Wof. Sci. Tech. Vol. 39, No. 5, 97-103, 1999 PP. IAWQ

0 1999 Published by Elsevin Science Ltd Printed in Great Britain. All rights reserved

0273-1223/99 $19.00 + 0.00 PII: SO273-1223(99)00113-4

COST-EFFECTIVE PRE-TREATMENT OF WASTEWATER

Fatma A. El-Gohary and Fayza A. Nasr

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

ABSTRACT

The implementation of low-cost, simple mitigation measures is required for the timely control and sustainable. management of pollution problems in developing countries. Recently, the use of anaerobic systems for wastewater treatment has received a growing attention since they represent an alternative cost- effective approach for removal of pollutants. Therefore, evaluation of the performance of an Upflow Anaerobic Sludge Blanket Reactor, as a pre-bea!ment step for industrial as well as domestic wastewater was fhe subject of this study. The results obtained showed fhat the performance of one-stage UASB at Bhrs hydraulic retention time (HRT) for domestic wastewater treatment was quite satisfactory. CODw and BOD,, removal values averaged 77% and 83%. Comparison of the performance of a one-stage versus two-stage reactor, having the same volume and operated at fhe same HRT (8 hr) and biomass concentration indicated an improvement in the quality of the two-stage effluent. With regard to the wastewater discharged from a potato-chips factory, the use of one-stage UASB at a detention time of 18hrs and an average organic load of 2.9 kg BOD/m3/d gave good results. Average residual values of COD, BOD, TSS and oil and grease in the treated eftluent were 650, 342, 203 and 63 mg/l, respectively. Operation of a two-stage pilot-scale UASB indicated better performance as expressed by COD and BOD removal values. Q 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved

KEYWORDS

Wastewater treatment; domestic; industrial; anaerobic treatment; UASB.

INTRODUCTION

In Egypt, the water pollution problem is quite serious, The largest amounts of pollutants discharged into water courses are organic compounds, either dissolved in effluents or associated with suspended matter. Domestic sewage and effluents from food industries are the main source of organic matter.

Food industry is one of the most important sectors in Egypt as far as production value is concerned. It represents 25% of the manufacturing industries. It is however, an important user of water and a major contributor to pollution loads discharged into Egypt’s water resources.

Since major part of the organic content of both wastes, consists of particulate material, good particle separation can improve the efficiency of a post-treatment step. Anaerobic treatment have been demonstrated to be feasible to pre-treat high strength and dilute complex water,(Lettinga et al., 1980; Grin et al., 1985; Geung et al., 1980; Yoda et al., 1985). Among several anaerobic processes, the Upflow Anaerobic Sludge Blanket Reactor (UASB) is by far the most widely applied anaerobic waatewater treatment system. This is not merely because of its process simplicity, but particularly also because of the relatively high loading

97

\I) Pergamon

PH: S0273-1223(99)00113-4

Wat. Sci. Tech. Vol. 39, No.5, pp. 97-103,1999IAWQ

@ 1999 Published by Elsevier Science LtdPrinted in Great Britain. All rights reserved

0273-1223/99 $19.00 + 0.00

COST-EFFECTIVE PRE-TREATMENT OFWASTEWATER

Fatma A. EI-Gohary and Fayza A. Nasr

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

ABSTRACT

The implementation of low-cost, simple mitigation measures is required for the timely control andsustainable management of pollution problems in developing countries. Recently, the use of anaerobicsystems for wastewater treatment has received a growing attention since they represent an alternative cost­effective approach for removal of pollutants. Therefore, evaluation of the performance of an VpflowAnaerobic Sludge Blanket Reactor, as a pre-treatment step for industrial as well as domestic wastewater wasthe subject of this study. The results obtained showed that the performance of one-stage VASB at 8hrshydraulic retention time (HRT) for domestic wastewater treatment was quite satisfactory. CODtot and BODtot

removal values averaged 77% and 83%. Comparison of the performance of a one-stage versus two-stagereactor, having the same volume and operated at the same HRT (8 hr) and biomass concentration indicatedan improvement in the quality of the two-stage effluent. With regard to the wastewater discharged from apotato-chips factory, the use of one-stage VASB at a detention time of 18hrs and an average organic load of2.9 kg BOD/mJ/d gave good results. Average residual values of COD, BOD, TSS and oil and grease in thetreated effluent were 650, 342, 203 and 63 mg/I, respectively. Operation of a two-stage pilot-scale VASBindicated better performance as expressed by COD and BOD removal values. © 1999 Published by ElsevierScience Ltd on behalf of the IAWQ. All rights reserved

KEYWORDS

Wastewater treatment; domestic; industrial; anaerobic treatment; UASB.

INTRODUCTION

In Egypt, the water pollution problem is quite serious. The largest amounts of pollutants discharged intowater courses are organic compounds, either dissolved in effluents or associated with suspended matter.Domestic sewage and effluents from food industries are the main source oforganic matter.

Food industry is one of the most important sectors in Egypt as far as production value is concerned. Itrepresents 25% of the manufacturing industries. It is however, an important user of water and a majorcontributor to pollution loads discharged into Egypt's water resources.

Since major part of the organic content of both wastes, consists of particulate material, good particleseparation can improve the efficiency of a post-treatment step. Anaerobic treatment have been demonstratedto be feasible to pre-treat high strength and dilute complex water,(Lettinga et al., 1980; Grin et ai., 1985;Geung et ai., 1980; Yoda et ai., 1985). Among several anaerobic processes, the Upflow Anaerobic SludgeBlanket Reactor (UASB) is by far the most widely applied anaerobic wastewater treatment system. This isnot merely because of its process simplicity, but particularly also because of the relatively high loading

97

98 F. A. EL-GOHARY and F. A. NASR

potentials of the system and the relatively high extent of sludge stabilization that can be accomplished with this process. It has been reported that the two-phase UASB treatment system would be superior to the single- stage ones, (Bull et al., 1984; Dinopoulou and Lester, 1989). The removal efftciency of a compartmented UASB reactor exceeds that of a non-compartmented reactor at the same total HRT by at least 10% (de Man, 1990). It was therefore, the objective of this study to evaluate the performance of the UASB reactor as a pre- treatment step for both industrial and domestic wastewater. Furthermore, comparison between the performance of one- and two-stage UASB systems will be investigated.

MATERIALS AND METHODS

wastewater

For domestic wastewater, the performance of one-and two-stage, laboratory-scale UASB, having the same volume and operated at the same HRT has been investigated. To get more practical data, a large-scale two- stage UASB system (total volume 2.2 m3) has been put into operation (Figure 1). Dimensions and operating conditions of the treatment systems are given in Table 1. Both systems were fed continuously with municipal wastewater through a connection from the sewerage system.

Table 1. Operational parameters of the treatment systems

Parameter

Domestic Wastewater

[ntemal Diameter Depth Volume HRT [nitial Biomass

Potato-Chips Wastewater

lntemal Diameter Depth Volume HRT initial Biomass

Jnit

cm 16 11 8 70 60 cm 240 300 300 340 335 .itre 40 25 15 1300 900 h. 8 5 3 5 3

g 11 22 22 22 25 25

:m cm ,itre h.

g/l

10 70 60 70 360 280 5 1385 791

18 W) 6(4) 22 22 22

One stage JASB

Two-Stage UASB (lab-scale)

1”’ Reactor 1

2"a Reactor

Two-stage UASB (Pilot-scale)

lS’ bactor E

2"O teeactor

1

Potato-chips Wastewater

For potato-chips wastewater, the use of one-phase laboratory-scale UASB reactor has been investigated. To compare the performance of one-phase versus two-phase UASB, a demonstration two-phase UASB reactor was designed and manufactured. The system was located at the premises of the potato-chips factory and fed continuously with the final effluent discharged as a result of production processes. The pH of the feed was adjusted by the addition of NaOH and maintained in the range from 6-7 throughout the study. A schematic diagram of the system is given in Figure 2.

The performance of the treatment systems was evaluated by monitoring the quality of the feed and the effluent of each treatment unit. Physico-chemical analyses were carried out according to APHA (1995). Examination of the presence of helminthic ovae were carried out according to the method recommended by the WHO (1989).

98 F. A. EL-GOHARY and F. A. NASR

p~tentials of the system and the relatively high extent of sludge stabilization that can be accomplished withthis process. It has been reported that the two-phase DASB treatment system would be superior to the single­stage ones, (Bull et ai., 1984; Dinopoulou and Lester, 1989). The removal efficiency of a compartmentedDASB reactor exceeds that ofa non-compartmented reactor at the same total HRT by at least 10% (de Man,1990). It was therefore, the objective of this study to evaluate the performance of the DASB reactor as a pre­treatment step for both industrial and domestic wastewater. Furthermore, comparison between theperformance of one- and two-stage DASB systems will be investigated.

MATERIALS AND METHODS

Municipal wastewater

For domestic wastewater, the performance of one-and two-stage, laboratory-scale DASB, having the samevolume and operated at the same HRT has been investigated. To get more practical data, a large-scale two­stage DASB system (total volume 2.2 m3

) has been put into operation (Figure 1). Dimensions and operatingconditions of the treatment systems are given in Table 1. Both systems were fed continuously withmunicipal wastewater through a connection from the sewerage system.

Table 1. Operational parameters of the treatment systems

Parameter Unit One Two-Stage UASH Two-stage UASHStage (lab-scale) (Pilot-scale)UASH

I" 20 .. IS 2""Reactor Reactor Reactor Reactor

Domestic Wastewater

Internal Diameter em 16 11 8 70 60Depth em 240 300 300 340 335Volume Litre 40 25 15 1300 900HRT h. 8 5 3 5 3Initial Biomass gil 22 22 22 25 25

Potato-ChipsWastewater

Internal Diameter em 10 70 60Depth cm 70 360 280Volume Litre 5 1385 791HRT h. 18 12(8) 6(4)Initial Biomass gil 22 22 22

Potato-chips Wastewater

For potato-chips wastewater, the use of one-phase laboratory-scale DASB reactor has been investigated. Tocompare the performance of one-phase versus two-phase DASB, a demonstration two-phase VASB reactorwas designed and manufactured. The system was located at the premises of the potato-chips factory and fedcontinuously with the final effluent discharged as a result of production processes. The pH of the feed wasadjusted by the addition of NaOH and maintained in the range from 6-7 throughout the study. A schematicdiagram of the system is given in Figure 2.

The performance of the treatment systems was evaluated by monitoring the quality of the feed and theeffluent of each treatment unit. Physico-chemical analyses were carried out according to APHA (1995).Examination of the presence of helminthic ovae were carried out according to the method recommended bythe WHO (1989).

Cost-effective pre-treatment of wastewater

Figure 1. First stage UASB reactor (volume: 1.3 m’) (potato-chips)

Figure 2. Schematic diagram of the pilot treatment plant (municipal wastewater).

RESULTS AND DISCUSSION

Sewage Charucterisfics: Physico-chemical characteristics of raw sewage fed to the treatment systems were consistent with a sewage of above average strength. Average values of total COD and BOD were 630 mgOr/l and 379 mgOa/l, respectively. The corresponding maximum values were 858 mgOa/l and 590 mgO2/1. Total suspended solids content ranged between a minimum value of 90 mg/l and a maximum value of 680 mg/l, with an average value of 338 mg/l. Mean concentrations of total nitrogen and total phosphorus were 40 mg N/l and 9 mg P/l, respectively. Bacteriological examination during the study period revealed a great variation in faecal colifotms density. Faecal coliform counts ranged between 2x10’ and 5x10’ MPN/l 00 ml.

Examination of the presence of helminthic ova (Nematods, Trematodes and Cestodes)indicated the presence of Ascaris spp. in almost all the samples examined. Asks-ovae count ranged between 80 ova/l and 2500 ova/l. Ancylostoma spp. were also detected in two samples during the study period. Trematodes (Fasciola spp.) were observed only once with a concentration of 80 ova/l. With regard to Cestodes, Taenia spp. and Hymenolepis nana-ovae were identified.

Performance of One-stage UASB Reactor : The efficiency of the UASB at 8 hrs HRT was quite satisfactory. Total COD removal values ranged from 60% to 85%, with an average value of 77%. Corresponding mean residual value was 145 mgOa/l. Average percentage removal values of BOD and TSS were 83% and 89%, respectively (Table 2). Residual suspended solids concentration in the reactor effluent ranged from a minimum value of 10 mg/l up to a maximum value of 40 mg/l, with a mean value equivalent to 24 mg/l. Oil and grease concentrations varied from 10 mg/l to 18 mg/l. Corresponding percentage removal values of oil and grease varied between 69% and 85%, with an average value of 82%.

Cost-effective pre-treatment of wastewater 99

Figure 1. First stage UASB reactor (volume: 1.3 m3)

(potato-chips)

RESULTS AND DISCUSSION

Municipal wastewater

Figure 2. Schematic diagram of the pilot treatment plant(municipal wastewater).

Sewage Characteristics: Physico-chemical characteristics of raw sewage fed to the treatment systems wereconsistent with a sewage of above average strength. Average values of total COD and BOD were 630mg02/1 and 379 mg02/l, respectively. The corresponding maximum values were 858 mg02/l and 590mg02/l. Total suspended solids content ranged between a minimum value of 90 mg/l and a maximum valueof 680 mg/l, with an average value of 338 mg/l. Mean concentrations of total nitrogen and total phosphoruswere 40 mg Nil and 9 mg P/l, respectively. Bacteriological examination during the study period revealed agreat variation in faecal coliforms density. Faecal coliform counts ranged between 2xl07 and 5xl09

MPN/lOOmi.

Examination of the presence of helminthic ova (Nematods, Trematodes and Cestodes)indicated the presenceof Ascaris spp. in almost all the samples examined. Ascaris-ovae count ranged between 80 ovall and 2500ovall. Ancylostoma spp. were also detected in two samples during the study period. Trematodes (Fasciolaspp.) were observed only once with a concentration of 80 ovall. With regard to Cestodes, Taenia spp. andHymenolepis nana-ovae were identified.

Performance of One-stage UASB Reactor: The efficiency of the UASB at 8 hrs HRT was quitesatisfactory. Total COD removal values ranged from 60% to 85%, with an average value of 77%.Corresponding mean residual value was 145 mg02/l. Average percentage removal values of BOD and TSSwere 83% and 89%, respectively (Table 2). Residual suspended solids concentration in the reactor effluentranged from a minimum value of 10 mg/l up to a maximum value of 40 mg/l, with a mean value equivalentto 24 mg/l. Oil and grease concentrations varied from 10 mg/l to 18 mg/l. Corresponding percentageremoval values of oil and grease varied between 69% and 85%, with an average value of 82%.

100 F. A. EL-GOHARY and F. A. NASR

Volatile fatty acids concentrations fluctuated between a minimum value of 19 mg/l and a maximum value of 57 mg/l, with an average value of 25 mg/l. Mean percentage removal value was 43%. It is worth mentioning that VFA concentrations in the reactor effluent depend greatly on the reactor efficiency: the higher the efficiency, the lower the residual volatile fatty acid concentrations and the higher the pH. Methane production was 0.42 m3/kg COD removed/d.

Parasitological examinations revealed the absence of almost all the helminthic ova in the UASB reactor effluent. This demonstrates the effectiveness of the UASB reactor for parasitic ova removal. Results of the

bacterial examination of UASB effluent indicated a reduction in faecal colifomrs by only one log.

Analysis of sludge samples taken at different levels was carried out. The results indicated that biomass concentration inside the reactor was acceptable. The sludge content ranged from a minimum value of 24.8 g/l to a maximum value of 29.8 g/l. Sludge activity was relatively low (0.21 g COD/g VSS/d).

Performance of the Laboratoty-scale Two-stage UASB Reactor: Comparison of the performance of a one- stage versus two-stage reactor, having the same volume and operated at the same HRT(8hr) and biomass concentration indicated an improvement in the quality of the two-stage effluent. Mean removal values for total COD and BOD were 79% and 83%, respectively. Soluble COD and BOD removal were 76% (Table 2).

Biogas production was around 0.22 m3/kg COD removal. The sludge methanogenic activity of the first reactor ranged between 0.144 and 0.219 g CH4 COD/g VSS.d, while that of the second reactor ranged between 0.163 and 0.297 g CI& COD/g VSSd.

Complete removal of parasitic ova as a result of filtration and aggregation in the sludge bed has been achieved. Faecal coliform bacterial counts were reduced by only one log.

The biodegradability of the organic matter was higher in the two-stage reactors as compared to the one-stage system. This has been reflected in the soluble COD and BOD removal values presented in Table (2).

Pilot-scale Two-stage UASB: Comparing the results of the pilot two-stage with the lab-scale, two-stage system, operated at the same HRT (8 hr) indicated higher removal values with regard to total COD and BOD removal values. On the other hand slightly lower removal values have been recorded for soluble COD and BOD (Table 2).

Table 2. Performance data of the one and two-stage UASB reactors

The improvement in total COD and BOD removal in the large-scale system is due to the higher removal values of suspended solids which averaged 84.6% during the study period.

The methanogenic activity of the sludge in the first reactor was 0.176 and 0.2 gCH4 COD/g VSS.d in the second reactor.

100 F. A. EL-GOHARY and F. A. NASR

Yolatile fatty acids concentrations fluctuated between a minimum value of 19 mgll and a maximum value of57 mgll, with an average value of25 mgll. Mean percentage removal value was 43%. It is worth mentioningthat YFA concentrations in the reactor effluent depend greatly on the reactor efficiency: the higher theefficiency, the lower the residual volatile fatty acid concentrations and the higher the pH. Methaneproduction was 0.42 m3/kg COD removed/d.

Parasitological examinations revealed the absence of almost all the helminthic ova in the UASB reactoreffluent. This demonstrates the effectiveness of the UASB reactor for parasitic ova removal. Results of thebacterial examination ofUASB effluent indicated a reduction in faecal coliforms by only one log.

Analysis of sludge samples taken at different levels was carried out. The results indicated that biomassconcentration inside the reactor was acceptable. The sludge content ranged from a minimum value of 24.8gil to a maximum value of29.8 gil. Sludge activity was relatively low (0.21 g COD/g YSS/d).

Performance ofthe Laboratory-scale Two-stage UASB Reactor: Comparison of the performance of a one­stage versus two-stage reactor, having the same volume and operated at the same HRT(8hr) and biomassconcentration indicated an improvement in the quality of the two-stage effluent. Mean removal values fortotal COD and BOD were 79% and 83%, respectively. Soluble COD and BOD removal were 76% (Table 2).

Biogas production was around 0.22 m3/kg COD removal. The sludge methanogenic activity of the firstreactor ranged between 0.144 and 0.219 g CH4 COD/g YSS.d, while that of the second reactor rangedbetween 0.163 and 0.297 g C~ COD/g YSS.d.

Complete removal of parasitic ova as a result of filtration and aggregation in the sludge bed has beenachieved. Faecal coliform bacterial counts were reduced by only one log.

The biodegradability of the organic matter was higher in the two-stage reactors as compared to the one-stagesystem. This has been reflected in the soluble COD and BOD removal values presented in Table (2).

Pilot-scale Two-stage UASB: Comparing the results of the pilot two-stage with the lab-scale, two-stagesystem, operated at the same HRT (8 hr) indicated higher removal values with regard to total COD and BODremoval values. On the other hand slightly lower removal values have been recorded for soluble COD andBOD (Table 2).

Table 2. Performance data ofthe one and two-stage UASB reactors

Raw Wastewater One-stage Two-stage DASB Two-stage DASBParameters Unit UASH (lab-scale) (Pilot-scale)

%R %R %RAv. Av. Av. Av.

COD!o! mg 02/1 630 77 79 85CODsol mg 02/1 235 68 76 68BOD!o! mg 02/1 379 83 83 83BODsol mg 02/1 139 74 76 70

The improvement in total COD and BOD removal in the large-scale system is due to the higher removalvalues of suspended solids which averaged 84.6% during the study period.

The methanogenic activity of the sludge in the first reactor was 0.176 and 0.2 gCH4 COD/g YSS.d in thesecond reactor.

Table 3. Performance data of the pilot scale two-phase UASB for potato-chips wastewater treatment

Parameter Unit

HRT=18hr* OV~CA HRT= 12 hr * OIWd Raw After % R % R

wastewater sedimantion 1st UASB 1 % R IZadUASB 1 % R 1st UASB / % R 1 2ndUASB 1 % R L--~ ~~~~~ I I 1 HRT=12hr ) 1 HRT=6hr 1 HRl=8 hr HRT=4hr pH I I

S94,“: 7 1 6-6.2 1 7.1 1 - 1 7.2 - - 7.1 7.3

Chemical oxygen 1 1

mg02/L 1 7058 1 2214-2725 1 1

580 1 74 1 316 1 29 1 94 1 423 82 294 2s 9s demand

Biochemical 1 meO?lL I 2729 -3415 I 1216-1482 1 199 1 80 115 41 95 151 116

* The indicated results are the average of 8 samples

Table 3. Performance data ofthe pilot scale two-phase VASB for potato-chips wastewater treatment

I I I I ,

HRT= 18 hr' O,"eral HRT= 12 hr' OnralParameter Raw After %R 0/0 R

Unit wastewater sedimantion tstUASB %R 2 nd UASB %R tstUASB %R 2nd UASB %RHRT=12hr HRT=6hr HRT=8hr HRT=4hr

pH 6-7 6-6.2 7.1 - 7.2 - - 7.1 - 7.3 - -Chemical ox~"gen mg02/L 5940 -7058 2214 - 2725 480 74 316 29 94 423 82 294 25 95demand

Biochemical mg02/L 2729 - 3415 1216 -1482 199 80 115 41 95 151 88 115 22 96OUl!en demandTotal kjeldahl mgN/L 118 - 213 87- 160 170 - 177 - - 135 - 154 - -nitrol!en

Total DhosDhates ml!!L 28 - 34 17 -21 14 - 13 - - 13.5 - 12 - -Total solids mglL 6331 - 7811 2213 - 3671 1558 17 1466 5.6 75 2119 40 1858 12 75at 105°CVolatile solid mgiL 4774 - 5612 1232·1625 898 24 359 38 92 335 87 287 14 93at 550°CTotal dissolnd mgiL 2763 - 4465 1752 - 3092 1349 19 1328 1.4 37 1999 23 1798 10 58solids at 105°C

Volatile dissolnd mglL 1602 - 1976 867 -1160 348 50 271 22.3 74 256 75 244 6 85solids at 550°C

Total suspended mgiL 3346 - 3569 461 - 579 217 45 138 31 95 121 76 60 45 97solids at 105°C

Volatile suspended mgiL 3036 - 3172 364 - 464 175 54 88 37 96 78 77 44 43 96solids at 550°COil and grease ml!!L 147 -152 71 - 104 35 46 31 31 76 63 35 36 37 71

* The indicated results are the average of8 samples

(Jo

~~

~.

io...,

I

§

102 F. A. EL-GOHARY and F. A. NASR

Wastewuter Characteristics: Analysis of the wastewater discharged from the potato-chips factory indicate wide fluctuation in physico-chemical characteristics. COD and BOD values ranged from 5206 to 13860 , and from 2040 to 6000 mgOJ1, with mean values of 8640 and 3685 mgOJ1, respectively. The presence of suspended solids as high as 7100 mg/l has been recorded, which constitutes 50% of the total residue on the average. Oil and grease concentrations varied from 102 to 200 mg/l.

One-phase laboratory-scale UASB: Preliminary experiments indicated that the optimum HRT is 18 hr. The OLR was around 2.9 kg BOD/m’.d. COD and BOD removal values averaged 86% and 82%. The SS removal efficiency was relatively high (91%). The biogas production rate was 0.37 m3ikg COD removed.

Two-phase pilot-scale UASB: To compare the performance of a two-phase versus one-phase UASB a pilot- scale two-phase system was operated at the premises of the factory to be able to take all variables into consideration. Two HRT were investigated (12 br and 18hr). Assessment of the available data indicated better performance of the two-stage UASB as compared to the one-stage. At a HRT of 18 hr. COD and BOD removal values were 94% and 95%. SS were reduced by 95%. When the system was operated at HRT of 12 hr a slight improvement in the aualitv of the final effluent was observed. A situation which GUI be attributed

of using anaerobic I . - w

to the rise in ambient temperature up to 40°C (Table 3). This emphasizes the benefits treatment in countries like Egypt with hot climates.

10000

9000 I4 raw W.W.

8000 asettled W.W.

7000 0 one stage UASB

6000 EHwo stage UASB

t B 5000

4000

3000

2000

1000

0

COD BOD TSS

Figure 3. Performance of the UASB reactors for the treatment of potato-chips wastewater.

CONCLUSIONS

Steady-state results indicate that the UASB is an efficient process for the removal of organic material and suspended solids from municipal sewage, as well as, agro-industrial wastewater at ambient temperatures, especially in regions with warm climate like Egypt. The reason is that, the use of UASB reactor as a pre- treatment step optimizes the separation of suspended particles and improves the efficiency of a post- treatment step. Furthermore, it produces less sludge with better quality, which is at the moment a determining factor of the cost and sustainability of the treatment process.

REFERENCES

APHA, American Public Health Association (1992) Standard methods for the examination of water and wastewater, 18”’ ed., Washington DC.

Bull, M. A., Sterrit, R. M. and Lester, J. N. (1984). An evaluation of single and separated-phase anaerobic industrial wastewater treatment in fluidized bed reactors. Biofechnol. Bioengng XXVI, 1054-1065.

De Man, A. W. A. (1990). Anaerobe zuivering van row rioolwater met behulp van korrelslib UASB-reakoren werkrapport, Eindrapportage Project Vakgroup Waterzuivering Landbouwuniversiteit Wageningen.

102

Potato-cbips Wastewater

F. A. EL-GOHARY and F. A. NASR

Wastewater Characteristics: Analysis of the wastewater discharged from the potato-chips factory indicatewide fluctuation in physico-chemical characteristics. COD and BOD values ranged from 5206 to 13860 ,and from 2040 to 6000 mgOz/l, with mean values of 8640 and 3685 mgOz/l, respectively. The presence ofsuspended solids as high as 7100 mg/l has been recorded, which constitutes 50% of the total residue on theaverage. Oil and grease concentrations varied from 102 to 200 mg/I.

One-phase laboratory-scale UASB: Preliminary experiments indicated that the optimum HRT is 18 hr. TheOLR was around 2.9 kg BOD/m3.d. COD and BOD removal values averaged 86% and 82%. The SSremoval efficiency was relatively high (91%). The biogas production rate was 0.37 m3/kg COD removed.

Two-phase pilot-scale UASB: To compare the performance of a two-phase versus one-phase UASB a pilot­scale two-phase system was operated at the premises of the factory to be able to take all variables intoconsideration. Two HRT were investigated (12 hr and 18hr). Assessment of the available data indicatedbetter performance of the two-stage UASB as compared to the one-stage. At a HRT of 18 hr. COD and BODremoval values were 94% and 95%. SS were reduced by 95%. When the system was operated at HRT of 12hr a slight improvement in the quality of the final effluent was observed. A situation which can be attributedto the rise in ambient temperature up to 40°C (Table 3). This emphasizes the benefits of using anaerobictreatment in countries like Egypt with hot climates.

10000

9000

8000

7000

6000~ 5000~

4000

3000

2000

1000

0

COD BOD

l1li raw w.w.• settled w.w.

CI one stage UASB

E1two stage UASB

TSSFigure 3. Performance of the UASB reactors for the treatment of potato-chips wastewater.

CONCLUSIONS

Steady-state results indicate that the UASB is an efficient process for the removal of organic material andsuspended solids from municipal sewage, as well as, agro-industrial wastewater at ambient temperatures,especially in regions with warm climate like Egypt. The reason is that, the use of UASB reactor as a pre­treatment step optimizes the separation of suspended particles and improves the efficiency of a post­treatment step. Furthermore, it produces less sludge with better quality, which is at the moment adetermining factor of the cost and sustainability ofthe treatment process.

REFERENCES

APHA, American Public Health Association (1992) Standard methods for the examination of water and wastewater, 18'h ed.,Washington DC.

Bull, M. A., Sterrit, R. M. and Lester, J. N. (1984). An evaluation of single and separated-phase anaerobic industrial wastewatertreatment in fluidized bed reactors. Biotechnol. Bioengng XXVI, 1054-1065.

De Man, A. W. A. (1990). Anaerobe zuivering van ruw rioolwater met behulp van korrelslib UASB-reakoren werkrapport,Eindrapportage Project Vakgroup Waterzuivering Landbouwuniversiteit Wageningen.

Cost-effective pm-treatment of wastewater 103

Dinopoulou, G. and Lester, J. N. (1989). Optimization of a two-phase anaerobic digestion system treating a complex wastewater. Envir. Technol. Lett. 10.799-814.

Geung, R. K., Pitt, W. W. Jr., Davis, G. M. and Koon, J. H. (1980). Energy conservation and scale-up studies for a wastewater treatment system based on a fixed-film anaerobic. Biotechnd, Eioeng., Symp., 10 pp. 295-316.

Grin, P., Roersma, R. and Lettinga, G. (1985). Anaerobic treatment of raw domestic sewage in UASB-reactor at temperatures from 9 to 20°C. Proceedings of the Seminar/Workshop: Anaerobic treatment of sewage, Swizenbaum (ed), Amherst, Mass. pp. 109-124.

Lettinga, G. and Vinken, J. N. (1980). Feasibility of the Upflow Anaerobic Sludge Blanket (UASB) process for the treatment of low strength wastes. Proc. 35th Industrial Waste Conference, Pudue University, pp. 625-634.

WHO (1989). Health Guidelines for the Use of Wastewater in Agricultural and Aquaculture. Tech. Rep. Ser. No. 778, Geneva.

Cost-effective pre-treatment of wastewater 103

Dinopoulou, G. and Lester, J. N. (1989). Optimization ofa two-phase anaerobic digestion system treating a complex wastewater.Envir. Technol. Lett. 10, 799-814.

Geung, R. K., Pitt, W. W. Jr., Davis, G. M. and Koon, J. H. (1980). Energy conservation and scale-up studies for a wastewatertreatment system based on a fixed-film anaerobic. Biotechnol., Bioeng., Symp., 10 pp. 295-316.

Grin, P., Roersma, R. and Lettinga, G. (1985). Anaerobic treatment of raw domestic sewage in UASB-reactor at temperaturesfrom 9 to 20°C. Proceedings of the Seminar/Workshop: Anaerobic treatment of sewage, Swizenbaum (ed), Amherst,Mass. pp. 109-124.

Lettinga, G. and Vinken, J. N. (1980). Feasibility of the Upflow Anaerobic Sludge Blanket (UASB) process for the treatment oflow strength wastes. Proc. 35th Industrial Waste Conference, Pudue University, pp. 625-634.

WHO (1989). Health Guidelines for the Use of Wastewater in Agricultural and Aquaculture. Tech. Rep. Ser. No. 778, Geneva.