Biotechnology Letters vol 6 NO 11 753-758 (1984)

TREATMENT OF DAIRY INDUSTRY WASTEWATER

WITH AN ANAEROBIC FILTER

P. R.C&-doba2”, F-Sanchez Riera2and F.Sineriz’

PROIMI (Planta Pilot0 de Procesos Industriales Microbiolbgicos) S.M.Tucuman - 4000 - R.Argent i na

SUMMARY

Concentrat ions of up to 10.2 g COD/L were appl ied to an horizontal anaerobic filter at 4O”C, obtaining efficiencies in COD removal of 85%. The contents of the reactor are kept mixed by recycl ing and at a pH value of 6.9.

The addition of al kal i to the inf 1 uent increases the product ion of biogas reaching a maximum of 250 L of methane per kg of COD removed.

INTRODUCTION

The amount of wastewater leaving a multiproduct dairy can reach

amounts of 2.3 1 itres of wastewater per kg of finished product and can

have a strength higher than 5.0 g COD/L (Carawan et al. ,1979). These

wastewaters could be treated by the standard methods: aerobic treatment,

chemical treatment or by simple irrigation. Anaerobic treatment has the

advantage of being far more economic when used in the mesophilic or

thermophi 1 ic range (Buswel 1 et al ., 1932), s i rice no power to aerate

wastewater is employed.

Important advances in wastewater treatment have been also

accompl ished with fixed film reactors (Henze and Harremoes, 19831, and

a great variety of wastewaters can be treated with high efficiency. The

use of anaerobic fi 1 ters (Young et al., 1369 and De Walle et al - ,1976),

inwhich there is a retention of biomass and a large area of contact

1 Career Investigator of the Consejo National ficas y TEcnicas (R. Argentina).

de lnvestigaciones Cienti-

2 Fellow of the Consejo National de lnvestiqaciones Cientificas y TSc- nicas (R. Argent i na) .

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with the wastewater, allows the handling of high organic loads. This

results in lower hydraul ic retention times and smal ler reactors (Sa’nchez

Riera et al ., 1982). Moreover the methane produced could be used as an

energy source for power or heat in other parts of the processing plant.

Dairy industry wastewater was treated in a pilot plant scale (3OL)

at room temperature using an anaerobic filter (Rittman et al., 1982).

A comparisson between UASB and DFSFF reactors was made in the paper by

van den Berg et al., (1983)) and the results would indicate that fixed

film reactor was n-ore effective.

The aim of this paper is to test the design and operational

conditions of an horizontal anaerobic filter operated at 40°C in order

to maximize the COD removal from an artificial wastewater similar to

the one encountered in the industry. The horizontal design was chosen

to try to minimize hydraul ic pressures in the system.

MATERIALS AND METHODS

Reactor. A bench scale reactor, built in PVC with an overall length of 460and 39 mm internal diameter was used for the experiments. Of the total volume of 0.47 L, 40s ,, was occu with an specific area of 8.99 cm’/cm 5

ied by l/4 inch ceramic saddles , resulting in a working volume

0f 0.29 L (~ig.1).

0 B Pump anaerobic filter

recirculation

Fig. 1: Scheme of the anaerobic treatment system.

Temperature was kept at 40 2 0.5”C !IY immersion of the reactor in

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a thermostatized water bath. The feed was provided by a peristaltic pump and consisted of solutions of dry whey in tap water and with a ptl of 6.1; di 1 ut ions were made to simulate real conditions and because it was not practical to get wastewater from industry every day.

To avoid any aerobic oxidation, the reconstituted whey was steril ized for 40 minutes with wet steam. In some occasions, sodium

hydrogen carbonate was added up to a final concent rat ion of 2.5 g/L and a pH of 6.9.

Recirculation of the contents was made with another pump after the separation of the gas produced. The flow of this pump could be 100 times

higher than the flow of the feed. The filter was filled with sludge from an anaerobic reactor (UASB)

that has been used for the treatment of distillery waste and the feed was started; initially the flow of the feed was kept low, neutralizing with sodium hydroxide whenever the pH was lower than 7.0. Operational status was reached after approximately three months of use.

Analysis. Total gas was measured with an inverted cylinder filled with salt water. Methane concentrations was analyzed with a Gow Mac 552 gas

chromatograph equipped with a TC detector using a column of silica gel (601'80 mesh) of 180 cm x 0.3 cm diameter .

Volatile fatty acids (VFA), N2 was used as carrier gas.

were determined with a Gow Mac 752 chromatograph’ equipped with a FID detector. A glass column (0.3~180 cm) filled with 10% SP-l2OO/H3PO4 on Chromosorb WAW 8O/lOO (Supelco, inc.) was used. N2 was employed as carrier gas.

Chemical oxygen demand (COD), was determined by the reflux method volatile sol ids (VS), by drying and ashing; nitrogen conteht by the Kjel dhal method; phosphorus by the vanadomolybdophosphor ic acid calorimetric method and alkalinity as mg CaCOj/L by potentiometric titration to pH = 4.0 ( APHA, AWWA, WPCF, 1976 )

RESULTS AND DISCUSS ION

The study of the performance of the reactor is divided into two

phases: 1) no additions and 2) alkalinity is added. The first phase was

undertaken to establish the performance of the system with the minimal

preparation or pretreatment of the wastewater since it is obvious that

any pretreatment would lead to a cost increase.

Fig. 2 shows the efficiency in the COD removal as a function of

the loading rate, The values of COD after treatment are also shown. The

efficiency reached a maximum of 93.8% at a loading rate of 2.9

kg COD/mj/day and remained at a level of about 85.0% at loading rates

up to TO.0 kg COD/mj/day. When alkal i was added, the efficiency is a

little higher and quite constant in the range 88.7 - 91.4% for loading

rates in the range 6.0 - 10.0 kg COD/mj/day. Though it is not shown,

addition at lower loading rates resulted in efficiencies not significantly

different to the ones obtained without bicarbonate.

In all cases the HRT was,one day and the different LR were

obtained by changing the concentration of the influent. The vaiues of

COD of the treated liquid at low LR are compatible with a direct

disposal of the effluent.

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100 - 90 - P /cc ,-O--.-__ --w_ o-o,-,

0’ --w_ ---_ 0-e o-------s ------_ 0

80- - 2.0

70- /c r* A- 1.5

60 - /;A 1.o 50-

A-A------A/'-- /A/

I. r- ./ /;’

- 0.5

l I I I I

2 4 6 8 10

ORGANIC LOADING RATE (kg CODh-d’day)

Fiq. 2: Efficiency of COD removal (o,o) and COD in the effluent - (AtA) , with HRT = 1 day. No addition: empty symbols.

Alkali added: filled.symbols. The efficiency is ( CODin - COD,ff )/CODin x 100.

Fig. 3 shows the production of methane and the yield of biogas

per kg of COD used as functions of the loading rate. At the higher LR

studied the production of methane was of 1.6 L CHb/L/day and 2.14

L CHb/L/day without and with the addition of alkali respectively

(Fig. 3b ). In this case, 3 volumes of biogas were produced per volume

of feed and per day with an HRT of one day.

The biogas produced contained 62.0 - 72.0% methane and there are

no great difference in the yield of methane (Fig. 3a ), with values of

about 71 .O% of the theoretical value 350 L CHq/kg COD removed.

The alkal inity added prevented the pH from falling below 6.9 and

increased the efficiency as contrasted with a pH of 6.5 when no

b i ca rbona te was added.

When alkali was added, the alkalinity in the liquid leaving the

system was 4 to 12% higher than in the influent. This fact would indicate

a conservation of the buffer capacity in the system, which would allow

either to decrease the amount of bicarbonate added, or to add it

discontinuosly.

The COD:N:P ratio in the reconstituted whey was l52:3.l:1, so no

nutrients were added. 32% of the total nitroqen and 27% of the phosphorus

present in the influent remained in the reactor, indicating that N and P

were not 1 imiting.

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s W F

8 1 400

0 300 8 2200

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2.4

ST u 1.6 3 21.2 0 2 0.8

0.4

1 I I I I I

2 4 6 8 10

When the loading rate was increased, the system became unstable

for a short t i me and in some cases it was necessary to decrease the flow

rate till the levels of methane production were recovered. In these

t rans ient per i# ods, VFA contents of up to 3.0 g/L occurred, however these

ORGANIC LOADING RATE (kg COD/m3/dayl

Fig. 3: Gas production and Yield (o---J : no addition; co---) : alkali added.

vai ues decreased quickly on lowering the feed rate.

L/hen the contents of the digester were studied, it was found that

the sludge was occupying the free spaces indicating that a certain

amount of the original floes were stable in these conditions. The

packing was not totally covered by a biomass film as has been expected,

and the recirculating flow, though quite high, was not strong enough

to force floes out of the system since no setteable sol ids were

recovered at the exit of the reactor. These findings would meet the

criteriaof the ,floc-based digester more than those of the attached-

film digester according to the review by Cal lander et al., (1983).

Towards the end of the studies recirculation was done at intervals

and the performance was maintained. Studies are being inducted to

establish the minimum recirculating time and flow.

CONCLUSIONS

The results presented here indicate that an horizontal anaerobic

filter could be used to treat effectively the wastewater of a

multiproduct dairy; the system was able to remove COD with a maximum

efficiency of about 90%. The concentrations in the effluent after

treatment ( 0.2 - 0.6 g COD/L ) were low in the range of loading rates

that would occur in the real situation, since the values commonly

present in the total effluent from a multiproduct dairy are around

5.5 g COD/L.

The addition of sodium hydrogen carbonate slightly increased the

efficiency at higher loading rates ( > 6.0 kg COD/m9/day ) but did not

significantly alter the efficiency at lower loading rates.

ACKNOWLEDGEMENT

The authors are very grateful for the finantial support given by lnternat ional Foundation for Science (Sweden), the Consejo National de lnvestigaciones Cientificas y TEcnicas and Secretarra de Ciencia y T&c-

n ica (R.Argent ina). The technical assistance of Silvia R. Valz-Gianinet is also acknowledged,

REFERENCES

Buswell, A.M., Boruff, C.A. and Wiesman, C,K.(1932) in Anaerobic Fermentations, A.M. Buswell and W.D. Hatfield, eds.(State Water Bulletin N”32), 146-151, Illinois.

Cal lander, I,J. and Barford, J.P.(1983).P recess Biochem.l8(4), 24-30. -

Carawan, R.E., Jones, V.A. and Hansen, A.P.(1979).J.Dairy Sci.62, 1243-1251.

De Wal le, F.B. and Chian, 1275-1295.

E.S.K. (1976) .Biotechnol. and Bioeng, 18,

Henze, M. and Harremoes, P, (1983).Water Sci” Technol -5, l-101.

Rittman, B-E., Strubler, C.E. and Ruzicka, T.(l982).J. Environ. Eng. Div. - ASCE 108, 900-912.

Sa’nchez Riera, F., Valz-Gianinet, S., Callieri, D. and SiAeriz, F. (1982) .Biotechnol. Letters k, 127-132.

van den Berg, L. and Kennedy, K.J. (1983) .Water Sci *Techno -3, 359-368.

Young, J.C. and McCarty, P*L.(I969) .J. Water Pollut. Control Fed. 4J, R 16.

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