INVESTIGATION OF AN ANAEROBIC-AEROBIC LAGOON SYSTEM

TREATING POTATO PROCESSING WASTES

Dr. James N. Dornbush* Dwayne A. Rollag*

William J. Trygstad**

INTRODUCTION

Various methods of treating potato processing wastes have been utilized during the past years, however, very limited data are available in the 1 iterature demonstrating the effectiveness of an anaerobic- aerobic la oon system for treating these wastes. Midwest Foods Corporation 4 formerly Fairfield Products, Incorporated) of Clark, South Dakota, presently utilizes such a system to treat the waste water generated from the production of frozen French-fried potatoes. The following discussion provides a case hi story of the successes and failures of the system.

When the potato processing plant was constructed prior to the 1970- 71 season, relatively little consideration was given to design and operation of the waste handling system. The waste water treatment facilities consisted of a screen and 25-acre stabilization pond. After the initial operating season in 1970-71, numerous complaints regarding offensive odors from the system were received by company and state authorities. Data obtained in June 1971 revealed that the stabilization pond was severely over1 oaded. The five-day biochemical oxygen demand (BOD5) of the liquid contents was 1180 milligrams per liter. Acting upon the complaints, state authorities directed the company to construct facilities capable of satisfactorily treating the wastes prior to the 1971-72 processing season.

*Professor and Associate Professor, Civi 1 Engineering Deparment, South Dakota State University, bookings, South Dakota. **Sanitary Engineer, Zenk Engineering, Albert Lea, Minnesota.

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Waste water flows and charac te r i s t ics had not been measured a t the processing plant; consequently, empirical design was a necessity. After discussions with representatives of the s t a t e , EPA, and the Civil Engineering Department a t South Dakota State University, the consulting engineers designed an anaerobic lagoon followed by a mechanically aerated basin proceding the existing s tab i l iza t ion pond. The anaerobic lagoon and aerated basin were has t i ly constructed by the company i n one corner of the existing pond although aeration equipment was n o t instal led unt i l March 1972.

Dur ing the 1971-72 potato processing season, waste water flows and charac te r i s t ics were studied1 t o evaluate the treatment system. Approximately 3500 gallons of water per ton of raw potatoes were used d u r i n g t ha t season and a l l units of the treatment system were severely overloaded, both hydraulically and organically. Removal e f f ciency of the pa r t i a l ly completed units was low. The e n t i r e system operated anaerobically and nuisance odors continued to generate compla nts. The h i g h water usage i n the plant coupled with unusually h i g h ra infa l l caused excessive dike erosion and ultimate disposal of the waste water from the plant during the coming season was a serious concern.

The company ins t i tu ted an intensive campaign of i n - p l a n t changes aimed a t waste reduction and water conservation a f t e r the 1971-72 operations including the ins ta l la t ion of a dry-abrasive peeler, elimination of the peel from the waste water, recirculat ion of flume water, and cooling water reuse plus numerous minor a l te ra t ions . The anaerobic lagoon was covered w i t h a two-inch layer of Styrofoam plus a straw mat to conserve heat and control odors. The aerators were also operated continuously throughout the summer and the 1 i q u i d contents of the s tab i l iza t ion pond were recirculated through the aerated lagoon t o a i d the recovery of the system and a l l ev ia t e the odors.

Evidence of recovery of the system was f i r s t noticed i n March 1973 and aerobic conditions prevailed i n the s tab i l iza t ion pond a t t h i s time. The 1973-74 waste discharge permit, issued by the South Dakota Department of Environmental Protection, required the company t o monitor i t s waste discharges and loadings t o the various treatment units. Data collected through t h i s monitoring program made i t possible t o determine the value of the anaerobic pond and the flow-through aeration basins for the treatment of potato processing wastes a t l i t t l e additional expense. Consequently, a more complete investigation of the anaerobic-aerated lagoon system was undertaken to determine both the condition of the treatment uni ts prior t o the 1973-74 processing season, and the loading and removal efficiency of the treatment uni ts .

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I

PLANT DESCRIPTION

Figure 1 is a f low diagram of the processing p l a n t operations. The production l i ne , approximately 600 f e e t i n length, i s basically a "straight-through" process. I n i t i a l l y , the raw potatoes are transferred from storage t o the mudp i t by fluming. Soi l and small quant i t ies of organic matter tha t s e t t l e i n the mudp i t a re pumped, as " s i l t water", periodically to a waste-receiving p i t while the flume water i s recycled.

The potatoes a re then conveyed over a scale into the preheat tank from which they are immersed i n a hot caustic solution to loosen and soften the skin. The resu l tan t highly a1 kal ine organic peel, which has the appearance of peanut but ter , i s pumped to a p i t , or a 500-gallon t a n k truck and transported from the plant to be combined w i t h corn s i lage and used as c a t t l e feed.

Peeling i s accomplished by a dry abrasive peeler.

The peeled potatoes pass on to a trim table where cu l l s and eyes are removed manually. The trimmed potatoes pass t o a holding t a n k from which they are augered to the French-fry cu t te rs . Sl ivers and other small pieces unsuitable for packaging are removed by automatic separators and other defective f r i e s a re removed manually. Culls, eyes, s l ivers and defects a re deposited in the waste flume.

The cut f r i e s are treated by a blanching process t o prevent discoloration and preserve the product. After the f r i e s are dewatered using a vibrating screen, they are precooked i n a deep-fat cooker. Excess cooking oi l i s removed using another vibrating screen. Wastes from blanching and cooking, including small amount of o i l , reach the raw waste stream.

Subsequently, the French-fries enter a two-stage deep freeze and then are .sized- automatically. Wastes include cooling wa defrosting operation and the rejected f r i e s from the s i z which are used as livestock feed. After packaging, transported t o another deep freeze t o await shipment.

As shown in Figure 1, the flume s i l t -water and raw streams evolved d u r i n g sor t ing, cut t ing, blanching, cookin were a l l flumed to the waste-receiving p i t , pumped

e r during the ng operation the f r i e s a re

waste water and freezing

t o a 20-mesh v i b r a t i n g screen and discharged by g r a v i t y . t o the lagoon treatment system. The caust ic peelings, screened sol ids and sol ids produced by the sizing operation were removed from the plant by trucks for livestock feed.

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1, Raw

Potatoes Recycled Water S i l t Water

[11 Scale

I Freezing --I Cooling Water

Preheat Tank

S1 udge Receiving

P i t

Caustic Peel L

I Trim Table

4 Fry Cutter &Sorter’} Slivers ?

I I

c Water

Cooker

O i 1

Tank Truck

Screened Sol ids To

Truck

t

Figure 1. Potato processing plant flow diagram at Midwest Foods Corporation, Clark, South Dakota.

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TREATMENT FACILITIES

The waste water treatment f a c i l i t i e s of the plant consist of an lagoon, aerated lagoon and s tab i l iza t ion pond a l l operated i n anaerobic

series as represented schematically i n Figure 2.

The anaerobic lagoon i s approximately rectangular in shape having a mean w i d t h and length of 100 and 170 f ee t , respectively. Originally the lagoon had a l iquid d e p t h of 20 f e e t b u t t h i s has been reduced substant ia l ly by the build-up of solids. The l iquid volume was about 100,000 cubic feet. To preserve heat and control odors, the anaerobic lagoon was covered with a two-inch thick layer of Styrofoam topped w i t h a straw mat.

The aerated lagoon i s t r iangular ly shaped w i t h a length of about 470 f e e t and a present volume of about 404,000 cubic f ee t . Originally, the aerated lagoon had a l iquid depth of 12 f e e t b u t sol ids deposition has reduced the average d e p t h t o l e s s than 10 f ee t . Six 25-horsepower f loat ing aerators are located in the basin as shown in Figure 2 . Waste water from the aerated basins flows by gravi ty t o a 22-acre s tab i l iza t ion pond. Discharge from the pond i s not practiced nor permitted.

The en t i r e three-basin treatment system was constructed w i t h l i t t l e a t tent ion t o inlet or ou t l e t conditions of the units. Manholes were not constructed where pipes pass th rough the dikes; consequently, operational f l e x i b i l i t y of the system i s limited t o controll ing the number of aerators i n operation as the waste water flows through the system. The dikes throughout the system were reconstructed and par t ia l ly rip-rapped following serious erosion a f t e r the 1971-72 operating season.

INVESTIGATION PROCEDURES

The primary investigation reported herein was conducted d u r i n g the period of August 1 t o November 14, 1973, although plant processing operations were limited t o a period of September 6 t o November 14. Dur ing t h i s period, the plant processed an average of 4.72 tons o f raw potatoes per hour o f operation or about 85 tons per day.

Samples were collected weekly from seven locations in the treatment system as shown in Figure 2. Raw waste, anaerobic lagoon and aerated lagoon eff luent samples were composited from grab samples collected a t two-hour intervals d u r i n g the day shift . Because the discharge permit required sampling from each quadrant of the s tab i l iza t ion pond, fou r grab samples were analyzed individually from this source. Samples were

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S T A B I L I Z A T I O N POND ( 2 2 acres) n

16 ANAEROBIC LAGOON

e N

I

Figure 2. Schematic f low diagram of t h e treatment system showing t h e sampling po in ts .

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refrigerated after collection and during transport to South Dakota State University where the analyses were performed. The time lapse between the end of sampling and arrival at the laboratory was less than two hours and analyses of the samples began immediately. A total o f fifteen different determinations were performed on the waste waster samples, with most of the analyses conducted in accordance with Standard Methods.* Most analyses were performed weekly although a few w m

monthly intervals.

Plant flows were measured using a three-inch Parshall flume installed between the vibrating screen and the anaerobic lagoon. Initially, a recorder was used to continuously measure flow; however, because of excessive vibration and solids accumulation in the float stilling well, the recorder was abandoned in favor of hourly manual flow measurements taken during the day shift when the plant was processing. Flume silt-water flow was estimated by recording the time of pump operation as the solids were pumped from the mudpit.

Details concerning the sampl ing and composi ting procedures, the particular method employed for analyses of samples and techniques of measuring flow have been rep~rted.~

CONDITION OF THE TREATMENT UNITS PRIOR TO THE 1973-74 CAMPAIGN

One of the objectives of the investigation was to determine if the anaerobic lagoon, aerated lagoon and stabilization pond had recovered from the overloaded conditions that existed from 1970-72. The contents of the stabilization pond were green instead of the pink that was evident during 1970-72 when anaerobic conditions prevailed. Whereas the pink coloration was indicative of the presence of purple sulfur bacteria which proliferate under anaerobic conditions, the green color demonstrated the presence of oxygen-producing algae which are normally present in a we1 1 functioning stabilization pond. Further indication that the stabilization pond was aerobic was the absence o f any noticable odors emanating from the pond. The aerated lagoon was also free of odors. Slight odors were noted in the immediate vicinity of the anaerobic lagoon. Furthermore, gas bubbles were observed at the surface of the anaerobic lagoon which would be expected when anaerobic decomposition was occurring.

In addition to the visual inspection of the waste water treatment facilities, several analytical determinations were performed to evaluate the conditions of the system. The average results obtained from these analyses are presented in Table 1.

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Table 1. AVERAGE ANALYTICAL RESULTS P R I O R TO THE 1973-1975 CAMPAIGN

Parameter Anaerobic Aerated S t a b i l i z a t i o n

1 agoon lagoon pond

Dissolved oxygen, mg/ 1 4.5

ORP, mv

NO,-N, mg/l

NH,-N, mg/l 0.31

8 .1

+63

0.05

0.85

10

The h i g h l y nega t i ve ox ida t i on - reduc t i on p o t e n t i a l , zero n i t r a t e - n i t r o g e n and h i g h amnonia-nitrogen concentrat ions shown i n Table 1 f o r t he anaerobic lagoon a re r e s u l t s t y p i c a l o f anaerobic cond i t i ons . The values presented i n Table 1 f o r t he aerated lagoon and s t a b i l i z a t i o n pond i n d i c a t e t h a t these u n i t s had re tu rned t o aerobic c o n d i t i o n s p r i o r t o the 1973-74 processing season. The d i sso l ved oxygen r e s u l t s should be considered approximate values because o f an unexplained i n t e r f e r e n c e t h a t occurred when t h e samples were f i x e d i n the f i e l d . The p o s i t i v e ox ida t i on - reduc t i on p o t e n t i a l s , low ammonia-ni t rogen concentrat ions and presence o f n i t r a t e s i n both u n i t s p rov ide a d d i t i o n a l evidence i n support o f t he conclus ion t h a t both u n i t s were aerobic immediately p r i o r t o the 1973-74 processing season.

QUANTITY OF RAW WASTE STREAMS

From a frequency d i s t r i b u t i o n p l o t o f f l ows gaged on an h o u r l y basis, t h e raw waste f l o w was 57 gpm o r l e s s 50 percent o f t h e t ime. N ine ty percent o f t h e time, f l o w was l e s s than 125 gpm. Highest f l ows occurred d u r i n g p l a n t clean-up, f l u s h i n g o f a plugged f lume o r du r ing d e f r o s t i n g operat ions. The average d a i l y f l o w ranged from a l o w of 54,720 gpd t o a h i g h o f 142,560 gpd. The average waste water f l o w du r ing the day s h i f t processing p e r i o d was about 64 gpm. Assuming t h i s average t o be r e p r e s e n t a t i v e o f t he e n t i r e processing per iod, a discharge o f 92,160 g a l l o n s per day would r e s u l t . Approximately 4.72 tons o f raw potatoes were processed per hour o f ope ra t i on . Based on the average f l o w o f 64 gpm, approximately 813 g a l l o n s o f waste water were produced per t o n o f raw potatoes processed.

S i l t - w a t e r was also pumped t o t h e anaerobic lagoon on an average of once per day. The average pumping t ime was 11.8 minutes a t a r a t e of 418 gpm r e s u l t i n g i n 4,932 g a l l o n s o f s i l t - w a t e r produced d a i l y . Based on an average i n p u t o f 85 tons o f raw potatoes per day, approximately 58 ga l l ons o f s i l t - w a t e r were produced per t o n o f raw potatoes. It should

unusual l y c lean be noted, however, t h a t d u r i n g t h e potatoes were rece ived a t t h e p l a n t .

1973-74 season

RAW WASTE CHARACTERISTICS

The q u a n t i t y o f raw p t a t 0 proce d per da ranqinq from 41 t o 122 tons w i t h an average

f a r i d considerably , o f 85 tons. The

c h a r a c t e r i s t i c s o f t he raw waste were a l s o h i g h l y - v a r i a b l e . On a t l e a s t one occasion, c a u t i c peel was discharged t o t h e waste stream causing maximum concentrat ions o f suspended so l i d s (SS) , and chemical oxygen demand (COD) and a ve ry h i g h pH.

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The average charac te r i s t ics (except pH) of the raw waste are included in Table 2. The pH of the raw waste ranged from 9.2 t o 11.6. The median pH value was 10.6 which was lower t h a n the median pH of 11.4 obtained i n the 1971-72 study,' undoubtedly the r e su l t of the reduction i n caustic peel allowed t o enter the waste stream. Temperature of the raw waste varied from 23 degrees to 27 degrees C w i t h the average being about 25 degrees C.

The impact of the new peeling process and the implementation of extensive water conservation measures were c lear ly evident when the BOD5, SS and COD concentrations shown i n Table 2 were compared with the 1971-72 study. The BOD5 and COD concentrations shown in Table 2 were about 70 percent higher than determined two years e a r l i e r while SS concentrations were about 225 percent higher. However, waste water flows during t h i s period had been reduced from 3500 t o 813 gallons per ton of potatoes processed. These concentrations would be considered excessive for the potato processing plant had i t n o t been f o r the reduced flows. The BODS, COD and SS loadings were 40.5, 84.6, and 67.7 pounds per ton of raw materials processed, which are qui te representative of the industry.

Total Kjeldahl nitrogen (TKN) and inorganic phosphorus t e s t s were performed to determine i f suf f ic ien t nutr ients were present in the raw waste t o support biological growth. The most commonly quoted requirement of the B0D:N:P r a t i o for aerobic biological treatment i s 100:5:1 while the raw waste water from the plant had a r a t i o of 100:7.1:26.7. I t would appear t h a t adequate nutr ients t o support aerobic biological growth were present although nitrogen deficiencies migh t occur d u r i n g periods o f extreme qual i ty variation.

Analyses of the flume s i l t waste pumped dai ly t o the waste stream were limited t o sol ids determinations. For f ive samples of the s i l t water, mean concentrations were 14,044 milligrams per l i t e r of SS and 61.1 m i l l i l i t e r per l i t e r of se t t leab le suspended sol ids a f t e r a 23-hour s e t t l i n g time.

Using average SS concentration of 14,044 milligrams per l i t e r and the average dai ly volume of 4,932 gallons, i t was calculated tha t 578 pounds of s i l t (6.8 pounds per ton of potatoes) were pumped t o the anaerobic lagoon per operating day. Assuming t h i s s i l t would occupy an average volume o f 61.6 m i l l i l i t e r s per l i t e r i n the anaerobic lagoon a f t e r s e t t l i ng , an average of 40.5 cubic f e e t of compacted s i l t was produced~ per operating day d u r i n g the 1973-74 season. A t this r a t e , a normal production year of about 245 days would produce approximately 9,925 cubic feed of compacted s i l t resul t ing i n a 9.8 percent reduction i n anaerobic lagoon.

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Table 2. MEAN CONCENTRATIONS AT TREATMENT UNITS

Determi na t i ona

Temperature, OC

pH - units (med i an )

BODS

COD

ss Total residue

Conductivity,

ORP, mv

Volatile acids

Total a1 kal ini ty

DO

Phosphorus

T KN

NO3-N

umho/cm

NH3-N

Raw waste (screened)

25.1

10.6

5,978

12,489

9,993

17 , 127

6,801

- -

2,590

- 1,277

308

0.22

29.3

Anaerobic 1 agoon

22.7

7.1

1,573

4,692

2,200

7,554

6,480

-396

956

3,853

- 7 06

180

0

50.2

Aerated 1 agoon

12.9

8.85

25 1

815

712

6,017

6,740

-52

3,527

1.2

450

44.4

56

5.1

Stabilization pond

11.7

9.5

59

47 1

149

6,678

8,567

-11.6

5,038

14.2

260

22.1

0.16

0

aAll units in mg/l unless otherwise noted.

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TREATMENT ACCOMPLISHMENTS

Table 2 a l so includes the mean concentrations of samples representing the eff luent of the anaerobic lagoon and the aerated basin as well as the contents of the s tab i l iza t ion pond. Becuase flow i s s t ra ight through the units, comparison of the concentrations will demonstrate the removals accomplished by the individual treatment units.

Anaerobic Lagoon

During the period of the investigation, the average retention time provided by the anaerobic lagoon was 8.2 days. Conditions for anaerobic treatment of the wastes were cer ta inly sat isfactory i n tha t the median pH was 7 .1 w i t h a range of 6.8 t o 7.4 and the temperature averaged 22.7 degrees C . Volatile acids ranged from a maximum of 1,380 milligrams per l i t e r ear ly i n the investigation t o 570 milligrams per l i t e r on the l a s t sample collected, w i t h a mean concentration of 976 milligrams per l i t e r . The mean vo la t i l e acids t o a lka l in i ty r a t i o was 0.25 and the oxidation- reduction potential ( O R P ) was -396 mv. These conditions have been descri bed4 as sat isfactory for the continued conversion of the organic material i n the lagoon t o carbon dioxide and methane.

I t i s important t o note tha t the raw waste pH was reduced from 10.6 t o about neutral i ty (pH of 7.1) i n the anaerobic lagoon. The buffering capacity of the system seemed t o be highly effect ive even when the pH of the raw waste was 11.4 t o 11.6.

Temperature of the anaerobic lagoon was above 21 degrees C throughout the investigation, only a few degrees lower than tha t of the raw waste. This temperature is well above a recommended minimum value of about 15 degrees C a t w h i c h anaerobic biological ac t iv i ty i s sharply curtailed. During the 1971-72 investigation of the system when the anaerobic lagoon was uncovered, the average temperature was about 12 degrees C . Thus , the Styrofoam-straw cover presently employed appears t o have contributed substant ia l ly t o maintaining a more sui table temperatue i n the anaerobic lagoon.

The loading ra tes and removal e f f ic ienc ies for the anaerobic lagoon are included i n Table 3.

These loading ra tes a re substant ia l ly higher t h a n those generally recommended for design of anaerobic lagoons. For example, the BOD, loading of 45.5 pounds per 1,000 cubic feet per day was three times higher than tha t recommended for anaerobic lagoons i n S o u t h Dakota. However, the unit obtained a 73.7 percent removal of BOD, w i t h nearly comparable removals of COD and SS.

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Table 3. LOADING RATE AND REMOVAL EFFICIENCY TREATMENT UNITS

Locat ion

Anaerobic lagoon, 1 bs/ 1 , O O O f t 3/day

BOD COD ss

Aerated lagoon, 1 bs/1,000 f t 3 / d a y

BOD COD ss

S t a b i l i z a t i o n pond, 1 bs/acre/day

BOD COD ss

Lagoon system, 1 bs/acre/day

BOD COD ss

Loading r a t e

45.5 90.0 76.0

3.0 8.9 4.2

8.8 28.5 24.9

Removals, %

73.7 62.4 77.9

81.8 82.6 67.6

76.5 42.2 79.1

99.0 96.2 98.5

aBased on t h e average d a i l y f l o w o f 92,160 ga l lons .

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Although t h e removals f o r t h e anaerobic lagoon were based on samples c o l l e c t e d over a comparat ive ly s h o r t p e r i o d and d i d n o t i nc lude data du r ing a severe w i n t e r per iod, t he removals appear rep resen ta t i ve o f t he u n i t du r ing w i n t e r cond i t i ons . For example, t h i r t e e n samples c o l l e c t e d du r ing t h e c u r r e n t season from October 1974 through March 1975 had mean removals o f 77.5 and 7.1. percent, r e s p e c t i v e l y , f o r BOD5 and ss.

S u f f i c i e n t inorgan ic n u t r i e n t s were present i n t h e anaerobic lagoon e f f l u e n t t o suppor t aerobic b i o l o g i c a l a c t i v i t y as i n d i c a t e d by an average BOD5:N:P r a t i o o f 100:25:90. Whereas t h e r a w waste BOD5 :N:P r a t i o was 100:7.1:26.7, i n d i c a t i n g a poss ib le n i t r o g e n d e f i c i e n c y a t c e r t a i n times, t h e BOD5:N:P r a t i o present i n t h e anaerobic lagoon e f f l u e n t revea ls t h a t t he anaerobic lagoon conserved t h e i no rgan ic n u t r i e n t s discharged t o it. The increased n i t r o g e n f r a c t i o n was probably due t o t h e reduc t i on i n carbon (BOD) brought about through t h e escape of carbon d i o x i d e and methane f rom t h e degradat ion o f n i t rogen- con ta in ing compounds. Because o f t h e h igher c e l l u l a r growth r a t e s and commensurate requirement f o r n i t rogen , an aerobic t rea tment u n i t would probably n o t b r i n g about a s i m i l a r conserva t ion o f n i t rogen . Therefore t h e use o f an anerobic lagoon appears t o be o f cons iderable va lue i n p r o v i d i n g a BOD5:N:P r a t i o s u i t a b l e f o r b i o l o g i c a l t rea tment o f po ta to wastes which migh t o therwise have been n i t r o g e n d e f i c i e n t .

Aerated Lagoon

Dur ing t h e i n v e s t i g a t i o n , t h e aerated lagoon prov ided an average r e t e n t i o n t ime o f near 33 days, s u b s t a n t i a l l y l onger than would normal ly be considered i n design o f a s i m i l a r u n i t . Undoubtedly, t h i s long r e t e n t i o n t ime was t h e r e s u l t o f t h e reduc t i on o f waste f l ows through water conserva t ion measures w i t h i n t h e p l a n t p r i o r t o t h e i n v e s t i g a t i o n .

Ma in ta in ing adequate d i sso l ved oxygen i n t h e aerated lagoon was a problem throughout t h e i n v e s t i g a t i o n . A1 though t h e mean concen t ra t i on of d i sso l ved oxygen was 1.2 m i l l i g r a m s per l i t e r , on two occasions d i sso l ved oxygen was zero when a t l e a s t one o f t h e s i x 25-horsepower ae ra to rs was n o t operat ing. Consequently, i t i s l i k e l y t h a t an oxygen d e f i c i e n c y e x i s t e d p e r i o d i c a l l y i n t h e aerated lagoon a l though odors f rom t h i s u n i t were n o t a problem.

Low temperatures i n t h e aerated lagoon were n o t a problem du r ing the i n v e s t i g a t i o n w i t h an average o f 12.9 degrees C; however, w i t h ext remely c o l d weather, i c i n g d i f f i c u l t i e s have occurred. I n mia- January 1975, a severe b l i z z a r d occurred and t h e f l o a t i n g ae ra to rs i c e d t o t h e e x t e n t t h a t severa l complete ly overturned. Dur ing t h e one and

"one-ha l f months t h a t t h e aera tors were i nopera t i ve , t h e aerated bas in became complete ly covered w i t h i ce , turned anaerobic and e f f l u e n t

16

qual i ty from the basin approached tha t of the anaerobic lagoon. When the aerators were placed i n operation, extremely noisome odors persisted for a few days; however, about ten days l a t e r the BODS of the eff luent was reduced t o 450 milligrams per l i t e r and the odor problem was eliminated.

The loading ra tes and removal e f f ic ienc ies of the aerated lagoon are included i n Table 3. These loading ra tes were low and, consequently, average removal of BODS, COD and SS were h i g h , 81.8, 82.6 and 67.6 percent, respectively. From the SS reduction, i t i s obvious t h a t the aerators do not provide adequate mix ing of the basin contents and tha t sedimentation plays an important part of the overall removals of the u n i t .

S tabi l izat ion Pond

The mean concentrations o f the contents of the s tab i l iza t ion pond are included in Table 2. The BOD, and SS concentrations of the pond exceeded the l imi t s extablished for discharge to surface waters i n South Dakota and, without additional treatment, could n o t have been discharged. However, because of the low hydraulic loading t o the pond, no d i r ec t discharge from the pond existed. The u n i t has served effect ively as an evaporation pond fo r ultimate disposal of the waste water throughout the f ive years of service and only d u r i n g the summer of 1972 was i t necessary t o employ some spray i r r iga t ion f o r the purpose of reducing the lagoon volume.

Pro l i f ic algal concentrations were the cause of the h i g h SS concentrations i n the pond and dissolved oxygen was always present i n the pond w i t h a mean concentration of 14.2 milligrams per l i t e r . I t appears from the to ta l Kjeldahl and ammonia nitrogen results tha t the algae have u t i l i zed nearly a l l the available nitrogen i n the pond.

During the 1973-74 processing season, the BOD5 loading t o the s tab i l iza t ion pond was low, averaging only 8.8 pounds of BOD5 per day. Consequently, overall reductions of BOD5 i n the pond were 76.5 percent (Table 3). By contrast , COD removals were only 42.2 percent, probably because of the high algae concentrations.

Lagoon System

The removals of the individual units and the lagoon system as a whole are presented i n Table 3 comparing the influent and e f f luent concentrations. I t will be observed by BODS, COD and SS removals fo r the en t i r e system were a l l i n excess of 96 percent.

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To emphasize the r e l a t i v e i inportance of t h e i n d i v i d u a l u n i t s , however, t h e removals based upon t h e raw waste l o a d a r e shown i n F igure 3. From these p i e graphs i t i s obvious t h a t the anaerobic lagoon i s the p r i n c i p a l u n i t o f t h e system accompl ishing n e a r l y 75 percent o f t h e o v e r a l l removal. Furthermore, t h e anaerobic lagoon d u r i n g t h e pe r iod of t h i s i n v e s t i g a t i o n operated e s s e n t i a l l y f r e e o f ob jec t i onab le odors.

Odors f rom t h e s t a b i l i z a t i o n pond have been t h e pr imary problem f o r t h e waste system and these were severe f o r t h e f i r s t two years when l i t t l e a t t e n t i o n had been g iven t o water conserva t ion and waste recovery. The water used a t t h e p l a n t con ta ins a concent ra t ion of s u l f a t e s i n excess o f 400 m i l l i g r a m s per l i t e r , and t h e produc t ion o f hydrogen s u l f i d e no doubt i n t e n s i f i e s t h e nuisance odors. When the s t a b i l i z a t i o n pond turned p ink i n 1971, probably as a r e s u l t o f photosynthe t ic s u l f u r b a c t e r i a as descr ibed by Slet ten, ’ a marked reduc t i on i n nuisance odors occurred. This p ink c o l o r p e r s i s t e d u n t i l aerobic cond i t i ons were es tab l i shed i n t h e s t a b i l i z a t i o n pond t h e f o l 1 owing summer.

It i s n o t suggested t h a t a t reatment system o f t h e na tu re descr ibed would be e q u a l l y successful f o r a l l s i m i l a r po ta to process ing p l a n t s . The success o f t h e o v e r a l l system can, however, be a t t r i b u t e d p r i m a r i l y t o t h e anaerobic lagoon. Even a f t e r t h e anaerobic-aerated lagoon components were added t o t h e e x i s t i n g s t a b i l i z a t i o n pond, a t l e a s t a year was requ i red be fore t h e anaerobic lagoon was f u n c t i o n i n g p roper l y . Because o f t ime l i m i t a t i o n s , l i t t l e cons ide ra t i on had been g iven t o p rov id ing t h e seed organisms requ i red t o r a p i d l y e s t a b l i s h an a c t i v e popu la t ion o f methane-forming organisms necessary t o break down t h e wastes w i t h o u t producing odors. Dur ing t h e t ime p e r i o d between processing campaigns, a c t i v e anaerobic d i g e s t i o n was es tab l i shed n a t u r a l l y , and t h i s t ime pe r iod when process ing wastes do n o t e n t e r t h e system appears h i g h l y b e n e f i c i a l toward recovery o f t h e e n t i r e system.

SUMMARY AND CONCLUSIONS

This i n v e s t i g a t i o n o f t h e t reatment system f o r t h e po ta to processing wastes a t Midwest Foods Corporat ion, Clark, South Dakota, covered a t h r e e and one-hal f month per iod. Dur ing t h i s t ime, a n a l y t i c a l determinat ions and f l o w measurements were u t i l i z e d t o c a l c u l a t e load ings and removal e f f i c i e n c i e s f o r t h e var ious t reatment u n i t s . The f o l l o w i n g conclus ions were drawn:

1. Immediately p r i o r cond i t i ons preva pond i n d i c a t i n g over1 oaded condi t

t o t h e 1973-74 process ing season, aerob ic l e d i n t h e aerated lagoon and s t a b i l i z a t i o n t h a t these u n i t s had recovered from t h e ons t h a t e x i s t e d p r i o r t o t h a t t ime.

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Stabil

/ Anaerobic Laaoon

Remainina 1. ization

, i~ i za t ion - J - Pond 5.7%

Anaerobic Lagoon 62.4%

Aerated

\-Stabilization Pond 2.8%

Figure 3. Average removals obtained by the various treatment units based on raw waste character is t ics .

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2. Utilization of a new dry-caustic peeling process and extensive in-plant water conservation had reduced the water usage from 3,500 gallons per ton of raw potatoes to approximately 813 gallons per ton.

3 . The anaerobic lagoon was an effective treatment unit in which average BODS and SS removals of 74 and 78 percent, respectively, were obtained despite an average BODs loading rate of 45.5 pounds per 1,000 cubic feet per day, over three times higher than the recommended design value.

4. The Styrofoam-straw cover on the anaerobic lagoon was effective in maintaining an adequate temperature in the lagoon and helpful in controlling odors. Although slight odors were detected in the vicinity of the anaerobic lagoon, they were not considered a nuisance during the period of investigation.

5. It is evident from the BOD5:N:P ratios obtained that it is advantageous to use an anaerobic lagoon prior to aerobic treatment if conservation of inorganic nutrients is desired.

6. The aerated lagoon, operating well within the BODs loading range, performed within anticipated efficiencies removing 82 percent of the BOD5 and 68 percent of the SS.

7. The stabilization pond was operating at about 50 percent of its design BODe loading. The BOD5 and SS removal efficiencies in this unit were 77 and 79 percent, respectively.

8. During this investigation, overall average removal efficiencies of the treatment system of 99, 98.5 and 96.2 percent were obtained for BODs, SS and COD respectively.

9. Silt build-up at the present rate of 40.5 cubic feet per operating day, could eventually decrease the volume of the anaerobic lagoon, thus reducing the retention time in the lagoon and possibly the efficiencies obtained by the anaerobic 1 agoon.

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REFERENCES

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3.

4.

5.

Hagin, T. L. A Study of the System Treating Potato Processing Wastes at Fairfield Products, Inc., Clark, South Dakota. Master o f -Science Thesis, South Dakota State University, Brookings. 1972.

American Public Health Association, Inc. Standard Methods for the Examination of Water and Wastewater, 13th edition. New York. 1971.

Trygstad, W . J. Investigation of the Anaerobic-Aerobic Treatment System Treating Potato Processing Wastes, Midwest Foods Corporation, Clark, South Dakota. Master of Science Thesis, South Dakota State University, Brookings. 1974.

Dornbush, 3. N. State-of-the-art: Anaerobic Lagoons, Second International Symposium for Waste Treatment Lagoons, distributed by Ross E. McKinney, University of Kansas, Lawrence. 1970. p. 382- 387.

Sletten, 0. and R. H. Singer. Sulfur Bacteria in Red Lagoons. Journal o f Water Pollution Control Federation. (43):2118. 1971.

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