Long term BOD determinations on biologically treated and untreated kraft mill effluent discharged to Lake Saimaa, Finland

Long term BOD determinations on biologically treated and untreated kraft mill effluent discharged to Lake Saimaa, Finland

Wafer R,~'arch Vol. ~. pr' 5~5 to 541. Pergamon Pre~s 1974. Prln~cd ~n Great Britain LONG TERM BOD DETERMINATIONS ON BIOLOGICALLY TREATED AND UNTREAT...

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Wafer R,~'arch Vol. ~. pr' 5~5 to 541. Pergamon Pre~s 1974. Prln~cd ~n Great Britain

LONG TERM BOD DETERMINATIONS ON BIOLOGICALLY TREATED AND UNTREATED KRAFT MILL EFFLUENT DISCHARGED TO LAKE SAIMAA, FINLAND H. HnDtrcrnm~o and M. F. WILSON Water Research Institute, National Board of Waters, Helsinki, Finland (Receired 12 January 19741

Abstract--Long-term BOD determinations have been carried out on kraft pulp mill effluent over a period of more than 200 days using the conventional dilution method and utilizing a special bottle sealing technique. Determinations were made at the temperatures 2, 5. 10 and 20°C on untreated effluent and on effluent treated by an experimental biological extended aeration treatment plant which treated effluent discharged to Lake Saimaa in eastern Finland. BOD curves have been constructed for up to a period of 200 days and the results indicate that untreated effluent exerts a two-stage BOD on receiving waters, the second stage commencing after approx. 28 days. Treated effluent was found to have a low BOD and showed no second sta~ of oxygen uptake. INTRODUCTION

ever, that the main constituents of pulping waste are wood sugars, organic acids, alcohols and lignin, the In Finland the consumption of water for the production proportion of the latter varying with the process. It is of pulp and paper is very large and these industries use a well known fact that, when discharged to a stream, about 75 per cent of all the water consumed. In partic- lignin has a high colouring effect and constitutes an ular the consumption of kraft mills is about 150-700 m 3 excessive organic load; however, the contribution made of water per ton of unbleached pulp and 200-650 m 3 by lignins to the long-term BOD is still not clear. per ton of bleached pulp; the lower figures being for Whereas Lawrance and Sakamoto (1959) found the mills where effective water circulation is employed microbiological oxidation of lignin to be very small, (Noukka, 1970). Many pulp mills are situated in the Woodard, Sproul and Atkins (1964) successfully develinterior of the country and the need for improvements oped an acclimated activated sludge which was specific in their waste treatment has become an important issue for the removal of lignin from pulp mill wastes and in recent years. able to utilize lignin as its sole source of carbon. The The long-term BOD determinations reported in this literature reveals that the work of Woodard et al. was paper were undertaken for the following reasons: successful in that they were able to develop a suitable (1) In order to investigate the long-term BOD ex- bacterial culture, and it is worth noting that this is in erted on Finnish natural inland waters as a result of conflict with the work of Zobell and Stadler (1940) who discharging untreated pulping effluent to such waters, pointed out that microorganisms which are capable of and in particular the extent of degradation of imporutilizing lignins are rare and the biological degradation tant constituents of the effluent such as lignins. (The is very slow. A previous investigation similar in nature to that effect of temperature on the degradation process is also an important factor to be taken into consideration in described here was carried out by Raabe (1968), who view of the extreme conditions of the Finnish climate). determined the long-term BOD of kraft pulping ef(2) In order to assess the effectiveness oftbe extended fluent over a period of 100 days and at a temperature aeration biological treatment process for the removal of 20°C. Raabe's work revealed a two stage BOD proof both primary and secondary BOD taking into con- cess, the first stage being rapid and attributed to the sideration the operation of the plant in Finnish condi- oxidation of the carbohydrate constituents and the second stage, which was slow, was "suggestive of the tions without the dosing of nutrients. The chemical nature and composition of pulping decomposition of the lignin and its byproducts and effluent varies significantly with the pulping process other decomposable organics". Although much research has been carried out on the and although a detailed analysis of the waste is rarely undertaken, such determinations as BOD, COD, biological treatment of kraft mill effluents by the use colour, suspended solids and lignin serve to charac- of the activated sludge process, this problem has been investigated in Finland for several reasons: terize the nature of the effluent. It may be stated how535

536

H. HIIDENFIEIMOand M. F. WtLSOh"

(a) The climate differs markedly from that in most other countries where similar research work has been carried out, the most important factor being extremes of temperature. (b) The extended aeration process has been investigated to a limited extent, and in the past, pilot plants have been of the conventional or high-rate activated sludge process. (c) Due to the acceleration of eutrophication in Finnish inland waters it has been necessary to attempt to eliminate the dosing of nutrients in biological treatment processes and this is possible in the extended aeration process. During the period 1967-1972 experiments were carried out in Finland and these showed that the extended aeration method can be succesfully applied in kraft mill effluent treatment. For a full account of the experimental pilot plant and treatment process the work of Hiidenheimo* (1969, 1970) should be consulted. EXPERIMENTAL The samples of untreated pulping effluent were taken below the mill (Kaukas Ltd., Lappecnranta)at a point of flow into a series of aeration lagoons; samples of treated effluent were taken from the outflow of the pilot plant which was situated at the same point. The samples were received for laboratory experiments within 4 h of being collected. The BOD determinations were carried out by using the standard dilution method, Standard Methods (1971). The required dilutions for a long-term experiment were estimated from a knowledge of the BODy values of previous samples, the COD, and an examination of previous results obtained from similar experiments. The dilution and seeding of the samples was carried out such that the amount of seed added was small and the dilution was sufficient to reduce the effects of any toxins present, e.g. mercaptans. It was also arranged that the concentration of the diluted sample was large enough to exert a measurable BOD and that the initial oxygen concentration was sufficient to last throughout the duration of the experiment i.e. such that reaeration of the samples could be avoided. (A reaeration technique has been employed by some workers, but it was felt that errors might possibly be introduced and it was avoided in this work). On the basis of the above factors, the untreated effluent was diluted to 1 per cent with dilution water prepared as given in Standard Methods (1971). The added seed was obtained from waters within the vicin* Copies of these publications may be obtained from the Water Research Institute, National Board of Waters, Helsinki, Finland.

ity of the mill and was the same seed normally used in BOD- tests; the seeding was 0-25 ml I- t at 20~C, 0.50 ml [-t at 10"C and 0.75 ml 1-~ at 5 and 2:C. For the treated water samples the dilution made was 2 per cent and the seeding was the same. The dilution water was made up from distilled water and its BOD was assumed to be zero: the BOD of the seeding water was the same as that of the untreated effluent. The incubation bottles were of the reagent type, of vol. 125 ml and fitted with ground glass stoppers. The procedure for preparing the samples for incubation was the standard BOD method except that the bottles were sealed by a special technique. First, in order to facilitate their removal, the stoppers were sprayed with Teflon (Fluoroglide Spray, Chem. Plast. Inc., U.S.A.); then, after filling, they were inserted and excess liquid was removed from the rim with a tissue. Finally, after drying in air for a few minutes, the bottles were completely sealed with vacuum wax which was applied hot to the glass rim. The wax used was Apiezon W+o (manufacturer Shell Chemicals Ltd) and this was found to be suitable as a high penetrating wax and was also easily removable with a suitable tool. Wax of this type provided a reliable seal for a period as long as 12 months. The oxygen content of the bottles was determined by the standard Winkler method and each bottle was used for one determination; throughout the period of the experiment at least duplicate analyses were carried out. The bottles were contained in four thermostat baths maintained at the separate temperatures and light was excluded. RESULTS AND DISCUSSION The results of BOD values determined over a period of approximately 370 days at different temperatures for untreated and treated effluent are presented in Tables 1 and 2 respectively. Results for up to 200 days are shown plotted in Figs. 1-4, and for untreated effluent in all cases the findings are in agreement with the results of Raabe (1968); i.e. each plot indicates a twostage BOD process taking place, the second stage commencing after a period of about 28 days incubation at each of the temperatures; this is depicted by the broken line drawn through the points. The first plateau occurring in the curves may be seen more dearly by consulting the numerical values presented in Table I. Between 21 and 28 days it is shown that at all temperatures the BOD reaches a constant value and then proceeds to rise again. Furthermore it is also apparent that the step in the curves becomes less pronounced as the temperature decreases and at 2°C it has virtually disappeared. As in previous work of this kind the broken curves for the untreated effluent suggest that

BOD determinations on kraft mill effluent

537

Table 1. BOD values for untreated kraft pulping effluent in the temperature range 2-20~C (values given as mg O: 1- t) Temperatures

BOD; BODt.= BOD=t BOD2s BOD,., BODs~ BODTz BOD;~ BODg~ BODao s BOD,3~ BODt99 BODa~7

20°C

10°C

240,246 264, 273 293,302 293, 287 349. 354 333, 331 329, 326 318 334, 340. 336 339, 334 353, 352, 359 356, 357

199, 180 187, 189 206,214 196, 226. 203 224, 206 285, 278 218, 211 241 202, 210 323 317,294, 255 291 217, 256

5~C

2°C

20, 25 101,107 114, 95 91, 98 155. 159 174, 145 185, 165

14, 24 0, 0 68, 50 25, 59 97, 102 73, 99

270, 181,244 232, 281 148.143,256 454 188, 152

90, 71, 91 108. 106 119,103, 94 83 115, 78

Table 2. BOD values for treated kraft pulping effluent in the temperature range 2-20°C (values given as mg 1- t) Temperatures

BOD7 BODt,t BOD2t BOD2a BOD4t BODs6 BODy6 BOD96 BODI0 ~ BODt3 t BODt98 BOD365

20°C

10~C

5°C

77, 74 95, 94 124, 118 135, 108, 111 126, 124 143, 133 135, 126 149, 145 151,152, 149 153, 142, 148 152, 156

44, 44 60, 53 89 73, 84 112. 88 61, 73 66, 71 88, 87 86, 70 54, 78 75 72, 71

8, 1 I 17 16, 11 12 19, 23 24, 39 17, 21 36, 38 42, 46 83.58 26, 23, 28 38.32

2 0 =C

2°C 0 O, O, O, O, O, 9

0 0 0 0 0

11, 14 23, 21, 13 34, 30 10, 48

~7 U n t r e a t e d o Treated y = 19( p i O'0"4ZOt) ~2 72 (I-iO00~t)+ 63(I-Io'OOZCXt'~)

400

....... v

~

~

~

~ V

---v-j /

y = 3 3 6 ( I - 1 0 "O'OflSt)

T_. 300

C]

o

ZOO y = 1 4 3 ( i - 1 0 "0"036 t ]

I00

I

ZO

I

40

I

60

I

80

I

IO0

1

I ZO

I

140

I

160

I

180

200

Days

Fig. 1. BOD curves for untreated and treated effluent at 20"C. (Broken curves indicate a two stage BOD).

H. HIIDE,,'HEIMO a n d M . F. 'A,'tLSON

538

IO°C

400

: Un t reat'ed

--

Treated

300

&

--

T

r,, 0 ,-n

~

y=254

(l

-

iO-0043')

r,

200

y = 7 5 ('1- I0- ° ° $ ° t )

O

iO0

o

I

I

20

I

40

60

I

o

I

80

I

100

I

I 20

140

I

160

I

180

200

Days B O D c u r v e s for u n t r e a t e d a n d t r e a t e d effluent at 10~C. ( B r o k e n c u r v e s indicate a t w o stage BOD).

Fig. 2.

400

--

500

-

Untreated o Treated

5oc

a

& &

T

A

r,

"

= ,. vn( I - 10O0154') -; = ~

0 0

y = 4 0 ( 1 - 1 0 -O'Olot )

200 O O rn 1(30-

///

°~"~"~'--~°1 20

° I 60

40

gl 80

_n

I

I00

F:I

1

120

I

140

I

~60

I 180

0 200

Days

Fig. 3.

BaD

curves f o r untreated and treated effluent at 5°C. ( B r o k e n curves indicate a t w o stage B O D ) . 2oc

400

--

Untreated o Treated

300

T

--

200

y = 1 0 4 ( 1-160"0=35t) a o

m

rOd

~

20

'

~

'

40

~

'

y= 3 2 ( I - I 0 "00064(t-70)

60

80

100

120

140

160

180

200

Days

Fig. 4.

BaD curves for untreated and treated effluent at 2°C. (Broken curves indicate a two stage BAD).

BOD determinations on kraft mill effluent there is a first stage which is related to the concentration of the carbohydrate constituent in the effluent, and a second stage which is indicative of the biological degradation of an oxidisable fraction of the lignin compounds together with any other slowly decomposable organic substances present. Examination of the curves for treated effluent reveals that the second stage has disappeared, suggesting that almost all of the carbohydrate and part of the oxidisable fraction of lignin may have been removed during the biological treatment process. It should be noted that, for the untreated effluent, any possibility of the second stage of oxygen uptake being due to nitrification of ammonia present (either from the standard dilution water or from the effluent itself) may be discounted. This is because in all cases the amounts of ammonia involved were so small as to produce a negligible effect on the overall oxygen uptake. For example, the standard dilution water contained only 0.6 mg NH 3 per litre and calculation shows that, were nitrification to occur, the overall oxygen uptake would only increase by approximately 2 mg l-t, compared to an actual second stage increase of 30-40 mg 1- t at 20°C. Moreover, if nitrification due to added ammonia were to produce a second stage of oxygen uptake, we would expect to observe it in the results for both untreated and treated effluent since the standard dilution water

539

used in both cases was the same; however, such was not the case. Likewise. calculation shows that ammonia nitrogen already present in the untreated effluent (see Table 3) would not contribute any measureable effect after dilution. The fraction of lignin remaining after biological degradation has been investigated by other workers. Kroner and Moore (1953) found that 41-46 per cent of lignin remained after approx. 20 weeks, and experiments carried out by Raabe (1968) showed that about 51 per cent of lignin remained after 15 weeks. Some guide to the degradation taking place during the extended aeration biological treatment process considered in this work may be obtained by examining results of chemical and biological analysis carried out over the periods of operation of the treatment plant, these results are summarised in Table 3. On average the BOD~ removal is 70 per cent, but the values for the permanganate number determined according to Deutsche Einheitsverfahren (1968) show that the reduction of COD by the treatment plant is on average about 30 per cent. The high permanganate number of the plant effluent together with the fact that it had an appreciable colour is an indication that much lignin remained in the treated water and was not removed during the extended aeration process. That the

Table 3. Results of chemical analyses of untreated and treated effluent from Kraft Mill, Kaukas Ltd., Finland (Birch and Pine Pulp Production). Results given are average values over the stated period. Nitrogen and phosphorus were not dosed during these periods Period

Untreated effluent: (Temperature, °C) pH BOD7 mg I- t KMnO, m g l - t TotalN m g l - t TotalP mglPilot plant: (Temperature, °C) Hydraulic load, m3m-3d - t Organic load, kg BOD7 m- 3 d- t Sludge load, kg BOD~ kg- t d- t Sludge quantity, kg m- 3 BOD~ removal, % KMnO4 removal, ~

20.7.1971-8.10.1971

29.10.1971-13.12.1971

27 6"8

14 6-7

106

150

430 2"3 0"5

546 2"8 0"4

22 1.7 0.18 0.07 2.6 73 24

13 1.7 0-26 0-09 2-8 67 15

Treated effluent:

pH

BOD7 m g 1- t KMn04 mgl-t

6"9 29 330

7'3 50 466

540

H. HHDENHEIMOand M. F. V¢[LSON

Table 4. Rate constants and ultimate oxygen demand values for untreated pulping effluent at 20:C obtained by curve fitting equation: Y=Li[I - 10-~'r] +L.[I -lO-k-'~]+L3[l - I0 -k'"-t'°] Parameter

L l mgl - t kt L_, mg l-I k,.

L3 m g l - I k3 to days

This work

Value determined by Raabe

18-9 0-,120 272 0.085 62.9 0-020 28

33 0-455 65 0-072 103 0.080 23

treated water had a low long-term BOD value and gave no secondary stage in the BOD curve suggests that the discharged coloured wastewater contained mostly nonoxidisable lignin compounds. The results in Table 3 also confirm that BODy values are not a good indication of the ultimate demand of the untreated effluent over the long-term. The long-term BOD, (Y), involving a secondary stage, may be expressed in terms of the equation: Y=L~ [1 - l O - ~ " ] + L: [ l - l O - ~ ' ] + +L3 [1 - l0 - k ' " - ' ° ' ] where: k t and k 2 are rate constants for the first stage fast and slow components respectively, and k 3 is the rate constant for the second stage. L values are ultimate oxygen demands. By means of a computor attempts were made to fit the data for the untreated effluent given in Table 1 to the above equation; this was done by carrying out a standard curve fitting procedure. This is useful in that it allows the determination of k and ultimate BOD values. It was found that successful fit could be achieved Table 5. Rate constants and ultimate oxygen demand values for untreated and treated effluent in the temperature range 2-20-C obtained by use of the equation: Y=L[I - 10-kl. . . . )] Temperature °C

20 10 5 2 20 10 5 2

L mg I- t Untreated effluent 336 254 210 104 Treated effluent 143 75 40 32

k

to

0.055 0-043 0-015 0.014

0 0 0 0

0-036 0.050 0-010 0.0064

0 0 0 70

only for the results obtained at 20~C, and the values of the parameters obtained are presented in Table 4; the results are compared with values found by Raabe (1968) who used a similar equation. Examination of the results in Table 4 reveals that the rate constants k, and k z for the first stage are strikingly similar to those of R a a b e - the ultimate demand values in our work being appreciably larger. The constants for the second stage differ quite markedly and this suggests that the nature of the lignin constituents in the effluents are different. Although the BOD values at the other temperatures could not be fitted to the six parameter equation, the results for both untreated and treated effluent given in Tables 1 and 2 could be fitted to the simplified expression: Y= L 1"1- I0 -k( . . . . ~] and this is shown by the full lines drawn in Figs. 1-4. The corresponding parameters are presented in Table 5. The results show the effect of temperature on the rate constant and ultimate demand value; it is apparent that the microbiological activity is affected, and this is reflected in the ultimate demand values which decrease with temperature. It is also worth noting that at 2°C the value of t o is 70 days for the treated effluent. The value of k for pulp mill effluent at 20°C is often reported to be 0.10, but Rennerfelt (1958) has pointed out that the value may vary considerably with the nature of the wastewater.

CONCLUSIONS (I) The work reported here shows that the long-term BOD of untreated kraft pulp mill effluent exhibits a two-stage process over a temperature range of 2-20°C. The second stage is thought to be mainly due to the oxidation of a fraction of the lignin compounds present and this oxidation becomes less significant as the temperature decreases. (2) The extended aeration biological treatment process appears to remove most of the oxidizable fraction oflignin compounds but an appreciable amount of nonoxidizable lignin products are discharged in the treatment plant effluent. This work suggests that this nonoxidizable lignin fraction is stable in natural waters. (3) The effect of temperature on the long-term BOD has been investigated for both untreated and treated effluent and it has been found that the ultimate demand decreases with temperature. Similarly the rate constants are also affected and the values at 20°C are between four and six times greater than those at 2°C.

BOD determinations on kraft mill etIlucnt REFERENCES Deutsche Einheitsverfahren zur Wasser, Abwasser und Schlammtmtersuchung. 3 v611igneubearbeitete Auflage, 5. Lieferung (1968) H4, Weinheim/Bergstrasse. Hiidenheimo H. (1969) Investigation of the biological treatment of pulp mill effluents by the use ofextended aeration. Part 1. Soil and Hyflrotechnical Investigations, Helsinki. Hiidenheimo H. (1970) Investigation of the biological treatment of pulp mill effluents by the use of extended aeration. Part 2. Soil and Hydrotechnical Investigations, Helsinki. Kroner R. C. and Moore W. A. (1953) The Persistence of lignin in river waters. 8th Purdue Ind. Waste Conf. Purdue Univ. Ext. Ser. 83, 122. Lawrance W. A. and Sakamoto W. (1959) The microbial oxidation of pure carbohydrate in the presence of calcium lignosulphonate. National Council for Stream Improvement, Tech. Bull. No. 80.

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Noukka K. (1970) The waste load of pulp and paper mills in waters and the possibilities to decrease it (in Finnish). Vesiensuojelutoimiston tiedonantoja no: 54. Helsinki. Raabe E. W. (1968) Biochemical oxygen demand and degradation of lignin in natural waters. J. Wat. Pollut. Control Fed. 40, 5 R 145. Rennerfelt T. G. V. (1958) BOD of pulp mill wastes, its determination and importance. Verh. Internat. Vet. Limnol. XIH, 545. Standard Methods for the examination of water and wastewater, APHA, AWWA, WPCF, 13th Edition (1971). Washington. Woodard F. E., Sproul O. T. and Atkins Jr., P. F. (1964) The biological degradation of lignin from pulp mill black liquor. J. War. Pollut. Control Fed. 36, 11, 1401. ZobeU C. E. and Stadler T. (1940) The oxidation of lignin by bacteria from ponds and lakes. Arch. Hydrobiol. 37, 163.