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HIGH STRENGTH DAIRY WASTE TREATMENT: A CASE HISTORY

Theodore S. Reeves, E.I.T.

Dufresne - Henry, Inc. Division Manager - Industrial Service Division

North Springfield, Vermont 05150

Douglas Lee Miller, P.E. Director of Research and Development

Dufresne - Henry, Inc. South Portland, Maine 04106

Richard F. Duda

Ben 6 Jerry's Homemade, Inc. <)dk' Waterbury, Vermont 05676

J: i.,&9~4 5 Facilities Manager 2.' 4,

ABSTRACT

Ben & Jerry's Homemade, Inc. operates a super premium ice cream manufacturing facility in Waterbury, Vermont. average of 24,000 gallons of ice cream per week, which is distributed throughout the eastern half of the United States and portions of Canada.

pretreatment facility to reduce the waste being discharged into the Village of Waterbury, Vermont publicly owned treatment works.

demand ( 5 day test) (BOD5) concentrations are typically above 10,000 milligrams per liter (mg/L), and often exceed 20,000 mg/L. also includes high amounts of butterfat (15% cream) and 13% egg yolks. to the high amount of sugar, chocolate and fillers in the ice cream, the subsequent wastes are also high in soluble BOD.

The facility produces an

In 1987, Ben & Jerry's elected to construct an aerated lagoon

Ben & Jerry's waste is extremely high in strength. Biochemical oxygen

The ice cream Due

The facility has experienced operational difficulties since start-up in September 1989. and aeration system failure. to assist in correcting deficiencies and optimizing system performance.

The difficulties were associated with organic overloading Dufresne-Henry was retained by Ben & Jerry's

This paper

- The for

summarizes the work performed and includes:

advantages and disadvantages of various aeration techniques this type of waste and the extreme Vermont winter climate.

L

. , In-house waste management techniques used to control waste generation within the manufacturing facility and subsequent loading to the pretreatment facility.

Additional treatment technologies reviewed and implemented for the pretreatment facility upgrade.

INTRODUCTION

Ben & Jerry's Homemade, Inc. is a manufacturer of super premium ice cream. Waterbury, Vermont.

Their main offices and manufacturing facility are located in

Ben 6 Jerry's has manufactured super premium ice cream on this site since 1985. higher amounts of cream and egg yolks, which gives the ice cream its smoother and richer flavor. category of ice cream. typically loaded with fillers, and include flavors such as "Heath Bar Crunch", "Mint Ore0 Cookie", "New York Super Fudge Chunk" and "Cherry Garcia". creates a very high strength *wastewater.

(later became the Department of Environmental Conservation, Agency of Natural Resources, Public Facilities Division), directed Ben & Jerry's to either upgrade the Village of Waterbury's Publicly Owned Treatment Works (POW) to accommodate the waste load generated by Ben & Jerry's or construct their own wastewater pretreatment facility. construct their own pretreatment facility.

Super premium ice cream is ice cream that is manufactured with

Ben & Jerry's is one of the originators of this The flavors that Ben & Jerry's produces are

The manufacturing process, due to the base mixes and fillers,

In 1987, the State of Vermont, Agency of Environmental Conservation

Ben & Jerry's elected to

Ben & Jerry's contracted with a consulting engineer to design the pretreatment facility. The design centered around aerated lagoons, with design criteria as outlined in Table 1.

The pretreatment process begins with the production wastewater (no domestic sanitary wastewater) discharging into a 7,500 gallon pre-cast concrete pump station. The wastewater is pumped by two 5 horsepower grinder pumps from the pump station across a parking lot and up a hill to the control building at the lagoons. the first cell. wastewater is aerated in cell 1 by five floating mechanical aerators; two fifteen horsepower units and three ten horsepower units. the first cell is a complete mix system and very little settling takes place within the first cell.

The influent wastewater then empties into Movement from one cell to another is by gravity. The

The treatment in

The wastewater then flows to the cell 2 , where it is aerated by four, 7 1/2 horsepower floating aerators. Cell number two is divided from cell number three by a vertical floating baffle with a window in the baffle. baffle is anchored to the opposite ends of the lagoon by mooring posts and is held in place on the bottom and side slopes by concrete anchor blocks. The wastewater flows to the cell 3 through the 4' x 4' window in the baffle. The third cell was designed to be a quiescent zone with the majority of the sludge settling designed to take place there.

The

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Wastewater Characteristics, Monthly Average

Average Daily Flow BODS, Influent

Loading Concentration

BOD5, Effluent Loading Concentration

25,000 GPD

1,000 lb/day 4,800 mg/L

100 lb/day 480 mg/L

Aerated Lagoons

Two lagoons, divided into three cells cell 1 400,000 gallons cell 2 500,000 gallons cell 3 500,000 gallons

Operating depth cell 1 = 7.7 feet

Hydraulic Detention Time 60 days 02 Requirements - Max day 2,250 lb/day

cell 2, 3 - 8.7 feet

TABLE 1 DESIGN PARAMETERS

Effluent from the pretreatment facility is discharged to the Village sewer. Flow is controlled by a pump and or a paddle wheel type batch controller. Ben 6 Jerry's permit allows a maximum discharge of 150 lbs. BODg/day, with 100 lbs BODs/day monthly average. requires the monitoring of Total Volatile Solids (TVS), however there is not a permit limit or requirement at this time.

The permit further

EXISTING CONDITIONS

Prior to construction of the pretreatment facility, Ben & Jerry's discarded their process wastes by land application and feeding much of the ice cream wastes to pigs. The ice cream wastes generated by manufacturing equipment were held in large garbage pails and became known as "pig buckets". of the pig buckets to his farm to be fed to his livestock.

A local farmer came regularly to the facility and hauled contents

The process wastes generated by cleaning equipment, cream blowoff, fruit

Each day the farmer would come and pump the wastes from the tank and juices and floors and equipment rinse, were collected in two 7,500 gallon tanks. land apply the wastes on his fields.

In 1987, the State of Vermont ordered Ben & Jerry's to either construct their own pretreatment facility prior to the POTW or upgrade the POTW to accept and process the ice cream wastes.

Ben & Jerry's retained a consultant to design the pretreatment facility. The original design engineer acted as Construction began in September 1988.

his own contractor and assumed the responsibility of constructing the pretreatment facility. In January 1989, the lagoons were filled for a

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leakage test and ultimately put into operation. by the engineer was a clay membrane. approximately three feet deep, Ben & Jerry's personnel noticed that the second lagoon was also gaining water. was not properly sealing the first lagoon.

The original liner selected After the first cell was filled to

This was an indication that the liner

The State of Vermont became involved and issued a "1272 Order", an agreement between the State and Owner that a deficiency has occurred in a constructed project permitted by the State. several tasks as part of the agreement. submit completed plans and specifications for review and approval, a leakage test for the liner was required, and a completion date established for the facility to go into operation.

The 1272 Order established The engineer/contractor had to

In April 1989, the spring thaw occurred and was accompanied by heavy rains. After the liner became saturated, it was not capable of withstanding the weight of overbearing material on top of it, on a greater than 3:l slope. The liner sheared and slid in two locations.

At the end of April 1989, the engineer/contractor was released by the Owner. bring the project into operation.

Dufresne-Henry was retained to replace the original engineer and

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The first task, Remedial Action Plan, was to review the design of the original engineer and determine whether it was capable of performing as designed. the project to verify the lagoon geometry. electrical and process components of the project were also completed. A fast paced completion schedule was developed by Dufresne-Henry, Inc. for the Owner to 'insure that the project would be completed as quickly as possible.

At the same time survey crews surveyed the completed portions of A review of mechanical,

The first change made in the project was to abandon the clay liner and replace it with a synthetic liner with chemically welded seams. allowed the liner to be placed in a shorter time frame. Negotiations with the State of Vermont resulted in a waiver of the lengthy testing process of the seams prior to placement of the liner ballast material, and ultimately operation of the pretreatment facility.

This

The geometry of the lagoons was modified slightly to allow for 3 : l side slopes in all areas. The slopes had been steeper in some areas prior to reconstruction. The presence of groundwater problems were noted in May 1989 during initial inspections of the lagoons. from "floating", an underdrain system was designed and installed under the perimeters of both lagoons to lower the groundwater.

In order to protect the liner

The project needed some substantive changes to the electrical system to bring the project into conformance with local codes. design of a motor control center to be entirely contained within the control building. project include a dissolved oxygen control system (designed to control the floating aerators), a pH control system to adjust pH of the influent, and a heater control system to operate the aerator heaters and cycle aerator operation during cold weather.

This involved the

Other additional electrical control systems designed for the

Construction on the project resumed in June 1989 with the installation of the underdrain and reshaping the lagoons to conform with specifications.

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The liner installation was completed in one day on July 13, 1989. selected was a polyvinyl chloride (PVC) liner manufactured and installed by PALCO Liners. percent failure rate. one week after liner installation.

The liner

All seam testing was also completed that day, with a zero The majority of the ballasting was completed within

A review of the aeration method selected by the original engineer suggested that a different aeration method would be prudent for this project especially in the harsh Vermont winters. The original engineer had issued a purchase order for floating mechanical aerators just prior to his being released by the Owner. decision was made to accept the aerators for installation. were accepted only after the manufacturer provided a warranty statement acceptable to the Owner effective for one year from the date of installation. The aerators arrived in August and were installed in the lagoons. sank, submerging the motor. manufacturer for repair.

After much debate and threatened legal action the The aerators

Immediately after floating one of the five horsepower units, it This unit was removed and returned to the

Finally in mid September 1989, the pretreatment facility began receiving production wastewater. was greater than three years.

The time from project conceptualization to start-up

WASTE CHARACTERISTICS

The process wastewater generated at Ben & Jerry‘s is very high strength. The average influent BOD through May 1990 was 9,621 mg/L. pretreatment facility was 47,900 mg/L BOD . Typically, 60-75% of the influent BOD concentration is in soluble Sorm. run between 2,500 mg/l and 5,000 mg/l. characteristics (flow, BOD5 concentration and load, TVS concentration, and COD concentration) for the operational period October through June is shown in Figure 1.

concentration for the period of September 1989 The one day high spike measured at the

Oils, and greases typically A summary of the influent

MONTH FLOW BOD CONC. BOD LOAD TVS CONC. COD CONC. (gal/day) ( m g 4 (lbslday) (” “/l)

OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL MAY

17112 12815 1949 1 20001 21718 1 7000 14166 14380

16385 9158 7925 8828

1 1497 10840 6616 8990

1694 1035 1375 1546 1604 1660 788

1089

10183 12400 6837 10983 6443 7690 10883 9140 8193 9602 7010 5 167 7590

JUNE 15095 8880 1033 7442 TO DATE 16844 9550 1359 783 1 10587

TABLE 2 INFLUENT CHARACTERISTICS (AVERAGE VALUES BY MONTH)

25 1

In an effort to quantify the strength of the wastewater at Ben & Jerry's, analyses of all of the different flavors of ice cream produced were completed by a contract laboratory. concentrations are between 225,000 and 450,000 mg/L. Therefore, small amounts of ice cream washed down the production floor drain can have a serious impact on the pretreatment facility.

It was found that the BOD5

Through observation and a pilot study with a dissolved air flotation (DAF) unit it was determined that wastewaters containing chocolate based ice cream wastes are more difficult to digest in the pretreatment facility. One day the production crew had a machine "blow out" sending an estimated 5,000 gallons of chocolate "mix" to the pretreatment facility. The dissolved oxygen in the first cell dipped to near zero for several days and slowly came back to "normal" levels of 2.0 to 3 . 0 mg/L. As the slug of chocolate mix worked its way through the lagoons additional difficulties in treatment became apparent and finally resulted in effluent permit violations.

Within days of starting the pretreatment facility, it became obvious that the facility was receiving influent flows in excess of design, ranging from 3,500 gallons one day to over 30,000 gallons the next. The average daily BOD5 loads were averaging 1.5-2.5 times the design load. At times, the pretreatment facility received influent BOD5 loads five and six times the design load.

Another aspect of a food processing facility generating wastewater is the cleaning-in-place (CIP) process. As one operator suggested, we are trying to nurture a biomass to breakdown an organic waste and inside the production facility are a "bunch of crazy people armed with germicides and biocides trying to kill every bug they see." Jerry's $s no exception. highest flows of the day, which contains wastewaters with chlorinated cleaners, acid washes, caustics and defoaming agents. The pH during CIP is apt to swing wildly. during a short time interval is difficult for the pretreatment facility and biomass to accommodate.

The CIP process at Ben & During CIP, the pretreatment facility receives the

This wide variation of wastewater characteristics

AERATED LAGOON TREATMENT

The use of aerated lagoons for the treatment of high strength dairy wastes is standard practice. This assumes that flows and loads can be equalized to take out the sharp peaks and valleys of high and low flows and loads. biologic treatment processes, is upset due to shock load. The pretreatment facility at Ben & JerryIs has shown several times that it can not be heavily loaded one day and starved the next; the biomass cannot adjust that quickly.

One of the problems with the aerated lagoon, as with many types of

Aerated lagoons are a good treatment system even when the flows and loads have a day-to-day fluctuation or even a diurnal fluctuation. absorb flow and load fluctuations of perhaps 50% from one day to the next. In a properly operating plant, the anaerobic bacteria in the facility will kelp to reduce the sludge Slanket accumulation.

They can

The disadvantages of aerated lagoons is that they are land intensive. Aerated The facility at Ben & Jerry's is greater than two acres in size.

lagoons are also susceptible to upset. This was demonstrated shortly after

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Ben &Jerry's started up their system and the frail biomass was wiped out by a acid wastewater that drove the pH down to 4.5 in the first cell.

AERATION

One of the first tasks on this project was a review of the aeration system selected by the original engineer. selected for the project was reluctant to provide even the most basic information, such as wiring diagrams. We originally recommended against purchase of their aerators, since we could not gain any guarantees regarding the performance of the units, especially in the winter. Eventually, the manufacturer threatened legal action to get his equipment on the project and the owner accepted shipment only after the manufacturer provided a warranty statement suitable to them.

The manufacturer originally

Direct drive aerators, "splashers", have some advantages in this type of application over other aeration systems. efficiency. that splashers will transfer greater than three pounds of oxygen per horsepower-hour in clean water conditions. Caution: This is clean water conditions and will be substantially less in dirty water or field conditions. water conditions, which may be somewhat conservative, a heavy load that additional aeration capacity is necessary.

First is oxygen transfer The manufacturers of this type of equipment typically agree

We commonly work with a 60% efficiency when designing for dirty but on a hot day with

The other real advantage to splashers is their mixing ability. Splashers move a lot of water to provide their aeration capability resulting in a homogeneous mixture within the body of water. Jerry's, 60 connected horsepower of aeration is in place and provides a very complete m i x of the lagoon when all of the units are operating. Cell 3 with 20 connected horsepower, the cell can be well mixed with splashers.

In Cell 1 at Ben 6

Even in

The disadvantages of splashers (limited to those with the motors mounted above the water line) for this installation, far outweigh the advantages. The biggest drawback to splashers is that they freeze up in the Vermont winter. Also, the splashers cool the water down as the water is atomized in the cold air. That same process that aerates the water also supercools it.

December 1989 was the second coldest month on record for the State of Vermont. F in the night. At those temperatures, the aerosols (mists) generated by the aerators would collect on the cold metal surfaces and form rime ice. This compounded the ice accumulation problems from the spray patterns collecting on the tether cables, floats and motor housings. personnel had to chop ice from the aerators every day just to keep the units operating. As the units operated, the spray pattern would also freeze at the edges, forming a dish trapping water inside. As the ice dish got larger and deeper, the water level would climb until the water overtopped the motor housing and caused the motor to short. difficulties these units had in operating in the cold weather in December 1989.

Routinely the temperature would dip to between -20 and -30 degrees

Ben & Jerry's

Figures 2 and 3 indicate the

During the winter of 1989-90, fifteen out of thirteen aerators failed at Ben & Jerry's. This included two units that were rebuilt on-site and

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A/- , , v

Fieure - 1 A surface aerator struggles to operate in subzero conditions.

Firmre 2 A frozen surface aerator in Cell 2 .

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returned to operation without returning the units to the manufacturer. units failed to operate primarily due to ice accumulation on the motors, which resulted in water entering the motor and causing the motor to short. Two of the aerators failed due to main thrust bearing failure, which may have been related to ice accumulation problems.

The

The manufacturer assured the owner and engineer that the units would continue to operate in the coldest weather and cited several installations where they currently operate. facilities found that the installations were typically pulp and paper or food processing plants with high temperature influent and short detention times. This does not allow the wastewater to be "supercooled" as it was at Ben & Jerry's. Jerry'swere at less than two degrees Celsius. This suppresses the biological activity of the processing, and also begins ice formation of the water as it enters the volute of the aerator and comes into contact with the air.

Verification of two of the cold weather

For most of the winter the lagoon temperatures at Ben &

To assist with cold weather operation, the manufacturer installed The operation and maintenance heaters in the volutes of the aerators.

literature provided with the aerators stated that the heater should be run for fifteen minutes prior to start-up of an aerator with ice accumulation on the impeller. Most of the time, the heaters would operate once, short and remain inoperative until the unit was pulled from the water and repaired. .When the heaters did work, they only melted a thin film of ice around the volute and then allowed the block of ice on the impeller to spin when the motor was started. spray pattern.

This did not allow for water to be splashed in a normal

Within the first ten days of December, seven of the units on the project had failed. The manufacturer of the failure was notified at the time of the first occurrence and they did not send a representative to the site until one month later, on January 5, 1990.

AERATOR RETROFIT

In order to provide continued aeration capability, the owner chose to lease seven aspirator units. four 7 . 5 hp units, and two 5 hp units. These were installed in the three cells of the facility during the latter part of December and the early part of January. The aspirators remained in place until the early part of April 1990. These units operated with much greater reliability in the cold weather since the exchange of air comes under the water level and does not involve splashing. The aspirators are not nearly as efficient at oxygen transfer as the splashers but are adequate. good mixers allowing the homogeneous mix to be maintained throughout the lagoons.

These include one 20 horsepower (hp) unit,

The aspirators are also very

As part of an upgrade preliminary design, the use of coarse bubble aeration for this installation was evaluated. We recommended against the coarse bubble aeration mostly from an efficiency standpoint. bubble system would have required twice as much connected horsepower to maintain the aeration in these basins partly due to their shallow operating depth. time for the air bubbles to become dissolved in the water.

The coarse

Since they are shallow, the system does not allow enough contact

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Fine bubble aeration was also evaluated and dismissed for much the same reason. produce calcium carbonate formation on the diffusers would have been a continuous maintenance issue.

The high levels of carbonaceous material in the wastestream would

WASTE MANAGEMENT TECHNIQUES

Many consultants have recommended internal waste management for dairy operations as the best way to maintain an effective pretreatment facility. It is most important for the staff of the production facility to keep in close contact with the operators of the treatment facility. little or no meaningful communication.

Often there is

The CIP staff are responsible for disinfecting all the equipment on the production floor with a variety of cleansers, biocides, emulsifiers, and rinses. Any or all of these chemicals in the wrong proportions can adversely effect a treatment facility. It has taken Ben & Jerry's seven long months to nurture a mature bacteria in their pretreatment system. during that period the bacteria were wiped out in the pretreatment facility due to problems in the manufacturing facility and several times were close to being destroyed.

dumped on the floor of the production facility and ultimately flowed to the pretreatment facility. As the slug of chocolate worked its way through the plant, it resulted in an upset. Several'effluent BOD5 violations resulted. Ben & Jerry's met with State officials several times to discuss the violations and the penalties for those violations.

Once

In February 1990 a high Strength batch of chocolate ice cream mix was

As a result, Ben & Jerry's management met with the production staff and

The main thrust for instituted an internal waste management plan. immediately and the results of the plan were profound. this plan was to turn the production areas from "wet" areas into "dry" areas. to the pretreatment facility, now are being vacuumed up in their concentrated forms. process was run and how often certain pieces of equipment were cleaned.

This plan went into effect

In other words, what previously had been hosed down the drains and

Several changes were made in the way that the CIP

Two other significant changes were made. First, the cream purge tank, a tank used to capture cream as a truck tank is washed out, was reworked such that there is no longer a "blow-off" of foam from the tank as it is emptied. This foam was pure cream and is high in BOD. the pipelines within the production area. Prior to CIP, the pipes are purged with an air driven scraper or "pig". some of the raw materials within the pipe to be recaptured prior to the CIP wash.

The second change was within

The use of the pig allows for

LOAD REDUCTION

As a resulc of the waste management plan and the efforts of the pretreatment and production facility staffs, the influent load to the pretreatment facility was cut in half in a very short time.

This emphasizes the theme that the production facility staff and the

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J

pretreatment facility staff must have an open dialogue all of the time. By their own admission, the production facility staff had the idea that the pretreatment facility was a big sink that could receive anything. They did not realize that the facility is a biological organism that eats and breaths like any other living system. Therefore, a steady, stable diet is required. Not the feast one day on 3,000 pounds BOD5 and the next only receive 150 pounds.

The change in the influent quality after instituting the internal waste management plan were impressive. Prior to initiating the plan on March 15, 1990, the plant received an average of 2,400 pounds BOD5 per day, an average flow of 19,700 gallons per day with peaks of 5,200 pounds and 28,600 gallons respectively. After instituting the plan (March 15, 1990 - May 31, 1990), those values were reduced to an average of 950 pounds BODg/day and 14,400 gallons per day flow.

PRETREATMENT PROCESS CHANGES

During the early spring the water temperature in the lagoons was increasing which accelerated biological activity. late February also increased the mixed liquor suspended solids (MLSS) in the lagoons. This increased the MLSS in the Cell 3 , which is a quiescent settling tank. However. durinn this period so much food was available for

The chocolate spill of

the microorganisms that. maintaining dissolved oxygen (DO) in Cell 3 was difficult.

In order to reduce the MLSS, maintain DO, and try to improve effluent quality, several changes were made. First, the baffle window was closed. This only allowed water and solids to enter the third cell by seeping under and around the baffle. solids settling to take place in Cell 3 and to decrease the suspended solids quantity in Cell 3 .

It was hoped that this would also allow for more

The DO metering system was altered to allow for more water to be drawn This additional from Cell 3 by the DO return pump than from Cells 1 or 2.

water was then brought to the head of the plant and to Cell 1. This system would allow for a recirculation system, where none was previously provided. MLSS would rise in Cell 1, remaining a higher strength homogeneous mix, and MLSS would drop in Cell 3 . analysis.

This result was confirmed by laboratory

The nutrient balance was studied for a one month period to determine requirements for additional nutrients. Through this study, it was found that the influent to the plant was slightly deficient in nitrogen. Quaternary ammonia, a typical cleaning agent found in dairy plants, was suspected as showing up as available nitrogen when it may be bound and not available. A feed pump was set up and ammonia was pumped to the influent to add some nitrogen to the system prior to the influent entering Cell 1.

A final process change was to raise the level of the effluent pump suction pipe to pull clear water from the surface all three. A PVC elbow was fitted to the effluent pipe and turned upward. piece was added to bring the suction point to about two feet below the surface of the lagoon. solids settling.

An additional PVC nipple

This water typically has less solids in it due to

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The final result was the effluent quality improved dramatically. effluent BOD5 went from 140 pounds average daily load in February to 17 pounds average for the month of May.

The

PROPOSED PRETREATMEXT FACILITY IMPROVEMENTS

During the first seven months of operation of the pretreatment facility, it became apparent that changes in the pretreatment process were needed to handle the generated wastes. Several alternatives are being evaluated that will include changes in the process and physical equipment changes.

The first issue to be addressed is aeration and maintaining an operative

Several other types of system throughout the year. and aspirator type aerators is favored at this time. aeration systems have been evaluated but were less desirable for this application.

A "combined technology" using surface splasher

The key issue for maintaining a viable treatment process is the cooperation of the production facility crew and their ability to follow the internal waste management plan. term process operation is assured and influent loads should remain at manageable levels (1,000 pounds/day BOD and 15,000 GPD flow). By decreasing the flow into the lagoons, t 2 e detention time of the plant is increased. At 15,000 GPD, the detention time for this plant would increase to 100 days which is more than adequate time for the process to work.

As long as the plan is followed, the long

Throughout the operation of the pretreatment facility, diurnal fluctuations in the pH of the influent along with varying BOD5 and COD concentrathons have been the norm. By including two days worth of equalizatidn several operational benefits can be realized. plant can be better controlled which would attenuate the high flow spikes that are common during the CIP runs.

influent varies throughout the day, especially if "cherry juice" is dumped. By providing equalization, the pH of the influent will naturally (for this wastewater) approach the range of 6.5 - 7.5 S.U. Further pH equalization occurs in the lagoons. emulsion created during CIP allowing for easier removal of the oil and grease portion of the influent. time of start-up of the facility and has led to clogged process piping.

The flow to the

Through sampling and testing it was determined that the pH of the

Additionally, pH can be controlled to break the

Oil and grease have been a problem from the

The greatest advantage to providing equalization will be the ability to absorb shocks to the system from product dumps on the production floor. This would alleviate the possibility of a 5,000 pound loading of chocolate entering the lagoons and adversely impacting the biomass. These higher loads could be fed to the lagoons over a longer period of time, allowing the biomass to assimilate the load.

Construction of a small slot (static) wedgewire screen would allow for the removal of large solids that are normally sent to the pretreatment plant. chocolate, nuts, fruit, cookies and candy bar. These represent less than one percent of the waste flowing to the plant, yet they contribute approximately three percent of the BODS load. These solids then would be

These are mostly fillers used in the ice cream and include pieces of

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treated as any other solid food waste and disposed of by regular garbage service, presumably landfilled.

The most important issue for upgrade of the existing pretreatment facility is the removal of butterfat prior to the lagoons. Ben & Jerry's ice cream has a very high butterfat content and this has a direct affect on the performance of the pretreatment facility. enters the pretreatment system bound in an emulsion from the CIP process. As the influent arrives in the lagoons, the biological process breaks down the emulsion and frees the butterfat. There is some concern that the aerators are separating the butterfat by a centrifuge type action. separating, the butterfat collects on the surface of the lagoons, particularly in Cell 1. odors.

The majority of the butterfat

After

It then spoils in the sun and gives off very strong

A myriad of technologies are available for removal of fatty materials from a wastewater. wastewater limits the options. Three technologies have been evaluated each with some specific benefit. These are dissolved air flotation (DAF), a rotary drum precoat filter and a centrifuge.

However, the high fat content of the ice cream

It is common to use a DAF to remove fats from a wastewater along with suspended solids. and met with mixed results. influent was a critical part of the system's performance. adjustment and addition of polymers a DAF system will not perform well with these operational variations. labor and maintenance intensive operation with a high operational cost (electrical, shelter, etc.). Since it appears that the capital and operational costs of the project will be high and the prospects of only mixed results, the recommendation was made to seek another technology.

Ben & Jerry's completed a pilot scale test of a DAF unit In reviewing the DAF data, the pH of the

Without proper pH

As a result, the operation of a DAF will be a

Rotary drum precoat filters are comprised of a large drum covered with fiberglass mesh and equipped with a vacuum pump on the inside of the drum. A vacuum is drawn on the drum and coated with a two to four inch layer of diatomaceous earth (DE). Wastewater is then pooled on the bottom of the drum and the suction draws the wastewater onto the drum and through the DE. A knife blade is laid along the long axis of the drum and scrapes a fine layer of DE and solids off of the drum face. of by landfilling or land application.

DAF. The pH is a critical parameter for successful operation of the filter. The pH needs to be dropped to around 4.0 to break the emulsion then returned to neutral where polymers can be effectively added to aid with settling and coagulation of solids on the face of the drum.

This material then is disposed

Similar problems arise from operation of the precoat filter as with the

After each run the drum must be cleaned with hot water and the drum then recoated with a new layer of DE.

The costs of operation and housing the equipment at Ben 6 Jerry's were estimated to be very high. house it along with an equally large storage area for storage of DE. unit estimated for this application runs a 40 horsepower vacuum filter resulting in a notable electrical cost. is labor intensive.

The precoat filter needed a sizable building to The

Again, the operation of the filter This would also result in high O W costs.

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For years dairies throughout the world have used centrifuges to remove the cream from whole milk. investigated for application at Ben & Jerry's to treat the wastewater prior to entering the lagoons.

In like fashion, a centrifuge is being

Installation and operation of the centrifuge will require only a small structure to house the centrifuge and a "steady" flow of wastewater to the unit. the FOG and solids will be stored for disposal by land application or landfilling.

Supernatant from the centrifuge will be directed to the lagoons while

This application is expected to be much less labor intensive and have lower O&M costs. than $50,000, while the initial costs for the DAF and precoat filter were greater than $100,000.

The initial cost of the centrifuge is expected to be less

CONCLUSIONS

The work completed by the original engineer was essentially correct and the pretreatment process is a solid one. which affected the project.

The design of a high strength dairy wastewater treatment facility must be very thorough in the examination of the waste stream. should be.taken throughout the production train for as long a period as is possible. has been completed, a thorough design process can begin.

Once a'design has been completed, it needs to be reviewed throughout the construction process to anticipate errors prior to their becoming fatal' errors as in the case of the clay liner originally installed in the lagoons. Further review may have uncovered that this liner will shear on a 3:l slope longer than 27 feet, which is what happened in the Spring of 1989.

that the initial biomass is being established within the lagoons. Long discussions can take place as to the merits of seeding a lagoon but the biomass will establish itself in time and seeding may not be necessary. initial bacteria that will grow in the process are lower order, simple bacteria and are easily susceptible to upset. the ground rules need to be set with the production staff so that upsets are minimized or eliminated. warranted for a short period while the biomass and the process is being established and the facility components are being proven.

However, some errors were made

The basis of design wofk was not as thorough as it should have been.

Many discreet samples

Once this The discharge records should be reviewed and verified.

The start-up process needs to be monitored closely. It is at this time

The

It is during start-up that

Operator assistance by a consultant may be

The aerators initially installed at Ben & Jerry's were guaranteed to work during the winter and they did not. A failure rate of 115 percent is absolutely intolerable. As equally frustrating is the lack of response by the manufacturer after the initial calls telling them nf the aerator failure. The short term resolution for the aerator dilemma forced Ben 6 Jerry's to impose upon the good nature of other operators in the area which no industry wants to do. lagoons in January and met.the oxygen requirements for the remainder of the season.

Seven aspirator type units were installed in the

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The long term resolution is to continue with the combined technology of This system should consistently meet the surface splashers and aspirators.

oxygen requirements of the process throughout the year and provide excellent mixing in all cells.

The recommended future process upgrade is targeted at reducing the amount of oil and grease prior to the influent reaching the lagoons. This will also reduced the high BOD5 load entering the lagoons by approximately fifty percent. reduced sludge accumulation, and reduced nuisance odors from oils and greases floating on the surface of the lagoons. out the flow to a more consistent feed rate to the lagoons, improve the ability to absorb high spikes or shock loads, and provide for pH equalization.

The other process benefits include lowered oxygen demand,

Equalization should even

The real key to operation of this system and any industrial wastewater

Producti,on management and staff need to realize that the I system is cooperation between the production facility and the (pre)treatment

facility. treatment facility/is not a "black hole" that magically makes wastewater disappear. Likewise, the treatment facility needs to understand that the reason the production facility is there is to produce ice cream (or whatever material). going to stop.

This is a popular concern for the solid waste advocates and it is equally appropriate here. The materials that become a dairy wastewater can be reduced in their volume. This is most easily done in the manufacturing process. Ben & Jerry's has realized that by picking up a waste off of their floor as a concentrate, rather than diluting and flushing down a drain, they have reduced the amount of wastewater requiring treatment. Therefore, their waste and manufacturing processes run more efficiently and more economically.

The treatment facility needs to realize that production is not

The most effective waste management techniques are source reduction.

261

Proceedings of the 1990 Food Industry

Environmental Conference November 12- 14, 1990

Atlanta, Georgia