Upload
hoangtu
View
220
Download
1
Embed Size (px)
Citation preview
r I
TOMATO FLUME WATER RECYCLE WITH OFF-LINE MUD REMOVAL
George E. Wilson' , Wal l y R. Rose', J e r r y Y. C. Huang 1
SUMMARY AND CONCLUSIONS
The wastewater management o b j e c t i v e f o r a tomato processor i s t o imple- ment sound and performance guaranteed systems which minimize wastewater r e l a t e d costs . i t was demonstrated t h a t i n s t a l l a t i o n and opera t i on o f an i n - p l a n t water r e c y c l e system w i t h o f f - l i n e mud removal would r e s u l t i n approximately 50% savings i n t h e t o t a l annual wastewater r e l a t e d costs. For the 35 ton /h r p l a n t evaluated, annual savings would amount t o approximately $47,000.
The '75 season performance parameter values were obta ined from i n v e s t i - g a t i o n o f f o u r modes o f operat ion; convent ional c leaning; convent ional c lean ing w i t h water recyc le; d i s c c leaner w i t h water recyc le; and, d i s c c leaner w i t h r e c y c l e and chemical coagulat ion- f l o c c u l a t i o n . Water consumption and t o t a l s o l i d s balances were made on each mode.
Using performance parameter values found i n t h i s p r o j e c t ,
Not s u r p r i s i n g l y the d a i l y average tonnage o f tomatoes processed i n - creased s u b s t a n t i a l l y w i t h d i s c c lean ing and water r e c y c l e as compared t o t h e convent ional system. An increase of 26% i n the tonnage o f tomatoes processed was r e a l i z e d w i t h the d i s c c leaner w i t h water r e c y c l e and chemical f l o c c u l a t i o n . These increases i n the d a i l y tonnage o f tomatoes processed may be p r i m a r i l y due t o t h e v i r t u a l e l i m i n a t i o n o f s o l i d s accumulation i n the dump tank w i t h consequent impaired product f low. temporary shutdown o f s h i f t ope ra t i on f o r dump tank clean-up was encountered du r ing the modes o f ope ra t i on w i t h water recyc le.
No i n c i d e n t o f
With respect t o the water consumption, t h e f o l l o w i n g f i n d i n g s were es tab l i shed i n t h i s study:
1. The m a j o r i t y of d a i l y water usage was opera t i ona l (48-61%) fo l l owed by clean-up (31-44%) and f i l l i n g (6-8%). v a r i a t i o n s i n percentage usage i n the var ious modes o f operat ions. I n a1 1 modes o f ope ra t i on approximately 7% was f i l l i n g ; approximately 55% opera t i ona l ; and approximately 39% clean-up.
A 26% decrease i n t h e average t o t a l d a i l y water usage was r e a l i z e d when d i s c c leaner w i t h water r e c y c l e and chemical f l o c c u l a t i o n r e l a t i v e t o t h e convent ional system was appl ied.
There were no s i g n i f i c a n t
2.
1. EUTEK, INC. , Process Development and Engineering, Sacramento, CA. 2.-.-National Canners Associat ion, Berkeley, CA.
157
3. A decrease i n the average u n i t water consumption r a t e r e l a t i v e t o counter-current f l o w convent ional c lean ing occurred when water r e c y c l e measures were appl ied. A 41% decrease i n average u n i t water consumption r a t e was r e a l i z e d when the d i s c c leaner w i t h water r e c y c l e and chemical f l o c c u l a t i o n (164 g a l / t o n ) was a p p l i e d r e l a t i v e t o t h e convent ional system (278 g a l / t o n ) .
With respec t t o t h e t o t a l s o l i d s balances, t he f o l l o w i n g conclusions were drawn:
1.
2.
3.
With t h e water r e c y c l e measures implemented, t h e s o i l s o l i d s removed f rom the dump tank per tonnage o f tomatoes processed were s i g n i f i - c a n t l y reduced; the s o i l s o l i d s l o s t t o t h e sewer per tonnage o f tomatoes processed were reduced s u b s t a n t i a l l y .
The est imated s o i l s o l i d s incoming t o the p l a n t pe r u n i t weight o f tomatoes processed ranged from 10 t o 20 lbs / ton , having an average o f 13 l b s s o i l s o l i d s pe r t o n o f tomatoes processed. The t o t a l s o i l loaded was est imated from the sum o f s o i l s o l i d s which were c o l l e c t e d f rom the dump tank, l o s t t o the sewer, and removed from t h e sludge th ickener . It appeared t h a t t h e amount o f s o i l t o the p l a n t v a r i e d considerably, depending on the type o f s o i l from which t h e tomatoes were grown, the mo is tu re content o f t he s o i l when t h e tomatoes were harvested, and the method o f tomato harvest ing.
E f f i c i e n t c l a r i f i c a t i o n o f t h e th ickenes ove r f l ow requ i res sur face l oad ing r a t e s o f l e s s than 1,000 g p d / f t . Approximately one- h a l f o f t h e g r a v i t y s e t t l e a b l e s o i l s o l i d s overf lowed from the th i ckener a t sur face l oad ing r a t e s o f 2,000 gpd / f t 2 .
INTRODUCTION
.,With the advent o f mechanical ha rves t i ng o f tomatoes, tomato processors noted an increase i n t h e s o i l accumulations w i t h i n t h e f lume system. o f t h e s o i l accumulated i n the i n i t i t a l f lumes o r b i n dumps. V e l o c i t i e s w i t h i n t h e b i n dump were i n s u f f i c i e n t t o scour s e t t l e d s o i l s o l i d s from t h e base. The r e s u l t a n t accumulation o f s o i l i n the b i n dump e v e n t u a l l y impaired product f l o w and r e q u i r e d processing downtime t o remove.
Most
There a r e two w i d e l y p r a c t i c e d procedures f o r m i t i g a t i n g the accumula- t i o n o f s o i l i n t h e b i n dump. from t h e b i n dump, t h i s ove r f l ow d ischarg ing t o the p l a n t ' s sewer system. The second procedure i nvo l ves processing downtime t o d r a i n o f f excess l i q u i d s and hand shovel t he accumulated s o i l i n t o an adjacent receptac le.
The f i r s t i s t o employ a h igh ove r f l ow r a t e
Several adverse impacts r e s u l t f rom t h e c u r r e n t procedure f o r hand1 i n g - - - b i n dump mud. I n t h e case o f t he h i g h ove r f l ow ra tes , t he excess water used
adds t o t h e h y d r a u l i c surcharge t o the sewer system from t h i s seasonal i n d u s t r y . The h igh s o i l loadings discharged t o munic ipa l t reatment systems r e s u l t i n ope ra t i an and maintenance problems. As a consequence o f t he necess i t y f o r
158
p e r i o d i c a l l y s h u t t i n g down t h e b i n dump t o remove accumulated s o i l , t h e t ime requirements f o r processing a g iven tonnage o f tomatoes a re extended r e s u l t i n g i n reduc t i on o f t he p l a n t ' s p r o d u c t i v i t y . This, i n t u r n , r e s u l t s i n f u r t h e r excess water use through t h e down-time p e r i o d and f o r t he a d d i t i o n a l r e q u i r e d cleanup and washdown.
P r o j e c t Object ives
Dur ing t h e 1974 processing season, a j o i n t l y sponsored EPA-NCA p r o j e c t was undertaken t o evaluate a l t e r n a t i v e water r e c y c l e system c o n f i g u r a t i o n s . B in dump model s tud ies were then undertaken i n t h e s p r i n g o f 1975 t o develop design data on an e f f i c i e n t system f o r i n t e r c e p t i n g s o i l s o l i d s i n t h e b i n dump and t r a n s p o r t i n g them t o the s o l i d s removal system w i t h o u t i n t e r f e r i n g w i t h product f low.
The o b j e c t i v e o f t h e '75 season tomato water r e c y c l e p r o j e c t was t o demonstrate a water r e c y c l e system which when used i n con junc t i on w i t h a normal b i n dump opera t i on would s i g n i f i c a n t l y reduce the adverse impacts associated w i t h c u r r e n t p r a c t i c e s . was 'employed. The recyc led water was used t o ma in ta in adequate scour ing v e l o c i t i e s w i t h i n t h e b i n dump w i t h o u t d e t r i m e n t a l l y a f f e c t i n g product f l ow . A s o l i d s removal system was const ructed w i t h i n t h e c losed loop t o remove t h e s e t t l e a b l e so l i d s and thereby prevent t h e i r accumulation w i t h i n the b i n dump. This r e c y c l e system was expected t o e l i m i n a t e excessive water usage r e l a t e d t o h i g h b i n dump ove r f l ow r a t e s as w e l l as those r e l a t e d t o clean-up down-time and extended opera t i ona l pe r iod f o r processing a g iven tonnage o f tomatoes.
An e s s e n t i a l l y c losed loop r e c y c l e system
Process Design, Operation, and Data A c q u i s i t i o n
F a c i l i t y Design and I n s t a l l a t i o n
The key process elements were a s o l i d s t r a p p i n g f a l s e bottom; an e j e c t o r f o r s o l i d s t ranspor t ; a screen w i t h screenings discharge hopper; a s o i l s o l i d s separat ing s w i r l concentrator; a sludge th ickener ; and a chemical c o a g u l a t i o n - f l o c c u l a t i o n system. As shown on F igu re 1, t h e s o i l s o l i d s passed through t h e f a l s e bottom and were t ranspor ted by an e j e c t o r t o the g r a v i t y screen. Here vines, rocks, and debr i s were separated and the s e t t l e a b l e s o i l s o l i d s i n t h e water were rou ted t o the s w i r l concentrator . So l i ds w i t h i n the s w i r l concentrator under- f low were f u r t h e r concentrated w i t h i n t h e sludge th ickener . A mechanical device was prov ided t o enhance the g r a v i t y t h i c k e n i n g process. bottom o f t h e th i ckener f o r f i n a l d isposal .
Thickened sludge was removed from the
The s w i r l concentrator ove r f l ow was recyc led t o t h e b i n dump through standpipes t o p rov ide a mot ive f o r c e f o r both the b i n dump scour j e t s and - the s o l i d s t r a n s p o r t i n g e j e c t o r . The sludge th i ckener supernatant was re tu rned as make-up water t o the b i n dump o r was discharged t o t h e sewer. The general c o n f i g u r a t i o n o f t he r e q u i r e d m o d i f i c a t i o n s t o e x i s t i n g b i n dump tanks i s i l l u s t r a t e d on F igu re 2. Th is c o n f i g u r a t i o n was developed
159
from model studies. ( l ) I t i s capable of intercepting and removing 80%+ o f the se t t leab le so i l entering with the product w i t h o u t a l te r ing product flow. The f a l se bottom area was 4 ' x 4 ' with 1 / 2 " tubes spaced a t 1-1/4" center-to-center.
The instal led system is shown on Plates 1 A and lB. The ejector- transported soil-laden water was pumped t o the gravity screen mounted above the swirl concentrator.
Grit and sand i n the incoming wastewater were separated and discharged w i t h the underflow from t h i s uni t . r a t e . design incoming flow r a t e of 500 gpm the swirl concentrator overflow ra t e was approximately 400 gpm. Overflow was returned t o the b i n dump through the scour j e t s and t r anspor t ing e jector .
Underflow loaded the ten foot diameter gravity thickener a t approxi-
The screenings were collected i n a gondola. ( 2 ) The screened water flowed by gravity t o the swirl concentrator.
An o r i f i ce opening controlled the underflow As designed, the underflow ra te was 100 gpm. W i t h the maximum
. mately 2,000 g p d / f t 2 . The thickener overflow ra t e was approximately equi- valent t o the swirl concentrator underflow rate . Level control was provided a t the dump tank t o regulate the amount of thickener overflow returned t o the system. T h i s prevented overflow from the b i n d dump. dump was topped-off, thickener overflow was bypassed t o the sewer. assured a single overflow p o i n t from the water recycle system t o the sewer. Only c l a r i f i ed water was discharged t o the sewer.
In order t o increase the thickener underflow sol ids concentration a vibrating thickening mechanism was instal led to break down b r i d g i n g of sol ids w i t h i n the thickening zone. Vibration was activated by pneumatic impactors. externally on the cone of the thickener to a s s i s t the flow o f sol ids t o the cone apex. Pneumatic impactors provided impacts a t 60-psi pressure a t controlled time intervals .
When the b i n This
In addition t o the internal mechanism an impactor was mounted
Thickener underflow was withdrawn periodically through a 6" diaphragm Underflow sludge was collected i n gondolas for subsequent disposal. valve.
Operational Modes and Monitoring Arrangement
During the study period, the following four modes of operation were investigated:
1 . Conventional cleaning without water recycle;
2 . Conventional cleaning w i t h water recycle;
3 . Disc cleaning w i t h water recycle; and,
4. Disc cleaning w i t h water recycle with chemical coagulation- flocculation.
162
PLATE 1A VIEW OF IN-TAKE PUMP, SCREEN, SWIRL CONCENTRATOR, SLUDGETHICKENERANDTUBEFLOCCULATOR
PLATE 1B GENERAL VIEW OF WATER RECYCLING FACILITIES
163
The monitoring program objective was t o evaluate each of the four modes of operation i n terms of to ta l water consumption and t o t a l soi l sol ids removed.
Conventional Cleaning--The conventional system consisted of four stages: Tomatoes were mechanically transported by elevators between stages.
dump tank, inside flume, dis t r ibut ion flume a n d , f i n a l r inse step.
As shown on Figure 3, counter-current use of water was employed i n the conventional system. The dis t r ibut ion flume water was recycled between the d i s t r i b u t i o n flume and tank-3. r inse was pumped t o the inside flume, Excess inside flume water flowed by g rav i ty t o tank-1 . and the dump tank. A s igni f icant savings i n water consumption had already been realized i n the counter-current mode of operation re la t ive t o systems i n which each stage operates independently. the tanks on each loop such tha t water qual i ty represented the water i n each Qf the flumes as designated 5W from the dump tank, 2W from the inside flume and 6W from d i s t r i b u t i o n flume. monitor ing the various flow rates .
for mass balances. During the conventional cleaning mode a s tea l plate was placed on top of the f a l se bottom. the dump t a n k were hand shoveled i n t o gondolas for subsequent disposal. S o i l samples from the gondolas were collected for the sol id concentration determinations.
A por t ion of water equal t o the f i n a l
There was an internal recycle loop between tank-1 Excess water overflowed from t a n k - 1 to the sewer.
Composite water samples were collected from
There were a to ta l of f i ve flow meters
The water samples were used t o determine the s o l i d concentrations
Soil sol ids accumulated w i t h i n
Conventional Cleaning w i t h Water Recycle--In t h i s mode of operation, the water recycle system was added t o the conventional mode of operation. Soil sol ids &re intercepted by the f a l se bottom and were transported by the ejector and pump t o the water recycle and of f - l ine mud removal system.
for this mode of operation. sample po in t s from which composite samples were collected for water q u a l i t y analyses.
mode of operation. As a consequence, the p l a n t frequently operated w i t h par t ia l shifts. Oftentimes the processed tomato tonnage was s ignif icant ly less than the p l an t ' s capacity. a n d removal of s e t t l eab le so i l was effected by the water recycle system, i t s a f f ec t on the productivity of the p l a n t and the f u l l ramifications on water use was not accurately assessed.
On Figure 4 are shown the flow metering the sample collection points There were a to ta l of 8 flow meters and 10
Irregular del iver ies of f i e l d harvested product occurred d u r i n g t h i s
Thus, while effect ive interception, transport ,
Disc Cleaner W i t h Water Recycle --In t h i s mode of operation, tomatoes were transferred from the dump t a n k to the disc cleaner and then t o the dis t r ibut ion flume and the f inal inspection stage as shown on Figure 5.
164
3
J l ,-----,
FINAL .INSPECTION
t
a --,, t :PROCESS WArER
: MAKE UP WATER ___- a :WATER METER
@ : WT€R QUALITY S4MPLE STATION
(FURTHER PROCESSING)
SEWEF
I FIG.3- FLOW DlAGRAM OF CONVENTIONAL CLEANING SYSTEM
165
SCREEN a SWlRL CONCENTRmOR
MSTRIBUTON FLUME
8 FINAL RINSE
0 LEGEND n-
SOLIDS
63
FINAL INSPECTION
PROCESS WATER
MAKE LP WATER
SOLIDS SURRY
WATER METER
WATER W I M SAhlRE 5TAlKX
Q
SEWER
(FURTHER PROCESSING)
FIG.4- FLOW DIAGRAM OF CONVENTIONAL CLEANING WITH WATER RECYCLE SYSTEM
166
++PflNAL 7 - LEGEND
T W T O PROWCT
PROCESS WATER FINAL
INSPECTION MAKEUP WTER
SOLm SLURAY
WATER METER
@ WATER QUALITY SEWER
@ BIN WMP LEVELCONTROL
TI-! n SAMRE 5fAllcN
SOLIDS
Q (FURTHER PROCESSING)
FIG5 - FLOW DIAGRAM OF DISC CLEANER WITH WATER RECYCLE SYSTEM
3
The disc cleaner replaced the inside flume conventional cleaning process t o remove t igh t ly adherent smear s o i l . In this u n i t the long exposure of tomatoes t o the turbulent action of water was replaced by short osure
The action of the discs moved the tomatoes through the u n i t , loosened and shipped off the so i l and threw the heavy so i l water into the t ray beneath the device. The rubber disc u n i t was equipped w i t h small whirl j e t spray nozzles, located t o provide f u l l coverage of the l a s t 2 f e e t of the u n i t w i t h no overlap. swirl concentrator.
t o the vigorous mechanical shipping action of s o f t rubber discs. t39
Water was collected and pumped to the gravity screen and
Disc Cleaner W i t h Water Recycle and Chemical Flocculation--The flow diagram i n t h i s mode of operation was similar to the previous flow scheme except f o r the addition of the internal chemical coagulation and flocculation a t the thickening stage as shown on Figure 6. The primary study objective i n this mode of operation was t o evaluate the effectiveness of chemical coagulation-flocculation w i t h respect to so i l sol ids removal efficiency and wastewater quali ty t o the sewer.
The chemical coagula ti on-f locculation mechanism consisted of four components: recirculation pump, tube f locculator , sl ip-stream turbidimeter, and chemical feeding mechanism. gri t tube, a 10" diameter t u b e surrounding the swirl concentrator underflow. Grit se t t l ed through the tube while t u r b i d underflow waters were withdrawn. A po r t ion of the flow was directed into the slip-stream turbidimeter which continuously monitored the turbidi ty . The chemical feed was automatically controlled t o be proportional t o the level of turbidi ty of the water.
The recirculat ing pump withdrew from the
The coagulant mix in and flocculation processes were accomplished i n a novel tube flocculator 9 4 ) comprised of a se r ies of discrete pipe sections. These pipes were coiled around the outer wall of the thickener, each down- stream section having a progressively larger diameter w i t h d iverg ing t rans i t ion members connecting adjacent sections. The coi l curvature and pipe diameter were careful ly pre-determined to e f f ec t a flow condition velo- c i t y gradient yielding optimum coagulation-flocculation resu l t s i n m i n i m u m time.
Plant Operation and Data Acquisition
The p l a n t operation and data acquisit ion comnenced w i t h the tomato season s t a r t d u r i n g the l a t t e r p a r t of August, 1975. t ions a re l i s t e d chronologically i n Table 1. e n t i r e season of tomato processing which lasted about 2 months.
The schedule of opera- The study period covered the
The plant operated three 8-hour s h i f t s per day, 6 days per week. .. - There were approximately 4 operators involved i n each s h i f t . One operator
was controll ing the r a t e of tomatoes t o the b i n dump and the other three operators were involved i n the following tasks:
168
1 I I I I I
I I I I I I I I I I I
-----
CCNCENTRATOR I
FLOCCULATOR U I
THICKENER 4 'I I.. t
MSTRIBUTICN FLUME I ) \ I
TANK.3
r FINAL I
LEGEND
U- 4
____--
PRODUCT 1' I INSPrCTlON I I *PROCESS WATER I i
t
8 SOLIDS
L--J--z:;wz: SEWEF + n *WATER METER
@ *WATER QUALITY SAMPLE STATION
Q "WMPLNELCONTROL
-
(FURTHER PROCESSING 1
FIG.6- FLOW DIAGRAM OF DSC CLEANER WITH WATER RECYCLE SYSTEM WITH FLOCCULATION
169
TABLE 1
CHRONOLOGICAL LISTING OF THE MODES OF OPERATION
Per iod o f Operation Modes o f Operation
3 Sept - 9 Sept, 1975 1 Conventional c lean ing
10 Sept - 14 Sept, 1975 Conventional w i t h Water Recycle
16 Sept - 20 Sept, 1975 & 30 Sept - 8 Oct, 1975
Disc Cleaner w i t h Water Recycle
I
22 Sept - 29 Sept, 1975 9 Oct - 11 Oct, 1975
Disc Cleaner w i t h Water ReCYCle and Chemical Coagula- t i on -F loccu la t i on
I
170
1. Organizat ion o f tomato b ins f o r processing;
2. Removal o f v ines and debr i s f rom v ine c o l l e c t o r s ;
3.
Three f u l l - t i m e NCA operators , one i n each s h i f t , were a t t h e p l a n t
1. Taking water meter readings a t t he beginning and end o f each s h i f t ;
Ma in ta in ing and clean-up o f the process ing f a c i l i t i e s .
throughout the s tudy per iod. The d u t i e s o f these operators were:
2.
3.
Taking sludge samples, one a t each s h i f t ;
Taking tomato product samples i n each s h i f t a t each washing stage;
4. Recording events and general observat ions;
5. Recording t o t a l number o f b ins processed;
6. Tabu la t ing r e s u l t s .
I S C O automat ic water samplers were used a t a l l sampling p o i n t s except two, one a t t h e i n f l u e n t water t o t h e s w i r l concentrator and the o the r a t t h e sludge th i ckener over f low. Roto Vee sampler developed by EUTEK was used. s i s t e d o f sample c o l l e c t o r , motor and remote c o n t r o l l i n g t imer . The Roto Vee, because o f i t s s imple design and operat ion, was e f f e c t i v e i'n c o l l e c t i n g samples having r e l a t i v e l y h igh s o l i d s concentrat ions such as the wastewater incoming t o t h e s w i r l concentrator , t i o n s was done w i t h a core sampler which c o l l e c t e d rep resen ta t i ve mud samples f rom deposi ted so i 1 so l i ds .
A t these sampling po in ts , an automat ic The Roto Vee sampler con-
Sampling f o r sludge so l i d s concentra-
I n t e r p r e t a t i o n o f Resul ts
Analys is o f Water Consumption
Water usage i n a t y p i c a l tomato processing p l a n t can be ca tegor ized as :
1. F i l l i n g
2. Operat ion o r process
3. Clean-up
F i l l i n g water represented t h a t used t o f i l l the dump tank and flumes. I t was normal ly requ i red a t t he end o f each washing pe r iod and p r i o r t o t h e beginning of t h e fo l l ow ing opera t ion s h i f t . Process water used f o r
171
opera t ion was t h a t which was cont inuous ly u t i l i z e d dur ing the s h i f t opera- t i o n , such as b i n wash, cont inuous spray onto t r a s h b e l t s f o r c lean ing pur - poses and f i n a l r i n s e waters. opera t ion pe r iod f o r c lean ing f l o o r s and f o r clean-up tanks, f lumes and o the r equipment du r ing the normal clean-up per iod. To ta l water consumption i n a t y p i c a l tomato processing p l a n t was the sum o f a l l t he water used f o r each above-mentioned purpose.
Clean-up water was used both dur ing t h e
The Average Water Consumption Rates--The t o t a l and u n i t water consump- t i o n r a t e s have been averaged and summarized i n Table 2.
I n t h e convent ional c lean ing mode, which represented an average o f s i x days operat ions, t he average amount o f tomatoes processed was 481 ton/day; t o t a l water usage was 133,500 gal/day; y i e l d i n g an average u n i t water consumption r a t e o f 278 g a l / t o n o f tomatoes processed.
As i n d i c a t e d on F igure 3, t he convent ional c lean ing system u t i l i z e d an e f f e c t i v e counter-current f l o w scheme, thereby reducing t o t a l p l a n t water u-sage s i g n i f i c a n t l y below t h a t o f o the r tomato p lan ts . p l a n t s w i t h o u t counter -cur ren t use o f process waters have b en repo r ted t o u t i 1 i ze approx imate ly 1200 g a l / t o n o f tomatoes processed. (57 S i g n i f i c a n t savings i n water volume used can be achieved through u t i l i z i n g counter- c u r r e n t f l o w measures. I n t h i s study, t he comparison o f the water r e c y c l e system w i t h o f f - l i n e mud removal was made r e l a t i v e t o a system i n which maximum water conservat ion through counter -cur ren t measures had a l ready been e f fec ted .
over f o u r consecut ive days o f operat ion, the average amount o f tomatoes processed was 445 ton/day; average water consumption was 109,100 gal /day. The average u n i t water consumption r a t e was 245 ga l / t on o r tomatoes processed.
Conventional tomato
The second mode o f convent ional opera t ion w i t h water recyc le averaged
Due t o the i n t e r m i t t e n t and i r r e g u l a r d e l i v e r y o f f i e l d harvested product du r ing t h i s per iod, t he r e s u l t i n g u n i t water usage r a t e should be viewed as suspect. S h i f t operat ions were f r e q u e n t l y l i m i t e d by q u a n t i t y o f tomatoes t o process. It would be expected under normal opera t ing cond i t i ons i n which q u a n t i t y o f f i e l d harvested products d i d n o t l i m i t p l a n t opera t ion t h a t t h e u n i t water usage i n t h i s mode o f opera t ion would be s i m i l a r t o t h a t found i n the o the r water recyc le modes o f operat ion.
Under the mode o f opera t ion o f d i s c c lean ing w i t h water recyc le , over twelve days of operat ion, t he average amount o f tomatoes processed was 594 ton/day and the average water consumption was 92,800 gal/day. The average u n i t water consumption r a t e was 156 g a l / t o n o f tomatoes processed. I n t h e f i n a l mode o f opera t ion o f d i s c c lean ing w i t h water recyc le w i t h chemical f l o c c u l a t i o n over e i g h t days o f operat ion, t he average amount o f tomatoes processed was 605 ton/day; w i t h an average water consumption o f 99,000 gal /day. The average u n i t water consumption r a t e was 164 ga l / t on
-Of tomatoes processed.
Several observat ions and conclusions can be drawn:
172
co P
I N
LD
* N W
In 7
d
W
7
0
5: m
m 7
0 0
m 0
7
7
0
0
N
m
"0,
F
4
01
v
c
0
c, Q
.r
5 ul c
0
V
L
W
c,
a)
4 L
W
>
4:
m
c Q
3
I K 4
a)
V
- 0 0
'". 7
d
0 0
In
d
7
0
0
In
d
r
7
4
K
0
c,
l8 L
a)
0
.r
n
0
0
m
co 7
0
0
m
m
co, 0 0
r,l
e
d
0
0
7
7
In
0 0
W
5
01
K
.C
?
- .r U In
* d d
m
In
In 0
W
W 3
l8 >
a)
cn 4
L
W
>
E
7
a 2 4
W
v,
c
K
0
173
1 . The tonnage of tomatoes processed daily increased substant ia l ly during the disc cleaner modes of operation. the tonnage of tomatoes processed was realized w i t h the disc cleaner w i t h water recycling and chemical flocculation re la t ive t o conventional cleaning w i t h o u t recycle. T h i s increase may be due t o the increase i n the soi l solids removal efficiency from the dump tank such tha t there was no s ignif icant accumulation of sol ids i n the dump tank which hindered the tomato processing operation. No incident of temporary shutdown of the operation was encountered d u r i n g the modes of operation w i t h water recycling measures.
A 26% increase in
2. A decrease of 26% i n average to ta l daily water usage i s realized w i t h disc cleaning w i t h water recycle and chemical flocculation re la t ive t o conventional cleaning w i t h o u t recycle. Decreases i n water usage were noted i n bo th clean-up and operation.
A s ignif icant decrease i n the average u n i t water consumption ra te occurred when disc cleaning w i t h water recycle was applied. 41% decrease in average u n i t water consumption ra te was realized when disc cleaner w i t h water recycling and chemical flocculation was applied re la t ive t o conventional cleaning w i t h o u t recycle.
3. A
Table 3 presents the percentage of average water consumption by operation mode. by clean-up (31%-44%) and f i l l i n g (6%-8%) purposes. cant variations i n percentage of daily to ta l under various modes of operation. Approximately 7% of daily water usage was f i l l i n g ; 55% for operational; and, approximately 39% for clean-up purposes.
The majority of daily water usage was operational (48%-61%) followed There were no s ign i f i -
Flow Balance i n Water Recycle Modes--The average flows t o the swirl concentrator during each of the three shifts for each operational mode investigated a re shown i n Table 4. about 100,000 ga l / sh i f t for a l l three operational modes. Flows were consistently lower d u r i n g the second sh i f t re la t ive t o the f i r s t and t h i r d s h i f t .
Flows t o the swirl concentrator were
There i s no apparent explanation.
For the operational modes w i t h water recycle the only source of water The average thickener discharged t o the sewer was the thickener overflow.
overflow t o the sewer (equal t o the total make-up water) i s a lso shown i n Table 4. The volume o f thickener overflow t o the sewer was approximately the same for a l l three water recycle operational modes.
t ra t ions under the various operational modes. the dis t r ibut ion flumes, there was no s ignif icant difference i n sol id concentrations. centration t o the sewer with water recycle.
---overflowed t o the sewer i n the conventional cleaning system. Between G % t o 3,000 mg/l o f s o l i d overf1oi;ed when recycle and reuse measures were used.
Mass Balance Analysis--On Table 5 a re presented the to ta l s o l i d concen- For the dump tank and inside
However, there was a s ignif icant reduction i n solid con- E i g h t thousand mg/l of s o l i d
174
t c( I v)
7
41
C
o
w *
*r- v
WU
O
Ch
?
0) v
l.L
>al
cp
: 0
8,'s
-
L
8 v) 0
c,
3
0
Y- L
W
> 0
4
c, 0
I- W
cn 4 L
al >
4:
7
7
-
L
0
c,
4 L
c, c
al V
c
0
V
L 3
v)
0
c,
7
.r-
B - LL
9
c,
- I-" 0)
cn 4
L
al >
4: -
L
al
l
c
40
,
al- v
-uo
Va
l
VI=
0
"&
S's
's
W
CY F
c
0
aJ *r
WY
-c
,
20: n
0
0
0
r- '0, - In
d
0 0
10 Y
F
0
0
o?
h
W
N
0 0
m
w
d
N
8
". W
W
d
W
N
0
0
d
0
o?
L
all
C
ma
l
176
0
m
N
m
0
m
e
Io
0
W
d
W
0 0
pz
0, 0 0
In
0,
0 0
W
0,
m
0 0
0, 7
0 0
aJ
0 0
cu 0,
I I
0
8
0
0 e
0
z:
8
0. 7
I I I I
0 0
e
0,
I I I I
177
The suspended s o l i d s concen t ra t i on i n the over f low from the sludge th i ckener du r ing the '75 season study was two- fo ld h igher than observed du r ing the ' 7 4 season study. Dur ing the ' 7 4 season study, t he th i ckener had been loaded a t approximately 1,000 g a l / d a y / f t z . t h i ckener was low enough t o i nsu re c l a r i f i c a t i o n o f the s w i r l concentrator underf low waters. mately 300-500 mg/l. I n the '75 season study, t he sludge th i ckener overf low r a t e was increased t o 2,000 ga l /day / f t 2 . i -esul ted i n an increase i n the ove r f l ow s o l i d s concentrat ions. It would appear t h a t t o achieve acceptable s o l i d s concentrat ions i n the th i ckener over f low the l oad ing should be maintained a t approximately 1,000 gpd / f tZ o r less.
Turbulence i n the
Thickener over f low s o l i d s concentrat ions were approx i -
The increased turbulence presumably
The s o l i d s concen t ra t i on i n the i n f l u e n t t o the s w i r l concentrator ranged from 6,000 t o 8,000 mg/l f o r a l l water r e c y c l e modes o f operat ion. The s o l i d s t o the s w i r l concentrator were those i n t e r c e p t e d by the f a l s e bottom and t ranspor ted by the e j e c t o r exc lud ing those separated by the g r a v i t y screen. The f a l s e bottom was q u i t e e f f e c t i v e i n i n t e r c e p t i n g s e t t l e a b l e s o i l s o l i d s . I n the convent ional c lean ing mode w i t h r e c y c l e $he b i n dump s o l i d s concen t ra t i on was 4,000 mg/l as compared t o 8,000 mg/l i n t h e i n f l u e n t t o the s w i r l concentrator .
So l i ds separated by the screen were p r i m a r i l y tomato seeds. 30 f t 3 of s o l i d s were c o l l e c t e d from the screen d a i l y . were p r i m a r i l y generated from broken tomatoes they were n o t taken i n t o account as s o i l s o l i d s loaded t o the p l a n t w i t h incoming raw tomatoes.
Approximately Since these s o l i d s
Comparing the s w i r l concentrator ove r f l ow s o l i d concentrat ions w i t h
This was t r u e f o r a l l modes o f opera- t h a t o f i n f l u e n t , i t was noted t h a t a reduc t i on o f o n l y 1,000 mg/l i n s o l i d concen t ra t i on was r e a l i z e d . t i o n . This r e s u l t i n d i c a t e d t h a t the m a j o r i t y o f t he s o l i d s were n o t s e t t l e - able. The s o l i d removal e f f i c i e n c y by the s w i r l concentrator was apparent ly a f f e c t e d by t h e p a r t i c l e s i z e d i s t r i b u t i o n o f t he s o i l , i n a d d i t i o n t o t h e o t h e r design parameters. on t h e type o f s o i l f rom which the tomatoes were grown, The type o f s o i l , t h e mois ture content o f t he s o i l when the tomatoes were harvested and t h e method o f tomato ha rves t i ng a l l a f f e c t e d the amount o f s o i l s o l i d s c a r r i e d t o t h e processing p l a n t . These "unaccountable" f a c t o r s might e x p l a i n t h e v a r i a t i o n s i n some o f t h e r e s u l t s obtained du r ing the p e r i o d o f study.
The p a r t i c l e s i z e d i s t r i b u t i o n was, i n t u r n , dependent
Dur ing t h e mode o f ope ra t i on o f the d i s c c leaner w i t h water r e c y c l e and chemical c o a g u l a t i o n - f l o c c u l a t i o n , a se r ies o f j a r t e s t s were conducted t o determine t h e optimum coagulant (Calgon Cat-Floc) concentrat ion. view o f t he d a i l y v a r i a t i o n s i n s o i l c h a r a c t e r i s t i c s , j a r t e s t s were conducted f o r several days. Resul ts i n d i c a t e d t h a t t he des i red coagulant concentra- t i o n ranged from 7 t o 15 mg/l.
I n
D i f f i c u l t i e s were encountered i n sampling du r ing the l a t t e r p a r t o f The composite samplers were o u t o f order, and, conse-
quent ly , t he grab sampling technique was used. i n s o l i d s concentrat ions i t was d i f f i c u l t t o c o l l e c t rep resen ta t i ve grab samples. t o t h e sewer.
- The study per iod. Due t o the sharp v a r i a t i o n s
This made i t d i f f i c u l t t o evaluate the q u a l i t y o f water overf lowed
178
Under convent ional c leaning, the t o t a l s o i l s o l i d s which were loaded t o t h e p l a n t were est imated f rom t h e sum o f s o i l s o l i d s accumulated i n the dump tank and l o s t w i t h over f low from the flumes t o the sewer. The former was determined by t h e t o t a l volume and concent ra t ion o f s o i l s o l i d s shoveled i n t o t h e gondolas. The l a t t e r was determined by t h e t o t a l over f low volume and s o i l concent ra t ion t o t h e sewer. For example, on September 4 t h the re were a t o t a l o f 11,779 l b s o f s o i l s o l i d s t o t h e p l a n t . O f t h i s , 7,384 l b s were est imated t o be l o s t t o the sewer w h i l e 4,395 l b s were shoveled o u t o f t h e dump tank i n t o gondolas. processed; t h e s o i l l oad ing per u n i t o f tomatoes was, f o r t h i s p a r t i c u l a r day, 24 l b s / t o n o f tomatoes processed, o r , s l i g h t l y i n excess o f 1% o f raw product weight ,
There were a t o t a l o f 489 tons o f tomatoes
Under t h e convent ional mode w i t h water r e c y c l e the t o t a l s o i l s o l i d s incoming t o t h e p l a n t were f rom th ree sources: dump tank, l o s t t o t h e sewer, and removed from t h e th ickener . For example, on September 10 th the re was a t o t a l o f 5,451 l b s of s o i l t o the p l a n t . O f t h i s , 1318 l b s were removed from the dump tank, 2,103 l b s were l o s t t o t h e sewer, and 2,030 l b s were removed f rom the th ickener . Since t h e r e was a t o t a l o f 433 tons o f tomatoes processed on t h i s day, the u n i t s o i l l oad ing per t o n o f tomatoes processed was 13 lbs / ton . were made on a l l data co l l ec ted .
s o i l s o l i d s removed from the
S i m i l a r d a i l y analyses
Average S o i l Loadings--Table 6 presents t h e average t o t a l s o i l loadings and t h e u n i t l gad ing r a t e s under each mode o f operat ion. As shown by t h e second column o f Table 6, approx imate ly 3,800 lbs/day o f s o i l s o l i d s were removed f rom t h e dump tank i n t h e convent ional mode w i thou t recyc le . Th is represents a u n i t s o i l l oad ing o f 7.9 l b s / t o n o f tomatoes processed. A s i g n i f i c a n t decrease i n s o i l s o l i d s removed from the dump tank was noted as the water r e c y c l e was implemented. For example, t he re were o n l y 1,447,
1293 and1244 lbs/day o f s o i l s o l i d s removed f rom t h e dump tank f o r conven- t i o n a l w i t h water recyc le, d i s c c leaner w i t h water recyc le , and d i s c c leaner w i t h water r e c y c l e and chemical coagulation-flocculation, respec t i ve l y . The u n i t s o i l s o l i d s removed f rom t h e dump tank were 3.3, 2.2, and 2.1 l b s / t o n r e s p e c t i v e l y f o r these th ree modes o f operat ion.
Data i s presented i n t h e f o u r t h and f i f t h columns o f Table 6 t h a t i n d i c a t e s t h a t t he re were 12.5 l b s o f s o i l per t o n o f tomatoes processed l o s t t o t h e sewer under convent ional c lean ing whereas the re were 4.1, 1.3 and 0.9 l b s / t o n l o s t t o t h e sewer i n modes w i t h water recyc le . t h a t s o i l s o l i d s l o s t t o the sewer decreased as water r e c y c l i n g was implemented.
Three p o i n t seven (3.7), 6.4, and 8.3 lbs o f soil/- i;on o f tomatoes processct
This i nd i ca tes
were removed f rom t h e th ickener i n t h e convent ional c leaning, d i s c c leaning, and d i s c c lean ing w i t h chemical f l o c c u l a t i o n modes, respec t i ve l y . Th is i n d i c a t e s t h a t t h e u n i t weight o f s o i l s o l i d s removed from the th ickener increases as more soph is t i ca ted removal measures such as chemical f l occu - l a t i o n were implemented.
I n t h e l a s t column a re presented the average s o i l s o l i d s l oad ing per u n i t o f tomatoes processed. ikienty, 11, 10, and 11 i b s o f s o i l / t o n of tomatoes processed were accounted f o r i n the convent ional , convent ional w i t h
-
179
L
W4
- c
no
0 o
C,C,
?u
m \
.r .r E
VI oco n
"3
l-
?
0
7
0
cu
?
W
m
03 h
rr) I I
\
VI n
7
v
- h
ry) -0
\
VI n
?
Y
0s
"C,
I I
c5
c 0
c, \
VI n
?
Y
m 0
ln
cu r
C,
VI 0
a
VI -0
r-L
o
w
?In 00
"C,
.C
"E
.r
m
F
*
h
cf pr
h
* ln
c 0
Y
01 h
0
m
cu cu
7
ru Y
m
ol ru 7
ID
h
m
m
d
x -
E
.r 0
OL
v)L
L
Y
ln 0
W
ln
d
d
* m ln - W
*
--
U
0
LL
?
U
0
LL 7
0
\ I
- 0
\ 3
L
WI
K
m
w
W-
-v
uz,
V
uw
VI=
.r \
03
?
4 c 0
C,
W t
c 0
u
.I-
L
W
0
4- 0
n
mi
c
ow
180
a
recycling, disc cleaner w i t h recycling, and disc cleaner w i t h recycling and chemical f locculation modes, respectively.
Several important conclusions can be drawn from the observations above:
1 . The apparent plant capacity for tomato processing increased with disc cleaning and water recycle.
2. The soi l sol ids removed from the dump t a n k per u n i t weight of tomatoes processed decreased s ignif icant ly as water recycling was applied.
3 . Soil loads to sewers per tonnage of tomatoes processed decreased a s water recycling was implemented.
4. Soil solids removed from the thickener per u n i t weight of tomatoes processed increased as water recycling was applied.
5. Incoming soi l sol ids per ton of tomatoes processed ranged from 10 t o 20 lbs/ton, having an average of 13 lbs of so i l per ton of toma toes processed.
Distribution of Soil Loadings--An analysis of soi l sol ids d i s t r i b u t i o n under each operational mode i s presented in Table 7. N i t h conventional washing, 39%’of the soi l was accumulated i n and removed from the dump tank. The balance of 61% was discharged t o the sewer.
The percentage of soi l sol ids discharged t o the sewer sharply decreased a s water recycling was implemented. In the conventional mode w i t h water recycle, 37X of the soi l sol ids were discharged t o the sewer. modes of operations with the disc cleaner, the percentage of soi l sol ids discharged t o the sewer decreased substantial ly.
For bo th
Soil sol ids accumulating i n and removed from the dump tank were reduced s ignif icant ly i n modes of operation w i t h recycle. so i l sol ids were effect ively intercepted and transported t o the swirl con- centrator . Only a small percentage of soi l sol ids accumulated i n the dump t a n k .
The majority of the se t t leab le
Economic Significance of Water Recycle W i t h Soil Removal
An economic evaluation was made of a typical tomato processor dischar- g i n g t o a municipal sewer. Charges for t h i s service a re usually established by the municipal agency so tha t the operating cost of i t s f a c i l i t y a re varied and dis t r ibuted according t o usage. However, t h i s practice often may be unfavorable t o the average tomato processor who operates on a seasonal basis.
181
I- w 0
d n
U 0
z
z L Y a
v)
73 .-
Y
- e- 0 Q
M
Lo
+- c 0
u
.I-
;r, L
W n
0
Y-
O
I I
e
W
0)
m c
W
>
ET 0
0
m
m h
m 0
m
v)
ui m e
N
N
V 0
LL 7
0
\ 3
L
WI
c
QW
W
I- c
v
v >
, V
o
w
lncT
.r-\ 03
d
h
W
W c
U 0
LL \
7
3
L
WI
c
QW
0-
I-v
V>
V
v
w
In-
..-\ (33
182
3
Cos t-Ef fec t i veness Eva1 ua t i on
On Table 8 are l i s t ed the industr ia l wastewater charges fo r Sacramento County, California as proposed fo r 1978.(6) Total charge i s the sum of f ive items: demand charges, loading charges, service charges, monitoring charges, and potable water use charges. in-plant water recycle w i t h so i l removal fo r the tomato processor, an evalua- t ion was made based on the parameter values obtained i n this study as l i s t e d on Table 9.
To i l l u s t r a t e the economic significance of
The following assumptions a re made:
1 . Period of operation - 60 days.
2.
3.
Solid (sg 1.5) concentration of the mud from the dump tank - 60%.
Solid (sg 1 . 2 ) concentration of the sludge from thickener - 30%.
4. Total u n i t so i l loading r a t e - 15 lbs/ton tomato processed.
5. U n i t so i l loadings (based on the average so l id dis t r ibut ion as indicated i n Table 6 ) .
Soi 1 Solids Removal
Soil Solids Removed From Thickener (1 bs/ton) from Dump Tank (lbs/ton)
Conventional In-P1 ant Treatment
5.9 2 .7
-- 11.1
6. Solid hauling cost - $3.00/yd3
7. In-plant f a c i l i t i e s cost - $40,000 Useable l i f e - 5 years, s t r a igh t l i ne depreciation Operational and maintenance cost - $20,000 annually fo r a l l systems.
8. Service - 2 miles - 8" diameter or 16 diameter inch miles.
The to ta l estimated annual cost consists o f the charges fo r dischar- g i n g in to the municipal sewer system, sludge hauling cost for hauling the collected sol ids t o the disposal f i e l d , the annual capital cost fo r i n - plant pre-treatment f a c i l i t i e s and annual operational and maintenance cost . The industrial wastewater charges i n Sacramento County by this typical tomato
rocessing plant w i t h and without in-plant treatment a re compared i n Table TO. The evaluation indicated tha t approximately $1.80/ton of tomatoes pro- cessed would be charged without water recycle and so i l removal. $.30/ton of tomatoes processed would be charged i f in-plant treatment were
Approximately
- implemented.
183
TABLE 8
4. Mon i to r i ng charge, per month
5. Potable water use charge, per 1,000 ft3
MOVTHLY INDUSTRIAL WASTEWATER UNIT CHARGES SACRAMENTO COUNTY, 1978
126.75
0.85*
1. Demand Charges Peak flow r a t e , per MGD Peak SOD loadins, Der lb/day Peak SS qoading, per l b l d a y
$ 1,069.00 0.39 0.10
2. Loading Charges Volume, per MG BOD5 Der 1,000 1 b SS, per 1,000 lb
85.25 43.00 42.80
3 . Serv ice charge for handl ing t h e f low, per diameter i n c h m i l e 17.00
184
TABLE 9
AVERAGE TOMATO PROCESSING PLANT \.IASTE!JATER PARAMETERS (BASED ON '75 SEASON STUDY)
I In -P lan t
Treatment and Conservation
Systems 1
Parameter
2. Average D a i l y Tomatoes Processed During Processing Season (ton/day)
3. Average D a i l y (Peak Monthly) Wastewater Flow Rate Dur ing Processing Season. (gal/day)
Conventional System
480
140,000
1. Average U n i t Water Use Rate (ga l / ton 1
4. Peak D a i l y Tomatoes Processed During Processing Season. ( ton lday)
280
520
I
5. Estimated Peak D a i l y Wastewater Flow Rate Dur ing Processing Season. (ga l l day )
6. Estimated Average Suspended So l ids (SS) Concentrat ion o f Wastewater. (mg/l)
7. Average Chemical Oxygen Demand (COD) o f Wastewater (mg/l,)
155,000
8,000
~--
2,750
I
8. Estimated Average 5-Day Biochemical Oxygen Demand o f Wastewater (mg/l )
1.100
160
600
90.000
1 DO, 000
800
185
TABLE 10
ESTIMATED ANHUAL MUIIICIPAL CHARGES TOMATO P R O C E S S I X KITH kdll WITHnliT II4-PLHilT TREATMENT
Estimated lAverag1 U n i t Costs f o r I
System Charge Basis Conventional
($ / ton)
1. Demand Charges Based On: Peak Flow Rate $ 0.07 Peak BOD's Loading 0.73 Peak SS Loading 0.43
2 . Loading Charges Based On: To ta l Flow 0.02 Tota l BOD's Loading 0.12 Tota l SS Loading 0.83
3. Serv ices Charges 0.02
4. Mon i to r ing Charges
5. Potable Water Use Charge
Estimated Tota l Annual Mun i c i pa l Charges $ 1.76
186
Estimated Average U n i t Costs f o r an n-Plant Treatment
System ($ / ton)
$ 0.03 0.11 0.02
0.01 0.95 0.14
0.02
0.01
$ 0.31
On Table 11 are compared the t o t a l annual costs w i t h and w i thou t i n - p l a n t pre-treatment. O&M increase, due t o the sav ing i n t h e munic ipa l charges, t he t o t a l annual u n i t c o s t savings i s est imated t o be approximately $1.3l / ton o f tomatoes processed w i t h i n - p l a n t t reatment. through use o f t he i n - p l a n t t reatment system demonstrat ing t h a t i n - p l a n t t reatment i s a c o s t - e f f e c t i v e approach.
While both cos ts i n sludge hau l i ng and i n - p l a n t
An est imated 53% savings would be r e a l i z e d
REFERENCES
1.
2.
3..
4.
5.
6.
B i n Dump Tank G r i t C o l l e c t i o n and Transpor t System Model Study, EUTEK, Report prepared f o r NCA, June 1975.
The S w i r l Concentrator, EPA R2-72-008, September 1972.
Cleaning and Lye Pee l ing o f Tomatoes Using Rota t ing Rubber Discs, Western Regional Research Center, USDA and Nat iona l Canners Asso- c i a t i o n , A p r i l 1974.
F l o c c u l a t i o n Apparatus, U.S. Patent No. 3,933,642, January 20, 1976.
L i q u i d Wastes f rom Canning and Freezing F r u i t s annd Vegetables, 12060 EDK, August, 1971.
EPA
I n d u s t r i a l U n i t Charge Rates i n Sacramento County, CA, D i v i s i o n o f Water Q u a l i t y , Department o f Pub l i c Works, County o f Sacramento.
187