Case History: Pretreatment of Textile Wastewaterinfohouse.p2ric.org/ref/31/30158.pdf · CASE...
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Transcript of Case History: Pretreatment of Textile Wastewaterinfohouse.p2ric.org/ref/31/30158.pdf · CASE...
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CASE HISTORY: PRETREATMENT OF TEXTILE WASTEWATER
Randy J u n k i n s , P.E.*
INTRODUCTION
The f i n i s h e d p r o d u c t s of t h e t e x t i l e s i n d u s t r y are m a n u f a c t u r e d f r o m wool, c o t t o n , s y n t h e t i c f i b e r s , o r c o m b i n a t i o n s thereof . The p r o c e s s i n g which t h e raw f ibers u n d e r g o are aimed toward:
0 Removal of n a t u r a l i m p u r i t i e s .
0 P r o v i d i n g desired q u a l i t i e s of s i g h t , t o u c h , and d u r a b i l i t y .
The degree t o which these o b j e c t i v e s are p u r s u e d d e t e r m i n e s t h e character is t ics of t h e wastewater g e n e r a t e d by a t e x t i l e m i l l . For example, t h e amount of o r g a n i c matter t h a t is removed from a f ab r i c i n t h e c o u r s e of n o r m a l t e x t i l e p r o c e s s i n g c a n be v i s u a l - i z e d when o n e c o n s i d e r s t h a t a b o u t 1 0 p e r c e n t of t h e g r o s s w e i g h t of a c o t t o n fabr ic c o n s i s t s of n a t u r a l i m p u r i t i e s w h i c h may be removed i n p r o c e s s i n g . For a f i r m t h a t m a n u f a c t u r e s 20 t o n s of f ab r i c per w e e k , a common p r o d u c t i o n l e v e l , t h i s means t h a t 2 t o n s per w e e k of i m p u r i t i e s are discharged t o t h e sewer and mus t be removed from t h e p l a n t e f f l u e n t . T h i s p a p e r p r e s e n t s a case s t u d y c o n c e r n i n g t h e t r e a t m e n t of t e x t i l e i n d u s t r y waste- waters. P r o d u c t i o n processes, wastewater s o u r c e s and character- istics, and wastewater management s t r a t eg ie s are d i s c u s s e d .
T e x t i l e m i l l o p e r a t i o n s c o n s i s t of v a r i o u s processes s u c h as weav ing , d y e i n g , p r i n t i n g , and f i n i s h i n g . These processes c a n i n v o l v e s e v e r a l steps, i.e. , s i z i n g , k i e r i n g , d e s i z i n g , b leach- i n g , m e r c e r i z i n g , etc., each c o n t r i b u t i n g a p a r t i c u l a r t y p e o f waste. T h e s o u r c e s of p o l l u t i n g compounds are t h e n a t u r a l impur- i t i e s e x t r a c t e d from t h e f i b e r , and t h e p r o c e s s i n g chemicals which are removed from t h e c l o t h a n d discharged a s waste.
*Manager, O&M S e c t i o n , WESTON D e s i g n e r s - C o n s u l t a n t s , West C h e s t e r , P e n n s y l v a n i a
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Y
I n b l e a c h i n g and d y e i n g t e x t i l e materials, some c o n t i n u o u s proc- esses are u t i l i z e d , b u t many batch u n i t o p e r a t i o n s , s u c h a s k i e r b o i l i n g and d y e i n g o p e r a t i o n s , are a l so used . These batch proc- esses p r o d u c e sudden c h a n g e s i n wastewater c o m p o s i t i o n . T h e type f ibe r b e i n g processed also affects t h e c o m p o s i t i o n of t h e w a s t e ; c o t t o n and l i n e n c o n t r i b u t e o r g a n i c matter from t h e n o n c e l l u l o s - ic mater ia ls t h a t are p r e s e n t i n t h e n a t u r a l f ibers , w h i l e wool c o n t a i n s s a n d , grease, and s u i n t wh ich are removed d u r i n g scour- ing . S y n t h e t i c f ibers may c o n t a i n s p i n n i n g o i l s and a n t i - s t a t i c d r e s s i n g s . The c o m p o s i t i o n of a p l a n t ' s e f f l u e n t w i l l therefore v a r y w i t h t h e f i be r s t h a t are b e i n g processed. V a r i a b i l i t y i n c o m p o s i t i o n i s a marked f e a t u r e of most t e x t i l e w o r k s e f f l u e n t s , and wide v a r i a t i o n s i n c o m p o s i t i o n , t e m p e r a t u r e , flow, and pH v a l u e s are p r e v a l e n t . T e x t i l e wastes are g e n e r a l l y colored, h i g h l y a l k a l i n e , and h i g h i n BOD, suspended s o l i d s , and temper- a t u r e .
E q u a l i z a t i o n is g e n e r a l l y a p r e l i m i n a r y t r e a t m e n t s t ep f o r t e x - t i l e wastes d u e t o t h e i r v a r i a b l e c o m p o s i t i o n . Chemica l c o a g u l a - t i o n and b io log ica l t r e a t m e n t are t h e t r e a t m e n t methods most of- t e n u s e d f o r removal of co lo r and d i s s o l v e d o r g a n i c s (i.e., BOD). Alum, f e r r o u s su l fa te , f e r r i c s u l f a t e , and f e r r i c chloride are used as c o a g u l a n t s , i n c o n j u n c t i o n w i t h lime and s u l f u r i c acid f o r pH c o n t r o l . Ca lc ium c h l o r i d e h a s a l so been found effec- t i v e i n s u c h p r o c e d u r e s as c o a g u l a t i n g woo l - scour ing wastes. B io log ica l t r e a t m e n t v i a t h e a c t i v a t e d s ludge process or t r ick- l i n g f i l t e r s is f r e q u e n t l y u s e d s u c c e s s f u l l y t o remove s o l u b l e o r g a n i c s .
I n - p l a n t m e a s u r e s t h a t c a n be implemented t o r e d u c e t h e q u a n t i t y and s t r e n g t h of t e x t i l e wastes i n c l u d e :
0 Good housekeep ing . 0 Process c o n t r o l . 0 Process chemical s u b s t i t u t i o n . 0 Chemical r e c o v e r y .
Close c o n t r o l of k i e r i n g , s i z i n g , and chemical u s a g e may r e d u c e p o l l u t a n t loads by 30 p e r c e n t . C h e m i c a l s u b s t i t u t i o n (example : u s e of ammonium s u l f a t e i n s t e a d of acetic acid f o r s c o u r i n g ) c a n a lso be a n e f f e c t i v e me thod t o r e d u c e i n - p l a n t BOD loads.
T h i s paper p r e s e n t s a case h i s t o r y c o n c e r n i n g t h e p r e t r e a t m e n t of a bleachery wastewater. The scope of t h e paper i n c l u d e s wastewater c h a r a c t e r i z a t i o n s t u d i e s , t r e a t a b i l i t y i n v e s t i g a - t i o n s , c o n c e p t u a l e n g i n e e r i n g d e s i g n , and t r e a t m e n t p l a n t o p e r - t i o n .
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I n i t i a l l y , a wastewater s o u r c e a n a l y s i s and c h a r a c t e r i z a t i o n s t u d y was c o n d u c t e d . T h i s w o r k i d e n t i f i e d t h e f o l l o w i n g major s o u r c e s o f wastewater:
0 S c o u r t a n k . 0 Bleachers. 0 Washers. 0 Boi l e r blowdown. 0 Water c o n d i t i o n i n g u n i t s .
T h e wastewater sampl ing s u r v e y i n d i c a t e d t h a t t h e p r i m a r y p o l l u - t a n t s of c o n c e r n were BOD, ss, a n d t e m p e r a t u r e .
F o l l o w i n g c o m p l e t i o n o f t h e wastewater s a m p l i n g t a s k , a bench- scale t r e a t a b i l i t y i n v e s t i g a t i o n was c o n d u c t e d i n order t o ob- t a i n n e c e s s a r y d e s i g n parameters. T h i s w o r k i n c l u d e d opera t ion of a l a b o r a t o r y - s c a l e , c o n t i n u o u s - f l o w a c t i v a t e d s l u d g e u n i t . D e s i g n parameters i d e n t i f i e d i n c l u d e d BOD remova l rates, oxygen r e q u i r e m e n t s , s l u d g e p r o d u c t i o n ra tes , aerobic s l u d g e d i g e s t i o n c o e f f i c i e n t s , and s l u d g e s e t t l i n g and d e w a t e r i n g characteris- tics.
The p r e t r e a t m e n t s t r a t e g y selected i n c l u d e d p r e l i m i n a r y s c r e e n - i n g for l i n t removal and a heat e x c h a n g e r for e n e r g y r e c o v e r y f o l l o w e d by e q u a l i z a t i o n and s u b s e q u e n t b i o l o g i c a l t r e a t m e n t v i a e x t e n d e d a e r a t i o n . T h i s paper describes t h e v a r i o u s t r e a t m e n t u n i t s u t i l i z e d and p r e s e n t s p l a n t o p e r a t i n g data.
CASE H I S T O R Y
G e n e r a l
The b l e a c h e r y s t u d i e d was s t r i c t l y a b l e a c h i n g and washing fa- c i l i t y t h a t u s e d n o d y e i n g o p e r a t i o n s a n d processed a p p r o x i m a t e - l y 47,000 l b of c l o t h per day . The p l a n t used a n o n - s i t e w e l l a s a p r o c e s s water s u p p l y s o u r c e . The w e l l water w a s d e m i n e r a l i z e d v i a ion -exchange before u s e , and t h e r e g e n e r a t i o n waste was com- b i n e d w i t h b o i l e r blowdown f o r d i r ec t d i s c h a r g e t o a n e a r b y r i v - er t h r o u g h a storm sewer. All process and s a n i t a r y wastes were o r i g i n a l l y e q u a l i z e d a n d s u b s e q u e n t l y d i s c h a r g e d t o a m u n i c i p a l sewer sys tem. C h e m i c a l s u s e d i n t h e p l a n t ' s b l e a c h i n g process i n c l u d e d e t h y l e n e oxide, hydrogen peroxide, c a u s t i c , sodium sil- icate, acetic acid, and b l e a c h i n g p e n e t r a n t s .
The l oca l m u n i c i p a l i t y came u n d e r pressure from t h e U . S . EPA t o meet its d i s c h a r g e c r i t e r a o f 8 5 - p e r c e n t removal of biochemical oxygen demand (BOD5) . S i n c e t h e b l e a c h e r y was a major c o n t r i b - u t i n g i n d u s t r y , t h e m u n i c i p a l i t y r e q u e s t e d t h a t t h e b l e a c h e r y
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m a i n t a i n its flow a t less t h a n 120 ,000 gpd, and discharge n o more t h a n 120 l b / d a y of BOD^ t o t h e sys tem. I n a d d i t i o n , there were other p r e t r e a t m e n t c r i t e r i a f o r suspended so l ids , o i l a n d grease, t o t a l d i sso lved s o l i d s , and c h l o r i n e demand which the b l e a c h e r y was required t o meet f o r d i s c h a r g e t o t h e m u n i c i p a l system.
Wastewater S o u r c e s , Q u a n t i t i e s , and Characterist ics
A wastewater s o u r c e a n a l y s i s and c h a r a c t e r i z a t i o n s t u d y was con- d u c t e d i n v o l v i n g o n - s i t e s a m p l i n g and c o n c u r e n t b i o l o g i c a l t r e a t a b i l i t y tests, i n c l u d i n g o p e r a t i o n of a b e n c h - s c a l e a c t i - v a t e d s l u d g e t r e a t m e n t process. Composite wastewater samples collected a t a n e x i s t i n g e q u a l i z a t i o n b a s i n were a n a l y z e d fo r raw waste c h a r a c t e r i z a t i o n . The a n a l y t i c a l d e t e r m i n a t i o n s per- formed i n c l u d e d wastewater f l o w , biochemical oxygen demand (BOD51 , chemical oxygen demand (COD) , o i l , t o t a l d i s s o l v e d so l ids (TDS), suspended s o l i d s (SS), p H , ammonia n i t r o g e n , t o - t a l p h o s p h o r u s , p h e n o l , s u l f i d e , and t o t a l chromium.
The f o l l o w i n g s o u r c e s were i d e n t i f i e d a s major c o n t r i b u t o r s o f wastewater from t h e b l e a c h e r y :
0 B l e a c h i n g O p e r a t i o n s .
- S c o u r t a n k . - Bleachers. - Washers.
0 Boiler Blowdown.
0 I o n Exchange U n i t s .
- Process water c o n d i t i o n i n g u n i t s . - Boiler feedwater c o n d i t i o n i n g u n i t s .
0 S a n i t a r y System.
The p l a n t ' s major wastewater f lows o r i g i n a t e d from t h e b l e a c h i n g u n i t o p e r a t i o n s , p a r t i c u l a r l y t h e washers. The boi ler blowdown a n d i o n e x c h a n g e r e g e n e r a t i o n streams c o n t a i n e d p r i m a r i l y i n o r - g a n i c p o l l u t a n t s (TDS, a c i d i t y , a l k a l i x i t y , etc.: , and zoiil6 be discharged t o t h e c i t y sewer d i r e c t l y , b y p a s s i n g any pretreat- ment f ac i l i t i e s . The s a n i t a r y wastewater f l o w f rom t h e p l a n t was discharged t o t h e c i t y s y s t e m v i a a s e g r e g a t e d sewer sys t em. The wastewater s o u r c e s and projected f lows are shown i n F i g u r e 1.
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1 30,000 GPD Scour Tank
19,000 GPD Bleachers
60,000 GPD Washers
Boiler Blowdown
Boiler Feed ‘HzO Ion I Exchange
11,000 GPD Directly to City Sewer
109,000 GPD to Treatment Facilim
FIGURE 1 WASTEWATER SOURCES AND PROJECTED FLOWS
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Twenty - fou r hour composite samples o f t h e wastewater collected d u r i n g a t h r e e - m o n t h period were a n a l y z e d t o d e f i n e t h e charac- terist ics of t h e b l e a c h e r y ' s process wastes. Tab le 1 p r e s e n t s a summary of raw wastewater character is t ics and t h e d e s i g n bas i s for t h e p r e t r e a t m e n t f a c i l i t i e s recommended and u l t i m a t e l y c o n - st r u c t e d . A summary of t h e p r e t r e a t m e n t r e q u i r e m e n t s w i t h which t h e b l e a c h e r y had t o comply is shown i n Table 2. A special require- ment , imposed by t h e local borough o n t h e b l e a c h e r y , was a BOD^ d i s c h a r g e l i m i t a t i o n o f 1 2 0 p o u n d s per day. T h i s l i m i t a - t i o n was imposed t o a s s u r e t h a t t h e m u n i c i p a l wastewater t r e a t - ment p l a n t c o u l d operate w i t h i n the i r NPDES discharge r e q u i r e - ments .
Process i n v e s t i g a t i o n
The d e g r e e of BOD r e d u c t i o n r e q u i r e d by t h e borough pretreatment s t a n d a r d s , t h e l imi t ed s p a c e a v a i l a b l e w i t h i n t h e p l a n t bounda- r ies , and a compliance s c h e d u l e o f a p p r o x i m a t e l y o n e year for m e e t i n g p r e t r e a t m e n t r e q u i r e m e n t s i n d i c a t e d t h a t some fo rm of b i o l o g i c a l t r e a t m e n t (e .g . , aerated l a g o o n , ac t iva ted s l u d g e , etc.) would be t h e most desirable process f o r e v a l u a t i o n v i a t r e a t a b i l i t y i n v e s t i g a t i o n s . T h e r e f o r e , a t r e a t a b i l i t y s t u d y was c o n d u c t e d t o o b t a i n t h e e s s e n t i a l d e s i g n p a r a m e t e r s f o r a n act i - v a t e d s l u d g e sys t em.
The t r e a t a b i l i t y program i n c l u d e d t h e o p e r a t i o n o f a c o n t i n u o u s - , f l o w , l a b o r a t o r y - s c a l e a c t i v a t e d s l u d g e u n i t . D e s i g n p a r a m e t e r s s t u d i e d i n c l u d e d BOD5 r emova l rates, oxygen r e q u i r e m e n t s , s l u d g e p r o d u c t i o n ra tes , s l u d g e s e t t l i n g and d e w a t e r i n g charac- terist ics, and aerobic s l u d g e d i g e s t i o n .
The wastewater f e e d u s e d i n t h e l a b o r a t o r y t r e a t a b i l i t y s y s t e m c o n s i s t e d o f 24-hour composites collected f rom t h e b l e a c h e r y 's e x i s t i n g e q u a l i z a t i o n b a s i n . The feed was a l so s u p p l e m e n t e d w i t h p h o s p h o r u s and n i t r o g e n t o e n s u r e s u f f i c i e n t n u t r i e n t s f o r bio- l o g i c a l t r e a t m e n t .
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Summary
Parame te r
F ~ O W , gpd
COD, mg/L
SS, mg/L
TDS, mg/L
O i l , mg/L
PH
Temper a t u r e
NH3-N, mg/L
TKN, mg/L
T-P, mg/L
T a b l e 1
of Des ign R a w Wastewater C h a r a c t e r i s t i c s 1
Va lue
120 ,000
660
2,080
(a f te r e x i s t i n g h e a t e x c h a n g e r )
P h e n o l , mg/L
S u l f i d e
T o t a l chromium
4 5
2,700
34
9
3 50c
7.0
71.5 ,
5.4
0.007
< 0 . 1
< 0.02
1 A t 120 ,000 gpd, mg/L = l b s / d a y . Does n o t i n c l u d e b o i l e r blow- down or i o n e x c h a n g e r e g e n e r a t i o n waters.
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T a b l e 2
Summary of B l e a c h e ry P r e t r e a t m e n t R e q u i r e m e n t s
P a r ame t e r
BODS, l b s / d a y ( = 1 2 0 mg/L a t 0.12 mgd)
COD, mg/L
SS, mg/L
TDS, mg/L
O i l , mg/L
PH
C12 Demand, mg/L
.Temper a t u r e
Cr+6, m g / ~
~ r + 3 , mg/L
P h e n o l , mg/L
CN, mg/L
A r s e n i c , mg/L
L e a d , mg/L
M e r c u r y , mg/L
Cd, mg/L
Cu, mg/L
N P , mg/L
S i lve r , mg/L
T i n , mg/L
Z i n c , mg/L
Fe, mg/L
P r e t r e a t m e n t R e q u i r e m e n t
1 2 0
600
250
300
1 0 0
6-9
1 2
150°F Max.
2.0
2.0
0.5
0 .5
0.5
1 . 0
1 .0
2.0
2.0
2.0
2.0
2.0
2.0
5.0
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I n order t o d e t e r m i n e BOD5 r emova l rates, it was n e c e s s a r y t o u s e a bio-mass acclimated t o t h e b i o d e g r a d a b l e f r a c t i o n of t h e o r g a n i c mater ia l p r e s e n t i n t h e b l e a c h e r y wastewater. For t h i s r e a s o n , acclimated m i c r o o r g a n i s m s were developed f rom t h e o p e r a - t i o n of a l a b o r a t o r y - s c a l e , a c t i v a t e d s l u d g e s y s t e m t h a t was f e d d a i l y on a c o n t i n u o u s basis.
Parameters m o n i t o r e d w i t h i n t h e b e n c h - s c a l e system i n c l u d e d i n - f l u e n t and e f f l u e n t f l o w rates, and BOD5, COD, and SS c o n c e n - t r a t i o n s . I n a d d i t i o n , t h e p H , t e m p e r a t u r e , s u s p e n d e d so l id s , v o l a t i l e s u s p e n d e d s o l i d s , and oxygen u p t a k e rates o f t h e mixed l i q u o r were a l so m o n i t o r e d . U t i l i z i n g t h i s data , d e t e n t i o n t i m e s , l o a d i n g ra t ios , BOD5 r emova l ra te c o e f f i c i e n t s , and p o u n d s of oxygen r e q u i r e d per pound of BOD5 removed were t h e n c a l c u l a t e d i n order t o c h a r a c t e r i z e t h e b i o l o g i c a l sys t em. The d e v e l o p m e n t of BOD removal k i n e t i c s by e v a l u a t i o n o f i n d i v i d u a l reactions was impract ical b e c a u s e of t h e c o m p l e x i t y o f t h e waste a n d t h e b i o c h e m i c a l r e a c t i o n s i n v o l v e d . T h e r e f o r e , e v a l u a t i o n o f k i n e t i c s w a s approached on a s impl i f i ed o v e r a l l basis. The BOD r e m o v a l k i n e t i c s d e v e l o p e d are shown i n F i g u r e 2.
For t h e c o n t i n u o u s f l o w s y s t e m , t h e e n e r g y and endogenous oxyqen r e q u i r e m e n t s were estimated g r a p h i c a l l y from pounds o f BOD5 removed and pounds o f t o t a l oxygen consumed per pound of VSS p e r day. F i g u r e 3 shows t h e r e l a t i o n s h i p be tween these two parame- ters. The i n t e r c e p t o f t h e l i n e a t z e r o BOD5 r emova l g i v e s t h e e n d o g e n o u s oxygen r e q u i r e m e n t i n p o u n d s p e r d a y per pound of VSS u n d e r a e r a t i o n . The slope of t h e l i n e g i v e s t h e e n e r g y oxygen r e q u i r e m e n t i n p o u n d s per pound of BOD5 removed.
The e n e r g y a n d endogenous oxygen r e q u i r e m e n t s a s c a l c u l a t e d from t h e c o n t i n u o u s - f l o w s y s t e m data were found t o be:
Ene rgy Oxygen Endogenous Oxygen
l b s 0 2 / l b BOD5 removed
lbs 02 /1 ,000 l b s VSS u n d e r a e r a t i o n
0.75 7.5
The r e q u i r e d p a r a m e t e r s f o r s i z i n g of a e r a t i o n e q u i p m e n t were c a l c u l a t e d from t h e l a b o r a t o r y da t a a s f o l l o w s :
Oxygen t r a n s f e r ra te c o e f f i c i e n t ( a ) - 0.99 Oxygen s a t u r a t i o n c o e f f i c i e n t ( P ) - 0.97
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5.
4.
3.
2.
1 .o .9 .8
.7
.6
.5
.4
.3
.2
.1 .1
,
m
I I I I I I t 1 1
.2 .3 .4 .5 .6 .7 .8 .9 1.0
ZOO5 Loading Ratio CioiSij
1
F I G U R E 2 BOD5 REMOVAL RATE C O E F F I C I E N T A S A FUNCTION O F BOD5 LOADING R A T I O
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1.2
1.0
0.8
0.6
IL 0 0.4 s A
0.2
0
ENDOGENOUS OXYGEN = 7.5 LBS 0 PER HOUR/I.&O LB MLVSS
I I I I I 0.2 0.4 0.6 0.8 1.0
LBS BODS REMOVED/LB. MLVSS UA/DAY
FIGURE 3 RELATIONSHIP BETWEEN BOD5 REMOVAL AND OXYGEN REQUIREMENTS
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The n e t amount of s l u d g e p roduced is a b a l a n c e be tween t h e amount of material s y n t h e s i z e d and t h e q u a n t i t y of b i o l o g i c a l growth d e s t r o y e d . Based on t h e data o b t a i n e d , t h i s v a l u e w a s es- timated t o be 0.69 pound of suspended s o l i d s p r o d u c e d per pound of BOD5 removed by t h e a c t i v a t e d s l u d g e sys t em.
D u r i n g o p e r a t i o n of t h e l a b o r a t o r y - s c a l e a c t i v a t e d s l u d g e sys- t e m , g r a v i t y s e t t l i n g tests were c o n d u c t e d t o d e t e r m i n e t h e set- t l i n g rate of t h e b io log ica l s o l i d s g e n e r a t e d . A summary of lab- o r a t o r y o v e r f l o w rates showing s e t t l i n g characterist ics of t h e biological s l u d g e is p r e s e n t e d i n Table 3 and i l l u s t r a t e d i n F i g u r e 4.
The major d e s i g n parameters d e t e r m i n e d from t h e l a b o r a t o r y t r e a t a b i l i t y i n v e s t i g a t i o n s f o r t h e a c t i v a t e d s l u d g e p r o c e s s are summarized i n Table 4.
Process D e s i g n
The factors w h i c h c o n s t i t u t e d t h e basis f o r p r o c e s s d e s i g n and for t h e economic e v a l u a t i o n of wastewater t r e a t m e n t a l t e r n a t i v e s were:
0 All u n i t s downst ream of t h e e q u a l i z a t i o n b a s i n would be d e s i g n e d f o r a flow of 1 2 0 , 0 0 0 gpd ( 8 4 gpm) and t h e c o n t a m i n a n t c o n c e n t r a t i o n s shown i n Table 1.
0 A treated e f f l u e n t BOD5 c o n c e n t r a t i o n o f 60 mg/L was selected ( 1 2 0 mg/L required) t o al low mee t ing both BOD5 and COD d i s c h a r g e l i m i t a t i o n s .
e The t r e a t a b i l i t y parameters e s t a b l i s h e d d u r i n g p r o c - ess i n v e s t i g a t i o n and summrized i n Tables 3 and 4.
A s impl i f i ed process f l o w d i a g r a m of t h e t r e a t m e n t s y s t e m de- v e l o p e d is i l l u s t r a t e d i n F i g u r e 5. The combined process waste- waters e n t e r t h e e x i s t i n g e q u a l i z a t i o n b a s i n , wh ich p r o v i d e s storage f o r 14 h o u r s , t o e q u a l i z e d a i l y v a r i a t i o n s i n f low and c o n c e n t r a t i o n s . The e q u a l i z a t i o n b a s i n a l so p r o v i d e s s u f f i c i e n t storage t o m a i n t a i n f e e d t o t h e t r e a t m e n t f a c i l i t i e s a t a re- d u c e d rate, b u t on a c o n t i n u o u s basis d u r i n g p l a n t shut-down periods .
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Table 3
Settling Characteristics of Bench-Scale Activated Sludge
Trial No . OFR - gpd/sq ft Influent SS Effluent SS
Clare* cu = 1%** mg/L mg/L
1 770 568 3,556 1
2 1,242 580 3,770 94
3 1,408 682 3,550 120
4 1,420 703 3,480 58
5 1, 087 699 3,720 50
6 772 57 6 4,100 16
7 646 462 4,330 20
8 547 325
Average 987 574
4,680
3,898
6
46
*Overflow rate required for clarification. **Overflow rate required for an underflow concentration of 1%.
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16.0
14.0
12.0
N 10.0 IFr X - 8.0
K 0 6.0
f u.
4.0
2.0
0.0
3.0 4.0 5.0
Influent SS, mg/l x 103
6.0
FIGURE 4 RELATIONSHIP BETWEEN INFLUENT SUSPENDED S O L I D S AND C L A R I F I E R OVERFLOW RATE
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Table 4
Summary o f I n v e s t i g a t i v e R e s u l t s
BOD5 Removal Rate C o e f f i c i e n t a t 20°C
Oxygen R e q u i r e m e n t
Ene rgy Oxygen, l b s O 2 / l b BOD5 removed Endogenous Oxygen, l b s 0 2 / h r per 1 , 0 0 0 l b s VSS under a e r a t i o n
Oxygen T r a n s f e r Characterist ics
Oxygen T r a n s f e r C o e f f i c i e n t ( a ) Oxygen S a t u r a t i o n C o e f f i c i e n t ( p )
E x c e s s B i o l o g i c a l S l u d g e P r o d u c t i o n ,
B i o l o g i c a l S l u d g e S e t t l i n g Characterist ics
lbs of SS/lb of BOD5 removed
L a b o r a t o r y O v e r f l o w R a t e , g p d / s q f t O v e r f l o w Suspended So l ids , mg/L Under f low Suspended So l ids , mg/L
Ra t io of VSS t o SS u n d e r Aeration
See F i g u r e 2
0.75 7.5
0.99 0.97
0.69
7 50 60
10 ,000
0.60
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-16-
VI 0
Lo
W p: 3 W
E H
E f f l u e n t from t h e e q u a l i z a t i o n b a s i n is pumped by two c e n t r i f u - g a l pumps t o a n a e r a t i o n b a s i n . The a e r a t i o n b a s i n is e q u i p p e d w i t h a d i f f u s e d a i r s y s t e m t o m a i n t a i n a minimum d i s so lved oxy- g e n c o n c e n t r a t i o n of 2 mg/L, and t o p r o v i d e c o m p l e t e l y - m i x e d c o n d i t i o n s . S u f f i c i e n t a e r a t i o n time ( 1 2 h o u r s ) is p r o v i d e d t o produce a n e f f l u e n t w i t h a n a v e r a g e BOD5 c o n c e n t r a t i o n o f 60 mg/L=
The e f f l u e n t f r o m t h e a e r a t i o n t a n k flows t o a 3 0 - f t d iameter f i n a l c l a r i f i e r . The f i n a l c l a r i f i e r was d e s i g n e d w i t h a n o v e r - f low rate of 450 gpd per square foo t , and t o p r o d u c e a minimum u n d e r f l o w s u s p e n d e d s o l i d s c o n c e n t r a t i o n o f 1 0 , 0 0 0 mg/L.
The o v e r f l o w from t h e f i n a l c l a r i f i e r f l o w s by g r a v i t y t h r o u g h a m a g n e t i c f low meter and t o a m u n i c i p a l i n t e r c e p t o r sewer. The u n d e r f l o w from t h e f i n a l c l a r i f i e r , which i s p r i m a r i l y b io log i - c a l s l u d g e , is removed by two r e t u r n s l u d g e pumps. A p o r t i o n of t h e u n d e r f l o w is r e t u r n e d t o t h e a e r a t i o n b a s i n s t o m a i n t a i n t h e desired mixed l i q u o r v o l a t i l e suspended s o l i d s c o n c e n t r a t i o n . Any e x c e s s s l u d g e p roduced i n t h e a e r a t i o n b a s i n is discharged t o a n aerobic d i g e s t e r / h o l d i n g t a n k . P e r i o d i c a l l y , t h e a i r t o t h e t a n k i s t u r n e d o f f , and t h e r e s u l t a n t s u p e r n a t a n t is re- t u r n e d t o t h e a e r a t i o n b a s i n . S l u d g e is c o n t r a c t h a u l e d t o a f i n a l d i sposa l s i te ( i . e = # l a n d f i l l and /o r m u n i c i p a l wastewater t r e a t m e n t p l a n t ) .
P l a n t Pe r fo rmance
The o p e r a t i n g e f f i c i e n c y of t h e b l e a c h e r y wastewater pretreat- '
ment p l a n t h a s been good. P l a n t p e r f o r m a n c e is shown i n Table 5.
SUMMARY
A case s t u d y c o n c e r n i n g p r e t r e a t m e n t of b l e a c h e r y wastes h a s been p r e s e n t e d . I n v e s t i g a t i v e r e s u l t s of a b i o l o g i c a l approach t o wastewater t r e a t m e n t have been p r e s e n t e d and shown t o be e f - f ec t ive . I t is emphas ized , however, t h a t d u e t o t h e v a r i a b i l i t y of t e x t i l e wastewater character is t ics , t r e a t a b i l i t y s t u d i e s s h o u l d be c o n d u c t e d o n a c a s e - b y - c a s e basis i n order t o i d e n t i - f y and c o n f i r m t h e r e q u i r e d d e s i g n parameters.
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Table 5
Bleachery Wastewater P r e t r e a t m e n t P l a n t P e r f o r m a n c e
Parameters
Flow, mgd
BOD, mg/L
COD, mg/L
S S , mg/L
I n f l u e n t C o n c e n t r a t i o n
D e s i g n A c t u a l
0.12 0.09
660 870
2,080 3,200
45 60
34 130
9 9
7 5
5 4
T e m p e r a t u r e , OF 95 130
E f f l u e n t C o n c e n t r a t i o n
16
380
30
20
7
1
1
92
Discharge L i m i t
0.12
120
600
250
100
6 to 9
150°F-Max.
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