Process Design for Treatment of Corn Wet Milling Wastes

8/13/2019 Process Design for Treatment of Corn Wet Milling Wastes

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Corn4

>I Steeping t--d Evaporationi

S eepwater

L----Fiber V

Corn Gluten Feed>

Washingr R9bI

L---- Starch-Gluten H gh Prote inSe pa rat io n Gluten Meal >e . . I

Fresh Water

StarchDrying

Modi f i edStarch

Corn Sugarand Syrups

Figure 1. Corn Wet Milling Process

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Afte r s t eep ing , the corn i s mildly mil led , t o break open the kernel,and release the germ w i t h as l i t t l e damage as poss ib le .i s se para ted from the ot he r components of the kernelw i t h hydroclones,and then dried and p ro ce ss ed t o e x t r a c t the corn o i l .germ i s added to the animal feed.

The germ

The oi l f ree

After separat ing the germ, the remainder of the s tarchand glu teni s released from the hulls.from the hulls by co un ter cu rre nt washing and scre enin g.

are dried, and combined w i t h the concen t ra ted s teepwate r and the o i l f r eegerm from previous steps tomake corn gluten feed.

The mixture of starch and p r o t e i n t h a t were separated from the hullsare processed t h r o u g h cen t r i fuges and a ser ies of smal l d iameterhydroclones.as well as removal of solubles from the s t a r c h .

The f r ee s ta rch and g l u t e n a r e separa tedThe hulls

T h i s r e s u l t s i n separa t ion o f the s ta rch and p ro te in ,

The p r ot ei n f r a c t i o n , r e f e r re d t o a scorn glu ten , i s concentra ted,f i l t e r e d , and dr ied .p r o t e i n a d d i t i v e t o f ee ds f o r b r o i l e r s .

Fresh water i s added t o the hydroc lone s ta t ion , a t the rate of about 12 t o

. 15 ga llo ns per bushel of corn processed. A s i g n i f i c a n t port ion ofthis water consists of condensates recovered dur ' ing evaporation off in ished products .

The product i s principal ly used as a h i g h

The f in ished s tarch product , s t i l l i n slurry form, may be d r i e dd i r e c t l y as an unmodified s tarch , or t r ea te d by various chemicalst o make modified starch. art of the s tarch s t ream i s hydrolyzedw i t h a c i d , enzymes, or a combination of acid and enzymes t o producecorn syrup o r dextrose .

WASTE SOURCES

The process shown i n F i g u r e 1 i s usua l ly re fe r red t o as the wetstarch process. The only waterborne waste from the wet s ta rchprocess i s the condensate res u l t ing from the evaporation ofsteepwater. The condensate conta ins vola t i les which are formedd u r i n g the stee ping pro cess, and a re vaporizedd u r t n g evaporat ion.

The sources of o ther l i q u i d wastes vary w i t h i n the wet m i l l i n gindustry, depending on the products made and the processes used.Typica l ly, i n a d d i t i o n t o the v o l a t i l e s , the waste stream mightcontain f i l t r a t e s from the preparation of modified starches,w i t h dissolved chemicals used f o r m o d i fi c a ti o n , and Somesoluble carbohydrate formed during the process. Another sourceof waste i s t h e impurities removed d u r i n g t h e r e f i n i n g o f cornsyrups and dextrose .

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These vola t i les and carbohydrates exert an oxygen demand whendischarged t o a s t ream or t o a municipal treatment plant .has been recognized f o r many y e a rs , and vari ous tre atm en tm thods

This

have been developed by members of the wet milling industry.f4, 5 , 6)WASTE CONTROL

CPC In te rna t iona l opera tes four wet mi l l ing p lan t si n the UnitedS t a t e s .t reatment p lants .d i rect ly to waterways. As awareness of th e envi ronmental e f fe c tsof d i rec t d i scharge inc reased , i t became ev iden t tha t th i s p rac t i cecould not continue.

Two of these pay f o r trea tm ent o f t h e i r w a st es i n municipalIn the past , the other two discharged waste

A co ns ul tin g eng ine eri ng company was r et ai ne d t o make a waste su rveya t one of our p la n t s , i n order to determine the requirements tomee t ex i s t ing e ff luen t s t andards .preliminary biolo gica l treatm ent design, based on t h e i r experiencewith in du st r ia l wastes , and the re su l ts of the survey.

The consultants prepared a

CPC International management was concerned about the risk involvedi n ins ta l l ing a t r ea tment p rocess w i t h no experimental d a t a t o

I t was f e l t t h a t maximum treatment efficiencywould r e s u l t i f s p e c i f i c t re a tm e n t d a t a were o b ta in e d f o r t hewaste stream.

. uppor t the design.

The waste summary also indicated that manufacturing process improve-ments m i g h t s ig ni f ic an t ly reduce the waste load t o be t r e a t e d .Therefore, i t was decided t o s tudy the t re a ta b i l i t y of the wastestream, and a t th e same time to conduct a vigorous waste loadreduction program. The waste load re du cti on was an impo rtan tand integral part of the over-all pollution abatement program.BOD o f the waste stream was reduced t o about one-half ofi t sor ig in al value by i so la ti ng sa ni ta ry wastes and sending them tothe municipal trea tment p la nt ; by ins ta l l a t io no f new processcontrol instruments in c r i t i ca l a r eas ; by operator and supervisort ra ining regarding process 1osse s sup port ed by an ex ten si ve wastestr ea m mo nito ring system ; and by abandoningan i n t e r m i t t e n t l yoperated process w h i c h generated a s ig n i f i c an t waste load.

TREATABILITY STUDIES

I t was expected th at the carbohydrates and vo la t i l es in the wastestream would be readily biodegradable.program was lim ite d t o study o f the biological t rea tment process .The biological process ut i l izes a mixed bacter ia l cul ture inc o n t a c t w i t h the waste stream, t o conver t soluble organics to

i n so l u b le b a c te r i a l c e l l s .

Therefore, the experimental

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lVumerous variations o f the b i o lo g ic a l process have been devel oped.Our consul tant recommended that the experimental program be1 m i e d t o e v a l u a t i on of aerobic processes .

The experimental work was conducted under the guidance f i r s t o fA. W Busch ( t h e n a t R i ce U n i v e r s i t y ) , and l a t e r W B. Davis( fo r me r ly a t Texas A M U n i v e r s i t y ) .

I t was d e c id e d t o st u dy t wo v a r i a t i o n s o f t h e a e r o bi c b i o l o g i c a l

process.i s s imply a l agoon where oxygen s s u p p li e d t o t h e m ix t ur e o fwaste and cu l tu re , fo l lo we d by a qu iescen t pond where the b iomassi s a l l owed t o s e t t l e . No biomass i s r e c yc l e d t o t h e a e r a t i o ntank.company, and was de sc ri be d by Mc Into sh and McGeorge.(6) Th isp ro ce ss r e q u i re s v er y l i t t l e o p e r a t o r a t t e n t i o n , b u t has th ed i s advant age t h a t t h e r e a r e no ope ra t i ng c on t r o l s t o c om pensatef o r v a r i a t i o n s i n w aste c h a r a c t e r i s t i c s o r c o n ce n tr at io n . Al a r g e l a n d a re a i s a l s o r e q ui r ed .

One was an aerat ed lagoon and s e t t l i n g process , which

This method o f t rea tmen t has been used by one wet m i l l i n g

The o the r sys tem s tud i e d was t h e compl e te l y mix ed ac t i va t e d s l u d g eprocess.

.by a g r a v i t y c l a r i f i e r .t an k can be c o n t r o l l e d by r e c y c l i n g c l a r i f i e r u nd e rf lo w.a dv an ta ge o f t h i s m etho d o f t r e at m en t i s t h a t o p e r a t i n g c o n d i t i o n scan be c o n t r o l l e d b y a d j u s t i n g t h e biom ass r e c y c l e r a t e .

T h i s c o n s i s t s o f an a e r a t i o n t an k , u s u a l l y f o l l o w e d

TheBiom ass c o n c e n t r a t i o n i n t h e a e r a t i o n

EXPERIMENTAL RESULTS - AERATED LAGOONThe ae r a t ed l agoon proce ss was s t u d i ed o n a p i l o t p l an t s ca l e .The ae ra t i on ta nk volume was 35,000 ga l lo ns , equipped w i th a5 -hp su r f a ce ae r a to r. The s e t t l i n g pond was a bout th e same s iz e .

I t was f ou nd t h a t a s a t i s f a c t o r y e f f l u e n t c o u l d be o bt a in e d a t

r e t en t i on t imes a s low as 4 days.was o b t a i n e d i n t h e s e t t l i n g pond, a l th o u gh o c c a s i o n a l l y i n warmwea the r clumps of s l udge f l o a t e d t o t he su r f ac e .

P r o j e c t i o n s o f t h e s i z e o f t h e f u l l s c a l e t r e at m e nt p ro ce ss showedt h a t s u f f i c i e n t l a n d was n o t a v a i l a b l e a t t h e p l a n t s i t e .no l a n d was a v a i l a b l e a d j a c e n t t o t h e p l a n t s i t e , an ex p en s iv epumping and pi p i n g system woul d have been req uir ed .i t was dec ided th a t the a c t iv a t ed s ludge process would be th em o s t e c o n o m i c a l f o r t h i s l o c a t i o n .

S a t i s f a c t o r y biom ass s e p a r a t i o n

Since

As a re s u l t ,

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ToA s D i r a t o r

Solenoid Subs t ra te

Valve 1 Reservoir

t 1 7

6

Pe

1

2 L i t e rPerco la tor

L i t e r

r c o l a t

A i r Diffuse

Eff luen tStorage

x

rs

A Rotameterrimer / \

unlpI

WasteM xedLiquor

Figure 2. Schematic Drawing of LaboratoryActivated Sludge Reactor

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P

n

S

C,aL

C,

.I

S

uS

1200

1000

800

600

400

200

01 2 3 4 5

T i m e , Hours

Figure 3 . Typical Batch Test Data

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100 200 300 400 500

Residual Biodegradable COD, mg/l

Figure 4. Typical Unit Rateo f Removal Curve

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1 .o

0.8

0.6

0.4

0.2

1 2 3

l b S o l u b le CODSuppl ied/ lb MLSS/Day

F i g u r e 5. Biomass Growth Ra te

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60

40

20

0

Continuous Reactor Data

2 3

lb Soluble CODSupplie d/lb MLSS/Day

Figure 6. Oxygen Utilization

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h33

Tr e a t edP D i s s o l v e d A i r F l o t a t i o n E f f l u e n

G r a v i t y [ IC l a r i f i e r

tExcess Biomass

F i g u r e 7. Trea tmen t P l an t F low Diag ram


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The h i g h suspended s o l i d s l e v e l i n t h e t r e a t e d e f f l u e n t n o t o n l yr e s u l t s i n f a i l u r e t o meet t he suspended s o l i d s c r i t e r i a , b u t a l s ocauses a high BOD due t o th e oxygen demand o f suspended b ac te r i a .

There has been a co n t in u in g program t o de te rmine th e cause o f thed i spe r s ed g rowth. Va r i ab l e s t h a t h ave been o r a r e be ing s t u d i e di n c l u d e s t a b i l i t y o f waste l o a d and pH, e f f e c t o f F/M r a t i o , f a c t o r sa f f e c t i n g t he g rowth of p ro tozoa , wh ich hav e g en e ra l l y been l a c k i n gi n t h i s s ys te m, a nd t h e e f f e c t o f ammonia n i t r o g e n c o n c e n tr a ti o n .The r e s u l t s o f t h i s w ork w i l l be i n c l u d e d i n t he p r o j e c t r e p o r t

t h a t w i l l be prepared upon comple t ion o f the dem ons t ra t ion gra n tprogram.

SUMMARY

Dur ing many years o f deve lopment o f the corn wet m i1 i n g p ro ce ssp r od u c t l o ss e s t o l i q u i d e f f l u e n t stre am s were g r e a t l y r ed uc edb y r e cy c l i n g p roce ss wat e rs , a nd r ec o ve r i n g s o lu b l e s as a by -produc t .

A s t h e n ee d f o r a d d i t i o n a l im pro ve me nt i n e f f l u e n t q u a l i t y becameknown product 1osse s we re f u r t h e r r educed by p r oce ss m od i f i c a t i o n s .L a b o r a t o r y t r e a t a b i 1i y s tu d i e s were u se d t o de t e rmi ne t h e r e q u i r e -ments f o r t rea tmen t o f the rem ain ing was te by th e comple te ly mixeda c t i v a t ed s l udge p roce s s.l a b or a to r y a nd f u l l s c a le o p e r at io n w i t h r e sp e ct t o r a t e o f s o l u b leCOD removal , oxygen requirements , and biomass growth ra te . Phy sica lc h a r a c t e r i s i c s o f t h e b io ma ss d i f f e r e d between t h e 1 aboratory andf u l l s c a l e p ro ce ss es .t h e l a b o r a t o r y, w h i l e d i s p er s e d i n d i v i d u a l b a c t e r i a has been ac on t i nu ing p rob l em i n t he f u l l s c al e p l an t . T his has r e s u l t e d i nf a i l u r e t o meet t h e d es ig n e f f l u e n t suspended s o l i d s a nd BODc oncen t r a t i ons . A p rogram t o d e t ermi ne t h e cause o f t h i s p rob l emi s s t i l l i n p rogress .

Good agreement was o b ta in e d between

Fi lamentous growth was a major p rob lem i n

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REFERENCES

(1) J e f f r i e s F. L., Corn Grinding as I ave Seen I t . Corn ProductsCompany.

( 2 ) Mohlman, F. W. and A J. Beck, In d u s t r i a l and Eng inee r ingChemistry 1:205 (1929).

( 3 ) P u l f r e y, A L., R. W. Kerr and H. R. R e i n t j e s , I n d u s t r i a lEngi ne er ing Chemistry 32: 483-1 487 (19 40 ).

(4 ) Van Patten, E. M. and McIntosh, G. H., I n d u s t r i a l a n d E n g i n e e r i n gChemistry 4:483-487 1952) .

( 5 ) H a t f i e l d , W D., In d u s t r i a l Wastes, Chapter 6 , Corn StarchProcesses W. Rudo lfs , E d it o r ) , Rhein hold Pu bl ish in g Company,1953.

(6 ) McIntosh, G. H. and G. G. McGeorge, Food Pr oc es sin g 25 No. 1,pp 82-86, January, 1964.

( 7 ) Busch, A W. , Chemical En gi ne er in g 2, 71-76, 83-86 (1965).

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Process Design for Treatment of Corn Wet Milling Wastes

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