Integrated system of activated sludge–reverse osmosis in the

treatment of the wastewater from the meat industry

Jolanta Bohdziewicz

*

, Ewa Sroka

Institute of Water and Wastewater Engineering, Silesian University of Technology, ul. Konarskiego 18, 44-100 Gliwice, Poland

Received 20 November 2002; received in revised form 11 January 2003; accepted 3 November 2003

Abstract

The work aimed at determining the effectiveness of the treatment of the wastewater coming from the meat industry in a hybrid system

combining the biological methods of activated sludge (in an SBR) and reverse osmosis. The tests carried out on the wastewater from the Meat
Processing Plant Uni-Lang in Wrzosowa showed that the biological treatment resulted in a sufficient removal of contaminants from the
wastewater, which consequently could be discharged into receiving water. In order to make it possible for the wastewater to be reused in the
production cycle, it was additionally treated with reverse osmosis.
# 2004 Elsevier Ltd. All rights reserved.

Keywords: Membranes; Reverse osmosis; Biological methods of activated sludge; Wastewater produced by the meat industry

1. Introduction

The wastewater from the meat industry is extremely

difficult to purify due to its specific characteristics, irregular
discharge and considerable content of organic, mineral and
biogenic matter. Meat processing plants use approximately
62 million m

3

of water per annum. Only a few per cent out

of this quantity is a component of the final product, the
remaining part is wastewater of high biological and
chemical oxygen demand, high fat content and high
concentrations of dry residue, sedimentary and total
suspended matter as well as nitrogen and chlorides. Since
this wastewater contains substantial amounts of proteins,
it putrefies easily and gives off nasty smells. It may also
contain disease microorganisms, eggs of ascaris and
intestinal parasites.

Contaminant loading of the wastewater discharged from

meat processing plants varies seasonally, daily or even on a
shift basis. In order to reduce wastewater contamination, the
production cycles of the meat processing plants, which are

run properly, deal with the separation and utilization of solid
waste.

More rigorous standards as far as environmental

protection is concerned, which require decreasing the
concentrations of nitrogen and phosphorus discharged into
receiving water, necessitated an increase in effectiveness of
wastewater treatment processes through modification of the
traditional methods or introduction of new technologies.
One of those methods is the application of membrane
bioreactors.

2. Materials

The wastewater was sampled from the Meat Processing

Plant Uni-Lang in Wrzosowa (southern Poland) whose
activity covers the slaughter and processing of pigs. It was
characterized by considerable pollutant load, substantial
amounts of suspended matter and high concentrations of
total nitrogen and phosphorus. The values of the basic and
eutrophic pollution indexes ranged widely during the whole
production cycle. The wastewater was of red and brown
colour, smelled nasty and tended to foam and putrefy. The

www.elsevier.com/locate/procbio

Process Biochemistry 40 (2005) 1517–1523

* Corresponding author. Tel.: [phone]; fax: [phone].

E-mail addresses: [e-mail] (J. Bohdziewicz),

[e-mail] (E. Sroka).

0032-9592/$ – see front matter # 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.procbio.2003.11.047

characteristics of the raw wastewater are presented in

Table 1

.

3. Apparatus

The treatment of the wastewater was carried out

biologically applying the activated sludge method in a
40 dm

3

chamber. The chamber was equipped with two

aeration pumps MAXIMA R manufactured by ‘‘Elite’’,
whose average capacity was 420 dm

3

air/h, and an RZR

2020 stirrer manufactured by ‘‘Heidolph’’, with adjustable
rotation velocity ranging from 40 to 2000 rpm.

Reverse osmosis was conducted in a high-pressure

apparatus type SEPA CF-HP equipped with a plate and
frame membrane module produced by ‘‘Osmonics’’, whose
active area was 155 m

2

. The system operated in the cross-

flow mode. The schematic of the installation is presented in

Fig. 1

. It consisted of a tank with the feed (1), high-pressure

pump (2), heat exchanger (3), manometers (4), membrane
module (5) and throttle valve (6). The system operated in the
cross-flow mode.

4. Methods

The whole research consisted of the following two basic

stages of wastewater treatment: biological treatment in an
SBR and post-treatment using reverse osmosis.

The activated sludge used during the biological treatment

was taken from the biological wastewater treatment plant of
the Meat Processing Plant Uni-Lang in Wrzosowa, which

ensured that the bacterial microflora had already been
adapted to the treatment of this type of wastewater.

After removing fat in a fat removal tank, the wastewater

was introduced into the bioreactor and stirred mechanically
without aeration, which ensured anoxic conditions indis-
pensable to denitrification. In the next stage of the process,
the bioreactor was aerated enabling the nitrification of the
wastewater and blowing out of the remaining gaseous
nitrogen. After sedimentation had finished, the treated
wastewater was discharged from the bioreactor.

It is widely known that the effect of wastewater treatment

in a sequential bioreactor (SBR) depends greatly on the
optimum process parameters, i.e. aeration intensity, acti-
vated sludge loading, hydraulic retention of wastewater in an
aeration chamber and the ratio between stirring time and
aeration time.

Our earlier investigations showed

[1]

that 840 dm

3

air/h

(840 dm

3

air/h, per 30 dm

3

liquid) proved to be the best

aeration intensity out of 420, 630 and 840 dm

3

air/h. Hence,

it was used throughout the whole research.

An attempt was also made to determine the most

favourable parameters for activated sludge operation.
Therefore, the first stage of the tests focused on the
determination of the most favourable retention time of the
wastewater treated in an activated sludge chamber. It was
being changed within the range of 12–36 h. The tests were
carried out in the bioreactor applying work cycles
characteristic of an SBR, i.e. filling up of the chamber with
wastewater (0.5 h), stirring (time varied from 3 to 17 h),
aeration (time varied from 5 to 17 h), sedimentation (1 h)
and discharge of clarified wastewater (0.5 h).

Three systems in which the ratio between the stirring time

and aeration time was 0.5 were tested: 12-h process, 24-h
process and 36-h process.

Subsequently, the system whose ratio between the stirring

time and aeration time of 0.3 (the 12-h process in which
anaerobic and aerobic treatment time was 9:3 h of stirring
and 6 h of aeration) was tested.

The next stage of the tests dealt with the selection of the

best sludge loading applying the values from the range of
0.05–0.75 g COD/g

T.S.

 d.

The determination of the optimum parameters of the

biological treatment of the wastewater enabled determina-
tion of the dynamics of contaminant distribution.

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–1523

1518

Table 1
Pollution indexes of raw wastewater, which after the treatment, can be returned to the natural receiving waters

Pollution indices

Concentration of pollution in raw
wastewater (g/m

3

)

Load (mean value) (kg/d)

Permissible standards (g/m

3

)

Range

Mean value

COD

2780–6720

4584

309.2

150

BOD

5

1200–3000

2100

126.8

30

Total nitrogen

49–287

198

13

30

Total phosphorus

15–70

32

2.1

5

a

Total suspension

112–1743

396

26.1

50

Detergents

7–21

11.3

0.75

5

a

For a treatment plant of wastewater flow below 2000 m

3

/d.

Fig. 1. The schematic of the installation type SEPA CF-HP.

In the last stage of the investigations, the wastewater treated

biologically under optimum operating parameters of the
activated sludge was additionally treated with reverse osmosis
applying the flat composite membrane DS3SC 1206366
manufactured by ‘‘Osmonics’’. The membrane process was
conducted at a pressure of 2.0 MPa and linear flow velocity of
2.0 m/s. This method, which combines the methods of
activated sludge in the SBR and reverse osmosis enabled a
reuse of the wastewater in the production cycle. The unit
biological process removed contaminants to the extent, which
allowed its discharge into receiving water (permissible
standards for a wastewater treatment plant whose daily flow
is below 2000 m

3

were as follows

[5]

: COD, 150 g/m

3

; BOD

5

,

30 g/m

3

; total nitrogen, 30 g/m

3

; total phosphorus, 5 g/m

3

;

total suspension, 50 g/m

3

; detergents, 5 g/m

3

).

5. Analytical procedures

COD, concentrations of phosphorus, total ammonium

and nitrate nitrogen were determined applying an SQ 18
photometer manufactured by ‘‘Merck’’

[2]

, whereas BOD

5

was assayed employing OxiTOP measuring cylinders
produced by ‘‘WTW’’

[3]

. The dry matter of the sludge

was determined by means of the gravimetric method

[4]

.

6. Results and discussion

6.1. Biological treatment of wastewater

The biological treatment of wastewater from the meat

industry aimed at decomposing organic matter and removing
biogenic compounds, i.e. nitrogen and phosphorus.

The first stage of the investigations focused on the

influence of aeration time on stirring time for different
retention times of the treated wastewater in the sequential
bioreactor.

Three systems were tested. Their retention times were 12,

24 and 36 h, and the ratio between the stirring time (t

s

) and

the sum of the aeration (t

a

) and stirring time was 0.5. The

obtained results are shown in

Fig. 2

. The tests were carried

out for the sludge loading of 0.15 g COD/g

T.S.

 d and

aeration intensity of 840 dm

3

air/h.

The conducted tests showed that the degree of removal

of organic, mineral and biogenic contaminants does not
depend on the time of wastewater retention in the activated
sludge chamber over the range of tested values. At the ratio
between stirring time and the sum of aeration and stirring
times of 0.5, COD for different times of wastewater
retention in the chamber changed by 0.4% and oscillated
around 97% (160 g O

2

/m

3

). A similar correlation was

observed for phosphorus whose removal ranged from 49 to
49.5%. Thus, it might be assumed that the time of
wastewater retention in the bioreactor longer than 12 h is
not economical.

The next stage of the investigations dealt with the

influence of the ratio t

s

/(t

s

+ t

a

) (t

s

, stirring time; t

a

, aeration

time) on the removal of contaminants from wastewater. The
effectiveness of wastewater treatment was tested at the same
wastewater retention time in the activated sludge chamber
(12 h), the same aeration intensity of 840 dm

3

air/h and the

activated sludge loading of 0.15 g COD/g

T.S.

 d, changing

the ratio between stirring time and the sum of stirring and
aeration times. The following systems were examined: 5 h of
stirring and 5 h of aeration (the ratio was 0.5); 3 h of stirring
and 6 h of aeration (the ratio was 0.3). The obtained results
are illustrated in

Fig. 3

.

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–1523

1519

Fig. 2. Comparison of the degree of contaminant removal with respect to retention time of wastewater in SBR sequential reactor.

The diagram reveals that the change in the ratio between

stirring time and the sum of stirring and aeration times
affects significantly the contaminant removal. Phosphorus
proved to be the most dependent indicator of wastewater
contamination. Its concentration for the ratio of 0.3
decreased in the purified wastewater by 87.3% (purified
wastewater 4.8 g P/m

3

), and by 49.3% for the ratio of 0.5

(purified wastewater 19.7 g P/m

3

). A similar correlation was

observed for total nitrogen. COD and BOD

5

displayed

smaller sensitivity to changes in the ratio between stirring
and aeration times. The obtained results revealed that 0.3 is a
more favourable ratio between stirring time and the sum of
stirring and aeration times. The degrees of wastewater
removal were the highest in this case.

In the subsequent stage of the tests, a number of attempts

to select the best-activated sludge loading for the examined
wastewater were made. The range covered 0.05–0.75 g
COD/g

T.S.

 d.

The tests were carried out at a constant content of dry

weight in the chamber of 5 g/m

3

, aeration intensity of

840 dm

3

air/h, retention time of wastewater in the bioreactor

of 12 h and t

s

/(t

s

+ t

a

) of 0.3.

Fig. 4

shows the results of the completed tests illustrating

the dependence of COD and BOD

5

removal on activated

sludge loading.

The diagram indicates that an increase in activated sludge

loading in the reactor chamber caused a decrease in the
removal of contaminants. COD depended on the changes in
the activated sludge loading over the whole range of tested
values (0.05–0.75 g COD/g

T.S.

 d). The maximum COD

removal was achieved for the loading of 0.05 g COD/
g

T.S.

 d and equalled 98.9% (raw wastewater, 5200 g O

2

/

m

3

), which resulted in a decrease in COD in the purified

wastewater to 57.2 g O

2

/m

3

. The lowest COD removal of

90.2% was obtained for the sludge loading of 0.75 g COD/
g

T.S.

 d. Its value for the purified wastewater was 509.6 g

O

2

/m

3

.

BOD

5

is not dependent on the applied loading. The

removal percentage remained constant for all applied
activated sludge loadings. The values of the pollution index
obtained did not decrease below 99%. BOD

5

of the purified

wastewater was at a level of 30 g O

2

/m

3

.

Fig. 5

presents the dependence between the percentage

removal of biogenic compounds (total nitrogen and
phosphorus) and the applied activated sludge loading.

The results show a strong dependence of biogenic

compounds removal in the purified wastewater on activated
sludge loading. As for total nitrogen, it reached the highest
value of 98.2% for the activated sludge loading of 0.15 g
COD/g

T.S.

 d. Whereas its concentration in the raw

wastewater was 530 g N

T

/m

3

, in the purified wastewater

it increased to a level of 9.5 g N

T

/m

3

. The lowest removal of

total nitrogen was 82.1% (raw wastewater, 236 g N

T

/m

3

;

purified wastewater, 42.2 g N

T

/m

3

) for the loading of 0.75 g

COD/g

T.S.

 d.

An analysis of phosphorus removal shows that it depends

mainly on the sludge loading. The highest removal of this

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–1523

1520

Fig. 3. Dependence of the degree of contaminant removal on ratio t

s

/t

s

+ t

a

for 12-h retention time of wastewater in activated sludge chamber.

Fig. 4. Dependence of COD and BOD

5

removal on activated sludge

loading.

biogene was achieved applying the activated sludge loading
of 0.15 g COD/g

T.S.

 d. It amounted to 87.3% (purified

wastewater, 4.8 g P/m

3

), while the lowest degree of removal

was obtained for the loading of 0.55 g COD/g

T.S.

 d, which

was 59.4%. It corresponds to phosphorus removal to the
level of 20.9 g P/m

3

in the purified wastewater.

In the further tests, the activated sludge loading of 0.15 g

COD/g

T.S.

 d, regarded as the most favourable, was used

and produced the best results in wastewater treatment.

Table 2

shows the results obtained in the investigations.

An analysis of the obtained results showed that the

purified wastewater could be discharged into receiving water
because it met the requirements of the Regulations of the
Ministry of Environmental Protection, Natural Resources
and Forestry, dated 5 November 1991, and none of the
pollution indexes exceeded the permissible standards.

The next stage of the research concentrated on the

determination of the dynamics of the contaminant distribu-
tion in the raw wastewater at the selected, most favourable
parameters of the biological wastewater treatment: activated
sludge loading, 0.15 g COD/g

T.S.

 d; aeration intensity,

840 dm

3

air/h; the ratio of stirring to stirring and aeration,

0.3; retention time of the wastewater in the bioreactor, 12 h.

The treatment cycle consisted of six stages: (1) filling up,

0.5 h; (2) stirring, 3 h; (3) aeration, 6 h; (4) sedimentation,
1 h; (5) chamber downtime, 1 h; (6) discharge of purified
wastewater, 0.5 h.

Fig. 6

depicts the dynamics of COD removal in

wastewater treatment. It shows that the organic pollution
index decreases drastically in the initial phase of the treatment.
After 2 h of stirring the content of the bioreactor, COD
decreases 16.5-fold and stabilizes at 133 g O

2

/m

3

. In the

aeration phase, COD decreases slightly by mere 33 g O

2

/dm

3

,

and during sedimentation remains at a stable level of 100 g
O

2

/m

3

.

Fig. 7

illustrates the dynamics of phosphorus removal

in the process of treatment of the same wastewater.

In the first phase of the process, i.e. stirring, anaerobic

conditions prevail. Bacteria Acinetobacter, capable of
excessive assimilation of phosphorus, cannot reproduce
because they are absolute aerobes. However, they make the
biosynthesis of spare substance in the form of polyhydrox-
ybutyric acid (PHB) emitting phosphorus residue, which is
indicated by the increase of phosphorus concentrations. In
the final phase of stirring (after 3 h), its concentration in the
wastewater was the highest and amounted to 13.6 g P/m

3

.

The second stage of the process consisted of aeration of the
content of the bioreactor and PHB accumulated by the
bacteria was ultilized as an easily accessible source of
carbon used for respiration and reproduction. The surplus of
energy was stored as polyphosphates which resulted in a
decrease in phosphorus content in the wastewater. The
intensity of the process was so great that the rate of
phosphorus intake was much higher than the rate of its
release during the stirring process. As a result, phosphorus
concentration decreased from 13.6 to 3.2 g P/m

3

at the end

of aeration. During 1-h sedimentation, phosphorus was
again released from the activated sludge to the water above,
which was indicated by the increase in its concentration.
The purified and clarified wastewater contained 4.8 g P/m

3

.

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–1523

1521

Fig. 5. Dependence of biogenic compounds removal on activated sludge
loading.

Fig. 6. Dynamics of COD removal in biological treatment of wastewater.

Table 2
Effectiveness of wastewater treatment applying activated sludge method under the most favourable operating conditions (activated sludge loading, 0.15 g COD/
g

T.S.

 d; aeration intensity, 840 dm

3

air/h; retention time in the bioreactor, 12 h; ratio t

s

/t

s

+ t

a

, 0.3)

Pollution indices

Raw wastewater (g/m

3

)

Retention, R (%)

Wastewater after activated
sludge bioreactor (g/m

3

)

Permissible standards
(g/m

3

)

COD

5300

98.1

102

150

BOD

5

2900

99.6

10

15

Total nitrogen

557

98.2

9.5

30

Total phosphorus

37.8

87.3

4.8

5

Ammonium

2.0

95.0

0.1

6

The decrease in phosphorus content observed in the initial
phase of the stirring could have been caused also by the fact
that the wastewater was being proportioned into the chamber
by means of cylinders, which caused its oxygenation. The
anaerobic conditions in the chamber started as late as after
45 min. (Each new portion of wastewater was added into the
chamber manually, which resulted in its oxygenation. The
diagram of phosphorus changes shows that it started to
increase as late as after 45 min, probably because the
anaerobic conditions started prevailing after that time.)

Fig. 8

illustrates a dependence of the changes in total

nitrogen concentration in wastewater treatment.

In the stirring phase the concentration of nitrogen

decreased. The same phenomenon was observed in the
initial phase of aeration. After approximately 5 h of
wastewater treatment (including 2 h of aeration), its value
decreased rapidly and then was only slightly decreasing till
the end of the process. In the stirring phase, total nitrogen
reduction took place due to the presence of oxygen in the
wastewater. After approximately 45 min, oxygen from the
wastewater was used up and anoxic conditions prevailed.

The next diagram (

Fig. 9

) illustrates changes in the forms

of total nitrogen during wastewater treatment.

Nitrate nitrogen present in the bioreactor chamber at the

beginning of the process came from the previous treatment

cycle. Its value was 20 g/m

3

. It decreased rapidly in the

initial phase of stirring because nitrates were used for
nitrate respiration by bacteria. After approximately 1 h,
only trace amounts of nitrate nitrogen remained in the
wastewater. Subsequently, after aeration had begun,
nitrification started and the concentration of nitrate nitrogen
increased. It reached the value of 21.5 g/m

3

in the final phase

of aeration.

As far as ammonium nitrogen is concerned, at the

beginning of anaerobic stirring its amount increased due to a
reduction in organic nitrogen, and then its level stabilized. In
the aerobic process, ammonia was used by organisms to
increase the biomass; its content in the wastewater decreased
rapidly to zero due to nitrification.

Only trace amounts of nitrite nitrogen occurred in the

wastewater during the stirring phase. After aeration had
started, it was released from the biomass cells and after
approximately 1.5 h of aeration, it turned into nitrate
nitrogen (the second phase of nitrification took place).

An analysis of the obtained results (

Figs. 6–8

) indicates

that in the cycle of biological treatment of wastewater there
are optimum stirring and aeration times after which
pollution indexes do not decrease any more. For this
process they were t

s

= 3 h and t

a

= 6 h, respectively.

6.2. Additional treatment of wastewater by means of
pressure driven membrane operations

As the results of the carried out investigations showed,

the wastewater from the meat industry can be purified only
to the extent, which enables the wastewater to be discharged
into receiving water. Since the meat industry uses huge
quantities of water, as mentioned herein, and thus produces
highly loaded wastewater, an attempt to treat it additionally
so that it could be reused in the production cycle was made.

Hence, after being treated biologically, the wastewater

was additionally treated with reverse osmosis.

Fig. 10

presents transport characteristics of the applied osmotic
membrane.

In the case of deionized water, in the range of

transmembrane pressures from 0.10 to 0.30 MPa, the

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–1523

1522

Fig. 7. Dynamics of phosphorus removal in biological treatment of waste-
water.

Fig. 8. Dynamics of total nitrogen removal in biological treatment of
wastewater.

Fig. 9. Changes in nitrogen forms during biological treatment of waste-
water.

volume water flux changed from 1.0 to 2.78

 10

6

m

3

/

m

2

s, respectively.

A dependence of the volume permeate flux on its

recovery degrees has also been determined (

Fig. 11

).

It has been found that during reverse osmosis the volume

permeate flux depended on its recovery degree to a small
extent. At permeate recovery of 20%, it decreased to
1.6

 10

6

m

3

/m

2

s, i.e. by a mere 10.6%.

The next stage of the research focused on the

effectiveness of additional treatment of wastewater during
reverse osmosis after it had been treated biologically
applying the activated sludge method. The obtained results
are shown in

Table 3

.

The degrees of contaminant removal obtained during

reverse osmosis were as follows: phosphorus was removed

to the value of 0.1 g P/m

3

, the concentration of total nitrogen

was 1.0 g N

T

/m

3

, COD and BOD

5

were relatively low—10

and 5 g O

2

/m

3

, respectively. It was concluded that the

purified wastewater could be then reused in the production
cycle of the plant.

7. Conclusions

The wastewater from the meat industry is very difficult

to purify due to its specific characteristics, variability,
considerable amounts of organic, mineral and biogenic
matter. This type of wastewater can be treated biologically
by means of the activated sludge method applying a low
sludge loading of 0.15 g COD/g

T.S.

 d, aeration intensity of

840 dm

3

air/h, constant sludge concentration in the chamber

of 5 g/dm

3

, retention time of wastewater in the bioreactor

of 12 h and the ratio of the stirring time to the sum of the
stirring and aeration times of 0.3. The wastewater thus
treated meets the requirements of the Regulations of the
Ministry of Environmental Protection, Natural Resources
and Forestry, dated 5 November 1991, and can be discharged
into receiving water.

The wastewater from the meat industry can be also

treated to the extent, which enables it to be reused in the
production cycle of a plant. In order to achieve a satisfactory
degree of wastewater purification, the hybrid process
combining the biological method of activated sludge and
reverse osmosis should be applied.

References

[1] Bohdziwicz J, Sroka E, Lobos E. Application of the system which

combines coagulation, activated sludge and reverse osmosis to the
treatment of the wastewater produced by the meat industry. Desalina-
tion 2002;144:393–8.

[2] User’s manual, Photometer SQ 118, Merck.
[3] User’s manual, Determination of BZT using respirometric method, Oxi

Top, firm WTW.

[4] Hermanowicz W, editor. Physicochemical testing of water and sewage.

Warsaw: Arkady; 1998.

[5] Regulation of the Ministry of Environmental Protection, Natural

Resources and Forestry, dated 5 November 1991, on the classification
of waters and conditions the sewage discharged to waters and soil
should satisfy, Journal of Law No. 116, item 501.

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–1523

1523

Fig. 10. Dependence of volume water flux on transmembrane pressure for
DS3S osmotic membrane.

Fig. 11. Dependence of volume permeate flux on its recovery degree for
reverse osmosis of wastewater after traditional treatment.

Table 3
Effectiveness of wastewater treatment through reverse osmosis after it was pre-treated applying the biological method

Pollution indices

Wastewater after activated
sludge bioreactor (g/m

3

)

Wastewater after RO process

Concentration (g/m

3

)

Retention, R (%)

COD

76

10.8

85.8

BOD

5

10

5.0

50.0

Total phosphorus

3.6

0.09

97.5

Total nitrogen

13

1.3

90.0