~ Pergamon Wal. Sci, Tech. Vol. 40, No. I, pp. 297-304, 1999CI999

Published by Elsevier Science Ltd on behalfof the IAWQPrinted in Great Britain. All rights reserved

0273-1223/99 $20.00 + 0.00PIT: S0273-1223(99)00398-4

ANAEROBIC TREATMENT OF POTATOPROCESSING WASTEWATER

GeorgeR. Zoutberg* and Zerrin Eker**

• BiothaneSystemsInternational, P.O. Box 5068,2600 GB Delft, TheNetherlands··Arbiogaz Cevreteknolojileri Instaatsanayi ve TicaretA.S., EskiBuyukdere Cad.EmektarSok.No. 7J Kat. 380660, 4 LeventIstanbul, Turkey

ABSTRACT

This paperdeals with the anaerobictreatmentof wastewaterfromthe potatoprocessingindustry. It is shownthat treatmentof this type of wastewater in VASB reactorshas successfully beenappliedat manycompanies.Apart from the Biothanetl VASB technology a new anaerobictechnology is presented: the Biobed'" EGSBtechnology. Presented is the first application of this technology in the potato processingindustryand also acomparison is made between this technology and the Biothanetl VASB technology. C> 1999 Published byElsevierScienceLtd 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 developmentsin the compact, high-rate Biobed'" EGSB anaerobic technology have led to a break-through in theNetherlands.

With more than 1800 plants world-wide (1997) covering different applications (food processing, chemicalindustry, pulp and paper industry), anaerobic treatment has gained widespread appreciation as a reliable andefficient means for reduction of COD (Hulshof Pol et al., 1997). Of all anaerobic processes thosetechnologies based on high-rate, compact, granular biomass technology, such as UASB and EGSB, have aleading 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 ofWageningen), the UASB (Upflow Anaerobic Sludge Blanket) technology was designed for treatment ofhighly concentrated wastewater in the sugar industry. Soon, applications in other markets emerged as theUASB technology matured into a stable, highly effective process for reducing discharge costs of industrialwastewater.

In the potato processing industry, several Biothane'" UASB plants have been built by Biothane Systems andits 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 UzayGida is presented .

For wastewater of fairly low temperatures and considerable fluctuations in COD composmon and loadthroughout 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 reactorinstalled at two different potato processing facilities in The Netherlands.

WASTEWATER TREATMENT: ANAEROBIC VERSUS AEROBICTREATMENT

Biological wastewater treatment in the potato processing industry normally starts with a removal step forsuspended materials, followed by biological treatment, such as anaerobic and aerobic processes. The majordisadvantage 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 haveturned 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 tes3 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 influentdistribution system. The water flows through a sludge bed consisting of anaerobic bacteria, which developinto a granular form. The excellent settleability (60 - 80 m/h) of these anaerobic granules enables highconcentrations 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 ofsludge, biogas and water is separated into three phases by means of a specially designed three-phaseseparator (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 allowablesuperficial 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 substantialhigher upstream velocity (10 m/h) than the Biothane® DASB settler (1.0 m/h).

Effluent

1 Granular sludgelwater2 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 processoperates under substantial higher COD loads (30 kg/m-.d) than the Biothane® DASB process (10 kglm3.d).

The result being that for a given COD load the Biobed® EGSB reactor volume is smal1er than for aBiothane® VASB reactor. Biothanef VASB reactors are typically rectangular or square, with an averageheight of 6.0 metres and are usually constructed in concrete. Biobed® EGSB reactors have a substantiallysmaller footprint. These high and narrow tanks are built in FRP (Fibreglass Reinforced Plastic) or stainlesssteel and have a typical height of 12 - 18 m. The height of the granular sludge bed In the Biothane® VASBreactor varies between I - 2 m and in the Biobed® EGSB from 7 - 14 m. A Biobedll> EGSB reactor isnormal!j built as a completely closed reactor resulting in a system with zero odour emission. Additionally, aBiobed EGSB reactor can be operated under overpressure, thereby making any use of gasholders andbiogas 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.

Biothane® DASB Biobed® EGSB3012 - 18++

105.5 - 6.5+/-

LoadHeightToxiccomponents"Vliquid settler rn/h 1.0 10Vliquid reactor m/h < 1.0 < 6.0vgas reactor rn/h < 1.0 < 7.0

·The excellent hydraulic properties of the Biobedl EGSB reactor make it possible to use a lot of anaerobiceffluent for dilution of the incoming wastewater. This makes it possible to treat wastewater containingcomponents 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, CaldicEuropoort, Hoechst Trevira Vlissingen B.V.).

Wastewater in the potato processing industry contains substantial amounts of suspended solids. TheBiothaneill 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 ofsuspended solids and therefore higher overal1 COD removal efficiencies. The Biobed<il EGSB process hasbeen designed for removal of soluble COD mainly. Therefore, the use of Biobed'" EGSB in the potatoprocessing industry is focused for those applications where the anaerobic effluent will be discharged tosewer or to a final aerobic post-treatment.

300 G. R. ZOUTBERG and Z. EKER

WASTEWATER CHARACTERISTICS OF SMITHS FOOD, PEKA KROEFAND UZAY GIDA

Smiths Food produces potato crisps and has chosen the BiothaneiZ UASB anaerobic treatment process forbulk-COD removal from their wastewater and aerobic final treatment to meet the discharge limits. It isimportant to realise that anaerobic treatment always is a form of pre-treatment. During this anaerobic stage80% of the COD is removed and converted to biogas. Only 1-2% of that COD is converted into newanaerobic biomass and, as a result, hardly any nitro,en (N) and phosphorus (P) are removed. The aerobicpost-treatment consists of a low loaded Carrousel (registered trade name of DHV Water) and aims atremoval of nitrogen and COD.

Peka Kroef produces potato and vegetable based halfproducts for the salad industry in Europe. The ratiopotatoes/vegetables is dependent on the season. As a consequence considerable fluctuations in the COD loadoccur. 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 basinswith a volume of 4000 m' each). Peka Kroef's production expansion plans required additional wastewatertreatment plant capacity. Expansion of the existing aerobic plant would lead to higher energy costs and ahigher sludge production. For this reason the possibility of anaerobic treatment was investigated. Due to thespecific characteristics of the wastewater (low temperature, COD load fluctuations, COD compositionfluctuations, high suspended solids (SS) concentrations) an alternative for the conventional UASB, theEGSB technology, was tested. Extensive laboratory research showed good results with this type of anaerobictreatment at temperatures of20-25°C.

Due to the innovative character of the application of the EGSB technology for this type of wastewater theDutch authorities awarded a subsidy of 450,000 Dutch guilders for the project. The anaerobic pre-treatmentserves as a "peak-shaver" (approximately 70% of the COD is removed and peaks in COD are levelled), thisresults 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 duringthe week. These variations can be found back in the composition of the wastewater . The increasedproduction capacity has led to a higher COD load in the wastewater. For this reason a Biothane'" UASBsystem is added between the existing pre-treatment and the existing Sequencing Batch Reactors (SBR). Atthe start-up in June 1998 the COD removal efficiency reached 75%, more results will be presented at theconference.

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: 1mm). After this screen the water enters a pre-clarifier designed at a surface load of 1 mJh for removal ofsuspended solids and residual fat, oil and grease. The settled solids are dewatered in a decanter and the waterflows by gravity into a buffertank of400 m3

• From the buffertank the water is pumped to a conditioning tankfor pH and temperature correction.

Conversion of COD takes place in the Biothane'" UASB reactor. The total anaerobic plant has a CODremoval efficiency of approximately 80%. The remaining COD and Kjeldahl nitrogen is removed in theaerobic post-treatment. The final COD concentration is less than 100 mgll and the Kj-N concentration is lessthan 10 mgll. The final effiuent is discharged to the municipal sewer.

Anaerobic treatment ofpalata processing wastewater 301

Table 2. Design wastewatercharacteristicsfor Smiths Food, Peka Kroefand Uzay Gida after screening andpre-settlement

Parameter Unit Smiths Food Peka Kroef UzayGida

Flow (average) m3/day 912 1,600 890

Flow (average after buffering) m3/h 38 67 (max. 90) 37

COD (total) mg/I 5,000 7,500 (varying) 4,500 (varying)

COD (soluble) mg/l 4,000 6,000 1,425

COD-load kg/day 4,560 12,000 4,005

PH 4.5-7.5 4.5 (after 5-9buffering)

Process temperature °C Average> 30°C average> 20°C > 15°C

TKN mg/l 286 (max. 400) 50-200 20-70P04-P mg/l 10-50 2-10

causllc

<:»contllinw

....""""nk400 ....

blag ••

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 treatmentplant ofSmiths Food is specified in Table 3.

THE WASTEWATERTREATMENTPLANT OF PEKA KROEF

Figure 4 shows a flow scheme of the plant of Peka Kroef. The wastewater from the potato and the vegetableprocessing plants follow similar but separate treatment lines. Coarse solids are removed in parabolic screensand most of the suspended solids in a pre-clarifier. The settled solids are dewatered in a decanter and theoverflow is fed into a buffer tankof 1000 013•

302 G. R. ZOUTBERG and Z. EKER

Table 3. Performance data wastewater treatment plant Smiths Food

Parameter Unit Value EfficiencyInfluent (data after primary

clarifier)Flow m3/d 517

t-COD mg/l 4,566s-COD mg/l 2,770

SS mg/l 890Anaerobic effluent

t-COD mg/l 926 80%s-COD mg/l 266 90%

SS mg/l 600N-Kj mg/l 196

Aerobic (final) effluentt-COD mg/l 165 96%s-COD mg/l 60 98%BOD mg/l 17

SS mg/l 82N-Kj mg/l 4

cauattc Conditioning tlnll Blobld Naeto,(211Um') (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 operationalflexibility. From the buffer tank the water is pumped to the conditioning tanks where the pH of thewastewater is controlled. Wastewater is then pumped to the Biobed" EGSB reactors where the CODconversion takes place. The conditioning tanks and the anaerobic reactors operate under 100 mbar pressureand 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 inplace. The Biobed'" process is very flexible in reactor configuration and, as a result, the reactor design couldcomply with this requirement. Additionally, strict restrictions with respect to odour and noise emission arein 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 increasenitrogen and phosphorus removal for final discharge to sewer.

THE WASTEWATER TREATMENT PLANT OF UZAY GIDA

At the treatment plant all particles with a diameter bigger than 0.75 mrn are removed by a coarse and finescreen . Subsequently the wastewater is sent to the pre-sedimentation chamber to remove the remainingsuspended solids and some residual fat, oil and grease (FOG). From here the water flows under gravity to abuffer tank. After balancing, the water is ~umped to the conditioning tank where the pH and temperature arecontrolled. From this tank the Biothane UASB reactor is fed. The anaerobic effluent is flowing undergravity via the conditioning tank to the aerobic post-treatment stage. For this last stage sequencing batchreactors are used and the COD concentration in the final effluent is lao mg COD/I. The scheme of thetreatment plant ofUZAY GIDA is given in Figure 5.

Pototo. Gnd Coarse Ie fln. ScrHnCom proc.nrno

HWastewater

h'--.J '--.J

Pr.tlorJfle<

'--.J

oo

Dlsch(J'ge

Figure S. Schematic representation of the pre-treatment. anaerobic treatment and post-treatment stage at UZAYG1DA.

Table 4. Performance data wastewater treatment plant Uzay Gida

Parameter Unit ValueInfluent (data after primary clarifier)Flow m3/d 890t-COD mg/l 4,500s-COD mg/l 1,425SS mg/l 1,275Anaerobic effluentt-COD mg/l 922s-COD mg/I 535SS mg/l 695SBR (final effluent)t-COD mg/l lOas-COD mg/l 80BOD mg/l 45SS mg/l 45

Efficiency

79%62%45%

89%85%

304 G. R. ZOUTBERG and Z. EKER

The effiuent characteristics of the Biothane'" UASB reactor during the start-up period and of the SBR systemare shown in Table 4.

CONCLUSION

Anaerobic wastewater treatment in the potato processing industry by means of the UASB process has gainedextensive experience over the last decade. The stability of the process, the ruggedness of its design and theall-year efficiency have contributed to its reliability. Ongoing technological research has recently enabledBiothane Systems to build its first Biobed~EGSB in the potato processing industry. The first results are verypromising.

REFERENCES

Abeling, U. and Seyfried, C.F. (1993). Anaerobic-aerobic treatment ofpotato-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 onAnaerobic 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.