- RBC TREATMENT OF SIMULATED POTATO PROCESSING WASTES

M. W . Cochrane and K. A . Dostal*

INTRODUCTION

This paper summarizes t h e obse rva t ions made dur ing t h e o p e r a t i o n of a p i l o t p l a n t RBC** (Rota t ing B i o l o g i c a l Contac tor ) f o r t h e t r ea tmen t of s imula ted p o t a t o p rocess ing wastes.

The RBC has n o t been used i n t h e United States f o r t r ea tmen t of p o t a t o p rocess ing wastes, and t h i s p r o j e c t w a s designed t o e s t a b l i s h a t least t h e f e a s i b i l i t y of t h i s t ype of t r ea tmen t .

The o b j e c t i v e of t h i s r e p o r t w a s t o c h a r a c t e r i z e t h e removal e f f i c i e n c y of t h e RBC under v a r i o u s o r g a n i c and h y d r a u l i c loadings and o t h e r v a r i a b l e parameters independent ly , which d i c t a t e d a s imula ted wastewater b e used t h a t w a s r e p r e s e n t a t i v e of t h e l a r g e v a r i e t y of p o t a t o process ing p l a n t s .

The .study w a s conducted a t t h e Environmental P r o t e c t i o n Agency's, Nat iona l Environmental Research Center (NERC) , C o r v a l l i s , Oregon , by members of t h e Na t iona l Waste Treatment Research Program.

TREATMENT PLANT DESCRIPTION & OPERATION

The RBC c o n s i s t e d of c i r c u l a r d i s c s mounted on a r o t a t i n g s h a f t . As t h e s h a f t r o t a t e d , t h e d i s c s r o t a t e d , which caused t h e b i o l o g i c a l s l i m e on t h e d i s c s t o become submerged a l t e r n a t e l y i n t h e wastewater and then exposed t o t h e a i r . n u t r i e n t s , and oxygen which were necessary f o r a e r o b i c t r ea tmen t .

I n t h i s way, t h e s l i m e organisms ob ta ined s u b s t r a t e ,

Continuous growth of new s l i m e organisms and s loughing o f f of o l d e r organisms caused a dynamic ba lance t o be reached between o r g a n i c removal and s ludge product ion . The s ludge produced i n t h e RBC must then b e sepa ra t ed from t h e l i q u i d and b e given f u r t h e r t r ea tmen t .

The RBC used i n this s tudy had the fo l lowing dimensions and o p e r a t i n g da ta :

Disc diameter Disc th i ckness D i s c spac ing

I 2 f t 318 inch 1-112 inch c e n t e r t o c e n t e r

"Respect ively, S a n i t a r y Engineer and Ch ie f , Food Waste Research Sec t ion , Nat iona l Waste Treatment Research Program, Nat iona l Environmental Research Center , C o r v a l l i s , Environmental P r o t e c t i o n Agency, 200 S.W. 35th S t . , C o r v a l l i s , OR 97330

**Autotrol Corp., Milwaukee, Wisconsin.

99

Disc mater ia l expanded polystyrene

No. of s t ages 6 Spec i f i c su r face a r e a of d i sc s Disc r o t a t i o n speed Drive motor (chain dr ive) 1/10 hp Run No. 1 and 2 - 118 hp Run No. 3 Overal l dimensions

No. of d i sc s per s t age 5

15 f t 2 / f t 3 10 rpm Run No. 1 and 2 and 20 rpm Run No. 3

6 3" (L) x2 5"(W) x28" (H)

Spec i f i c surface a rea was t h e t o t a l su r f ace area of t h e d i s c s divided by t h e "shaft-length volume" occupied by the d i sc s . The s h a f t length w a s approximately 4 f e e t .

A photo of t h e RBC is shown i n Figure 1.

Nutrient addi t ion was considered necessary s i n c e analyses of i n f l u e n t samples a t t h e start of t he p ro jec t showed a t t i m e s t he re was less ni t rogen and phosphorus than required t o m e e t t h e general ly accepted 100:5:1 (B0D:N:P) r a t i o s .

Figure 2 is a flow diagram of t h e treatment p l a n t . Concentrated potato feed was pumped from cold s torage (4OC) and joined with a d i l u t i o n stream of tap water before en ter ing a primary c l a r i f i e r where t h e sur face s e t t l i n g r a t e was always less than 300 gpd/f t2 . S e t t l e d e f f l u e n t from t h e primary c l a r i f i e r flowed by gravi ty t o s t a g e one of t h e RBC. nit rogen and phosphorus n u t r i e n t s w a s a l s o pumped t o t h e i n f l u e n t l i n e .

A s o l u t i o n of

In f luen t t o t h e RBC i n s t a g e one took place a t t h e water sur face level while flow between s t ages 1 and 2 , 2 and 3, 4 and 5, and 5 and 6 occurred 3 / 4 inch. above t h e bottom of the b a f f l e s through a 1-112 inch diameter hole. Flow from s t a g e 3 t o 4 took p lace through a 1 inch diameter hose Qn t h e s i d e of the u n i t 4-1/2 inches from t h e bottom. Eff luent flow occurred a t 3 inches above t h e bottom through a 1 inch diameter opening.

Disc r o t a t i o n w a s counterclockwise when looking from i n f l u e n t t o e f f l u e n t end. speed gear box, and chain dr ive.

Power f o r r o t a t i o n w a s provided by an e l e c t r i c motor, v a r i a b l e

Liquid level i n t h e RBC w a s cont ro l led a t about 8 inches depth by the l i q u i d level con t ro l box which a l s o provided a s l i g h t f lush ing a c t i o n which prevented clogging of t h e RBC e f f l u e n t l i n e and subsequent increase i n b i o l o g i c a l s o l i d s concentrat ion i n the RBC mixed l i quor .

Hydraulic detent ion t i m e s t u d i e s were conducted using sodium chlor ide as a t r a c e r and an e l e c t r i c a l conductivity meter. Two runs were made under s teady s ta te conditions. r a t e , and the second was at 0.25 gpd / f t2 . clean RBC, i .e . , no b i o l o g i c a l growth o r wastewater w a s on t h e d i s c s o r i n t h e mixed l i quor .

The f i r s t run w a s a t 0.61 gpd / f t2 hydraul ic Both runs were made using a

100

I Tap Water

4

Discharge Primary

z Clarifier

Nutrient El Somp/e

Feed Cold Storage

Conc. Feed Pump

Baffle a t Bot

.Sol id

with I g 0 Opening tom (Typical 1

Baffle

Con t ro I s

Sample

Cold

Storage

Liquid Level Con tro I

Box

DISCHARGE TO DRAIN

FIGURE 2. TREATMENT PLANT FLOW D JAG RAM

102

Microb io log ica l examinations of t h e d i s c s l i m e and mixed l i q u o r were kep t g e n e r a l i n n a t u r e . Dai ly n o t e s were made of s l i m e morphology. Microscopic s l i d e s were examined p e r i o d i c a l l y f o r r e l a t i v e q u a n t i t i e s of broad groups of microorganisms in t h e mixed l i q u o r and d i s c s l i m e . Photos were taken of t h e RBC and microscopic s l i d e s a t v a r i o u s t i m e s t o r eco rd g e n e r a l changes i n r e l a t i o n t o load ing rates.

I n f l u e n t and e f f l u e n t samples were t aken as e i t h e r grab o r composite w i t h t h e composite samples c o l l e c t e d e i t h e r a u t o m a t i c a l l y by g r a v i t y sampler o r on a p e r i o d i c b a s i s by hand ove r 18 t o 24 hours .

Samples of i n f l u e n t u s u a l l y w e r e t aken every day, Monday through F r i d a y , and e f f l u e n t samples were c o l l e c t e d on Tuesday, Wednesday, and F r iday .

E f f l u e n t samples were taken from t h e s i x t h s t a g e mixed l i q u o r . t h e samples were p laced i n graduated c y l i n d e r s and allowed t o se t t le f o r 3 hours . hours of s e t t l i n g . Sludge w a s c o l l e c t e d only a f t e r 3 hours s e t t l i n g .

Then,

Superna tan t samples were c o l l e c t e d a f t e r 1 hour and 3

Table 1 lists t h e ana lyses performed.

Table 1. I n f l u e n t and E f f l u e n t Analyses

I n f l u e n t

PH T-Alk COD COD(S) BOD BOD(S) TOC SOC ss vss TKN NH3-N Total-P

Ef f l u e n t E f f l u e n t (1 h r s e t t l i n g ) ( 3 h r s e t t l i n g )

COD

ss

PH T-Alk COD COD(S) BOD BOD(S) TOC s oc ss vs s TKN NH 3-N To ta l -P

(S) = soluble ( f i l t r a t e from 0.45 p membrane f i l t e r )

Mixed l i q u o r samples from the t h i r d s t a g e were s e t t l e d i n a graduated c y l i n d e r , and t h e s u p e r n a t a n t a f t e r 3 hours s e t t l i n g was ana lyzed f o r t u r b i d i t y . s t a g e mixed l i q u o r s .

S e t t l e a b i l i t y tests were run on bo th t h i r d and s i x t h

10 3

Dissolved oxygen w a s measured i n t h e f i r s t and s i x t h s t a g e mixed l i q u o r s wi th a YSI probe. Temperature w a s measured i n t h e primary c l a r i f i e r , mixed l i q u o r , and ambient a i r . R e l a t i v e humidity and tempera ture of t h e ambient a i r were recorded a u t o m a t i c a l l y on a continuous r e c o r d e r .

RESULTS

F igure 3 p r e s e n t s the r e s u l t s of t h e t r a c e r s tudy of h y d r a u l i c d e t e n t i o n t i m e . t i m e w i t h 1/8 inch s l i m e w a s c a l c u l a t e d t o be 1 7 . 1 and 6 . 3 hour s , r e s p e c t i v e l y . From F igure 3 t h e corresponding va lues are 13.7 and 4.5 hours . No a t t e m p t w a s made t o c o r r e c t d e t e n t i o n t i m e f o r t h e e f f e c t of b i o l o g i c a l s o l i d s i n t h e mixed l i q u o r . The d e t e n t i o n t i m e i n F igure 3 does n o t i nc lude primary o r secondary s e t t l i n g t i m e .

A t 0.25 g p d / f t 2 and 0 .61 g p d / f t 2 t h e t h e o r e t i c a l h y d r a u l i c d e t e n t i o n

The RBC w a s s t a r t e d by f i l l i n g t h e mixed l i q u o r tank wi th e f f l u e n t from a t r i c k l i n g f i l t e r a t t h e C o r v a l l i s , Oregon, munic ipa l wastewater t r ea tmen t p l a n t . i n i t i a l l y wh i l e e f f l u e n t w a s r ecyc led 100 p e r c e n t t o t h e i n f l u e n t end. When s l i m e began t o appear on t h e d i s c s , a s t e a d y f eed rate w a s e s t a b l i s h e d and r'ecycle w a s d i scon t inued .

Batch f e e d wi th d i l u t e s y n t h e t i c p o t a t o waste w a s used

Table 2 shows t h e average and range of i n f l u e n t and e f f l u e n t parameters , i n f l u e n t l o a d i n g rates, and removal e f f i c i e n c i e s .

TOC and SOC were run i n a d d i t i o n t o COD and BOD, b u t t h e r e s u l t s were i n c o n s i s t e n t f o r Runs #I and 112 due t o sample p r e s e r v a t i o n technique . The o r g a n i c carbon load ing rate (lbs/1000 f t 2 / d a y ) w a s about 40 t o 45 p e r c e n t of t h e COD load ing rate i n Run 8 3 on a t o t a l and s o l u b l e bas is.

Run #3 produced 80 t o 90 pe rcen t removal of TOC and SOC.

VSS removal p a r a l l e l e d SS w i t h 95 t o 100 p e r c e n t of t h e SS be ing v o l a t i l e i n b o t h i n f l u e n t and e f f l u e n t .

Table 2 shows va lues ob ta ined f o r 3 hour s e t t l e d samples, b u t 1 hour s e t t l e d samples produced e q u i v a l e n t d a t a f o r COD and SS removal.

Mixed l i q u o r d a t a are summarized i n Table 3 . d a t a r e f e r t o 3 hour s e t t l e d samples. produced about 20 t o 50 p e r c e n t g r e a t e r volumes of w e t s o l i d s dur ing Runs $1 and 8 2 , b u t du r ing Run 83, one hour and t h r e e hour samples y i e l d e d about t h e same volumes of s ludge . Sludge f l o t a t i o n dur ing Run $3 even caused 1 hour s l u d g e volumes t o b e less than 3 hour volumes o c c a s i o n a l l y .

The p e r c e n t s o l i d s One hour s e t t l e d samples

104

Temp. 2OoC Tracer NaCI Detention Time Through RBC only

Curve for clean disc and clean water.

I I I I I 0 0.20 0.40 0.60 0,80 1.00

HYDRAULIC RATE - GPD/ F T ~

FIGURE 3. MEAN HYDRAULIC DETENTION TIME.

105

Table 2. Influent and Effluent Data,

COO ( Total) COD Goluble) an e

I n f Range __ Eff lnf Eff

732 126 671-828 57-218 469 323-546 40-136 946-2610 58-205

1860-2510 174-412 1620 1% 1420-lMO 113-303 2337 332 1710-3100 207-519 1675 142 2193 313

BOD (Soluble) BOD (Total) 508 99 200-635 70-115 297 53 391-560 51-55

1588 161 1160-2280 125-230 958 60 658-1330 25-110 1785 198 1520-21 90 11 5-457 1370 74 1260-1480 66-82

Inf lbs BOD/lOM) ft'/day Inf l b s CoO/lwO ftz/day 1.52 1.40-1.73 1.06 0.42-1.33 4.86 2. €0-6.32 3.35 2.50-4.20

10.6 9.2 -12.3 9.0 7.48-10.8

Parameter

3 Run m. 1 Run m. 2 Run m. 3

Parameter Run No. 1 Run m. 2 Run m. 3

Parameter Run m. 1 Run No. 2 Run No. 3

Parameter Run no. 1 Run m. 2 Run m. 3

Parameter Run No. 1 Run No. 2 Run m. 3

Parameter Run No. 1 Run m. 2 Run No. 3

Parameter

Run m. 1 Run m. 2 Run m. 3

T-A1 k ss 44 46 12-82 24-65 184 70 130-290 40-100 53 74 14-129 37-103 377 95 240-500 34-180

143 40 16-407 12-80 536 124 380-680 90-160

pH+ T-KN 6.8 6.6 6.8-6.8 5.3-7.0 42.9 25.3 35.6-44.9 18.7-33.1 6.6 6.4 6.3-6.9 5.9-6.8 1W.5 58.3 90.5-107 44.4-81 .O

6.5 5.6 6.0-6.6 5.1-6.1 137 76.0 133.0-140 76.0- -- Wr-N Total -P

30.0 2.7 28.9-31 .O 1.4-5.0 45.3 36.6 44 .O-47 .O 28 .O-46.0 70.9 23.1 63.0-81 .O 5.4-48.0 103.7 99.6 91.0-116 79.8-110 77.5 41.6 73.0-82.0 --- 121.5 110.0 118-125 110- --

BOD/COD (Average) Inf COD:N (Range) Average Range

0.71 0.80 0.29-0.94 0.71-0.89 17.4:l 16:l-19.7:l 16.7: 1 -33.9:l 0.74 0.66 0 . 6 7 4 8 2 0.464.75 23.6:l 18.2:1-22.8:1 0.78 0.63 0.71-0.86 0.58-0.68 20.5:l

Nutrient addition made before Inf Sanpling Station 'Data in mg/l unless otherwise notcd. median Value

Reimvals and loadings based on 3-hour s e t t l i n g . Inf 2O0C

91 81 -95 95 93-96 91 88-94

I Raaval BOO(S) 92 91-92 96 93-99 95 95-96

X Ranoval 55 54 17-86 73 54-93 76 67-80

I Renmval T-KN 40 42 42

X Reimval Total-P 19 8

11

Inf CO0:P Range

16.1:l 16:l-17.6:l 22.9 :1 14.9:l-32: 1 23.5:l 19.4:l-27.5:l

Run No. 1 - Av. 0.25 gpd/ft' to ta l hydraulic f l a Run No. 2 - clv. 0.25 gpd/ft' total hydraulic flow Run No. 3 - Av. 0.61 gpd/ftz to ta l hydraulic flow

Table 3. Mixed Liquor Data

RUN NO. 1 Parameter

D.O. (mg/l) Temp. ("C)

PHt S s (mg/l) .So lids*

RUN NO. 2 Parameter D.O. (mg/l) Temp. ("C)

PHt s's (mg/l) Solids*

First Stane Aver age Range

4.4 -- 16.5 15.2-17.6 6.8 --

1.7 1.3-2.3 15.8 15.2-16.5

Sixth Stage Average Range

7 .O -- 14.6 13.3-15.8 -- -- 523 4 20-7 00

48 40-55

5.5 5.3-5.6 14.3 14.2-14.4

-- -- 951 380-11 60 38 7-63

RUN NO. 3 Parameter D.O. (mg/l) Temp. ("C)

PHf ss (mg/l) Solids*

2.0 1.0-2.5 16.3 15.3-17.5

4.4 2.6-5 .O 14.5 12.5-16.5 5.7 4.6-5.9 1237 360-1970 79 66-91

?Median value *3-hr settling, % volume of sludge in 1000 ml glass cylinder.

10 7

Percent s o l i d s f o r t h i r d s t a g e mixed l i q u o r averaged about t h e same ( f o r 1 hour and 3 hour samples) as t h e s i x t h s t a g e samples.

Table 4 shows s e t t l e d s ludge d a t a from 3 hour s e t t l e d samples. One hour s e t t l e d samples were n o t taken f o r s ludge a n a l y s i s o t h e r t han f o r p e r c e n t s o l i d s which i s t h e same as t h e mixed l i q u o r one hour s ludge volumes d i scussed above r e f e r r i n g t o Table 3 .

The p e r c e n t s o l i d s d a t a i n Table 4 should n o t b e used as a b s o l u t e v a l u e s f o r scale-up work. These va lues are in t ended t o show on ly re la t ive amounts of w e t s ludge t h a t would r e q u i r e pumping f o r f u r t h e r t r ea tmen t .

No a t t e m p t w a s made t o show q u a n t i t y of s ludge s y n t h e s i z e d because of t h e need f o r a much more r i g o r o u s sampling program, which w a s beyond t h e scope of t h i s s tudy .

F igu re 4 p r e s e n t s the COD removal c h a r a c t e r i s t i c s f o r t h e t h r e e runs made dur ing t h i s s tudy . hour s e t t l e d samples w i t h the r e s u l t be ing Y = 0.93~.

The d a t a shown were gene ra t ed from t h r e e

COD a p p l i e d is t o t a l i n f l u e n t COD and COD removed is t o t a l i n f l u e n t COD minus s o l u b l e e f f l u e n t COD.

The l i n e a r r e l a t i o n s h i p shown i n F igu re 4 w i l l undoubtedly d i s c o n t i n u e a t some h i g h e r l oad ing and t h e p e r c e n t removal w i l l beg in t o f a l l o f f . l o c a t i o n of t h i s b reakpo in t w a s n o t determined due t o t e rmina t ion of the p r o j e c t a f t e r t h r e e runs.

The

F igu re 5 shows t h e average e f f l u e n t c o n c e n t r a t i o n of s o l u b l e COD dur ing t h e o r g a n i c l o a d i n g rates covered i n t h e s tudy . 3 hour s e t t l e d e f f l u e n t , however, 1 hour s e t t l e d e f f l u e n t r e s u l t s were e s s e n t i a l l y t h e same.

The d a t a r e p r e s e n t s

F igu re 6 summarizes t h e suspended s o l i d s of s e t t l e d e f f l u e n t samples. The lowes t c o n c e n t r a t i o n ob ta ined was 40 mg/l which occur red dur ing t h e lowes t l oad ing rate. t h e 3 hour samples.

Data from 1 hour samples c l o s e l y p a r a l l e l e d t h o s e from

An a t t empt w a s made t o c o r r e l a t e COD removal e f f i c i e n c y and r e l a t i v e numbers of microorganisms i n the d i s c s l i m e and mixed l i q u o r , b u t t h e r e s u l t s d i d n o t appear t o b e s i g n i f i c a n t .

F igure 7 shows t h e t y p i c a l appearance of t h e s l i m e on s t a g e 3 and 4 d i s c s . The s l i m e w a s smoother and somewhat less pa tchy on s t a g e s 1 and 2 and more patchy on s t a g e s 5 and 6 . from s t a g e s 1 t o 6 .

Slime c o l o r v a r i e d from cream t o brown

108

P 0 W

Table 4. S e t t l e d Sludge Data*

Run No. 1 Parameter Average Range

1480

1220

48

168

482

1210

147

60

885-2130

6 79-1840

40-55

96-239

226-650

68 2-21 20

62-203

36-77

Run No. 2 Average Range

3340 2160-6590

2680 166 0- 555 0

38 7-63

872 810-1180

1370 124 0-1 600

2790 1060-6780

367 174-560

165 110-220

- Average Range

2890 1760-3800

2280 1260-3180

79 66-91

790 365-12 30

1310 1140-1470

2230 1050-36 60

267 240-294

162 158- 1 7 2

*3-hr s e t t l i n g i n 1,000 m l g l a s s cy l inde r t X Volume of Sludge

LL 0 0 0

\ w A I

w > 0 z w w n 0 0

n - m

n

15

IO

5

0

- Inf. Temp 2OoC Hydr. Rate 0.25-0.61 gpd/ft2 Disc Rotation 10-20 rpm /

/ 3-hr. Settled Eff.

.

@ .

/ Y=0.93X

0 5 IO 15 20 COD APPLJED-LBS/I,OOO FT*/DAY

FIGURE 4. REMOVAL CHARACTERISTICS

110

I 0 w 2 a,

0 0 u

a 5

0

Inf. Temp. 20.C Hydr. Rate 0.25 -0.61 gpd /ft2 Disc Rotation IO-20rpm 3-hr. Settled Eff. /

L 1 1 1

100 150 200 250 SOLUBLE EFFLUENT COD-MG/L

FIGURE 5. SOLUBLE EFF. COD vs APPLIED COO

111

0 C

OD

AP

PLI

ED

-LB

S/I,

OO

OFT

*/D

AY

-

-

Iv

0

UI

0

0

0

I I

I 1

When t h e s l i m e sloughed o f f t h e d i s c s , i t became p a r t of t h e mixed l i q u o r s o l i d s which had t h e appearance of b i l l owing marabou f e a t h e r s as p resen ted i n F igure $. Clumps twice t h a t s i z e were observed dur ing the s tudy .

The l a r g e s t mass shown i n t h e photo i s about 3x5 i nches .

Microscopic examination of mixed l i q u o r and d i s c s l i m e s h m e d a l l t r o p h i c l e v e l s of organisms, i nc lud ing worm and exc luding mammals. However, t h e s t r u c t u r a l components of the biomass were most ly f i lamentous b a c t e r i a and fung i .

There were no a p p r e c i a b l e odors from t h e RBC u n i t i t s e l f , b u t dur ing sucondary c l a r i f i c a t i o n q u i t e o f f e n s i v e odors were ev iden t as a r e s u l t of anae rob ic cond i t ions .

CONCLUSIONS

Within t h e range of load ings of t h e s tudy , t h e RBC proved t o be an e f f i c i e n t method of t r ea tmen t f o r s y n t h e t i c p o t a t o p rocess ing wastewater. However, e f f l u e n t COD and SS concen t r a t ions were h i g h e r than those gene ra l ly cbns idsred accep tab le f o r d i scha rge t o r e c e i v i n g waters, and a d d i t i o n a l t r ea tmen t of t h e a f f l u e n t may b e r equ i r ed .

All t h e o b j e c t i v e s of t h e p r o j e c t were n o t m e t due p r i m a r i l y t o l o g i s t i c problems. p r o j e c t , which caused s toppages i n l i n e s and b a f f l e openings and r e s u l t e d i n unsteady s ta te c o n d i t i o n s . a t load ing rates beyond those used i n t h e s tudy .

ACKNOWLEDGMENTS

The s l i m e grew " fu l l - sca l e" s i z e under a "p i lo t -p l an t " s i z e

This problem would have become overwhelming

Apprec ia t ion goes t o t h e fo l lowing f o r t h e i r p a r t i c i p a t i o n i n t h i s s tudy:

Robert J. Bum, EPA, Denver, Colorado

E. S t e w a r t Avery, EPA, P a c i f i c Northwest Water Labora tory , Corva l l i o , Oregon

Auto t ro l Corp., Milwaukee, Wisconsin

The It. T. French Co., She l l ey , Idaho

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