Anaerobic/aerobic treatment of meat processing

wastewater

RIFAAT A. WAHAAB AND M. HAMDY EL-AWADY*

Water Pollution Control Department, National Research Centre, Dokki, Cairo, Egypt

Summary

The meat processing industry is believed to produce highly polluted wastewater. Analysisof such wastewater indicated that the waste was highly contaminated with organiccompounds as indicated by COD (1544 mgO2 l)1), BOD (646 mgO2 l)1), and TSS (1155mg l)1). Moreover, oil and grease concentrations reached 144 mg l)1 treatment of rawwastewater using Up¯ow Anaerobic Sludge Blanket (UASB) followed by Rotating Bio-logical Contactors (RBC) was studied. Efficiency of the UASB for the removal of CODtotal,BODtotal, TSS, and oil and grease was 56%, 56%, 85%, and 58%, respectively. The quality ofthe UASB effluent barely complies with the regulatory standards for discharging waste-water into the sewerage network. UASB effluent was subjected for further treatment usinga RBC unit to improve the quality of the treated effluent for reuse in irrigation purposes.Residual COD, BOD, TSS, and oil and grease, following RBC, was 132 mgO2 l)1,40 mgO2 l)1, 44 mg l)1, and 10 mg l)1 respectively. The overall efficiency of the treatmentunits provided good quality effluent. The overall percentage removal of COD, BOD, TSS,and oil and grease was 91.5%, 94%, 96%, and 91%, respectively. Based on the quality ofthe treated effluent and guidelines recommended for wastewater reuse, it may be con-cluded that a slight to moderate restricted irrigation is applicable to reuse the treatedeffluent in the green belt around the factory. Disinfection should be applied to ensure thesafety of such a process.

Introduction

Environmental pollution is seriously increasingthroughout the world because of economic growthand increased human activity. Wastewater is oneof the major pollution problems brought about bysuch development. The enormous investment inwastewater treatment is increasing not only inprimary cost but also the endless running cost thatgenerates no economic pro®t. Anaerobic waste-water treatment (AnWT)-combined with properpost-treatment represents the ideal solution forenvironmental protection. Several advantages areassociated with the application of anaerobictreatment, including: (1) low energy requirement,(2) little sludge produced, and (3) production ofmethane gas as a source of energy (Lettinga et al.,1992). Anaerobic treatment and a combination ofmechanical and physical/chemical methods arerecommended for wastewater pre-treatment of

food industry e�uent at high organic load (Von-Hagel, 1988). AnWT is e�ective in removing bio-degradable organic compounds, leaving someother organic substances and mineralized com-pounds in the treated e�uents. These compoundstherefore have to be removed ± if necessary ± byan additional post-treatment step to reach ac-ceptable water quality levels for dischargingwastewater into surface water or sewerage net-work. The ability of uplow anaerobic sludgeblanket (UASB) technology to treat wastewaterwas evaluated, and proved to be e�ective, ac-complishing soluble BOD, soluble COD, and TSSremovals (Housley et al., 1994 ; Boardman et al.,1995). The utilization of anaerobic treatmenttechnology using UASB for the treatment of food-processing wastewater such as e�uents from meatpacking and sugar plants achieved good results(Speece, 1983). Anaerobic/aerobic processes de-sign for optimum removal of COD, TSS andnitrogen of food processing wastewater were pre-sented (Yoda et al., 1985; Collivignarelli et al.,1990). The aim of the present study is toinvestigate treatability of meat processing waste-

*Dr Rifaat A. Wahaab and Dr M. Hamdy El-Awady are bothAssociate Professors of Water Pollution Control in the Environ-mental Sciences Division of the National Research Centre, Dokki,Cairo, Egypt

The Environmentalist 19, 61±65 (1999)

0960-3115 Ó 1999 Kluwer Academic Publishers 61

water and to asses its applicability for reuse inirrigation.

Materials and methods

The wastewater used in this study was produced bythe Kengary Company, a meat processing com-pany located in 6 October City, south-west Cairo.A schematic diagram of the maufacturing pro-cesses is shown in Fig. 1. The measured ¯ow ofwastewater discharged from the di�erent sectionsare 35 m3/day from manufacturing processes,25 m3/day washing water, 50 m3/day from boilersand 90 m3/day from the retort machine. The total¯ow was about 200 m3/day. Anaerobic pre-treat-ment (Up¯ow Anaerobic Sludge Blanket) followedby aerobic post-treatment (Rotating BiologicalContactor) were chosen for the present study.

UASB

A schematic diagram of the Up¯ow AnaerobicSludge Blanket (UASB) reactor used in this studyis given in Fig. 2a. It was made from a plexiglascylinder to permit internal observation. The in-ternal diameter and height of the reactor were10 cm and 60 cm, respectively. The total net vol-ume of the reactor was 4.3 l and the e�ectivevolume excluding the gas collector was 3.75 l. Thereactor had four outlets and one inlet. The inlet ofthe reactor was located at 1.0 cm above the bot-tom. The reactor was installed in a room with atemperature of 25 + 2 °C. Digested sludge(15 g VSS l)1) was transferred to the reactor fromthe nearby Zenin Anaerobic Pilot Plant, Cairo.The reactor was operated at a hydraulic retentiontime (HRT) of 8 hours over a period of 2 weeks toachieve steady state followed by 8 weeks opera-tion. The pH-value of the raw wastewater wasadjusted between 8.0 and 8.5 using 10% NaOHand was kept constant around that range byadding bu�er solution (0.5 g Na2CO3/l g COD).The volume of biogas produced was measured byusing water displacement method. The UASB ef-¯uent was connected to the RBC inlet.

RBC

The Rotating Biological Contactor (RBC) unitused in this study is shown in Fig. 2b. It consists ofa 5.2 l basin, divided into four compartments ofequal volume. Each compartment accommodated8 (PVC) discs of 0.14 m diameter. The total sur-face area of the discs and the surface hydraulicload were 0.985 m2 and 189.4 m2/m3, respectively.Fig. 1. Schematic diagram of meat processing industry.

Fig. 2. Schematic diagram of the UASB-Reactor and RBC-System.

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Wahaab et al.

Discs were approximately 50% submerged andwere rotated at 5 rpm. The applied hydraulic loadwas 0.0132 m3m)2day)1, and the correspondingaverage organic load was 0.288 Kg BOD5 m)2

day)1. The RBC opens into a ®ve litre sedimen-tation tank. Composite samples of the rawwastewater, UASB-e�uent and RBC-e�uent werecollected and analysed in accordance with theAmerican Standard Methods (APHA, 1992).

Results and discussion

The characteristics of raw wastewater, as well asUASB-e�uent and RBC-e�uent are recorded inTable 1, and illustrated graphically in Figs 3±6.

Raw wastewater characteristics

The raw wastewater was acidic in nature(pH 5.3)5.8). Total chemical oxygen demand

(COD) ranged between a minimum value of1180 mgO2 l

)1 to a maximum value 2160 mgO2 l)1,

with an average value of 1544 mgO2 l)1. The

corresponding values of total BOD ¯uctuatedbetween 450 mgO2 l

)1 and 945 mgO2 l)1, with an

average value of 646 mgO2 l)1. The average value

of total suspended solids (TSS) was 1155 mg l)1.Oil and grease concentrations reached 144 mg l)1.The results indicate that the characteristics of theraw wastewater do not comply with the regulatorydischarge standards for the industrial wastewaterinto the sewerage network.

UASB-e�uent

The quality of the reactor e�uent con®rms thee�ectiveness of the UASB as a pre-treatmenttechnology for meat processing wastewater. TotalCOD and BOD removal values were 51% and56%, respectively. The corresponding residualvalues were 684 mgO2 l

)1 and 284 mgO2 l)1, in

Table 1. E�ciency of the UASB reactor followed by RBC for the treatment of Meat processing wastewater

Parameters* Unit Raw Treated Samples Overall

Min. Max. Ave. UASB-Reactor RBC-Unit%R

Min. Max. Ave. %R Min. Max. Ave. %R

pH-value ± 5.3 5.8 ± 7.6 8.0 ± ± 7.1 7.8 ± ± ±COD (T) mgO2/L 1180 2160 1544 424 1051 684 56 68 160 132 81 91.5COD (sol) mgO2/L 686 813 1045 218 528 391 63 31 76 63 84 93.4BOD5 (T) mgO2/L 450 945 646 148 503 284 56 20 68 40 86 94BOD5 (sol) mgO2/L 220 430 311 69 248 133 57 11 26 20 85 9410 minSett.Solids

ml/L 6 10 8 <0.1 <0.1 0.0 1.0 0.0 100 100

30 min 8 12 10 <0.1 <0.1 0.0 1.0 0.0 100 100TSS mg/L 613 2020 1155 98 323 170 85 31 54 44 74 96O & G** mg/L 90 144 110 32 56 46 58 8.6 13 10 78 91

* Average of six successive replicates.** Oil and grease and all extractable matters by chloroform.

Fig. 3. Variation in COD values of raw and treatede�uents along the treatments units.

Fig. 4. Variation in BOD values of raw and treatede�uents along the treatments units.

63

Anaerobic/aerobic treatment of meat processing wastewater

average, respectively. TSS ranged between98 mg l)1 and 134 mg l)1, with an average valueof 85 mg l)1. The removal value reached 85%.Average concentration of oil and grease was46 mg l)1, and a removal value of 58% wasachieved. The biogas production rate in this ex-periment was very low. The volume of the biogasproduced ranged between 70 ml and 90 ml day)1,with an average value of 80 ml day)1 Cumulativevalue of biogas per week reached 700 ml.

RBC-e�uent

The results recorded in Table 1 indicate that thequality of the UASB-e�uent narrowly compliedwith the Egyptian Standards regulating dischargeof wastewaters into the sewerage network.Therefore, proper post-treatment is requiredwhen, for example, using the treated e�uent toirrigate the green belt around the factory. RBCwas used for that purpose. The results obtainedindicate very good carbonaceous matter elimina-tion as re¯ected in the removal of BOD (86%),COD (81%), TSS (74%), and oil and grease(78%). Residual BOD values varied from20 mg l)1 to 68 mg l)1, with an average value of40 mg l)1. Corresponding COD values rangedfrom 68 mgO2 l

)1 to 160 mgO2 l)1, with an aver-

age value of 132 mgO2 l)1, respectively. A re-

moval value of 96% in the concentration of TSSwas achieved. Oil and grease concentration in the®nal e�uent ranged between 8.6 mg l)1 and13 mg l)1. The removal value reached 91%.

It is worth mentioning that the overall percentremoval of COD, BOD, TSS, and oil and greasewere 91.5%, 94%, 96% & 91% respectively.Moreover, the quality of the treated e�uent couldbe used for irrigation of green belt around the®rm, taking into consdieration that disinfectionshould be applied where moderate restricted irri-gation is recommended.

Sludge

Weekly analysis of the sludge collected from theUASB reactor indicate that the concentration ofthe sludge ranged from14 g VSS 1)1 to 18 g VSS l)1,with an average value of 15 g VSS l)1.

A regular analysis for the sloughed biomass ofRBC was conducted. Table 2 summarizes thevariation in characteristics and quantity of thesloughed biomass along the di�erent cascades.However the sludge produced was of goodquality. Sludge volume index (SVI) for 1st, 2nd,3rd, and 4th cascades were 45, 45.3, 68, and 80,respectively. Regarding the attached biomass, thediscs in the ®rst cascade were covered with athick bio®lm. The structure of the bio®lm in the®rst cascade and partially in the second cascade,seemed to be spongy rather than smooth instructure. In the successive cascades the discswere covered with a thinner bio®lm layer andwere relatively smooth in appearance.

Fig. 5. Variation in TSS values of raw and treated ef-¯uents along the treatment units.

Fig. 6. Variation in oil and grease values of raw andtreated e�uents along the treatment units.

Table 2. Characteristics of sloughed sludge from RBC cascades following steady state condition.

Parameters 1st

cascade2nd

cascade3rd

cascade4th

cascade

Sludge volume (ml/L) 140 130 150 160Total Sludge weight at 105°C (g/L) 3.12 2.87 2.21 2.0Volatile matters (%) 63% 58% 43% 32%Sludge volume index (SVI) 45 45.3 68 80

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Wahaab et al.

Conclusions and recommendations

1. In view of the present rapid depletion ofwater resources in Egypt, and the great demand ofwater especially in the newly constructed indus-trial areas, it is essential to formulate an overallwater resources management plan which includesthe reuse of the treated e�uent for irrigationpurposes.

2. It could be summarized that the UASB-reactor is su�cient to produce treated e�uent thatcomply with the standards of discharging indus-trial wastewater into the sewerage network.

3. Sequential treatment of UASB followed byRBC produce an e�uent quality applicable forirrigation purposes, taking into consideration thatdisinfection is essential to minimize health risksassociated with e�uent reuse.

Acknowledgement

The authors wish to thank Professor Fatma El-Gohary, Professor of Water Pollution, NationalResearch Centre, Cairo, Egypt, for her continuoussupport and encouragement.

References

APHA, AWWA, WPCF. (1992) Standard Methods for theExamination of Water and Wastewater. 18th edn.,Washington.

Boardman, G.D., Tisinger, J.L. and Gallagher, D.L. (1995).Treatment of clam processing wastewaters by means ofup¯ow anaerobic sludge blanket technology. WaterResearch, 29, 1483±1490.

Collivignarelli, C., Urbini, G., Fameti, A., Bassetti, A. andBarbaresi, U. (1990) Anaerobic ± aerobic treatment ofmunicipal wastewater with full-scale UASB and at-tached bio®lm reactors.Water Sci. Tech, 22(1/2) 475±82.

Housley, J.N. and Zoutberg, G.R. (1994). Application of thebiothane wastewater treatment system in the soft drinksindustry. J. Inst. Water. Environ. Manage, 8, (3) 239±245.

Lettinga, G.A. de M., Van der Last, A.R.M., Wiegant, W.,Van Knippenberg, K., Frijns, J. and Van Buuren,J.C.L.(1992) Anaerobic treatment of domestic sewageand wastewater.1st Middle East Conference in ``WaterSupply and Sanitation for Rural Areas'', Cairo, Egypt,pp. 164±170.

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