I- 3 Pollution and EnergyW7 - InfoHouseinfohouse.p2ric.org/ref/31/30791.pdf · Gas Management System 7. ... ture microbial) operation possible if ... the reactor gas as produced,

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zcardi Corporation is converting 3 distillery wastes to methane gas using of an anaerobic reactor of inno- vative design. In operation since De- cember 1981, the reactor currently supplies the e uivalent of 600 million Btu daily to %e distillery boilers. At the same time, the plant effluent quality is exceeding re ulatory re-

of waste to energy could be employed by many industries that produce or- anic wastes, while at the same time

Relping them become more energy independent and reduce waste treat- ment costs.

Anaerobic digestion is a process whereby microorganisms (microbes) multiply by metabolizing organic matter in the absence of oxygen. The end products of this process are chief- ly methane as, carbon dioxide and

traditionally used for treatment of municipal wastewater sludges. Until recently, it has not received much attention from industry, although many industries discard by-products which are readily degradable by an- aerobic microbes.

Requiring very little, if any, out- side energy, the microbes are capable of reducing the biochemical ox gen

produce good quality fuel gas. The only requirements for such a process are an ap ropriate microbial environ-

into intimate contact with the mi- crobes.

In December 1981, Bacardi Corpo- ration started up a 3 mil gal fixed media anaerobic reactor at its San Juan rum distillery, which is the world’s largest. By May 1982, the reactor was generating enough me- thane gas to replace approximately 75 barrels of fuel oil per da . At the

tillery waste was being significantly reduced.

Currently, Bacardi is the only rum roducer in Puerto Rico which puri-

ies its wastewater before discharging it into the ocean. However, the in- vestment for treatment will probably make it possible for Bacardi to re- place most of its imported fuel oil with methane gas when the second reactor begins operation. Depen- dence on fuel oil will then be signifi- cantly reduced, with sugar cane mo- lasses used for both product feedstock and boiler fuel.

The anaerobic reactor is packed

The major components of the Bacardi waste treatment and gas recovery sys- tem fit within a triangular site on the edge of the distillery. Shown in the cen- ter (from top) are the 120 ft. diam anaer- obic reactor, the 75 ft diam holding tank and the gas storage sphere.

*

quirements. This type o f conversion

microbial ce P 1 mass. The process is

demand (BOD) of the wastes an dy also

ment an c f a means to bring the waste

same time, the BOD load o r the dis-

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Pollution and EnergyW7 Management Through the Anaerobic Approach

by L. Michael Szendrey, Ph.D., Paul E. Schafer and George H. Dorion, Ph.D.

SEPTEMBER/OCTOBER, 1982 INDUSTRIAL WASTES

Reprinted by permission from INDUSTRIAL WASTES, September/October 1982.

,

le1 with the prototype, test a variety of operating conditions, anticipate and test process variations which could change waste treatment condi- tions, train operators and test other wastes. To date, the media packed pilot reactors have achieved a higher BOD removal and gas production than the contact pilot reactor. Piloted

solids buildup in the tank bottom. Pilot plants in operation for nearly two years show no solids buildup on the tank bottom or on the media itself.

Once the treatment plant is in sta- ble operation, personnel require- ments are expected to be low. To date, Dr. Szendrey (who is responsi-

A view of the B. F. Goodrich “Vinyl-Core” media consisting of alternating flat and corrugated sheets welded into bales. Due to high shipping costs for full size mod- ules, the plastic media was shipped unassembled and was fabricated into full size modules at the job site.

variables will include thermophilic operation, addition of trace metals, and high rate operation.

Operation The reactor was loaded with mi-

crobial seed, mosto and water in the first week of December 1981. The distillery was closed for the annual 40 day shutdown on December 15; dur- ing this period the digester contents stood at the ambient temperature of 70 F. When the distillery was re- started in late January 1982, mosto was fed to the reactor at a rate of approximately 50,000 g d. Gas was generated almost imme B iately. Since the gas handling system was not yet ready to go on line, all the gas was flared.

Wastewater feed rate to the reac- tor was slowly increased. Table 2 sets forth current operating conditions.

About 1,000 mg/l suspended solids overflows with the effluent, a reduc- tion from an average of 6,000 mg/l in the influent. There is no indication of

INDUSTRIAL WASTES

ble for other Bacardi duties as well as the treatment plant) employs two an- alytical chemists who routinely ana- lyze samples drawn from the reactor. Plant o erations involves mainte-

the anaerobic microorganisms through periodic adjustment of pH and temperature. Moving equipment is minimal; the largest motors drive the gas compressors. An operator su- pervises the plant at night; daytime operation is handled by the laborato- ry staff. The operating staff will con- sist of not more than four full time persons.

Operating Costs O erating costs are under 2 cents

per Ii, of BOD removed, or, in terms of fuel gas, under $2.00 per million Btu produced. Labor is the largest operating cost, followed by electricity and purchase of sodium hydroxide, the neutralizing a ent. Other, less expensive, neutrakzing chemicals may be used in the future. Methane

nance o P the correct environment for

production is expected to increase when steady state operation of the treatment plant is achieved, which will reduce unit operating costs.

Ex erience to date tends to indi-

one-fifth to one-tenth of what would be expected from a conventional aerobic system such as activated sludge.

Applications

lar wastes may find this tec nique appropriate. Many modifications are possible, for example:

0 Gas storage is not essential unless gas production can be utilized.

0 Holding tanks are not necessary for very constant waste flows or may be sized to hold only enough waste, such as four, six or twelve hours’ flow to dampen cyclical flow variations. Many industries have unused tank- age, which could be used for holding and equalization.

Reactor effluent suspended sol- ids can be reduced by clarification.

Aerobic treatment can further reduce reactor effluent BOD and sus- pended solids to meet stringent stream limitations for direct discharg- ers or to reduce sewer service sur- charges for indirect dischargers. In- dustries currently using aerobic treat- ment for high strength wastes can add an anaerobic reactor ahead of the aerobic plant and reduce aerobic plant energ requirements while gen-

sludge generation. Screens, grit chambers or clarifi-

ers may be installed ahead of the reactor to remove inert solids.

For wastes not as warm as Ba- cardi’s, inexpensive heat sources such as reactor effluent, condenser blow- down or heat from methane-driven equipment may be used.

With or without the various per- ipheral devices, the Bacardi process appears applicable to still-bottom wastes, s ent grain liquors, centrates, pulp an c r paper wastes, sweet or acid cheese whey, food packing and meat packing wastes, liquid extraction raf- finates, sludge heat treatment side- streams, corn products wastes, pro- tein extraction wastes, winery wastes and many others.

Conversion of by-products to usa- ble fuel has roven to be an environ- ~ ~

in the eyes of the public and a hedge against fuel price increases while re- maining potentially profitable. m About the Authors L . Michael Szendrey is a project officer and George H . Dorion is vice president for the Bacardi Corporation. Paul E . Schafer is a project manager for Black 6. Veatch, consulting engineers.

cate t K at the operating costs are from

a Other industries dischargin

erating fue r gas and vastly reducing

mentally e f? ective action, favorable

SEPTEMBER/OCTOBER, 1982

/ Waste Treatment System 1. Holdina Tank 2. Cooleri

3A. Anaerobic Reactor Tank 3B. Second Anaerobic Reactor

Tank (To Be Constructed) 4. pH Control System 5. Nutrient Feed System 6. To Ocean Outfall

Gas Management System 7. Gas Compressors 8. To Boilers 9. Gas Storage SDhere

10. Gas Flare- ’

Figure 2. The Bacardi plant process.

sheets welded into 2 by 2 by 4 f t bales. The result is rectan ular bales

the downflowing liquid onto the tube sidewalls and into contact with the microbes. Rising gas bubbles further deflect the liquid and provide addi- tional turbulence for contact with the organisms. A microbial growth about

in. thick has been observed on the pilot plant media. This is a nearly ide- al thickness, as it allows adequate pas- sage through the tubes which are approximately 1% in. in least cross sectional dimension.

The chief purpose of the media is to bring the liquid into contact with the organisms and to prevent their loss in the effluent. “Vinyl-Core” and other media are widely used in aero- bic filter towers where the wastewa- ter is introduced at the top and allowed to trickle downward through the media against an upward flowing current of air. The Bacardi plant is the first example of using such media in an anaerobic treatment system. According to Goodrich, “Vinyl-Core” can withstand temperatures above 135 F without deformation, thus making thermophilic (high tempera- ture microbial) operation possible if so desired in the future. The bottom layers of the media have thicker walls than the upper layers for structural strength.

The media is supported on con-

of vertical, sinuous tubes w a ich guide

SEPTEMBER/OCTOBER, 1982

Crete beams that also carry a grid of perforated pipe through which gas or water may be pumped to purge the media, if necessary. The reactor floor is equipped with 24 ports for recircu- lation or drawoff from the bottom layer. Effluent exits through eight ris- er pipes adjacent to the interior sur- face of the tank wall and rises to over- flow boxes near the top of the tank which control the liquid level. From the boxes, effluent is carried down- ward to a buried peripheral manifold leading to the effluent pumps. Liquid in the tank is recirculated from the bottom to the pool surface above the media by ei ht pumps located exter-

tion rate is variable.

Auxiliary Systems Auxiliary systems (Fig. 2) equalize

flow, provide the appropriate micro- bial environment and handle the gas. Flow is equalized in a 700,000 gal holding tank fitted with side entry propellers to keep solids in suspen- sion. Recent operating experience in- dicates that flow can be equalized in the reactor itself. From the holding tank, the wastewater is pumped through coolers to the anaerobic reac- tor. Provisions are available to add nutrients to the wastewater; however, no nutrients have been required to date. Facilities for storage and feed of sodium hydroxide (caustic soda) for

nally aroun Cf the tank. The recircula-

neutralization are also provided. Both the nutrients and the caustic can be fed at the transfer pump suction which provides mixing with the waste.

Influent waste temperature is re- duced from 175 F to 100 F by coun- terflow plate and frame heat ex- changers using water recirculated through cooling towers. The temper- ature in the reactor is consistently maintained at 98 to 100 F.

Gas is recovered from the reactor dome at a pressure of 27 in. water column, or less. It is planned to feed all the gas to the boilers, but a waste gas flare is provided for startup and emergencies (equipment outage). Electric motor driven gas compres- sors compress the gas to 17 psi for feeding to the boilers and to 60 psi for storage in the 30,000 cu ft gas storage sphere. The storage sphere is in- tended to compensate for variations in gas production and fuel demands. The dual fuel boiler burners use all the reactor gas as produced, and fuel oil is used only where it is required to make up for any deficiency in the fuel supply.

Pilot Plant Bacardi has constructed a three-

reactor pilot plant which treats distill- ery waste. Each reactor has a 3,000 gal capacity. The chief purposes of the pilot plant are to operate in paral-

INDUSTRIAL WASTES

with B. F. Goodrich “Vinyl-Core” media which provides a large surface area to which methane forming bac- teria adhere. The distillery waste en- ters at the top of the reactor tank, is mixed with recirculated mixed li- quor, flows downward through the media and is collected at the bottom for recirculation and discharge. Gas is produced throu hout the tank, rises upward in bub % les and is collected and compressed for feeding to the distillery boilers.

The reactor design at this large commercial scale is unique and has been patented. Bacardi is marketing the process, with articular emphasis

which generate medium and high strength soluble organic wastes.

Project Requirements The waste to be treated consists

primarily of com lex spent organic

b the fermentation and dgistillation

characteristics are listed in Table 1. This waste which is called “mosto,” would be considered very strong by any measure.

The treated effluent will be dis- charged to, and mixed with the mu- nicipal wastewater treatment plant effluent in a 10 ft diam ocean outfall, now under construction. This com- bined flow will then be dispersed at a depth of 160 ft into the coastal waters of the Atlantic Ocean more than a mile from the shore.

Process Selection By 1974, the company had ascer-

tained that the mosto produced at the distillery was biologically treatable by anaerobic treatment processes. However, various non-biological dis- posal methods were also evaluated, among them incineration, conversion to animal feed, wet oxidation and land disposal. Engineers from the Black & Veatch, Kansas City, Missou-

on its applicabi P ity to industries

residues from still E ottoms, enerated

o r sugar cane molasses. Raw waste

INDUSTRIAL WASTES

Valves and Pump

Figure 1. A diagram of the Bacardi anaerobic reactor.

/ (.. Drawoff Ports

,-influent Pbe (4 Each)

Effluent Drawoff

Gas or Liquid (3 Each) Purge Pipes

ri, and Capacete, Martin & Associ- ates, San Juan, Puerto Rico, consult- ing engineering firms were retained in January 1980 to design an anaero- bic treatment plant. The recom-

rather than a contact reactor, and cited the following advantages and disadvantages. Advantages:

0 Lower operating cost; no ener- gy-intensive mixing required.

Smaller tank volume because of higher throughput rate.

0 More stable system because of high retaina e or organisms and abili-

0 Longer retention of microbes because of the fixed habitat.

0 Fallback option to remove the media and operate as a mechanically mixed digester if packed digester fails to perform as expected. Disadvanta es:

mended a media-packe cy reactor

ty to absorb 5 oad variations.

Cost o f media. 0 No previous large-scale experi-

0 A six week lon er construction ence.

period required for t a e assembly and

installation of media. The cost of media was justified by

by a considerable body of literature and pilot plant experience developed by Bacardi and what the engineer considered to be a conservative de- sign based upon fundamental micro-

. The longer construction time biologd. cause by media installation had to be accepted.

Description of the Anaerobic Reactor

The reactor (Fig. 1) is the essential functional element of the treatment

al. The reactor measures 120 ft in diam and 42 ft in depth from the sur- face of the base slab to the haunch of the domed roof. The media occupies 340,000 cu ft to a depth of 30 ft. The total area for microbial habitat within the tank is equal to about 270 acres.

The B. F. Goodrich media consists of alternating flat and corrugated

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plant; all other devices are peripher- -~ -

SEPTEMBER / OCTOBER, 1982