figs 2 and 4, except at the temperature of 10°C. As the film was accumulated to this extent, the flow length of liquid was presumably reduced by an accumulation of film between the filter Renewal
Renewal
I1.
.n.
Sm
Cm
Y
b
media. Also, the bottom of the film was blackened to show a sign of anaerobic decomposition. This anaerobic decomposition is assumed to have an ill effect on the effluent. Except at temperatures of 5 and 10°C, S reached a maximum immediately after the beginning of the growth-phase. Therefore, it is estimated that S is constant in the growth-phase. This can be explained by the following assumptions: anaerobic decomposition attains to equilibrium and the contacting area is constant with a narrow ribbon flow. The mean rate of BOD removal in the growthphase (Sin) is summarized in Table 2. Figure 6 shows the effect of temperature on the Sm value. The value of Sm'was at a maximum at 15°C. The actual BOD loading varied somewhat with the temperature condition, because the concentration of the influent decreased with time as shown in Fig. 5. The BOD removal efficiency was also at a maximum at 15°C, Referring to Fig. 2, the film weight in the growth phase, which remained virtually constant at temperatures up to 15°C, became lower at higher temperatures. It is considered that the decrease of Sm at temperatures above 15°C is due chiefly to differences in the amount of the active film. This phenomenon may also be attributable to anaerobic decomposition at the bottom of the film. At 20°C, the Sm value at 5.01 day-1 was 0.77 times higher than that at 8.61 day-1. The value of Sm was not proportional to the flow rate. 1.0
Influent
I
I
I
i
1'7 I00
+~ +s.o, aay-'~
T 1D Ot
so
~JEO.5 0
E
/ ~ o/
i 9
~ I 13
c, , ~ ~ , ~ , ~
' I
I 17
~
:
+ I I
I 21
I
I I
I
I 5
I
I 9
O'clock
Fig. 5. The time chart of BOD concentration during a day
at 30°C.
0
I
I
I0 20 Temperature, *C
,
I 30
0
Fig. 6. The effects of temperature on the mean rate of
BOD removal (Sin),the mean rate at which SS was washed out (Cm)and the BOD removal efficiency(E).
3~0
"1 H ( ) N I ) A
31]d,I.
\l()l(}
NIAISt
~.or-~-
'l he rate at which SS was washed out The rate at which SS was washed out (C) shown in Figs 3 and 4 was approximately constant ira the growth-phase except for the period from t i0 to 120 days at 5 C. The above result can be explained b~ assuming that the contacting area between the film and liquid is constant with a narrow ribbon flow. The mean rate at which SS was washed out in the growth-phase (C,,) is summarized in Table 2. The effect of temperature on the C,, wdue is shown in Fig. 6. The value of C,, increased slightly as the temperature rose. It is concluded that the film is sheared more easily by liquids at high temperatures. At 2ffC, the C,, value at 5.01 d a y - ~ was 0.56 times higher than that at 8.61 day- ~. The value of C,, was proportional to the flow rate. The yield and atttolysis coefficients By transforming equation (2), the following equation is obtained: (dX/dt) + C .......... X
S Y .... X
b
(3)
where SS washed out from the filter is considered to be a part of the film. When the relationship between [(dX/dt) + C]/X and S/X are plotted, the values of the yield coefficient (Y) and the autolysis coefficient (b) can be determined as the slope and the intercept of the straight line obtained, repectively. Figure 7 shows the result obtained at 20°C and a flow rate of 8.61 day ~. The values of Y and b were calculated by the method of least squares. The values of Yand b at each temperature are summarized in Table 2. The correlation coefficient (r) at each temperature was greater than 0.95. Figure 8 shows the effects of temperature on Y and b. The value of b became higher as the temperature rose. It is estimated that the autolysis of the film proceeds at high temperatures. The higher the temperature, the higher became the value of Y, except at a temperature of 10'~C. The following reports on the
y
I
~
T ------r~j-O. JO~-- ---o
X3-~.
c~
- - o .... 0-
/a
"
./
0.5
-
0. I 0
/I~
'
>.7
D,/
T
,
0.05
"
/
/
b e.----je'" I IO
..~ -I~5.0 1day-' ,n
I 20
Temperature,
~
I-
0
30 *C
Fig. 8. The effects of temperature on the yield coefficient (Y) and the autolysis coefficient (b).
yield coefficient of the activated sludge process have been made. The yield coefficient was maximum at 20~C (Friedman & Schroeder. 1972), slightly higher at 15 C and constant at temperatures except 15~C (Hashimoto & Toriyama. 1977J. and constant between 4 and 2 O C and tower at 31~C (Sayigh & Malina. 1978l, It is necessary to take into account the effect of anaerobic decomposition with respect to the higher values of Yat high temperatures. If the resulting product from anaerobic decomposition mcreases B O D in the effluent, the real rate of B O D removal by the film is greater than that measured. The value of Y at a high temperature becomes lower, because the value of S/X in equation /3) becomes larger and the slope of the straight line obtained becomes smaller, It seems to be probable that Yis constant with respect to temperature. At 20' Ck the values of Y and b were approximately constant with respect to the flow rate. It is predicted that in the same waste, the values of Y and b are constant at the same temperature regardless of the loading condition. CONSIDERATION
OF THE GROWTH
OF THE FILM
The ,qrowth equation ~?/ the.film 0.14
'
'
'
Correlation
Z7"
'
I
'
"
i
coefficient
tri'O.9~3
o.,o
'"
I
o/_
oO~O
In this experiment, the rate of BOD removal and the rate at which SS was washed out were approximately constant in the growth-phase. Assuming that the rate of B O D removal and the rate at which SS was washed out in the growth-phase are constant, equation (2) becomes as follows: dX
~1
0
X
~ --0.06
dt
• (Y) • 0.842
,
, S -~,
I 0.I0
,
g day-t
,
,
Y'Sm-b'X-Cm
(4)
where
Infercept(b) • 0.043 '
-
, 0.20
g-I
Fig, 7. Determination of the yield coefficient (Y) and the autolysis coefficient (b) at 20°C and a flow rate of 8~61 day- 2.
S m = mean rate of B O D removal in growth-phase, g day ~ C,, = mean rate at which SS was washed out in growth-phase, g d a y - ~. By integrating equation (4) by the initial condition of
Temperature effect on microbial film growth X = Xo at t = to, the growth equation of the film in the growth-phase is obtained. X -
Y' S~ - C,, [1 - e -b(t-t°)] + X0"e -b(t-t°) (5) b
25"C IO0 ~ 3 0 ° C
9e
20°C
?,
381 15°C
IO°C
5"C.
90
where 80
to = period of lag-phase, days Xo = film weight accumulated within lag-phase, g. To
The results calculated by equation (5) using the experimental values in Table 2 are shown in Figs 2 and 4. The values calculated approximately agree with the experimental values. It is concluded that the growth of the film in the growth-phase can be estimated by equation (5).
60
ooL 0
I00
200
Period, Growth capacity
When t becomes large in equation (5), e -b"-'°) approaches 0 and X approaches (Y. S,. - C,,)/b. That is, Go= lim X -
Y . S ~ - C,,
t-~
(6)
b
where G~ is given the name "growth capacity" and is equal to the film weight in the stationary-phase. When the loading, filter and temperature conditions are given, G~ expresses the maximum weight to which the film can increase in that filter. Figure 9 shows the effect of temperature on the G~ value. The value of G~ increased with the decrease of temperature. This is due to the fact that b becomes lower at low temperatures. At 20°C, the value of G~ at 5.01 day-~ was closer to that at 8.61 day-~. This is due to the f~ct that S,, was not proportional to the flow rate, although C,, was. Figure l0 shows the period taken until the film weight reaches G~. The higher the temperature, the shorter this period became. It is seen from Figs 9 and 10 that at low temperatures, the film reaches the stationary-phase slowly but that the amount finally accumulated is large, while at high temperatures, the
300
400
500
doys
Fig. 10. The period taken until film weight reaches the growth capacity. stationary-phase is reached rapidly but the final amount is small. At 5°C, the film weight at the time the experiment finished, was 55.7~o of G~. It takes more than 500 days at 5°C for the film weight to reach 99~ of Go. If the experiment at 5°C had not been stopped on the 126th day, the film weight would have increased further. The film at temperatures of 10 and 15°C sloughed after 113 and 89 days, respectively. Sloughing is when the film slides down irregularly from the surface of the media. In this study, sloughed SS is distinguished from the product of part of the film being continuously sheared by liquid. When the forces of adhesion between the film and the media are weakened by anaerobic decomposition (Heukelekian, 1945; Schulze, 1957) or macro-fauna grazing (Reynoldson, 1939; Holtje, 1943), the media can no longer support the film and the film sloughs. If the Gc value is larger than the amount of film which the media can support, the Gc value cannot be obtained practically, because the film sloughs before it reaches Go. Growth rate
24
I
I
I
0,~4
c~ 20
0.20
T
oJo ~: X <3
lo
AX
+ 5.0 1 day -I I
0
I
'10
z
I
20
,
I.
30
Temperature, =C
Fig. 9. The effects of temperature on the growth capacity (Go) and the mean growth rate (AX,,).
As seen from equation (4), as the film weight increases, the growth rate decreases and becomes 0 at X = Go. In order to evaluate the growth rate at various temperatures, the growth rate at X = Gel2 is examined. This rate is termed the "mean growth rate (AX,,)'. AX,, is obtained by substituting X = Gel2 for equation (4). AXr,=
X=~o/2
~
(7)
The value of AX,, is plotted in Fig. 9. The AX,, value was at a maximum at 15°C, because S,, became maximum at 15°C. The decrease of AX,. at temperatures above 15°C is also influenced by the increases of C,.. In the case of 20°C, the AX,. value at 5.0 1 day- 1 was closer to that at 8.61 day- 1.
3s2
H()NI)A and ,I. MAISt 'q()l() CON('I,USIONS
The following conclusions may be drawn as the results of this study : (1) The effects of temperature on the factors which control the growth of the film were examined by using a model filter. The rate of B O D removal was at a m a x i m u m at 15C. The rate at which SS was washed out increased as the temperature rose. The yield coefficient and the autolysis coefficient became higher as the temperature rose. The yield and autolysis coefficients were approximately constant regardless of the flow rate. {2) The growth pattern of the film after the start of feed application can be divided into the lag-phase, the growth-phase and the stationary-phase. The growth of the film in the growth-phase can be estimated by equation (5). (3) The growth capacity defined by equation (6) increased as the temperature decreased. This is due to the autolysis coefficient which becomes lower at low temperatures. O n the other hand, the period necessary to reach the stationary-phase was shorter at high temperatures. (4) The mean growth rate defined by equation (7) was at a m a x i m u m at 15°C. Acknowledqement--The authors wish to express their thanks to Mr T. Nakayama for his assistance in the accomplishment of the experimental program. REFERENCES
Cooke W. B. & Hirseh A. (1958) Continuous sampling of trickling filter populations. Sewaye Ind. Wastes 30. 138-156. Friedman A. A. & Schroeder E, D. (1972) Temperature effects on growth and yield of activated sludge. J. Wat. Pollut. Control Fed. 44, 1433 1442. Hashimoto S. & Toriyama A. (1977) Kinetic studies on the
influence of temperature upon the purification pertormante of activated sludge process {Part 2)..I. J,pan Sew. Wks ,Is.s. 14, (161), 26 36 iin Japanese). Hawkes H. A. {1961l An ecological approach to some bacteria bed problems..J. Inst. Sew. Puri£ No, 2. 105 127 Hawkes H. A. (1965) Factors inltuencing the seasonal incidence of fungal growths in sewage bacteria beds. I~g. ,l Air H/at. Pollut. 9, 693 714. Hawkes H. A. & Shephard M. R. N. 11972} The effect of dosing-frequency on the seasonal fluctuations and vertical distribution of solids and grazing fauna in sewage percolating filters. Water Res. 6, 721 730. Heukelekian H. (1945t The relationship between accumulation, biochemical and biological characteristics of film, and purification capacity of a biofilter and a standard filter. Sewage Wks J. 17, 23- 38. Holtje R. H. {I943) The biology of sewage sprinkling filters. Sewage l+~s J. 15, 14 29. Kuwahara R. & Momoi I. 11967) Biological studies on the trickling filter in a human waste disposal plant. Wat. Pur(ll Liquid Wastes Treat. 8, No. 3, 25 32 (in Japanese). Reynoldson T. B. (1939) The role of macro-organisms in bacteria beds. J. hist. Sew. Pur(ll No. 1, 158-168. Sayigh B. A. & Malina J. F. (1978) Temperature effects on the activated sludge process. J. Wat. Pollut. Control Fed. 50, 678 687. Schulze K. L. (1957) Experimental vertical screen trickling filter. Sewaye Ind. Wastes 29. 458-467. Shephard M. R. N. & Hawkes H. A. (1976) Laboratory studies on the effects of temperature on the accumulation of solids in biological filters. Wat. Pollut. Control 75, 58- 72. Solb6 J. F. de L. G., Ripley P. G. & Tomlinson T. G. {t974) The effects of temperature on the performance of experimental percolating filters with and without mixed macro-invertebrate populations. Water Res. 8, 557-573. Tomlinson T. G. (1946) Growth and distribution of film in percolating filters treating sewage by single and alternating double filtration, d. Inst. Sew. Pur(ll No. 1, 168- 178. Tomlinson T. G. & Hal1 H. (1955) The effect of periodicity of dosing on the efficiency of percolating filters. J. Inst. Sew. Purifi No. 1, 40 47. Williams N. V. & Taylor H. M. {1968} The effect of Psychoda alternata (Say.), (Diptera) and LumbrMllus ricatis (Levinsen) (Enchytraeidae) on the efficiency of sewage treatment in percolating filters. Wetter Res. 2, 139 150.