ELSEVIER

Bioresource Technology 65 (1998) 5 l-55 0 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain 0960-8524198 $19.00

PII:SO960-8524(98)00025-X

A MESOPHILIC: DIGESTION AN UNHEATED

OF BREWERY WASTEWATER IN ANAEROBIC FILTER

K. Leal,” E. Chacin,” E. Behling,” E. Gutierez; N. Fernandeza & C. F. Forstef*

“School of Civil Engineering, University of Zulia, l?O. Box 526, Maracaibo, Venezuela hSchool of Civil Engineering, Birmingham University, Edgbaston, Birmingham, UK.

(Received 28 November 1997; revised version received 13 January 1998; accepted 16 January 1998)

Abstract An anaerobic jilter (5.8 nz’) operated at ambient temperature was used to treat brewery wastewatel: The hydraulic retention time was maintained at a constant value (10 h) throughout the trial. The start-up period, to achieve fully stabilized conditions, was 6 months. At an applied loading rate of about 8 kg CODlm’d, the mean COD removal was 96% and the mean gas production was 7.1 m3/d. The methane content of the biogas was higher than is nformally found. During the steady state regime it was 80-95%. The results show that, when the ambient temperature is high, an anaerobic jilter can operate in the mesophilic range and be used to treat brewery wastewater successfilly. 0 1998 Elsevier Science Ltd. All rights reserved

Key words: Anaerobic digestion, brewery wastewater, anaerobic filtration.

INTRODUCTION

Anaerobic digestion is a process which has been used within the wastewater treatment industry for a considerable period of time. However, until relatively recently, it has been considered as a technology only for solids processing. The develop- ment of immobilized biomass systems, which separated the solids’ retention time from the hydraulic retention time, has led to the increasing popularity of anaerobic reactors as high-rate processes for the treatment of industrial waste- waters. These processes achieve COD reductions which are usually better than 70%. A recent survey (Nyns, 1994) has shown that, within the European Union, there are 330 anaerobic digesters treating industrial wastewaters. This is a significant increase compared with an earlier survey made in 1984 (Demuynck & Nyns, 1984) and is one which cannot be accounted for merely by the increase in the

*Author to whom correspondence should be addressed.

number of member states in the EU. The data in Fig. 1 are typical of the way in which the use of this technology is increasing. On an international basis, the total capacity of one process, the upflow sludge blanket reactor, installed between 1976 and 1993 was 57 x lo3 m3 treating some 500 tonnes COD/d (Biothane Systems International).

The wastewaters generated by breweries are highly polluting, typically, they would have a chemical oxygen demand (COD) in the range of 1200-3000 mg/l and a COD:BOD ratio of about 15 (Ruffer & Rosenwinkel, 1984). As such, they are the type of wastewater for which anaerobic digestion would be an acceptable treatment. Certainly, brewery wastewaters have been treated successfully

30

1 I ??

- . 1976 1978 1980 1982 1984

Fig. 1. Number of anaerobic digesters in The Netherlands (+) and Germany (0).

<l

52 K. Lea1 et al.

by various types of digester, ranging from fixed film systems (Lo & Liao, 1989) and completely stirred tank reactor (Brooking et al., 1990) to a expanded- bed digesters (Yongming et al., 1993). Indeed, the survey of digesters in the EU has shown that 12% of them were being used to treat wastewaters from breweries (Nyns, 1994).

Digesters treating brewery wastewaters are gener- ally operated in the mesophilic range, using biogas to provide the necessary heat. However, in tropical countries, the use of reactors which operate at ambient temperatures may be a real possibility. The successful application of an upflow sludge blanket digester for the treatment of brewery wastewater at 215°C has been reported previously (Yan & Tay, 1996). This paper describes the performance of a mesophilic anaerobic filter in Venezuela treating the wastewaters from a brewery without any supplemen- tary heating.

METHODS

The anaerobic filter, which was made from stainless steel, had a diameter of 1.47 m, an overall height of 3,954 m and was packed with PVC Raschig rings (21 mm internal diameter x 285 mm long). These were supported on a distribution plate fitted 287 mm from the base. The working volume of the packed filter was 5843 m3. The reactor was not heated, but the ambient temperatures were such that the temperature in the digester was between 34 and 39°C throughout the trial. The wastewater from the brewery, the composition of which is given in Table 1, was settled and pumped to the reactor (Milroyal, Model AMR l-58A-142SM) at a fixed rate of 584.3 l/h, giving a hydraulic retention time of 10 h. During the first 78 days of the trial, sodium bicarbonate was also added to the digester to give a working concentration of 1000 mg/l.

Alkalinity values of the influent and the treated effluent were measured by the standard titrimetric method using 0.05 M H2S04 (Greenberg et al., 1992). COD values were measured colourimetrically using a commercial dry block/sealed tube (2 ml) unit (Hach 1500 mg/l). Effluent pH values were measured with a standard meter (Corning, 140). The

Table 1. Chemical characteristics of the raw brewery waste

Parameter

COD P” Alkalinity Nitrogen Phosphate Iron

Concentration (mg/l)

Maximum Minimum Mean

3900 1400 2832 8 5.2 6.7

1670 430 600 16 27 20

7.8 12 4 7 z

biogas was collected by downward displacement of acidified (O-05 M H2S04) water and its composition measured with a portable gas meter (Gasranger 73 GR, Crowcon Instruments Ltd), the calibration of which was checked with known mixtures of methane and carbon dioxide. The volatile fatty acid (VFA) concentrations in the treated effluent were measured by gas-liquid chromatography (Perkin Elmer Autosystem) using a FFAP Quadrex capillary column (15 m x 0.25 mm ID). Oxygen-free nitrogen was used as the carrier gas at a flow-rate of 29 ml/min and the eluted fatty acids were detected by flame ionization. Their concentrations were measured by an integrator (PE Eelson 1022) which had been pre-calibrated with a standard mixture of fatty acids. Prior to analysis, the samples were filtered through a membrane filter (O-45 pm) and mixed with formic acid (1 part acid to 10 parts filtrate). The sample volume used was 1 ~1.

RESULTS AND DISCUSSION

Alkalinity measurements after day 78, when the bicarbonate supplements had been stopped, showed that there were still considerable fluctuations; from 430 to 1700 mg/l. This situation continued for a

100

90

80

70

16

16

14

12

B "i

10 8

$

8 s

8 0

6

4

,2

,O 0 50 100 150 200 250 300

TIME (days)

Fig. 2. COD removal (*) and loading (0) data for the trial period.

A mesophilic digestion of brewery wastewater 53

I i + a- i i :L”, ?? , ,

100

90

60

70

8

60s

E 508

Y 40 9

k 30

20

10

0

0 50 100 150 200 250 300

TIME (days)

Fig. 3. Gas production (+) and gas composition (a) data.

further 77 days. Thereafter, alkalinity values stabi- lized and remained at between 1100 and 1500 mg/l until the end of the trial.

The COD removal data are given in Fig. 2. These show that for the first 80 days the removal efficien- cies were poor and very erratic. The efficiency then stabilized for about 80 days with a mean value of 62.5 14.6% after which it. rose steadily to a peak value of 96.2f 1.2%. This needs to be compared with the performance data for the treatment of brewery wastewaters reported by other workers. A 5 year survey of a mesophilic digester (a completely

9-l ??

. 0 50 100 150 200 250 300

TIME (days)

Fig. 4. Variations in the digestor pH.

1200

1000

s J_ 800

g

d s g 600

8 w s t " 400 a

200

0 0 50 100 150 200 250 300

TIME (days)

Fig. 5. Changes in the acetic acid concentrations.

stirred tank reactor) treating the effluent from a plant producing lager showed that efficiencies were, in the main, > 90% (Wheatley et al., 1997) and a study using an upflow sludge blanket reactor at ambient temperatures (average working temperature of 21.8”C) gave a COD removal of 89% (Yan & Tay, 1996). In other words, the performance of the filter currently being examined was very comparable with what has been reported by other workers. The COD loads which were applied to the digester are also given in Fig. 2 and show that, although there were fluctuations throughout the trial period, two separate loading regimes can be defined. The first, which covered the initial period of about 100 days, applied a load of about 5 kg COD/m3 d. This coincided with the period of relatively poor COD removal, the start-up phase. The second had an applied loading rate of about 8 kg COD/m3 d. These loading rates are less than those reported previously for an anaerobic fluidized bed digester treating brewery wastes at ambient temperatures, 27-30 kg COD/m3 d (Yongming et al., 1993), but are compar- able with those reported for an upflow sludge blanket reactor, 12.2 kg COD/m3 d (Yan & Tay, 1996). This is typical of the effect that reactor configuration can have on performance.

The daily gas production data are given in Fig. 3. They show that, initially, the gas production was

54

roa

50

a

K. Lea1 et al.

0 50 100 150 200 250 300

TIME (days)

Fig. 6. Changes in the propionic acid concentrations.

poor and it was only after day 70 that significant volumes of gas were produced. The mean value at this time (70-180 days) was 6.1 f0.4 m3 d. At this point, the gas production increased and became more stable with a mean value of 7.1 kO.3 m3 d. The methane content of the biogas is also given in Fig. 3. This shows a similar pattern, with the amount of methane gradually increasing as the digester stabi- lized. It is interesting to note the very high methane concentrations @O-95%) which were recorded in the final steady state phase. No explanation can be given for this.

The variations in the pH values of the final effluent (Fig. 4) show a similar pattern; wide fluctua- tions for the first period of about 100 days, a transi- tion period also of about 100 days and a final relatively stable period. The mean pH during this stable period was 7.05. The gas chromatography analyses showed that the concentrations of the higher acids ( > C-4) were negligible, comprising less than 05% of the total, They were, therefore, not taken into consideration in any further interpreta- tion of the VFA variations. The concentrations of the individual volatile fatty acids, acetic, propionate and butyric, are given in Figs 5, 6 and 7, respectively. The changes in these concentrations are relatively similar. Initially, the concentrations were high, but after about 40-50 days had fallen to what might be

600

600

0 50 100 150 200 250 300

TIME (days)

Fig. 7. Changes in the butyric acid concentrations.

thought of as realistic operating values. It can be seen that there were peaks in the concentrations of all three acids followed by a gradual reduction. This occurred twice. On the first occasion, these peaks did not occur simultaneously. For acetate it happened on day 66, for propionate on day 81 and for butyrate on day 71. On the second occasion, the peaks all occurred on day 179. It is not known what caused these peaks to occur.

The operational stability of an anaerobic reactor can be judged in a variety of ways: the gas produc- tion, the gas composition or the VFA balance. The Water Pollution Control Federation design manual for anaerobic digestion (Parkin & Owen, 1986) recommends that the concentration of butyric acid should be below 15 mg/l, that the concentration of acetic acid should be less than 800 mg/l and that the ratio of propionic acid to acetic acid should be less than 1.4. The final butyrate concentrations did not conform to the design manual criterion, being about 25-30 mg/l (Fig. 7) and, before this final period of operation, had been significantly higher. The acetate concentrations, after the initial 10 days, were always less than the proscribed value of 800 mg/l (Fig. 5). Fig. 8 presents the way in which the propionate:ace- tate ratio varied over the operational period and it can be seen that, with one exception, all the values were less than the design manual figure, even during

A mesophilic digestion of brewery wastewater 55

1.6

1.4

1.2

g 1

P

ij 0.6 . .

k

S 0 3 0.6

g

0.4

0.2

C

0 50 100 150 200 250 300

TIME (days)

Fig. 8. Changes in the propionate:acetate ratio.

the start-up phase when a degree of instability might have been expected.

CONCLUSIONS

1. In a tropical country such as Venezuela, the ambient temperature was sufficiently high to maintain a digester temperature in the mesophilic range.

2. Stabilization of the digester, based on gas produc- tion, pH and alkalinity fluctuations, took about 5 months.

3. After the stabilization period, the filter achieved a COD removal in excess of 90% with a specific gas yield of 0.15 m3 CH&g COD removed.

ACKNOWLEDGEMENTS

The financial support of Consejo de Desarrollo Cientifico y Humanistic0 CONDES during this work is gratefully acknowledged.

REFERENCES

Brooking, J., Buckingham, C. & Fuggle, R. (1990). Constraints on effluent plant design for a brewery effluent treatment and waste disposal. 1. Chem. E. Symp., 116, 109-126.

Demuynck, M. & Nyns, E. J. (1984). Biogas Plants in Europe, Catholic University of Louvain, Louvain- la-Neuve, Belgium.

Greenberg, A. E., Clesceri, L. S. & Eaton, A. D. (eds) (1992). Standard Methods for the Examination of Water and Wastewater, 18th edn, APHA, AWWA, WEF, Washington.

Lo, K. V. & Liao, P. H. (1989). Anaerobic digestion of brewery wastewater using fixed film reactor Can. Agric. Engng, 31,61-63.

Nyns, E. J. (1994). A Guide to Successful Industrial Imple- mentation of Biomethanisation Technologies, Institute Wallon, Namur, Belgium.

Parkin, G. F. & Owen, W. F. (1986). The fundamentals of anaerobic digestion of waste water sludges J. Environ. Engng, 112, 867-920.

Ruffer, H. M. & Rosenwinkel, K-H. (1984). The treat- ment of wastewater from the beverage industry. In Surveys in Industrial Wastewater Treatment, eds D. Barnes, C. F. Forster & S. Hrudey, Vol. 1, Pitman, London, pp. 69-127.

Wheatley, A. D., Fisher, M. B. & Grobicki, A. M. W. (1997). Application of anaerobic digestion for the treat- ment of industrial wastewaters in Europe. J. CZWEM, 11,39-46.

Yan, Y. G. & Tay, J. H. (1996). Brewery wastewater treatment in UASB reactor at ambient temperature. J. Environ. Engng, 122, 550-553.

Yongming, L., Yi, Q. & Jicui, H. (1993). Research on the characteristics of start-up and operation of treating brewery wastewaters with an AFB reactor at ambient temperatures. Water Sci. Technol., 28, 187-195.