WASTE CONTROL I N THE PROCESSING OF SWEET POTATOES
by
N. V. Colston and C.
Smallwood, Jr.*
INTRODUCTION
I n North C a r o l i n a p l a n s are underway t o develop a v e g e t a b l e proc e s s i n g i n d u s t r y t o complement e x i s t i n g f r e s h market o u t l e t s .
North C a r o l i n a grows about one t h i r d of t h e n a t i o n ' s t o t a l sweet
p o t a t o crop and r a n k s second behind L o u i s i a n a i n p r o c e s s i n g . This
y e a r t h r e e North C a r o l i n a p l a n t s are a c t i v e l y engaged i n p r o c e s s i n g
sweet p o t a t o e s . L a s t y e a r t h e r e were four--one b e i n g f o r c e d t o
d i s c o n t i n u e canning o p e r a t i o n s because of a s s o c i a t e d water p o l l u t i o n
problems. I f t h e v e g e t a b l e p r o c e s s i n g i n d u s t r y is t o grow i n North
C a r o l i n a , o r perhaps even t o c o n t i n u e t o e x i s t , new a n d / o r improved
methods and technology f o r coping w i t h i t s l o c a l environmental impact
must b e developed.
Tabor C i t y Foods, I n c . , of Tabor C i t y , North C a r o l i n a , p r o c e s s e s
approximately 45 p e r c e n t of t h e S t a t e ' s pack. Located i n a n
economically d e p r e s s e d community o f 3,000, t h e p l a n t p r o v i d e s employment f o r a b o u t 500 people and cash-crop o u t l e t f o r a n unknown
number of farmers. The p l a n t a l s o c o n t r i b u t e s t h e m a j o r i t y o f
wastes e n t e r i n g t h e c i t y ' s o u t d a t e d sewage t r e a t m e n t f a c i l i t y . The
c i t y i s p r e s e n t l y i n t h e p r o c e s s of b u i l d i n g a new.sewage t r e a t m e n t
f a c i l i t y , which, by n e c e s s i t y , had t o b e overdesigned t o accommodate
t h e canning p l a n t waste. R e a l i z i n g t h e a s s o c i a t e d problems of sweet
p o t a t o canning, Tabor C i t y Foods sought a s s i s t a n c e from North C a r o l i n a
S t a t e U n i v e r s i t y . The i n d u s t r y and t h e U n i v e r s i t y t o g e t h e r developed,
s o u g h t , and were g r a n t e d an Environmental P r o t e c t i o n Agency Demons t r a t i o n Grant t o h e l p a l l e v i a t e waste problems, i n c r e a s e p l a n t
e f f i c i e n c y , and develop a w a s t e management technology f o r t h e sweet
potato processing industry.
The p r o j e c t ' s purpose i s t o make changes i n equipment and o p e r a t i o n s
t o demonstrate e f f e c t i v e water and wastewater management i n sweet
p o t a t o p r o c e s s i n g . The p r o j e c t encompasses waste abatement and water
u s e throughout t h e p l a n t from f r e s h w a t e r i n t a k e through p r e t r e a t m e n t .
The s p e c i f i c o b j e c t i v e s are:
*Civil Engineering Department, North C a r o l i n a S t a t e U n i v e r s i t y ,
R a l e i g h , N. C.
**This i n v e s t i g a t i o n w a s supported by funds from t h e Environmental
P r o t e c t i o n Agency 9 Off i c e of Research and Monitoring , under Grant No.
12060 FRW and Tabor C i t y Foods, Tabor C i t y , N. C .
85
1) I n s t a l l a n d / o r modify a d r y c a u s t i c p e e l i n g p r o c e s s and
demonstrate i t s e f f e c t i v e n e s s f o r water and waste
reduction.
2)
I n s t a l l and d e m o n s t r a t e wastewaters p r e t r e a t m e n t f a c i l i t i e s
f o r t h e r e d u c t i o n of w a s t e l o a d s .
3)
Determine t h e economic i m p l i c a t i o n s of t h e water and
waste management t e c h n i q u e s demonstrated.
4)
Formulate g u i d e s f o r w a t e r and wastewater management i n
sweet p o t a t o p r o c e s s i n g .
The 1 9 7 1 p r o c e s s i n g season o f September through December w a s used f o r
p r e l i m i n a r y s t u d i e s and a n a l y t i c a l e v a l u a t i o n s r e q u i r e d t o e s t a b l i s h
bench mark q u a n t i t i e s and c h a r a c t e r i s t i c s of water consumption, waste
p r o d u c t i o n , and p l a n t o p e r a t i n g procedures. T h i s w a s n e c e s s i t a t e d by
t h e l a c k of i n f o r m a t i o n r e g a r d i n g t h e p r e s e n t " s t a t e of t h e art" of
sweet p o t a t o p r o c e s s i n g .
CANNING PROCESS
An o u t l i n e and d e s c r i p t i o n o f major s w e e t p o t a t o p r o c e s s i n g o p e r a t i o n s
are e s s e n t i a l f o r u n d e r s t a n d i n g water consumption and waste p r o d u c t i o n
characteristics.
The major p r o c e s s i n g s t e p s are:
Receiving and Unloading
Sweet p o t a t o e s a r r i v e a t t h e p l a n t i n t r u c k s which are unloaded
e i t h e r by a front-end l o a d e r o r a l a r g e "vacuum c l e a n e r - l i k e "
a p p a r a t u s . Some f i e l d d i r t f a l l s o f f t h e p o t a t o d u r i n g t h e t r a n s f e r
operations.
The p o t a t o e s are conveyed through a reel washer t o remove d i r t
attached t o the potatoes.
Preheating
The p o t a t o e s are p r e h e a t e d i n a water b a t h of approximately 105" F f o r
a couple of minutes t o enchance t h e a c t i o n of t h e l y e b a t h .
Lye Bath
P o t a t o e s are immersed i n a b o i l i n g 15 p e r c e n t l y e s o l u t i o n f o r
approximately two minutes t o f a c i l i t a t e p e e l removal and reduce
manual trimming o p e r a t i o n s . The g r e a t e r t h e p e e l l o s s , t h e g r e a t e r
t h e waste produced and t h e less u s a b l e p r o d u c t l e f t .
86
P e e l Removal
P e e l s a r e removed by a r o t a r y washer which removes most of t h e
s o f t e n e d p e e l and p a r t of t h e p o t a t o .
Snipping
Large r o t a r y s n i p p e r s are used t o remove r o o t s o r s t r i n g s from sweet
p o t a t o ends.
Abrasive P e e l e r s
Sandpaper-like c o u n t e r r o t a t i n g r o l l e r s are used t o smooth t h e
potato surface.
Brush Washer
Counter r o t a t i n g b r i s t l e r o l l e r s i m p a r t a f i n a l s h e e n t o t h e s u r f a c e
of t h e p o t a t o .
Trimminq
The f r e s h l y p e e l e d p o t a t o e s are i n s p e c t e d and manually trimmed.
Product n o t s u i t a b l e f o r canning i s r e j e c t e d .
Sizing
A r o t a t i n g drum w i t h v a r i a b l e s i z e openings s e p a r a t e s p o t a t o e s by
sizes.
S1i c i n q
Large p o t a t o e s move through a series of c u t t i n g machines which f i r s t
h a l f and t h e n q u a r t e r t h e p o t a t o e s .
Grad i n g
P o t a t o e s on t h e g r a d i n g b e l t a r e manually checked f o r s i z e and q u a l i t y .
Filling
The r a w p r o d u c t moves o n t o a c i r c u l a r hand pack f i l l e r w i t h a series
of openings around i t s o u t e r edge. P o t a t o e s are t h e n raked i n t o cans
p a s s i n g below a s t h e c i r c u l a r t o p r o t a t e s .
Syruping
Most canned s w e e t p o t a t o e s are packed i n a syrup medium o f s u g a r and
water heated t o a t e m p e r a t u r e j u s t below b o i l i n g .
87
Closing
A s e a l i n g machine p l a c e s a l i d on each can and a p p l i e s p r e s s u r e t o
s e a l t h e can.
Retorts
High p r e s s u r e steam r e t o r t s are used t o cook t h e canned p r o d u c t f o r
v a r y i n g p e r i o d s of t i m e , depending on can s i z e , s y r u p c o n t e n t , and
t h e average t e m p e r a t u r e of t h e c o n t e n t s when p l a c e d i n t h e r e t o r t s .
Coo 1i n g
On removal from t h e r e t o r t s , c a n s are passed through a c o o l i n g c a n a l .
Labeling and Packaging
Labels are p a s t e d on c a n s and t h e c a n s are p l a c e d i n cases f o r s t o r a g e
and e v e n t u a l shipment.
Before t h e e x i s t i n g c o n v e n t i o n a l p r o c e s s could be modified, a s e a s o n ' s
o p e r a t i n g d a t a on t h e r e l a t i o n s h i p of water usage and waste charact e r i z a t i o n t o p l a n t p r o d u c t i o n had t o be e s t a b l i s h e d . The e x i s t i n g
l a b o r a t o r y a t t h e p l a n t w a s geared up t o make t y p i c a l s a n i t a r y engin e e r i n g a n a l y t i c a l t e s t s , and t h e l a b o r a t o r y t e c h n i c i a n w a s brought
t o North C a r o l i n a S t a t e U n i v e r s i t y f o r a week of i n t e n s i v e t r a i n i n g .
Necessary equipment, chemicals, and s u p p l i e s w e r e purchased f o r t h e
plant laboratory
.
The p l a n t i n s t a l l e d n i n e t e e n (19) water meters t o determine u n i t
p r o c e s s u s e r a t e s . Daily r e a d i n g s were t a k e n o f t o n s of i n p u t ,
o p e r a t i n g h o u r s , and d a i l y p r o d u c t i o n . The breakdown of water consumption p e r t o n o f sweet p o t a t o e s processed and p e r case of number
2-1/2 cans produced a r e g i v e n i n Table 1.
The r e t o r t i n g o p e r a t i o n s u t i l i z e s t h e l a r g e s t amount of water ( 3 8 . 8 % )
of any s i n g l e o p e r a t i o n . There i s no s u b s t a n t i a l amount of o r g a n i c
material i n t h i s water. The water u t i l i z e d f o r steam g e n e r a t i o n
and syrup p r o d u c t i o n i s consumptive i n t h a t i t i s e i t h e r packed i n
cans o r e v a p o r a t e s .
A n a l y t i c a l q u a l i t y measurements were made a t Tabor C i t y Foods and
a t North C a r o l i n a S t a t e U n i v e r s i t y . A l l p r o c e d u r e s were i n accordance w i t h t h e 1 9 7 1 Environmental P r o t e c t i o n Agency Methods f o r
Chemical A n a l y s i s o f Water and Wastes. I n a d d i t i o n , a l l samples
were passed through a twenty-mesh s c r e e n p r i o r t o a n a l y s i s a t t h e
r e q u e s t of t h e Environmental P r o t e c t i o n Agency. A composite sample
c o n s i s t i n g of f o u r g r a b samples were t a k e n a t each sampling s t a t i o n
each o p e r a t i n g day, o r as o f t e n as f e a s i b l e . Chemical oxygen demand,
s e t t l e a b l e s o l i d s , t e m p e r a t u r e , and pH o b s e r v a t i o n s w e r e made on each
88
TABLE 1
Unit Process Water Use in Conventional
Sweet Potato Processing
Unit Process
Gal/Ton
Input
Gal/Case
112-112 Cans
% of Total
Water Use
First Washer
79
2.8
3.0
Preheat er
15
0.54
0.5
W/D Washer
2 80
9.9
10.9
Snippers
110
4.0
4.4
Abrasive Peeler
140
4.8
5.3
96
3.4
3.7
1000
35.0
38.5
Cleanup
240
8.6
9.5
Cooling
31
1.0
1.1
Boiler Water
415
15.0
16.5
Belt Wetting
130
4.7
5.2
Syruping
36
-
1.3
1.4
TOTALS
2572
91.0
100.0
Brush Washer
Retort
89
sample c o l l e c t e d . Biochemical oxygen demand, suspended s o l i d s , d i s s o l v e d s o l i d s , n i t r o g e n , and phosphorus measurements were made less
f r e q u e n t l y . The r a n g e and a v e r a g e c o n c e n t r a t i o n s of wastes f l o w s
f o r t h e c o n v e n t i o n a l u n i t p r o c e s s e s are p r e s e n t e d i n T a b l e 2.
Whole sweet p o t a t o e s were s t u d i e d i n t h e l a b t o d e t e r m i n e t h e pounds
of COD, BOD, carbon, n i t r o g e n , and phosphorus p e r pound of whole d r y
weight. The sweet p o t a t o e s examined had zn a v e r a g e m o i s t u r e c o n t e n t
o f 76 p e r c e n t .
One pound o f sweet p o t a t o e s ( d r i e d a t 103" C) w a s
found t o produce 1.06 pounds COD, 0.49 pound BOD5, 0.38 pound of
carbon, 0.0184 pound o f n i t r o g e n , and 0.0016 pound of phosphorus.
I f t h e poundage w a s based on t h e w e t weight o f t h e p o t a t o , t h e s e
f i g u r e s have t o be m u l t i p l i e d by 0.24.
T h i s means t h a t f o r e v e r y
pound o f sweet p o t a t o n o t p u t i n c a n s and e n t e r i n g a l i q u i d waste
stream, one can e x p e c t 0.252 pound COD, 0.118 pound BOD5, 0.091 pound
of t o t a l carbon, 0.0044 pound of n i t r o g e n , and 0.000384 pound of
phosphorus.
The t o t a l pounds of BOD5, COD, t o t a l and suspended s o l i d s d i s c h a r g e d
p e r t o n of r a w p r o d u c t i n p u t from c o n v e n t i o n a l u n i t p r o c e s s e s
u t i l i z e d i n sweet p o t a t o p r o c e s s i n g are p r e s e n t e d i n Table 3. The
d a t a p r e s e n t e d r e p r e s e n t s t h e waste l o a d a f t e r p a s s i n g samples through
a twenty-mesh s c r e e n . It is i n t e r e s t i n g t o n o t e t h a t t h e major s o u r c e s
of waste p r o d u c t i o n (synonymous w i t h p r o d u c t l o s s ) are c r e a t e d by p e e l
removal, a b r a s i v e p e e l i n g , and s n i p p i n g o p e r a t i o n s . A l l f i g u r e s shown
i n t h i s t a b l e end up i n t h e l i q u i d waste stream.
-
S t u d i e s were undertaken t o d e f i n e a n d / o r I d e n t i f y t h e mass b a l a n c e
of sweet p o t a t o e s through t h e p r o c e s s i n g p l a n t . A s a r e s u l t of t h e s e
i n v e s t i g a t i o n s , the following information w a s generated:
Raw p r o d u c t s t u d i e s r e v e a l e d t h a t 5 p e r c e n t (100 l b s / t o n )
of t h e p r o d u c t when r e c e i v e d w a s f i e l d d i r t .
S o l i d waste g e n e r a t i o n s t u d i e s r e v e a l e d t h a t 9.5 p e r c e n t
(190 l b s / t o n ) of r a w p r o d u c t , u n f i t f o r canning f o r v a r i o u s
r e a s o n s , w a s t r u c k e d away f o r d i s p o s a l .
Product y i e l d s t u d i e s r e v e a l e d t h a t 40 p e r c e n t (800 l b s / t o n )
w a s p l a c e d i n c a n s and became a s a l e a b l e p r o d u c t .
Liquid waste s t u d i e s r e v e a l e d t h a t 160 pounds of s o l i d s d r i e d
a t 103' C were g e n e r a t e d p e r t o n of r a w product i n p u t
(Table 3) a f t e r s c r e e n i n g . Dividing t h e 160 pounds by
0.24, t h e p e r c e n t t o t a l s o l i d s i n a r a w sweet p o t a t o , g i v e s
680 pounds of s o l i d s p e r t o n of r a w p r o d u c t i n p u t . O r , 33
p e r c e n t of t h e r a w p r o d u c t ends up i n a l i q u i d waste stream.
90
.
TABLE 2
Waste C o n c e n t r a t i o n s f o r Unit P r o c e s s e s U t i l i z e d i n Conventional Sweet P o t a t o Processing#
Unit P r o c e s s
F i r s t Washing
Preheater
P e e l Removal
Snippers
W
F.’
Abrasive P e e l i n g
Brush Washer
Retort
BOD (mg/L)
Average
Range
COD (mg/L)
Average
Range
T o t a l Nitrogen
as N(mg/L)
Aver age
T o t a l Phosphorus
a s P(mg/L)
Average
990
460-2400
3,700
1300-8900
12
3,700
2400-4500
9,300
4700-14000
45
17.0
7800-23000
32,000
10000-45000
320
40.0
5,900
2600-8600
16,000
8100-40000
140
23.0
14,000
7900-20000
22,000
1600-40000
330
50.0
3,500
1300-4700
6,400
2000-9600
71
9.2
130-260
0
0
-
13,000
76
44-110
210
Cleanup
2,200
5 30-62 00
3,800
2200-10000
-
TOTAL
EFFLUENT*
8,600
4000-13000
22,000
12000-31000
210
#After 20-mesh s c r e e n i n g
*Excluding R e t o r t Waters
1.1
29.0
TABLE 2 ( c o n t i n u e d )
Unit P r o c e s s
Total Solids
(mg/L)
Range
Aver a g e
Suspended S o l i d s
(mg/L)
Average
Range
F i r s t Washing
2 ,100
8 00-8 7 00
1,200
3 0 0- 1500
28
6-40
P r e h e a t er
8 ,400
6500-11000
1,600
600-2660
32
5-64
P e e l Removal
35 ,000
12000- 48 00 0
7,700
2500-10500
5 30
350-750
Snipp e r s
1 3 ,000
5300-18000
3,800
600-7 100
2 80
75-500
Abrasive P e e l i n g
23,000
6600-36000
4,400
1100-6 7 00
470
60-7 30
4 ,300
2800-8700
1,200
350-4500
74
18-160
300
2 60- 370
0
0
870
6 30-1 100
\D
10
Settleable Solids
(ml/L)
Average
Range
Brush Washer
Retort
Cleanup
TOTAL
EFFLUENT*
2,700
2 2 00- 32 00
26 ,000
7000-67000
# A f t e r 20-mesh s c r e e n i n g
*Excluding R e t o r t Waters
3 ,800
1 400-8000
0
250
0
60-570
TABLE 3
Waste Loads P e r Ton of I n p u t f o r Unit P r o c e s s e s
U t i l i z e d i n Conventional Sweet P o t a t o P r o c e s s i n g *
Total Solids
l b s/ t o n
Suspended
Solids
l b s / t on
BOD
lbs/ ton
COD
l b s/ t o n
F i r s t Wash
0.7
2.4
1.4
0.8
P r e h e a t er
0.5
1.2
1.1
0.2
30.0
75.0
83.0
18.0
5.5
15.0
12.0
3.6
16.0
25.0
26.0
5.1
Brush Washer
2.8
5.1
3.4
1.0
Retort
0.6
1.8
2.5
0
C 1eanup
4.4
7.7
5.5
1.8
0
6.8
25.1
0
60.0
140.0
160.0
30.0
Unit P r o c e s s
P e e l Removal
Snipp er s
Abrasive P e e l i n g
M i sc e l l aneo us
TOTAL EFFLUENT
*Rounded o f f and a f t e r 20-mesh s c r e e n i n g
93
5)
The sum of t h e p e r c e n t a g e s accounted f o r a s d i r t , s o l i d w a s t e ,
y i e l d , and l i q u i d waste i s 87.5 p e r c e n t . The remaining 1 2 . 5
p e r c e n t i s b e l i e v e d t o r e p r e s e n t t h e q u a n t i t y of sweet p o t a t o
d i s c h a r g e d i n t o t h e l i q u i d w a s t e stream t h a t w i l l n o t p a s s
a twenty-mesh s c r e e n . A l l waste samples were passed through
a twenty-mesh s c r e e n p r i o r t o a n a l y s i s a t t h e r e q u e s t of t h e
Environmental P r o t e c t i o n Agency. This would i n d i c a t e t h a t a
t o t a l of 45.5 p e r c e n t (910 l b s / t o n ) of t h e r a w product e n t e r s
t h e l i q u i d waste stream p r i o r t o s c r e e n i n g . T h e r e f o r e , a l l
f i g u r e s p r e s e n t e d i n Tables 2 and 3 should b e a d j u s t e d upward
by 1 . 4 (45.5
3 3 ) t o r e p r e s e n t waste g e n e r a t i o n b e f o r e
screening.
A summary of water u s e , l y e consumption, and waste g e n e r a t i o n p e r t o n
and p e r case of number 2-1/2 c a n s f o r c o n v e n t i o n a l sweet p o t a t o canning
i s p r e s e n t e d i n Table 4 .
PROPOSED CHANGES AND PROCESS MODIFICATIONS
The 1971 p r o c e s s i n g d a t a g a t h e r e d from Tabor C i t y Foods i s b e l i e v e d
t o r e p r e s e n t t h e c u r r e n t "state of t h e a r t " of c o n v e n t i o n a l s w e e t
p o t a t o canning technology. Table 4 , t h e c h a r a c t e r i z a t i o n summary,
d r a m a t i c a l l y i n d i c a t e s t h e s e v e r i t y of t h e problem f a c i n g s w e e t
p o t a t o canners. Each of t h e s e problem areas b e a r s d i r e c t l y on a
p r o c e s s o r ' s economic c o m p e t i t i v e n e s s and imposes a p o t e n t i a l
p o l l u t i o n a l l o a d on t h e l o c a l environment. A p r o c e s s o r , f o r example,
who i s a b l e t o r e a l i z e a g r e a t e r y i e l d , n o t o n l y h a s more s a l e a b l e
product f o r t h e same e x p e n d i t u r e b u t r e d u c e s h i s c o s t of waste t r e a t ment. A twofold g a i n !
The purpose of t h e second y e a r of t h e EPA d e m o n s t r a t i o n g r a n t i s t o
d e s i g n , i n s t a l l , demonstrate, and e v a l u a t e f o u r t e c h n i q u e s o f
i n c r e a s i n g y i e l d , lowering canning c o s t s , and reducing t h e environmental impact of sweet p o t a t o canning. S p e c i f i c a l l y , f o u r means of
a s s i s t i n g t h e p r o c e s s o r and t h e environment w i l l b e demonstrated.
These are d r y c a u s t i c p e e l i n g , l y e r e c o n d i t i o n i n g , h i g h p r e s s u r e water
system, and p r e t r e a t m e n t of waste.
Dry C a u s t i c P e e l i n g
Conventional vat t y p e ( h o t d i p ) l y e p e e l i n g became t h e major t e c h n i q u e
of removing t h e p e e l s of f r u i t s and v e g e t a b l e s d u r i n g World War 11.
The s i m p l i c i t y , economy, and l a b o r s a v i n g advantages of l y e p e e l i n g
allowed t h e U.S. t o meet t h e demand f o r processed f r u i t s and v e g e t a b l e s
a t a t i m e when t h e r e e x i s t e d a c u t e s h o r t a g e s of l a b o r and materials.
The t e c h n i q u e s of l y e p e e l i n g developed d u r i n g World War I1 a r e s t i l l
used today.
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TABLE 4
C h a r a c t e r i z a t i o n Summary of Conventional Sweet P o t a t o P r o c e s s i n g *
P e r Ton
Parameter
A.
Liquid
P e r Case
#
BOD
(lbs)
60
2.1
COD
(1bs)
140
5.0
T. S o l i d s ( l b s )
160
5.7
S. S o l i d s ( l b s )
30
1.0
B.
S o l i d Waste ( l b s )
200
7.1
C.
Dirt
100
3.5
D.
Water ( g a l l o n s )
2600
92.0
E.
Lye (50%) ( g a l l o n s )
9.2
*Rounded o f f
# A f t e r 20-mesh s c r e e n i n g
95
0.32
I n 1967-68, Graham, Huxsoll, e t a l , a t t h e USDA'S Western Research and
Development D i v i s i o n , Albany, C a l i f o r n i a , announced t h e development of
a new method of p e e l i n g p o t a t o e s . T h e i r d r y c a u s t i c method w a s based
on t h e a p p l i c a t i o n of i n f r a r e d h e a t t o l i g h t l y c a u s t i c t r e a t e d p o t a t o e s
followed e s s e n t i a l l y by mechanical p e e l removal.
A t e n t o n p e r hour i n f r a r e d p e e l i n g system, based on t h e GrahamHuxsoll model, i s scheduled f o r i n s t a l l a t i o n i n t h e Tabor C i t y Foods'
p l a n t t h i s summer. The a n t i c i p a t e d changes i n o p e r a t i n g c h a r a c t e r i s t i c s from a p p l i c a t i o n of t h i s new technology are: 1) lower p e e l
l o s s , 2) lower water consumption, 3) lower l y e consumption, 4 ) i n c r e a s e d product y i e l d , and 5) d i s p o s a l of g e n e r a t e d s o l i d s as a
so l i d w a s t e .
Lye Reconditioning
The use of a r o t a r y drum f i l t e r f o r r e c o n d i t i o n i n g l y e by removing
s o l i d s and s p e n t l y e from t h e l y e vat i s expected t o reduce t h e l y e
consumption by i n c r e a s i n g t h e u s e f u l l i f e of t h e l y e .
High P r e s s u r e Water System
Through t h e u s e of h i g h p r e s s u r e s p r a y n o z z l e s , e q u a l o r s u p e r i o r
removal e f f i c i e n c y can be o b t a i n e d u s i n g less water. The u s e of
less water a l s o means waste c o n c e n t r a t i o n s w i l l be g r e a t e r , f a c i l i t a t i n g easier p r e t r e a t m e n t .
Waste P r e t r e a t m e n t
The i n s t a l l a t i F n o f a v i b r a t i n g s c r e e n followed by a r o t a r y drum f i l t e r
i s expected t o r e d u c e t h e waste l o a d t o t h e m u n i c i p a l i t y and reduce
sewer u s e s u r c h a r g e s . The s o l i d s removed by t h e v i b r a t i n g s c r e e n and
r o t a r y drum f i l t e r w i l l be disposed of i n a s a n i t a r y l a n d f i l l .
The t o t a l a n t i c i p a t e d e f f e c t o f new technology u t i l i z e d i n s w e e t
p o t a t o p r o c e s s i n g as opposed t o c o n v e n t i o n a l technology i s p r e s e n t e d
i n Table 5.
The economic i m p l i c a t i o n s of t h e water and waste r e d u c t i o n t e c h n i q u e s
demonstrated w i l l b e determined f o r i n d i v i d u a l p r o c e s s e s and f o r t h e
Budgeting p r o c e d u r e s w i l l b e used t o d e t e r m i n e c o s t s ,
t o t a l plant.
r e t u r n s , and changes i n n e t revenue due t o t h e new technology.
Economic i m p l i c a t i o n s f o r d e v i s i n g water and waste r e d u c t i o n p o l i c i e s
w i l l be determined from a comparative a n a l y s i s of t h e c o s t of i n p l a n t
water and waste r e d u c t i o n and wastewater t r e a t m e n t c o s t s .
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TABLE 5
Anticipated Effect of New Technology Utilization in
Sweet Potato Processing as Compared to the
Conventional "State of the Art"
Parameter
Conventional
Technology
40%
Product Yield
2600
Water (gal/ton)
Advanced
Technology
45-50
1400-1600
BOD (lbs/ton)
60
10-15
COD (lbs/ton)
140
25-35
30
1-5
Total Solids (lbs/ton)
160
35-45
Solid Waste (lbs/ton)
200
600-700
Suspended Solids (lbs/ton)
Lye Consumption (gal/ton)
9.2
97
%
4-7
Guides f o r water and wastewater management f o r t h e sweet p o t a t o proc e s s i n g i n d u s t r y w i l l b e formulated. The r e s u l t s of t h i s d e m o n s t r a t i o n
g r a n t can be used as management g u i d e l i n e s f o r a p p l i c a t i o n s of i n f r a r e d
p e e l i n g , l y e r e c o n d i t i o n i n g , h i g h p r e s s u r e water systems, and p r e t r e a t ment i n t h e sweet p o t a t o p r o c e s s i n g i n d u s t r y .
SUMMARY AND CONCLUSIONS
The c o n c l u s i o n s t h a t can b e drawn from t h e f i r s t y e a r of t h e demons t r a t i o n g r a n t on water and waste management i n sweet p o t a t o proc e s s i n g are:
1) The s a l e a b l e product y i e l d u t i l i z i n g c o n v e n t i o n a l
p r a c t i c e s of sweet p o t a t o canning i s 40 p e r c e n t .
2)
The r a t e of water consumption i s 2,600 g a l l o n s p e r
t o n o f raw product i n p u t , o r 91 g a l l o n s o f water p e r
case o f 2-1/2 c a n s produced.
3)
Conventional sweet p o t a t o p r o c e s s i n g w i l l produce
60 pounds BOD, 140 pounds COD, 160 pounds t o t a l s o l i d s ,
and 30 pounds suspended s o l i d s p e r t o n o f i n p u t a f t e r
twenty-mesh s c r e e n i n g .
4)
I f t h e sweet p o t a t o canning p r o c e s s o r s are t o c o n t i n u e
t o exist i n North C a r o l i n a , s t e p s must b e t a k e n t o
i n c r e a s e product y i e l d , lower p e e l l o s s , lower water
consumption, and s i g n i f i c a n t l y r e d u c e t h e l o c a l impact
of t h e waste r e l e a s e d from t h e p l a n t s .
98