Table 2. Effect of Type of Steeping Process on Starch Yield and Starch Loss in By-products.

Grains Starch Starch Protein Starch Starch treatment yield recovery in in in

starch hull fibre (%) (%) (%) (%) (%)

~ ~ ~ ~ ~~~~ ~

Counter-current 66.3 90.2 1.0 11.1 36.5 (control) 50 h

Counter-current 66.5 90.4 0.77 10.8 35.8 with agitation for 10 h

3.2 In the plant

The steeping process with circulating the mixture of corn grains and steeping water for 25 h was applied in Tura plant and continued twice for 15 d, each time. The milling on each day reached 150 t and the results showed that: 1) The starch yield was higher to about 1% in comparison with

2) The protein content of starch decreased to 0.3%. 3) Glucose syrup product was very clear which confirms the

These results are very valuable from the economical point of view because they lead to reduce the steeping period by half and increase the capacity of the steeping unit. At the same time the new process increases yield and quality of produced starch.

the usual counter-current.

lower protein content.

Bibliography [l] Kerr, R . W.: “Chemistry and Industry of Starch.” Academic Press,

[2] Whistler, R. L., and E. F. Pashall: “Starch Technology” Vol. 2,

[3] Radley, J . A .: “Starch Production and Technology”. Applied

[4] Blessin, C. W., R. A . Anderson, W. L. Deatherage and G . E .

[5] Cox, Mary J . , M. M. MacMasters and B. E . Hilbert: Cer. Chem. 21

[6] Joyce, A . B. , J . E . Tarner, J . S . Wall and R. J . Binler: Cer. Chem.

[7] Kudron, J.: Szesziper 19 (1971), 25; C. A. 76 (1972), 155908. [8] Roushdi, M. , Y. Ghali and A . Hassanean: StarcMStarke 31 (1979),

[9] Grindel, R . S.: StarcMStarke 17 (1965), 298.

New York 1950.

Academic Press, New York 1967.

Science Publisher, London 1976.

Znglett: Cer. Chem. 48 (1971), 528.

(1944), 447.

44 (1967), 281.

78.

[lo] Grindel, R. S.: Ger. Patent 1,301,976; C. A. 76 (1969), 114439. [ l l ] Gillenwater, D. L., G. B. Pfundstein and A . R. Harvey: U.S.

Patent 3,597,274; August 1971, cited in “Edible Starches and Starch-derived Syrups’’ (1975).

[12] Vegter, J . : U.S. Patent 3,595,696; July 1971, cited in “Edible Starches and Starch-derived Syrups” (1975).

[13] CPC International, Inc.: U. S. Patent 7,416,230; C. A. 84 (1976), 57393.

[14] KernpJ W.: Starch/Starke 23 (1971), 89. [15] Meuser, F., H. German and H . Huster: “Progress in Biotechnology

I”, New Approaches to Research on Cereal Carbohydrates, June 24-29 (1984), 161-180.

[16] Anderson, R. A . , and V . F. Pfeifer: Cer. Chem. 39 (1959), 98. [17] A. 0. A. C.: “Official Methods of Analysis”, 11th Ed., Washing-

ton, D. C. 1970.

Address of authors: Dr. Abbas Hassanean, Production Manager, Starch 8~ Glucose Company, Tura Factory, and Adel Abdel-Wahed, Chief Sector, Tura Factories, Cairo (Egypt).

(Received: February 3, 1986)

tors in Application of Anaerobic Fluidized Bed Reac-

Biological Waste Water Treatmenr By J. J. Heijnen, W. A. Enger, A. Mulder, P. A. Lourens, A. A. Keijzers and F. W. J. M. M. Hoeks, Detft (The Netherlands)

From pilot experiments (0,3-3,6 m3) and full scale application (300 m3) it is shown that the improved anaerobic fluid bed technol- ogy represents a very reliable and compact high-rate technology for the purification of highly fluctuational industrial wastewater. A two- stage process (acidification/methanation) appeared to have advan- tages with respect to process stability as well as purification capacity. On full scale the average purification capacity, reached six months after start-up, was 28 kg COD/m3 day (based on the volume of the methane reactor), with peaks of 50 kg COD/m3 day. Further increases in capacity may be expected in the future.

Anwendung der anaeroben Wirbelschichttechnik bei der biolo- gischen Abwasser-Behandlung. Anhand von Pilotversuchen (0,3-0,6 m3) und Versuchen im Produktionsmaastab (300 m3) wird gezeigt , daR die entwickelte anaerobe Wirbelschichttechnik ein sehr zuverlassiges kompaktes Hochleistungsverfahren darstellt fiir die Reinigung der stark variablen industriellen Abwasser. Es zeigte sich, daR ein 2stufiges Verfahren groBe Vorteile bietet in bezug auf Pro- zeastabilitat und Reinigungskapazitiit. Die Abbauleistung im Pro- duktionsmaastab erreichte nach sechs Monaten einen Mittelwert von 28 kg CSB/m3 Tag (bezogen auf den Methan-Reaktor) und einen Spitzenwert von etwa 50 kg CSB/m3fI’ag. Eine weitere Steigerung der Kapazitat in Zukunft ist nicht ausgeschlossen.

* Lecture presented by J. J . Heijnen at the 36th Starch Convention of the Arbeitsgemeinschaft Getreideforschung at Detmold, April 24 to 26,1985.

starchlstarke 38 (1986) Nr. 12, S. 419-428 41 9 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986 0038-9056/86/1212-0419$02.50/0

1 Introduction in recent years anaerobic processes have gained importance as an alternative to conventional aerobic processes in the field of waste water purification. Furthermore it has been shown that fluidized bed reactors offer attractive advantages with respect to purification capacity [l]. in such a fluidized bed reactor the biomass grows as a thin biofilm attached to a carrier (Fig. 1).

D I O g a S

T

I w a s t e w a t e r f l o w ai

Figure 1. Flow sheet of an anaerobic fluidized bed reactor.

The biolayer covered carrier is maintained in a fluidized state by an upward flow of waste water, Because of the high settling velocity of the particles (= 50 d h ) , retention of the biomass on the carrier poses no problems. A comparison of the main aspects of fluidized bed technology and conventional floccu- lated sludge technology is provided in Table 1.

Table 1. Comparison of Flocculated Sludge and Fluidized Bed Technology.

Flocculated Sludge Ffuidized Bed

1 Settling rate 1 mh 2 Inert sediment accumulates in

5 Biomass S kg/m3 4 Superficial liquid velocity

5 Reactors are large, low and wide

6 Large area requirement

sludge

<1 mh

1 Settling rate SO mh 2 Inert sediment washes through

3 Biomass 40 kg/m3 4 Superficial liquid velocity

5 Reactors are compact, tall and

6 Small area requirement

reactor

10-30 m/h

slender

From Table 1 it appears that, due to the high settling velocity of the particles and the resulting high biomass concentration, the fluidized bed system becomes very compact and requires little space. Despite these potential advantages some major prob- lems remain unsolved [2 , 31 (see also Table 2 ) : - Separation of surplus sludge from the carrier is necessary, as

is return of the carrier into the reactor. Especially in a corrosive anaerobic environment such a separation device is cumbersome;

- Continuous control of the fluidized bed height - too much energy consumption due to high waste water

recycle ratios (often > 10); - no homogeneous distribution of the upward flowing waste

water across the reactor area on full scale sized systems can be attained yet;

- attachment of the biomass on the fluidized carrier does not always occur.

The potential advantages of the fluidized bed system made this system highly attractive for Gist-brocades which was seeking a solution for its waste water problems (arising from the manufac- ture of yeast, antibiotics and enzymes and from all sorts of chemical processes). Therefore Gist-brocades has performed research on lab and pilot scale since 1979 to develop an anaerobic fluidized bed system with the advantages mentioned but without any of the disadvantages. This research has led to the construction of a full scale anaerobic fluidized bed installation in Delft (the Nether- lands) which was started up succesfully between February and August 1984. Some characteristics of the Gist-brocades fluidized bed system for anaerobic waste water treatment are (see also Table 2): - There is no need for a continuous control of fluidized bed

height; - a device for carrierbiolayer separation (to remove surplus

sludge) is not needed; -the recycle of waste-water is minimal. The ratio of recycle

flow to waste water flow is < 1, leading to a low energy consumption

- the problem to obtain a homogeneous liquid distribution has been solved by developing a suitable liquid distributing device (see also Section 5).

Table 2. Specific Properties of the Gist-brocades Anaerobic Fluidized Bed System.

~~ ~ ~~

Reported in Literature

- Control biolayer thickness by mechanical carrierbiolayer se- paration plus carrier return

- High recycle ratio (9 1) - Liquid distribution problematic

- Attachment of biomass is some-

- Normal surplus sludge produc- times problematic

tion

~

Gist-brocades System

- Biolayer thickness remains constant

- Low recycle ratio - Liquid distribution at fullscale

- Biolayer formation no problem no problem

- Very low surplus sludge pro- duction

The obvious result is a waste water treatment system merely presenting advantages. This paper will present the develop- ment of the anaerobic treatment system on laboratory, pilot and full scale. The following subjects will be covered: - 1 or 2-Stage process design; - acidification in a pilot scale fluidized bed reactor; - purification of pre-acidified waste water in a methane pro-

- start-up experience of the full scale 2-stage anaerobic ducing pilot scale fluidized bed reactor;

fluidized bed unit in Delft.

2 1- or 2-Stage Configuration in Anaerobic Fluidized Bed Treatment Systems Whenever anaerobic purification processes are considered one is faced with the question what the advantages and disadvan- tages of 1 or 2-stage process configuration are. In the 1-stage configuration acidification and methanation occur in the same reaction space. In the 2-stage configuration microbial acidification takes place in the first reactor and the produced lower fatty acids (mainly acetic acid to valeric acid) are converted to CH4/CO2 in a second reactor (Fig. 2). In

420 starcwstarke 38 (1986) Nr. 12, S. 419-428

t

COD

acidification methanation

Figure 2. Flow sheet 2-stage anaerobic processes.

general, the methanogenic activity of the sludge in the 2-stage process proves much higher (factor 3) than that in the 1-stage process 11, 41. Therefore it appears that the purification capacity of the 2-stage process is better than that in the 1-stage process. In addition, there are indications that the 2-stage process has a greater stability where large fluctuations (in concentration and com- pounds) in the waste water composition [4] are concerned. A very wide variety of organic compounds can be converted in the acidification reactor, even under severe stress conditions, into a small number of lower fatty acids (acetic acid, propionic acid, butyric acid). This means that despite large variations in the waste water composition the methane reactor is only exposed to invariably the same three fatty acids. Based on these considerations Gist-brocades has performed 1 and 2-stage anaerobic fluidized bed experiments on lab- (25 1) and pilotscale (3 600 1). The general results with 1 and 2-stage processes are presented in Table 3 (see also [l], [5-71). From Table 3 it is obvious that the 2-stage process offers many advantages like - higher reactor purification capacity due to higher sludge

- simpler process control due to less pH controllproblems and

- no problems with biomass stability during reactor stops, - much better process stability with highly fluctuating waste

activity,

due to constant biofilm thickness,

water.

Table 3. Comparison of 1- and 2-Stage Anaerobic Fluidized Bed Systems.

1-Stage 2-Stage

COD + CH4 COD + Fatty acids + CH4

- sludge activity 0.8 g/g day

- sludge activity 1" stage 0.8 g COD/g day 2" stage 2.0 g COD/g day

- biolayer thickness variable - biolayer thickness constant - pH-control difficult - pH-control absent or easy - C&-sludge unstable at no - CH4-sludge stable at no feeding

- high process stability feeding

acidification T = 1.5 h methanation r = 1.5 h C-load 24 kg C/mVdav C-conversion 17 kg Clm) day

3 = anaerobic purified waste water

1 = waste water 2 = acidified waste water

n

1

2

2500 -

3

0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324 - + h

Figure 3. anaerobic fluidized bed system.

Purification of a high variable waste water in the 2-stage

maximal biodegradability of about 70%. The effluent of the second stage contains less than 100 ppm fatty acids carbon (at an influent concentration of about 2 500 m@ Total Organic Carbon). Figure 3 shows that despite very high fluctuations in reactor load 16-32 kg C/m3/day or about 40-80 kg COD/m3/day) and despite the short hydraulic residence time the effluent quality does not deteriorate. Therefore it can be concluded that the 2- stage anaerobic fluidized bed system enables a compact and highly reliable purification of "tough" waste waters.

3 Acidification of Waste Water in an Anaerobic Fluidized Bed Reactor (Stage 1) In a pilot fluidized bed reactor (volume 3.6 m3, height 18 m, diameter 0.5 m) sand (0.1-0.3 mm) was used as carrier. The fluidization liquid velocity in the reactor was maintained at about 18 m/h [5]. Waste water was pumped directly from a yeast factory. The composition of the waste water was COD = 4500 m@, SO,'- = 800 m@, Kj-N = 250 mg Nfl, sus- pended solids were about 500 m@ and the pH = 6. The waste water was fed into the reactor to obtain a liquid residence time of 1.8 h. The reactor temperature was 37°C and no inoculation was used.

Table 4. Microbiological Development of an Acidification Fluidized Bed Re- actor.

Conditions Waste WaterlReactor

SO$-= 800mgA pH-6 COD= 4 500 mg/l

Kj-N = 250 mgA z = 1.8 h, 37"C, V = 3600 1 sand 0.1-0.3 mm carrier, superficial. vel. 18 mh

1 Microbial Development day 0-3 full acidification pH = 5.7 day 3-25 full SOi--reduction pH = 6.2 day 25-390 partly CH4-production pH = 6.8

CH4-Activity Sludge (on Acetic Acid) day 42 0.3 g CODlg DM day day 215 0.8 g CODlg DM day

Figure 3 illustrates the high stability of the 2-stage anaerobic fluidized bed system. During this experiment waste water was taken continuously from the main sewer at the production facility of Gist-brocades, Delft. This water was fed, without hydraulic buffering, into a lab scale ( 2 x 25 1) 2-stage anaerobic fluidized bed system with 1.5 h residence time in each stage. The waste water has a

It appeared (Table 4) that microbial acidification was com- pleted after only several days. The pH in the reactor dropped to 5.7. The subsequent microbial sulfate reduction was complete after 2-3 weeks (Fig. 4). Due to the SO,'--reduction to sulfide, which produces alkalin- ity, the pH increased to 6.2. Completion of the SO,'--reduction

starch/stiirke 38 (1986) Nr. 12, S. 419-428 421

Table 5. Steady State Performance of an Acidification Fluidized Bed Reactor.

1 4 0 0 -

~ 1 2 0 0 - m E - 1 0 0 0 -

- . c 0

m +

L 8 0 0 -

SO:- r e d u c t i o n

. ~ n f l u e n t w a s t e w a t e r

a c i d i f i e d w a s t e w a t e r

0 4 8 12 1 6 2 0 2 4 2 8 3 2

T i m e ( d a y s )

Figure 4. SO$--reduction in the acidification fluidized bed reactor.

was, unexpectedly, followed by CH4-production (Fig. 5). Before gas production had been virtually absent. From Figure 5 it appears that biogas production increased rapidly until day 65 and after day 150. The intervening will be

15 10 15 13 15

1 8 2 4 1 8 2 4 1 8 1 4

V s u p I m l h t

c T (hl

l C O O = - I C O D ; I C O D - 4 - 5 011 9 g / l 4 - 5 Q f l

t 4 o

Biomass concentration 25 kg VSS/m3 Liquid residence time 1.4 h COD-load 80 kg/m3 day CH4-productivity 7 Nm3/m3 day Biolayer thickness 70 pm Liquid superficial velocity 18 r d h

Organic COD +Fatty acids 40% CH4 25% S2--COD 10% Non-biodegr. 25%

Fatty acids acetic acid 70% Propionic acid 20% Butyric acid 10%

The biomass concentration in the fluidized bed was 25 kg VS/ m3. This value was constant over the reactor height and did not change significantly during the 390 day period. The biolayer thickness on the sand carrier was rather uniform at about 70 pm. The surplus sludge production was very low, 0.02 g/g COD, and was present as suspended volatile material in the reactor effluent. Apparently there was a steady state between biolayer growth and biolayer loss due to shearing because the height of the fluidized bed in the reactor remained constant. A separate control of biofilm thickness was therefore not necessary. In the Pictures 1, 2 and 3 the carrier particles

I I I ' I I I 1 I I I I I I I I 1 0 4 0 9 0 1 4 0 190 2 4 0 290 3 4 0 390

- T i m e ( d a y s )

Figure 5. experiment.

Biogas production during the fluidized bed acidification

Picture 1. Light microscope photograph (particle J 0.4 mm).

discussed below. This CH4-formation occurred under severe stress conditions for methane bacteria (pH = 6.2, sulfide con- centration about 150 mgA), this illustrating the highly effective biomass retention in this system. At the end of the experimental period a biogas production of 12 Nm3/m3 reactor day (60% CH4) was attained, which is equivalent to a COD-purification capacity of 20 kg/m3 day (Table 5). Due to the increased purification the pH in this acidification reactor rose from 6.2 to 6.8 (day 380). It might be argued that the C& gas production originated from H2 produced by acidification reactions. However, from batch experiments it appeared that the sludge CH4-activity with acetic acid as substrate increased from 0.3 g COD/g VS/day at day 30 to 0.8 g COD/g VS/day at day 215. It must, therefore be concluded that mainly acetic acid served as a methanogenic substrate in the acidification reactor. H2 was probably used for SO;--reduction [101. Picture 2. SEM picture.

422 starch/stlrke 38 (1986) Nr. 12, S. 419-428

production (and COD-purification) is possible despite the low liquid residence time of 1.4 h.

Picture 3. SEM picture of acidification biolayer.

covered with acidifying biolayers are shown. Especially Picture 3 clearly shows that the biolayer contains a multitude of different kinds of microbes needed to acidify the numerous organic compounds present in the wastewater. At the maximum applied COD load of 80 kg COD/m3 day the conversion was as follows: - Production of fatty acids 40% - CH4 production 25%

- Non-biodegradable 25% The produced fatty acids were acetic acid, propionic acid, butyric acid with a relative COD value of 70%/20%/10%. During the experiment the COD/Kj-N/SOt- concentrations of the influent waste water were doubled over a period of 85 days (d 65-150, Fig. 5) , and the liquid residence time was increased to 2.4 h. It appeared that CH4-production ceased (Fig. 5) and that acidification remained intact. The termination of the CH4- production was probably caused by H2S inhibition (about 270 mg H2S/l at pH = 5.7). Accordingly, the biogas contained about 90% COz and 10% H2S. From this experiment it can be concluded that microbial acidification in a fluidized bed reactor is easily achieved with very low sludge production and that also a significant CH4

- S2-production 10%

T - 2 4

0 .- n

4 Methane Production on Pre-acidified Waste Water in a Fluidized Bed System (Stage 2) Part of the acidified waste water from the acidification fluidized bed referred to above was fed into a second fluidized bed reactor (volume 0.3 m3, height 6 m, diameter 0.25 m, sand as carrier 0.1-0.3 mm) at liquid residence times of 1-3 h [6, 71. The results after 4 months operation are shown in Table 6.

Table 6. Anaerobic Purification in an Anaerobic Fluidized Bed Reactor of Pre- acidified Yeast Waste Water (Stage 2).

Biomass concentration Liquid residence time Liquid superficial velocity COD-load fatty acids COD conversion Gasproduction Sludge activity Biolayer thickness

40 kg VSS/m3 l h 10 mlh 60 ks/m3 day 55 kg/m3 day 30 m3/m3 day

50 pm 2 g/g day

Because of the steady growth of methanogenic bacteria on the fluidized camer after 4 months a COD-purification capacity of 55 kgCOD/m3/day was achieved at a liquid residence time of 1 h. The biomass concentration in the reactor was 40 kg VS/m3. The development of the biogas production is shown in Figure 6. As can be seen, the biogas production increased rapidly (doubl- ing time about 9 d) reaching values of 32 m3 biogas/m3 reactor/ day (65-70% CH4). A reactor stop of 3 weeks presented no problems (day 116-day 137, Fig. 6). Unfavourable waste water compositions (e. g. pH = 9.5 at day 35, 55 in Fig. 7), only led to transient decreases in the biogas production, and a rapid return of the original gasproduction rate was observed. No losses of biomass were even observed during the experiment shown in Figure 6, which was continued

1 6

1 2

6

r I I I 1 1 1 I 1 " 1 1 ' " " ' I

10 20 30 40 50 60 70 80 90 100 110120 130140150 160170180190?00

-Time (days)

PH=9.5

T=2 5 C

PHr9.5

Figure 6. Biogas production in an an- aerobic fluidized bed reactor with preacid- ified yeast waste water.

starchhtarke 38 (1986) Nr. 12, S. 419-428 423

10 20 30 40 50 60 70 80 90 100 110120 130140 150 160170180 190200

for about 1% years. This points to high process reliability. The purification efficiency for fatty acid removal was very high after a start-up period of about 2-3 months, as can be seen from Figure 7, which shows the acetic acid concentration in the effluent of the anerobic fluidized bed reactor. In the first 2-3 months the acid concentration was relatively high due to insufficient biomass. After 3 months a residual value of 20 mg/l was obtained, indicating an acid removal efficiency of nearly 99% (see also Table 6). The short increases in acid concentration (day 110, day 160, Fig. 7) were due to decreased liquid residence times and hence higher reactor loadings. After a short period the higher loading was found to be purified, probably due to increased biomass growth. During this experiment butyric acid became comletely eliminated (see Fig. 8). Contrary to this, propionic acid conversion only started when the acetic acid concentration became lower than about 200 ppm (Fig. 9). This phenomenon is probably due to the unfavourable

-Time (days) fed with pre-acidified waste water.

thermodynamics of the propionic acid conversion into acetic acid at higher acetic acid concentrations. From microscopic observations it appeared that the methanogenic biomass was firmly attached to the sand carrier. Pictures 4 and 5 show some SEM photographs. Picture 6 shows a light microscope photograph of a carrier covered with methanogenic sludge. From these pictures it can be seen that the biolayer mainly contains a micro-organism that much resembles Methanobac- terium soehngenii [9], which converts acetic acid to CH4/C02. The biolayer thickness on the sand grain was relatively constant during the experiment at 50 p. The activity of the biomass was very high, about 2 g COD/g VS/day and finally a biomass concentration of nearly 40 g VSn was obtained. From these results (see [6], [ll] for more details) it can be concluded that a very high purification capacity (> 50 kg COD/m3/day) can be obtained in an anaerobic fluidized bed reactor after a relatively short start-up period.

I I I I I I I 1 I I 20 40 60 80 100 120 1.40 160 180 200 - Tirne(days) n

Figure 7. Acetic acid concentration in the effluent of an anaerobic fluidized bed reactor

20 40 60 80 100 120 110 160 180 200 Figure 8. Purification of butyric acid in a - Time (days) methanogenic fluidized bed.

424 ~~~~~~~~~

starchhtlrke 38 (1986) Nr. 12, S . 419-428

20 40 GO 80 100 120 140 160 180 200

4

Picture 4. Ch-bacteria in biolayer on sand grain (bar is 1 pm).

Picture 5. Ch-bacteria in biolayer on sand grain (bar is 1 pm)

After the succesful completion of these pilot experiments on performance (process capacity, reliability and ease of start-up) of the 2-stage anaerobic fluidized bed process, Gist-brocades decided to design and build a full scale unit for anaerobic treatment of waste water from the Delft production facility. The results and performance of this unit will be presented in the next Section (see also [8]).

Picture 6 . Light microscope photograph of Ch-bacteria on carrier particle = 0.4 mm.

5 Full Scale Anaerobic Waste Water Purification in A 2-Stage Anaerobic Fluidized Bed Reactor Based on the results of anaerobic waste water purification in a 2-stage fluidized bed process, as mentioned above, a full scale unit was designed and built in Delft (Fig. lo), the Netherlands. The unit is made up by 2 identical reactors, the acidification reactor (R1) and the methanogenic reactor (R2) (see Fig. 11 for the flow sheet). Each reactor has a total volume of 390 m3 and is 21 meters high. The waste water, mainly from a bakers yeast production facility, is fed directly from the sewer into Rl, without hydraulic buffering. The fluidized bed volume in each reactor is 215 m3, where each reactor has a cross sectional area of 17 m2. Other important parts of the reactor are: -The three-phase separator B, where gas and liquid are

separated from the entrained particles, - the liquid pumping chamber C , from which the recycle pumps

(2, 3) are fed and from which treated waste water leaves the reactor,

- the gas buffer chamber D, which is maintained at a pressure of 0.35 Bar, enabling the transport of biogas without a gas buffer or gas compressor to the boiler house over a 1 km distance.

starch/st&ke 38 (1986) Nr. 12, S. 419-428 425

Figure 10. 2-stage anaerobic fluidized bed process for treatment of Gist-brocades waste water in Delft (the Netherlands).

6000- s 0)

- 5000 -

b 2 4 0 0 0 - E g3000- 0 a - g 2 0 0 0 - . E -

1000- -

Fluidized I bed I

' kg CHL-C0D1rn3 day laverage over volume 4 of bath reactors)

- - 25OC

- 2 0 0 spill of nitric acid @ COD in influent is law

-16 - -

- 1 2

- 8

-start start R1 R2 less SO:-

- 4 4 4 + , I I I I , , , , , , , I I , , , , , , ,

Fluidized

.II Methanation R2

~..

I Purified 4 wastewater &

Figure 11. Flow sheet of the 2-stage fluidized bed anaerobic treat- ment process.

The main reason for this highly integrated design was to ensure safety. The biogas of this unit is highly corrosive (it contains 1-2% H2S) and is also highly toxic, thus forming a potential hazard for the health of those who live within 100 m of the unit. The reactors are made of glass fiber-reinforced polyester with PVC lining, and without thermal insulation (not needed due to short liquid residence time). The following conditions were applied at start-up: The liquid superficial velocity was 8-20 m/h, the liquid resi-

dence time in the fluidized bed was 1.8-1.2 h. The applied waste water flow was 180 m3/h at 5 = 1.2 h and under these conditions a low recirculation flow of 50 m3/h was needed. Due to the relatively low recirculation the energy consumption of the recycle pumps (2, 3, Fig. 11) was only about 20 kW. Each reactor received 140000 kg of sand (0.1-0.3 mm). Full scale fluidization experiments (using the naked sand) showed the expansion curves on lab scale (1 1) and full scale to be identical (see Fig. 12).

h hetght f lu id ized bed

T e m p 18OC ,i f u l l s c a l e . 1 1 0 t

1 l . 1 .o

ful l s c a l e , 8 0 t I

l a b s c a l e , 1 k g

c I I I I I I I I I 1 I -

10 20 V s u p ( m t h )

Figure 12. scale.

Fluidization experiments with bare sand on lab- and full-

The design of the liquid distributor proved therefore adequate to ensure a homogeneous fluidization. The start-up of the unit took place in February 1984 (Fig. 13). First R1 (day 33, 1984) was started up, without inoculation. After about 1 week acidification was complete due to the development of fast growing acidification biolayers [5 ] . Two weeks after the start of R1 (day 48, 1984) feeding of completely acidified waste water was begun in R2. R2 was inoculated with only 1 m3 of sand which contained methanogenic biolayers. The methane reactor R2 did not operate in a satisfactory manner during the first 60 days (day 33-93,1984, Fig. 13) of the start-up period. The reason for this malfunctioning was too low a waste water temperature (20-30°C) and a far too high SO:- content (about 1400 mgA) of the waste water, which both hamper methanogenesis. From day 93 (Fig. 13) this was corrected and from that moment on the waste water composition was COD = 3150 mg/l, SO:- = 275 mgA, pH = 6.2-6.4, T = 37"C,

starchktarke 38 (1986) Nr. 12, S. 419-428

suspended solids = 500 mg/l. From Figure 13 it can be seen that after day 93, within 4 months, the gas production increased from 400 m3/day to about 4500 m3/day (about 67% C Q ) . Figure 14 shows the COD conversion capacity which reached a daily value of 8500 kg. Most of the COD-conversion was achieved in R2 and from Figure 14 a daily COD conversion capacity in this reactor (Rz) was calculated at 28 kg COD/m3 day (day 220,1984). From figure 14 it is also obvious that about 20-30% of the COD-conversion occurred already in R1 due to methanogenesis in this acidification reactor (see also Section 3). The COD purification in the period considered was about 60-70%, which is about the maximum value for anaerobic purification of this waste water. The purified waste water only contained minor amounts of fatty acids (< 100 mg/l fatty acid COD at an influent fatty acid content of about 2000 mg/l). The biomass was attached firmly to the sand, attaining a value of about 20 g VSA in R1 and Rz. The methanogenic activity for acetic acid conversion was very high. Biomass from RI contai- ned an activity of 0.5 g CODlg VSlday and in R2 the activity was 2-3 g COD/g VS/day. SO:--reduction was entirely effected in R1.

acidif icat ion

. . . . . . . . . . . . . . . . . . . . . 0 50 100 150 200

day number 1986

Figure 14. system, Gist-brocades, Delft.

COD-conversion in the two-stage anaerobic fluidized bed

Some observations during the start-up period of the fluidized bed process pointed to the extremely high process stability. Figure 13 indicates that during some days there were peaks of high NOT-concentrations in the waste water (marked by 1). During these peaks, NOT-concentrations (NO, was used for cleaning in the production facility) of up to 1200 mg/l were measured. Close inspection of the gas production rate (Fig. 15) showed that in the presence of NO; the gas production ceased (day 214-215). However, after passage of the NO; peak the gas production recovered within an hour. Another interesting aspect of Figure 15 is the highly variable gas production. At a daily average of 170 m3/h, peak gas produc- tions of 360 m3/h were recorded. This is due to the fact that waste water was fed directly from the sewer into the treatment system without hydraulic buffering. This means that hourly variations in COD concentrations (see also Fig. 3 for an analoguous laboratory experiment) resulted in high variations of gas production due to the short liquid residence time in the 2- stage system. These peak gas productions provide a measure of the potential available purification capacity in the system. The gas production of 360m3/h (of which about 260m3/h originated in Rz) is equivalent to a COD-conversion capacity of 34 kg COD/m3/day (calculated with reference to Rl + Rz) and 52 kg COD/m3/day (calculated with reference to Rz). Such capacities are in accordance with the pilot experiments referred to above and with the values calculated from biomass activity and biomass concentration. Therefore it can be conclu- ded that the fluidized bed system is highly stable with respect to severe variations in reactor load. Finally Figure 16 shows the stability of the fluidized bed system where pH-shocks (pH < 3 and > 10 in the waste water) are concerned. It appears that such peaks are already smoothed very effectively in Rl. In summary the first full scale anaerobic fluidized bed system in Europe combines an easy start-up with a high purification capacity and an excellent stability, as appears from the perfor- mance and start-up. In addition it has been shown that the full scale unit attains nearly the pilot results (on hourly basis). The design load of the full scale unit (12-15 t COD/day removal) is expected to be achieved in the near future.

n

a I m I 1 1 1 1 I 1 I

207 208 209 210 211 212 213 214 216 210 717 day number l a 8 4

Figure 15. Biogas production in the stage anaerobic fluidized bed system, brocades, Delft (hourly values).

two- Gist-

starchhtarke 38 (1986) Nr. 12, S . 419-428 427

Bibliography

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in f luent 1 a c i d i f i c a t i o n

12 14 16 18 20 h

PH (bf +

7-1

d a y 209

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15 17 19 2 1 $3

Figure 16. High pH peak (alkaline) in wa- ste water feed to R1 (a); low pH peak (acid) in waste water feed to R1 (b).

6 Conclusion It has been shown that the two stage anaerobic fluidized process, as developed by Gist-brocades, enables a fast and reliable anaerobic purification of a highly variable waste water. The first full scale unit has been successfully started up in Delft. A second full scale unit is being started up in Prouvy (France) and a third unit is under construction in Delft.

[ l ] Heijnen, J . J.: ,,Technik der Anaeroben Abwasseneinigung“, Chemie, Ingenieur, Technik 56 (1984), 526.

[2] Henze, M . and P. Harremoes: “Anaerobic Treatment of Wastewa- ter in Fixed Film Reactors”. In IAWPRC Specialized Seminar, June 16-18, Copenhagen 1982.

[3] Schwitzenbaum, M . S.: Enzyme Microbiol. Technol. 5 (1983), 242 [4] Cuhen, A , : Ph. D. Thesis, University of Amsterdam 1982. [5] Heijnen, J . J . : “Acidification of Wastewater in an Anaerobic

Biological Fluidized Bed”. Proceedings of the Eur. Symp. Novem- ber 23-25 1983, Noordwijkerhout (Netherlands), p. 176.

[6] Heijnen, J . J . : “Development of a High-rate Fluidized Bed Biogas- reactor. Anaerobic Waste Water Treatment”. Proceedings of the Eur. Symp. November 23-25 1983, Noordwijkerhout (Nether- lands), p. 283.

[7] Heijnen, J. J . : “Anaerobic Waste Water Treatment”. Proceedings of the Eur. Symp. November 23-25 1983, Noordwijkerhout (Netherlands), p. 259.

[8] Enger, W. A. , and J . J . Heijnen: ,,Start-up of a Full Scale Anaerobic Fluidized Bed Treatment of Yeast Waste Water”. 12th IAWPRC Biennial International Conference, Amsterdam 1984.

[9] Huser, B., K . Wuhrmann, and A. J . B. Zehnder: Arch. Microbiol. 132 (1982), 1.

[lo] Mulder, A . : “Anaerobic Purification of S04-containing Wastewa- ter (in Dutch)” Report of Researchproject Gist-brocades, Agricul- tural University of Wageningen 1978-1980, published 1983.

Address of authors: J. J . Heijnen, W . A. Enger, A . Mulder, P . A . Lourens, A . A . Keijzers and F. W. J . M. M . Hueks, c/o Gist-brocades, Industrial Enzymes Division, Wateringseweg 1, P. 0. Box 1,2600 MA Delft (Holland).

(Received: July 26, 1986)

Saccharification of Tapioca Starch Residue with a Multienzyme Preparation of Aspergillus ustus

By T. R. Shamala and K. R. Sreekantiah, Mysore (India)

Enzyme preparation obtained by cultivating Aspergillus ustus on rice straw-wheat bran mixture (7 : 3) possessed cellulase, D-XylanaSe, p-D- glucosidase, a-amylase, amyloglucosidase and pectinase activities. Used at 2% level with tapioca starch residue (TSR) slurry gelatinized at 80°C or pressure cooked, it yielded 45-60% reducing sugar and degraded 52-65% of the fiber material. Enhanced saccharification (72%), fiber degradation (75%) could be achieved by pretreating the substrate with mineral acid. Fermentation of the hydrolysates with Saccharomyces cerevisiae produced 29-36 ml alcohol per 100 g of sun dried TSR. Data on TSR hydrolysis by a-amylase and amylo- glucosidase, A. ustus enzyme preparation individually and in combi- nation with amyloglucosidase, in acid’ pretreated or untreated TSR are presented.

Verzuckerung von Tapioka-ReststLirke rnittels eines Multi- enzyrn-Prgparates von Aspetgillus ustus. Ein durch Ziichtung von Aspergillus U S ~ U S auf einer Mischung von Reisstroh und Wei- zenkleie (7 : 3) erhaltenes Enzympraparat besaS Cellulase-, D-Xyla- nase-, p-D-Glucosidase-, a-Amylase-, Amyloglucosidase- und Pekti- nase-Aktivitaten. Die Anwendung von 2% auf eine bei 80°C verklei- sterte oder druckgekochte Suspension von Tapiokastarke-Restmate- rial (TSR) ergab 45-60% reduzierende Zucker und baute 52-65% des Fasermaterials ab. Durch Vorbehandlung des Substrates mit Mineralsaure konnten erhohte Verzuckerung (72%) und verstarkter Faserabbau (75%) erzielt werden. Die V e r g h n g des Hydrolysates mit Saccharumyces cereuisiae ergab 29-36 ml Alkohol je 100 g des sonnengetrockneten TSR. Daten iiber die TSR-Hydrolyse durch a-Amylase und Amyloglucosidase, A. ustus-Enzympraparat allein und in Kombination mit Amyloglucosidase bei saurebehandeltem oder unbehandeltem TSR werden mitgeteilt.

starcMstarke 38 (1986) Nr. 12, S. 428-432 8 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986 0038-9056/86/1212-0428$02.50/0