- Email: [email protected]
Anaerobic treatment of potato processing wastewater
~ Pergamon
Wal. Sci, Tech. Vol. 40, No. I, pp. 297-304, 1999
CI999 Published by Elsevier Science Ltd on behalf of the IAWQ Printed in Great Britain. All rights reserved
0273-1223/99 $20.00 + 0.00
PIT: S0273-1223(99)00398-4
ANAEROBIC TREATMENT OF POTATO PROCESSING WASTEWATER George R. Zoutberg* and Zerrin Eker* * • BiothaneSystemsInternational, P.O. Box 5068, 2600 GB Delft, TheNetherlands ··Arbiogaz Cevre teknolojileri Instaatsanayi ve TicaretA.S., Eski Buyukdere Cad. EmektarSok. No. 7J Kat. 380660, 4 LeventIstanbul, Turkey
ABSTRACT This paper deals with the anaerobictreatmentof wastewaterfrom the potato processingindustry. It is shown that treatmentof this type of wastewater in VASB reactorshas successfully been applied at manycompanies. Apart from the Biothanetl VASB technology a new anaerobictechnology is presented: the Biobed'" EGSB technology. Presented is the first application of this technology in the potato processingindustryand also a comparison is made between this technology and the Biothanetl VASB technology. C> 1999 Published by ElsevierScienceLtd on behalfof the IAWQ. All rightsreserved.
KEYWORDS Anaerobic; Biobedtl EGSB; Biothanetl UASB';potato; high rate; low temperature; suspended solids. INTRODUCTION Wastewater in the potato processing industry contains high concentrations of biodegradable components, such as starch and proteins (Abeling and Seyfried, 1993, Hadjivassilis et al., 1997). Though the Biothane'" UASB technology has established an impressive track record for this kind of wastewater, new developments in the compact, high-rate Biobed'" EGSB anaerobic technology have led to a break-through in the Netherlands. With more than 1800 plants world-wide (1997) covering different applications (food processing, chemical industry, pulp and paper industry), anaerobic treatment has gained widespread appreciation as a reliable and efficient means for reduction of COD (Hulshof Pol et al., 1997). Of all anaerobic processes those technologies based on high-rate, compact, granular biomass technology, such as UASB and EGSB, have a leading position (more than 750 plants). The well-known Dutch supplier Biothane Systems holds a worldwide market share of approximately 32%. Developed in the Netherlands in the early 70s by Biothane Systems (in co-operation with the University of Wageningen), the UASB (Upflow Anaerobic Sludge Blanket) technology was designed for treatment of highly concentrated wastewater in the sugar industry. Soon, applications in other markets emerged as the UASB technology matured into a stable, highly effective process for reducing discharge costs of industrial wastewater. In the potato processing industry, several Biothane'" UASB plants have been built by Biothane Systems and its world-wide partners, for customers such as McCain Foods (French fries) and Pepsico (potato crisps). 297
298
G. R. ZOUTBERG and Z. EKER
Recent additions of Biothane® UASB plants in the Pepsico network include Greece (Tasty Foods, Athens), Turkey (Uzay Gida, Istanbul) and Poland (E. Wedel, Warsaw) . In this article the plant installed at Uzay Gida is presented . For wastewater of fairly low temperatures and considerable fluctuations in COD composmon and load throughout the year, Biothane Systems has developed a new type of anaerobic technology. This Biobed ® EGSB (Expanded Granular Sludge Bed) technology is able to handle the above mentioned circumstances, while it even further reduces the overall footprint because of the use of typically high and slender reactors. In this article a comparison is made between a Biothane® UASB reactor and a Biobed" EGSB reactor installed at two different potato processing facilities in The Netherlands. WASTEWATER TREATMENT: ANAEROBIC VERSUS AEROBIC TREATMENT Biological wastewater treatment in the potato processing industry normally starts with a removal step for suspended materials, followed by biological treatment, such as anaerobic and aerobic processes. The major disadvantage of full aerobic treatment are the high operating costs (electricity, sludge handling, maintenance). Especially the costs for sludge dewatering and sludge disposal (dumping and incineration) have increased substantially over the years. As a result most of the Dutch potato processing companies have turned to the use of anaerobic removal of COD in their wastewater by means of UASB reactors. Biothane~
UASB versus Biobed"') EGSB
The UASB (Upflow Anaerobic Sludge Blanket) technology and the EGSB (Expanded Granular Sludge Bed) technology both make use of granular anaerobic biomass . Both processes have the same operation .principles, but differ in terms of geometry, process parameters and (usually) construction materials.
1 Sludqerbromass Inl t 2 Gas ba ffle pla tes 3 Re turn se ttl d sludge
Influent
Figure I. A cross-section of the Biothane" UASB reactor.
In both processes wastewater is fed into the reactor at the bottom through a specially designed influent distribution system. The water flows through a sludge bed consisting of anaerobic bacteria, which develop into a granular form. The excellent settleability (60 - 80 m/h) of these anaerobic granules enables high concentrations of biomass in a small reactor volume. The granules do not contain an organic carrier material, such as sand or hasalt. In the sludge bed the conversion from COD to hiogas takes place . In both reactor types the mixture of sludge, biogas and water is separated into three phases by means of a specially designed three-phase separator (or settler) at the top of the reactor. The purified effluent leaves the reactor via effluent laundries, biogas is collected at the top and sludge settles back into the active volume of the reactor. One of the most important design parameters for both types of reactors is the maximum allowable superficial upflow liquid velocity in the settler. Upflow velocities in excess of this maximum design value
Anaerobic treatment of potato processing wastewater
299
result in granular sludge being washed out of the reactor. The Biobed® EGSB settler allows a substantial higher upstream velocity (10 m/h) than the Biothane® DASB settler (1.0 m/h).
Effluent
1 Granular sludgelwa ter
2 Settled granular sludge
Influent
) >-- - -
Figure 2. A cross-section of the Biobedt> EGSB reactor.
Another important design parameter is the maximum allowed COD load. The Biobed® EGSB process operates under substantial higher COD loads (30 kg/m-.d) than the Biothane® DASB process (10 kglm 3.d). The result being that for a given COD load the Biobed® EGSB reactor volume is smal1er than for a Biothane® VASB reactor. Biothanef VASB reactors are typically rectangular or square, with an average height of 6.0 metres and are usually constructed in concrete. Biobed® EGSB reactors have a substantially smaller footprint. These high and narrow tanks are built in FRP (Fibreglass Reinforced Plastic) or stainless steel and have a typical height of 12 - 18 m. The height of the granular sludge bed In the Biothane® VASB reactor varies between I - 2 m and in the Biobed® EGSB from 7 - 14 m. A Biobedll> EGSB reactor is normal!j built as a completely closed reactor resulting in a system with zero odour emission. Additionally, a Biobed EGSB reactor can be operated under overpressure, thereby making any use of gasholders and biogas compressors redundant. The general differences between both processes are shown in Table I. Table I. Comparison between the main characteristic parameters of Biothane® VASB and Biobed® EGSB.
Load Height Toxic components" Vliquid settler Vliquid reactor vgas reactor
rn/h m/h rn/h
Biothane® DASB 10 5.5 - 6.5 +/-
Biobed® EGSB 30 12 - 18 ++
1.0 < 1.0 < 1.0
10 < 6.0 < 7.0
·The excellent hydraulic properties of the Biobed l EGSB reactor make it possible to use a lot of anaerobic effluent for dilution of the incoming wastewater. This makes it possible to treat wastewater containing components that are toxic in high concentrations, but biodegradable at low concentrations (e.g. formaldehyde). This feature has been applied for several chemical plants (Dupont de Nemours, Caldic Europoort, Hoechst Trevira Vlissingen B.V.).
Wastewater in the potato processing industry contains substantial amounts of suspended solids. The ill Biothane VASB process is characterised by longer hydraulic retention times than that of the Biobed'" EGSB process. As a consequence, use of the Biothanef" VASB process results in a higher removal of suspended solids and therefore higher overal1 COD removal efficiencies. The Biobed
300
G. R. ZOUTBERG and Z. EKER
WASTEWATER CHARACTERISTICS OF SMITHS FOOD, PEKA KROEF AND UZAY GIDA Smiths Food produces potato crisps and has chosen the Biothane iZ UASB anaerobic treatment process for bulk-COD removal from their wastewater and aerobic final treatment to meet the discharge limits. It is important to realise that anaerobic treatment always is a form of pre-treatment. During this anaerobic stage 80% of the COD is removed and converted to biogas. Only 1-2% of that COD is converted into new anaerobic biomass and, as a result, hardly any nitro,en (N) and phosphorus (P) are removed. The aerobic post-treatment consists of a low loaded Carrousel (registered trade name of DHV Water) and aims at removal of nitrogen and COD. Peka Kroef produces potato and vegetable based halfproducts for the salad industry in Europe. The ratio potatoes/vegetables is dependent on the season. As a consequence considerable fluctuations in the COD load occur. During the summer months July, August and September the processed vegetables are cocktail onions, cucumber and gherkins. During the other months mostly carrots and celeriac are processed. Until now the wastewater of Peka Kroef was treated in a conventional aerobic treatment plant (two basins with a volume of 4000 m' each). Peka Kroef's production expansion plans required additional wastewater treatment plant capacity. Expansion of the existing aerobic plant would lead to higher energy costs and a higher sludge production. For this reason the possibility of anaerobic treatment was investigated. Due to the specific characteristics of the wastewater (low temperature, COD load fluctuations, COD composition fluctuations, high suspended solids (SS) concentrations) an alternative for the conventional UASB, the EGSB technology, was tested. Extensive laboratory research showed good results with this type of anaerobic treatment at temperatures of20-25°C. Due to the innovative character of the application of the EGSB technology for this type of wastewater the Dutch authorities awarded a subsidy of 450,000 Dutch guilders for the project. The anaerobic pre-treatment serves as a "peak-shaver" (approximately 70% of the COD is removed and peaks in COD are levelled), this results in a more constant load to the aerobic stage. The factory ofUZAY GIDA produces potato and corn crisps and has a production process that varies during the week. These variations can be found back in the composition of the wastewater. The increased production capacity has led to a higher COD load in the wastewater. For this reason a Biothane'" UASB system is added between the existing pre-treatment and the existing Sequencing Batch Reactors (SBR). At the start-up in June 1998 the COD removal efficiency reached 75%, more results will be presented at the conference. The design parameters for the three above mentioned anaerobic installations are shown in Table 2. THE WASTEWATER TREATMENT PLANT OF SMITHS FOOD Figure 3 shows the flow scheme of this plant. Coarse solids are removed in a parabolic screen (mesh size: 1 mm). After this screen the water enters a pre-clarifier designed at a surface load of 1 mJh for removal of suspended solids and residual fat, oil and grease. The settled solids are dewatered in a decanter and the water flows by gravity into a buffertank of 400 m3• From the buffertank the water is pumped to a conditioning tank for pH and temperature correction. Conversion of COD takes place in the Biothane'" UASB reactor. The total anaerobic plant has a COD removal efficiency of approximately 80%. The remaining COD and Kjeldahl nitrogen is removed in the aerobic post-treatment. The final COD concentration is less than 100 mgll and the Kj-N concentration is less than 10 mgll. The final effiuent is discharged to the municipal sewer.
301
Anaerobic treatment of palata processing wastewater
Table 2. Design wastewater characteristicsfor Smiths Food, Peka Kroefand Uzay Gida after screening and pre-settlement Parameter Flow (average) Flow (average after buffering) COD (total) COD (soluble) COD-load PH
Unit m3/day m3/h mg/I mg/l kg/day
Process temperature TKN P04-P
°C mg/l mg/l
Smiths Food 912 38 5,000 4,000 4,560 4.5-7.5 Average> 30°C 286 (max. 400)
Peka Kroef 1,600 67 (max. 90) 7,500 (varying) 6,000 12,000 4.5 (after buffering) average> 20°C 50-200 10-50
UzayGida 890 37 4,500 (varying) 1,425 4,005 5-9 > 15°C 20-70 2-10
causllc
blag ••
<:»
contllinw
....""""nk 400 ....
Ibypas .....tIo~ Figure 3. Schematic representation of the pre-treatment stage and the anaerobic treatment stage at Smiths Food.
The performance of the combined Biothane'" UASB anaerobic - Carrousel~ aerobic wastewater treatment plant of Smiths Food is specified in Table 3. THE WASTEWATERTREATMENT PLANT OF PEKA KROEF Figure 4 shows a flow scheme of the plant of Peka Kroef. The wastewater from the potato and the vegetable processing plants follow similar but separate treatment lines. Coarse solids are removed in parabolic screens and most of the suspended solids in a pre-clarifier. The settled solids are dewatered in a decanter and the overflow is fed into a buffer tank of 1000 013 •
G. R. ZOUTBERG and Z. EKER
302
Table 3. Performance data wastewater treatment plant Smiths Food Parameter Influent (data after primary clarifier) Flow t-COD s-COD SS Anaerobic effluent t-COD s-COD SS N-Kj Aerobic (final) effluent t-COD s-COD BOD SS N-Kj
Unit
Value
m 3/d mg/l mg/l mg/l
517 4,566 2,770 890
mg/l mg/l mg/l mg/l
926 266 600 196
80% 90%
mg/l mg/l mg/l mg/l mg/l
165 60 17 82 4
96% 98%
cauattc
Efficiency
Conditioning tlnll
(211Um')
Blobld Naeto, (213110 m')
preoClariftor
..,.tion
blogas
Figure 4. Schematic representation of the pre-treatment stageandthe anaerobic treatment stageof PekaKroef.
The anaerobic plant consists of two identical streets, giving Peka Kroef a high degree of operational flexibility. From the buffer tank the water is pumped to the conditioning tanks where the pH of the wastewater is controlled. Wastewater is then pumped to the Biobed" EGSB reactors where the COD conversion takes place. The conditioning tanks and the anaerobic reactors operate under 100 mbar pressure and are made from FRP. It is possible to operate without a gasholder or a compressor. The factory ofPeka Kroefis situated in a rural area where strict building height restrictions (12 m) are in place. The Biobed'" process is very flexible in reactor configuration and, as a result, the reactor design could comply with this requirement. Additionally, strict restrictions with respect to odour and noise emission are in place. Due to the design of the Biobed ill EGSB reactor this system operates under a "zero odour emission" guarantee. The Biobed~ EGSB plant was commissioned in May 1998. In the next three years Peka Kroef
Anaerobic treatment of potato processing wastewater
303
will implement process modifications to their aerobic wastewater treatment plant in order to increase nitrogen and phosphorus removal for final discharge to sewer. THE WASTEWATER TREATMENT PLANT OF UZA Y GIDA At the treatment plant all particles with a diameter bigger than 0.75 mrn are removed by a coarse and fine screen . Subsequently the wastewater is sent to the pre-sedimentation chamber to remove the remaining suspended solids and some residual fat, oil and grease (FOG). From here the water flows under gravity to a buffer tank. After balancing, the water is ~umped to the conditioning tank where the pH and temperature are controlled. From this tank the Biothane UASB reactor is fed. The anaerobic effluent is flowing under gravity via the conditioning tank to the aerobic post-treatment stage. For this last stage sequencing batch reactors are used and the COD concentration in the final effluent is lao mg COD/I. The scheme of the treatment plant ofUZAY GIDA is given in Figure 5.
Pototo. Gnd Coarse Ie fln. ScrHn Com proc.nrno Wastewater
Pr.tlorJfle<
H
h
'--.J
'--.J
'--.J o o Dlsch(J'ge
Figure S. Schematic representation of the pre-treatment. anaerobic treatment and post-treatment stage at UZAY G1DA.
Table 4. Performance data wastewater treatment plant Uzay Gida Parameter Influent (data after primary clarifier) Flow t-COD s-COD SS Anaerobic effluent t-COD s-COD SS SBR (final effluent) t-COD s-COD BOD SS
Unit
Value
m 3/d mg/l mg/l mg/l
890 4,500 1,425 1,275
mg/l mg/I mg/l
922 535 695
79% 62% 45%
mg/l mg/l mg/l mg/l
lOa 80 45 45
89% 85%
Efficiency
304
G. R. ZOUTBERG and Z. EKER
The effiuent characteristics of the Biothane'" UASB reactor during the start-up period and of the SBR system are shown in Table 4. CONCLUSION Anaerobic wastewater treatment in the potato processing industry by means of the UASB process has gained extensive experience over the last decade. The stability of the process, the ruggedness of its design and the all-year efficiency have contributed to its reliability. Ongoing technological research has recently enabled Biothane Systems to build its first Biobed~ EGSB in the potato processing industry. The first results are very promising. REFERENCES Abeling, U. and Seyfried, C.F. (1993). Anaerobic-aerobic treatment of potato-starch wastewater. Wat. Sci. Tech. 28(2), 165-176. Hadjivassilis I., Gajdos, S., Vanco, D. and Nicolaou M. (1997). Treatment of wastewater from the potato chips and snacks manufacturing industry. Wat. Sci. Tech. 36(2-3), 329-335. Hulshoff Pol L., Hartlieb E., Eitner A. and Grohganz D. (1997). GTZ sectorial project promotion of anaerobic technology for the treatment of municipal and industrial sewage and wastes. In: Proceedings of the IIh International Conference on Anaerobic Digestion, Sendai, Japan, Volume 2, pp. 285-292. Versprille, A. I., Frankin, R. J. and Zoutberg G. R. (1994). Biobed~, a successful cross-breed between VASB and fluidized-bed. In: Seventh International Symposium on Anaerobic Digestion, RSA (Pty) Ltd, Goodwood, pp. 587-590.
Wal. Sci, Tech. Vol. 40, No. I, pp. 297-304, 1999
CI999 Published by Elsevier Science Ltd on behalf of the IAWQ Printed in Great Britain. All rights reserved
0273-1223/99 $20.00 + 0.00
PIT: S0273-1223(99)00398-4
ANAEROBIC TREATMENT OF POTATO PROCESSING WASTEWATER George R. Zoutberg* and Zerrin Eker* * • BiothaneSystemsInternational, P.O. Box 5068, 2600 GB Delft, TheNetherlands ··Arbiogaz Cevre teknolojileri Instaatsanayi ve TicaretA.S., Eski Buyukdere Cad. EmektarSok. No. 7J Kat. 380660, 4 LeventIstanbul, Turkey
ABSTRACT This paper deals with the anaerobictreatmentof wastewaterfrom the potato processingindustry. It is shown that treatmentof this type of wastewater in VASB reactorshas successfully been applied at manycompanies. Apart from the Biothanetl VASB technology a new anaerobictechnology is presented: the Biobed'" EGSB technology. Presented is the first application of this technology in the potato processingindustryand also a comparison is made between this technology and the Biothanetl VASB technology. C> 1999 Published by ElsevierScienceLtd on behalfof the IAWQ. All rightsreserved.
KEYWORDS Anaerobic; Biobedtl EGSB; Biothanetl UASB';potato; high rate; low temperature; suspended solids. INTRODUCTION Wastewater in the potato processing industry contains high concentrations of biodegradable components, such as starch and proteins (Abeling and Seyfried, 1993, Hadjivassilis et al., 1997). Though the Biothane'" UASB technology has established an impressive track record for this kind of wastewater, new developments in the compact, high-rate Biobed'" EGSB anaerobic technology have led to a break-through in the Netherlands. With more than 1800 plants world-wide (1997) covering different applications (food processing, chemical industry, pulp and paper industry), anaerobic treatment has gained widespread appreciation as a reliable and efficient means for reduction of COD (Hulshof Pol et al., 1997). Of all anaerobic processes those technologies based on high-rate, compact, granular biomass technology, such as UASB and EGSB, have a leading position (more than 750 plants). The well-known Dutch supplier Biothane Systems holds a worldwide market share of approximately 32%. Developed in the Netherlands in the early 70s by Biothane Systems (in co-operation with the University of Wageningen), the UASB (Upflow Anaerobic Sludge Blanket) technology was designed for treatment of highly concentrated wastewater in the sugar industry. Soon, applications in other markets emerged as the UASB technology matured into a stable, highly effective process for reducing discharge costs of industrial wastewater. In the potato processing industry, several Biothane'" UASB plants have been built by Biothane Systems and its world-wide partners, for customers such as McCain Foods (French fries) and Pepsico (potato crisps). 297
298
G. R. ZOUTBERG and Z. EKER
Recent additions of Biothane® UASB plants in the Pepsico network include Greece (Tasty Foods, Athens), Turkey (Uzay Gida, Istanbul) and Poland (E. Wedel, Warsaw) . In this article the plant installed at Uzay Gida is presented . For wastewater of fairly low temperatures and considerable fluctuations in COD composmon and load throughout the year, Biothane Systems has developed a new type of anaerobic technology. This Biobed ® EGSB (Expanded Granular Sludge Bed) technology is able to handle the above mentioned circumstances, while it even further reduces the overall footprint because of the use of typically high and slender reactors. In this article a comparison is made between a Biothane® UASB reactor and a Biobed" EGSB reactor installed at two different potato processing facilities in The Netherlands. WASTEWATER TREATMENT: ANAEROBIC VERSUS AEROBIC TREATMENT Biological wastewater treatment in the potato processing industry normally starts with a removal step for suspended materials, followed by biological treatment, such as anaerobic and aerobic processes. The major disadvantage of full aerobic treatment are the high operating costs (electricity, sludge handling, maintenance). Especially the costs for sludge dewatering and sludge disposal (dumping and incineration) have increased substantially over the years. As a result most of the Dutch potato processing companies have turned to the use of anaerobic removal of COD in their wastewater by means of UASB reactors. Biothane~
UASB versus Biobed"') EGSB
The UASB (Upflow Anaerobic Sludge Blanket) technology and the EGSB (Expanded Granular Sludge Bed) technology both make use of granular anaerobic biomass . Both processes have the same operation .principles, but differ in terms of geometry, process parameters and (usually) construction materials.
1 Sludqerbromass Inl t 2 Gas ba ffle pla tes 3 Re turn se ttl d sludge
Influent
Figure I. A cross-section of the Biothane" UASB reactor.
In both processes wastewater is fed into the reactor at the bottom through a specially designed influent distribution system. The water flows through a sludge bed consisting of anaerobic bacteria, which develop into a granular form. The excellent settleability (60 - 80 m/h) of these anaerobic granules enables high concentrations of biomass in a small reactor volume. The granules do not contain an organic carrier material, such as sand or hasalt. In the sludge bed the conversion from COD to hiogas takes place . In both reactor types the mixture of sludge, biogas and water is separated into three phases by means of a specially designed three-phase separator (or settler) at the top of the reactor. The purified effluent leaves the reactor via effluent laundries, biogas is collected at the top and sludge settles back into the active volume of the reactor. One of the most important design parameters for both types of reactors is the maximum allowable superficial upflow liquid velocity in the settler. Upflow velocities in excess of this maximum design value
Anaerobic treatment of potato processing wastewater
299
result in granular sludge being washed out of the reactor. The Biobed® EGSB settler allows a substantial higher upstream velocity (10 m/h) than the Biothane® DASB settler (1.0 m/h).
Effluent
1 Granular sludgelwa ter
2 Settled granular sludge
Influent
) >-- - -
Figure 2. A cross-section of the Biobedt> EGSB reactor.
Another important design parameter is the maximum allowed COD load. The Biobed® EGSB process operates under substantial higher COD loads (30 kg/m-.d) than the Biothane® DASB process (10 kglm 3.d). The result being that for a given COD load the Biobed® EGSB reactor volume is smal1er than for a Biothane® VASB reactor. Biothanef VASB reactors are typically rectangular or square, with an average height of 6.0 metres and are usually constructed in concrete. Biobed® EGSB reactors have a substantially smaller footprint. These high and narrow tanks are built in FRP (Fibreglass Reinforced Plastic) or stainless steel and have a typical height of 12 - 18 m. The height of the granular sludge bed In the Biothane® VASB reactor varies between I - 2 m and in the Biobed® EGSB from 7 - 14 m. A Biobedll> EGSB reactor is normal!j built as a completely closed reactor resulting in a system with zero odour emission. Additionally, a Biobed EGSB reactor can be operated under overpressure, thereby making any use of gasholders and biogas compressors redundant. The general differences between both processes are shown in Table I. Table I. Comparison between the main characteristic parameters of Biothane® VASB and Biobed® EGSB.
Load Height Toxic components" Vliquid settler Vliquid reactor vgas reactor
rn/h m/h rn/h
Biothane® DASB 10 5.5 - 6.5 +/-
Biobed® EGSB 30 12 - 18 ++
1.0 < 1.0 < 1.0
10 < 6.0 < 7.0
·The excellent hydraulic properties of the Biobed l EGSB reactor make it possible to use a lot of anaerobic effluent for dilution of the incoming wastewater. This makes it possible to treat wastewater containing components that are toxic in high concentrations, but biodegradable at low concentrations (e.g. formaldehyde). This feature has been applied for several chemical plants (Dupont de Nemours, Caldic Europoort, Hoechst Trevira Vlissingen B.V.).
Wastewater in the potato processing industry contains substantial amounts of suspended solids. The ill Biothane VASB process is characterised by longer hydraulic retention times than that of the Biobed'" EGSB process. As a consequence, use of the Biothanef" VASB process results in a higher removal of suspended solids and therefore higher overal1 COD removal efficiencies. The Biobed
300
G. R. ZOUTBERG and Z. EKER
WASTEWATER CHARACTERISTICS OF SMITHS FOOD, PEKA KROEF AND UZAY GIDA Smiths Food produces potato crisps and has chosen the Biothane iZ UASB anaerobic treatment process for bulk-COD removal from their wastewater and aerobic final treatment to meet the discharge limits. It is important to realise that anaerobic treatment always is a form of pre-treatment. During this anaerobic stage 80% of the COD is removed and converted to biogas. Only 1-2% of that COD is converted into new anaerobic biomass and, as a result, hardly any nitro,en (N) and phosphorus (P) are removed. The aerobic post-treatment consists of a low loaded Carrousel (registered trade name of DHV Water) and aims at removal of nitrogen and COD. Peka Kroef produces potato and vegetable based halfproducts for the salad industry in Europe. The ratio potatoes/vegetables is dependent on the season. As a consequence considerable fluctuations in the COD load occur. During the summer months July, August and September the processed vegetables are cocktail onions, cucumber and gherkins. During the other months mostly carrots and celeriac are processed. Until now the wastewater of Peka Kroef was treated in a conventional aerobic treatment plant (two basins with a volume of 4000 m' each). Peka Kroef's production expansion plans required additional wastewater treatment plant capacity. Expansion of the existing aerobic plant would lead to higher energy costs and a higher sludge production. For this reason the possibility of anaerobic treatment was investigated. Due to the specific characteristics of the wastewater (low temperature, COD load fluctuations, COD composition fluctuations, high suspended solids (SS) concentrations) an alternative for the conventional UASB, the EGSB technology, was tested. Extensive laboratory research showed good results with this type of anaerobic treatment at temperatures of20-25°C. Due to the innovative character of the application of the EGSB technology for this type of wastewater the Dutch authorities awarded a subsidy of 450,000 Dutch guilders for the project. The anaerobic pre-treatment serves as a "peak-shaver" (approximately 70% of the COD is removed and peaks in COD are levelled), this results in a more constant load to the aerobic stage. The factory ofUZAY GIDA produces potato and corn crisps and has a production process that varies during the week. These variations can be found back in the composition of the wastewater. The increased production capacity has led to a higher COD load in the wastewater. For this reason a Biothane'" UASB system is added between the existing pre-treatment and the existing Sequencing Batch Reactors (SBR). At the start-up in June 1998 the COD removal efficiency reached 75%, more results will be presented at the conference. The design parameters for the three above mentioned anaerobic installations are shown in Table 2. THE WASTEWATER TREATMENT PLANT OF SMITHS FOOD Figure 3 shows the flow scheme of this plant. Coarse solids are removed in a parabolic screen (mesh size: 1 mm). After this screen the water enters a pre-clarifier designed at a surface load of 1 mJh for removal of suspended solids and residual fat, oil and grease. The settled solids are dewatered in a decanter and the water flows by gravity into a buffertank of 400 m3• From the buffertank the water is pumped to a conditioning tank for pH and temperature correction. Conversion of COD takes place in the Biothane'" UASB reactor. The total anaerobic plant has a COD removal efficiency of approximately 80%. The remaining COD and Kjeldahl nitrogen is removed in the aerobic post-treatment. The final COD concentration is less than 100 mgll and the Kj-N concentration is less than 10 mgll. The final effiuent is discharged to the municipal sewer.
301
Anaerobic treatment of palata processing wastewater
Table 2. Design wastewater characteristicsfor Smiths Food, Peka Kroefand Uzay Gida after screening and pre-settlement Parameter Flow (average) Flow (average after buffering) COD (total) COD (soluble) COD-load PH
Unit m3/day m3/h mg/I mg/l kg/day
Process temperature TKN P04-P
°C mg/l mg/l
Smiths Food 912 38 5,000 4,000 4,560 4.5-7.5 Average> 30°C 286 (max. 400)
Peka Kroef 1,600 67 (max. 90) 7,500 (varying) 6,000 12,000 4.5 (after buffering) average> 20°C 50-200 10-50
UzayGida 890 37 4,500 (varying) 1,425 4,005 5-9 > 15°C 20-70 2-10
causllc
blag ••
<:»
contllinw
....""""nk 400 ....
Ibypas .....tIo~ Figure 3. Schematic representation of the pre-treatment stage and the anaerobic treatment stage at Smiths Food.
The performance of the combined Biothane'" UASB anaerobic - Carrousel~ aerobic wastewater treatment plant of Smiths Food is specified in Table 3. THE WASTEWATERTREATMENT PLANT OF PEKA KROEF Figure 4 shows a flow scheme of the plant of Peka Kroef. The wastewater from the potato and the vegetable processing plants follow similar but separate treatment lines. Coarse solids are removed in parabolic screens and most of the suspended solids in a pre-clarifier. The settled solids are dewatered in a decanter and the overflow is fed into a buffer tank of 1000 013 •
G. R. ZOUTBERG and Z. EKER
302
Table 3. Performance data wastewater treatment plant Smiths Food Parameter Influent (data after primary clarifier) Flow t-COD s-COD SS Anaerobic effluent t-COD s-COD SS N-Kj Aerobic (final) effluent t-COD s-COD BOD SS N-Kj
Unit
Value
m 3/d mg/l mg/l mg/l
517 4,566 2,770 890
mg/l mg/l mg/l mg/l
926 266 600 196
80% 90%
mg/l mg/l mg/l mg/l mg/l
165 60 17 82 4
96% 98%
cauattc
Efficiency
Conditioning tlnll
(211Um')
Blobld Naeto, (213110 m')
preoClariftor
..,.tion
blogas
Figure 4. Schematic representation of the pre-treatment stageandthe anaerobic treatment stageof PekaKroef.
The anaerobic plant consists of two identical streets, giving Peka Kroef a high degree of operational flexibility. From the buffer tank the water is pumped to the conditioning tanks where the pH of the wastewater is controlled. Wastewater is then pumped to the Biobed" EGSB reactors where the COD conversion takes place. The conditioning tanks and the anaerobic reactors operate under 100 mbar pressure and are made from FRP. It is possible to operate without a gasholder or a compressor. The factory ofPeka Kroefis situated in a rural area where strict building height restrictions (12 m) are in place. The Biobed'" process is very flexible in reactor configuration and, as a result, the reactor design could comply with this requirement. Additionally, strict restrictions with respect to odour and noise emission are in place. Due to the design of the Biobed ill EGSB reactor this system operates under a "zero odour emission" guarantee. The Biobed~ EGSB plant was commissioned in May 1998. In the next three years Peka Kroef
Anaerobic treatment of potato processing wastewater
303
will implement process modifications to their aerobic wastewater treatment plant in order to increase nitrogen and phosphorus removal for final discharge to sewer. THE WASTEWATER TREATMENT PLANT OF UZA Y GIDA At the treatment plant all particles with a diameter bigger than 0.75 mrn are removed by a coarse and fine screen . Subsequently the wastewater is sent to the pre-sedimentation chamber to remove the remaining suspended solids and some residual fat, oil and grease (FOG). From here the water flows under gravity to a buffer tank. After balancing, the water is ~umped to the conditioning tank where the pH and temperature are controlled. From this tank the Biothane UASB reactor is fed. The anaerobic effluent is flowing under gravity via the conditioning tank to the aerobic post-treatment stage. For this last stage sequencing batch reactors are used and the COD concentration in the final effluent is lao mg COD/I. The scheme of the treatment plant ofUZAY GIDA is given in Figure 5.
Pototo. Gnd Coarse Ie fln. ScrHn Com proc.nrno Wastewater
Pr.tlorJfle<
H
h
'--.J
'--.J
'--.J o o Dlsch(J'ge
Figure S. Schematic representation of the pre-treatment. anaerobic treatment and post-treatment stage at UZAY G1DA.
Table 4. Performance data wastewater treatment plant Uzay Gida Parameter Influent (data after primary clarifier) Flow t-COD s-COD SS Anaerobic effluent t-COD s-COD SS SBR (final effluent) t-COD s-COD BOD SS
Unit
Value
m 3/d mg/l mg/l mg/l
890 4,500 1,425 1,275
mg/l mg/I mg/l
922 535 695
79% 62% 45%
mg/l mg/l mg/l mg/l
lOa 80 45 45
89% 85%
Efficiency
304
G. R. ZOUTBERG and Z. EKER
The effiuent characteristics of the Biothane'" UASB reactor during the start-up period and of the SBR system are shown in Table 4. CONCLUSION Anaerobic wastewater treatment in the potato processing industry by means of the UASB process has gained extensive experience over the last decade. The stability of the process, the ruggedness of its design and the all-year efficiency have contributed to its reliability. Ongoing technological research has recently enabled Biothane Systems to build its first Biobed~ EGSB in the potato processing industry. The first results are very promising. REFERENCES Abeling, U. and Seyfried, C.F. (1993). Anaerobic-aerobic treatment of potato-starch wastewater. Wat. Sci. Tech. 28(2), 165-176. Hadjivassilis I., Gajdos, S., Vanco, D. and Nicolaou M. (1997). Treatment of wastewater from the potato chips and snacks manufacturing industry. Wat. Sci. Tech. 36(2-3), 329-335. Hulshoff Pol L., Hartlieb E., Eitner A. and Grohganz D. (1997). GTZ sectorial project promotion of anaerobic technology for the treatment of municipal and industrial sewage and wastes. In: Proceedings of the IIh International Conference on Anaerobic Digestion, Sendai, Japan, Volume 2, pp. 285-292. Versprille, A. I., Frankin, R. J. and Zoutberg G. R. (1994). Biobed~, a successful cross-breed between VASB and fluidized-bed. In: Seventh International Symposium on Anaerobic Digestion, RSA (Pty) Ltd, Goodwood, pp. 587-590.