integrated system of activated sludge–reverse osmosis in the treatment of the wastewater from the...

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Process Biochemistry 40 (2005) 1517–1523

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 m3 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

* Corresponding author. Tel.: +48 32 237 1698; fax: +48 32 237 1047.

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

[email protected] (E. Sroka).

0032-9592/$ – see front matter # 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.procbio.2003.11.047

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

J. Bohdziewicz, E. Sroka / Process Biochemistry 40 (2005) 1517–15231518

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/m3)

Load (mean value) (kg/d) Permissible standards (g/m3)

Range Mean value

COD 2780–6720 4584 309.2 150

BOD5 1200–3000 2100 126.8 30

Total nitrogen 49–287 198 13 30

Total phosphorus 15–70 32 2.1 5a

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 m3/d.

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 dm3 chamber. The chamber was equipped with two

aeration pumps MAXIMA R manufactured by ‘‘Elite’’,

whose average capacity was 420 dm3 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 m2. 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

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

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 dm3 air/h

(840 dm3 air/h, per 30 dm3 liquid) proved to be the best

aeration intensity out of 420, 630 and 840 dm3 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/gT.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 1519

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 m3 were as follows [5]: COD, 150 g/m3; BOD5,

30 g/m3; total nitrogen, 30 g/m3; total phosphorus, 5 g/m3;

total suspension, 50 g/m3; detergents, 5 g/m3).

5. Analytical procedures

COD, concentrations of phosphorus, total ammonium

and nitrate nitrogen were determined applying an SQ 18

photometer manufactured by ‘‘Merck’’ [2], whereas BOD5

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.

Fig. 2. Comparison of the degree of contaminant removal with resp

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 (ts) and

the sum of the aeration (ta) 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/gT.S. � d and

aeration intensity of 840 dm3 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 O2/m3). 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 ts/(ts + ta) (ts, stirring time; ta, 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 dm3 air/h and the

activated sludge loading of 0.15 g COD/gT.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.

ect to retention time of wastewater in SBR sequential reactor.


Fig. 3. Dependence of the degree of contaminant removal on ratio ts/ts + ta for 12-h retention time of wastewater in activated sludge chamber.

Fig. 4. Dependence of COD and BOD5 removal on activated sludge

loading.

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/m3), and by 49.3% for the ratio of 0.5

(purified wastewater 19.7 g P/m3). A similar correlation was

observed for total nitrogen. COD and BOD5 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/gT.S. � d.

The tests were carried out at a constant content of dry

weight in the chamber of 5 g/m3, aeration intensity of

840 dm3 air/h, retention time of wastewater in the bioreactor

of 12 h and ts/(ts + ta) of 0.3.

Fig. 4 shows the results of the completed tests illustrating

the dependence of COD and BOD5 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/gT.S. � d). The maximum COD

removal was achieved for the loading of 0.05 g COD/

gT.S. � d and equalled 98.9% (raw wastewater, 5200 g O2/

m3), which resulted in a decrease in COD in the purified

wastewater to 57.2 g O2/m3. The lowest COD removal of

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

gT.S. � d. Its value for the purified wastewater was 509.6 g

O2/m3.

BOD5 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%. BOD5 of the purified

wastewater was at a level of 30 g O2/m3.

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/gT.S. � d. Whereas its concentration in the raw

wastewater was 530 g NT/m3, in the purified wastewater

it increased to a level of 9.5 g NT/m3. The lowest removal of

total nitrogen was 82.1% (raw wastewater, 236 g NT/m3;

purified wastewater, 42.2 g NT/m3) for the loading of 0.75 g

COD/gT.S. � d.

An analysis of phosphorus removal shows that it depends

mainly on the sludge loading. The highest removal of this


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

loading.

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

biogene was achieved applying the activated sludge loading

of 0.15 g COD/gT.S. � d. It amounted to 87.3% (purified

wastewater, 4.8 g P/m3), while the lowest degree of removal

was obtained for the loading of 0.55 g COD/gT.S. � d, which

was 59.4%. It corresponds to phosphorus removal to the

level of 20.9 g P/m3 in the purified wastewater.

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

COD/gT.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/gT.S. � d; aeration intensity,

840 dm3 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.

Table 2

Effectiveness of wastewater treatment applying activated sludge method under the m

gT.S. � d; aeration intensity, 840 dm3 air/h; retention time in the bioreactor, 12 h

Pollution indices Raw wastewater (g/m3) Retention, R (%

COD 5300 98.1

BOD5 2900 99.6

Total nitrogen 557 98.2

Total phosphorus 37.8 87.3

Ammonium 2.0 95.0

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 O2/m3. In the

aeration phase, COD decreases slightly by mere 33 g O2/dm3,

and during sedimentation remains at a stable level of 100 g

O2/m3. 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/m3.

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/m3 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/m3.

ost favourable operating conditions (activated sludge loading, 0.15 g COD/

; ratio ts/ts + ta, 0.3)

) Wastewater after activated

sludge bioreactor (g/m3)

Permissible standards

(g/m3)

102 150

10 15

9.5 30

4.8 5

0.1 6


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

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

water.

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

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

wastewater.

cycle. Its value was 20 g/m3. 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/m3 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 ts = 3 h and ta = 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


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

DS3S osmotic membrane.

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/m3)

Wastewater after RO process

Concentration (g/m3) Retention, R (%)

COD 76 10.8 85.8

BOD5 10 5.0 50.0

Total phosphorus 3.6 0.09 97.5

Total nitrogen 13 1.3 90.0

volume water flux changed from 1.0 to 2.78 � 10�6 m3/

m2 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 m3/m2 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

Fig. 11. Dependence of volume permeate flux on its recovery degree for

reverse osmosis of wastewater after traditional treatment.

to the value of 0.1 g P/m3, the concentration of total nitrogen

was 1.0 g NT/m3, COD and BOD5 were relatively low—10

and 5 g O2/m3, 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/gT.S. � d, aeration intensity of

840 dm3 air/h, constant sludge concentration in the chamber

of 5 g/dm3, 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.

integrated system of activated sludge–reverse osmosis in the treatment of the wastewater from the...

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