For 11 powerless days after Hurricane Wilma, backup generators kept a unique shrimp farm operating.
As Hurricane Wilma swept across Florida on the morning of October 25, 2005, the peninsula’s liquid heart—Lake Okeechobee—slowed the storm’s passage to a crawl. For three brutal hours, Wilma buffeted the town of Clewiston on the lake’s southern shore with gusts up to 170 miles per hour, toppling hundreds of trees and utility poles in and around the community.
In the Everglades near Clewiston, 60 miles from the ocean, OceanBoy Farms Inc. raises organic saltwater shrimp. In pristine water pumped from a subterranean aquifer into a complex system of pipes and ponds lined with high-density polyethylene, OceanBoy maintains a closed ecosystem, carefully managed with respect to alkalinity and nutrient levels.
OceanBoy is the largest US shrimp producer to receive US Department of Agriculture organic certification. During the latter half of 2005, the firm harvested, processed, and packaged more than 1.2 million pounds of organic shrimp—all without a drop of wastewater leaving its property.
Despite significant damage to its buildings and other facilities, OceanBoy didn’t lose a single shrimp to Hurricane Wilma. Within minutes after utility power failed, backup generators sensed the outage and leaped into action.
The firm continued to operate on generator power for 11 days until utility power was restored.
Wells 1,000 Feet Deep
OceanBoy owns more than 2,500 acres at two separate locations: LaBelle Farm, 4 miles south of LaBelle, FL, and Little Cypress Farm near Clewiston. The firm has 133 acres of shrimp production ponds: 17 ponds, each with a capacity of 4.5 million gallons, on 38 acres at LaBelle Farm; and 24 ponds, each with a capacity of 7.5 million gallons, on 95 acres at Little Cypress Farm. The ponds average 6 feet in depth and hold a total of 256.5 million gallons of water.
The remainder of the acreage consists of expansion space for additional production ponds, some natural wetlands that must be preserved to comply with state law, and artificial water-treatment ponds through which water circulates en route back to the production ponds.
The water in OceanBoy’s ponds originates as groundwater pumped from six artesian wells (two at LaBelle Farm and four at Little Cypress Farm). They tap the brackish, alkaline Floridan Aquifer at a depth of 1,000 feet.
Total pumping capacity is 1,600 gallons per minute at LaBelle Farm and 3,200 gallons per minute at Little Cypress Farm. The piping at each location consists of 15,000 linear feet of corrugated PVC pipe.
With monthly electric utility bills of $75,000 to $100,000, OceanBoy spends an average of $1 million a year on electricity. “It’s our single largest operating cost—more than payroll, more than shrimp feed,” says Jay Wilson, vice president of operations.
Aeration Equipment Is Crucial
Each 4-acre pond has 28 pieces of floating aeration equipment, Wilson explains. “Twenty-two paddle-wheel aerators operate full-time, churning the water to create oxygen. In the center of each pond is a floating aspirator, like an oxygen mask in a hospital, that supplies pure oxygen 24 hours a day. A high-pressure jet engine tied to an oxygen-generation system pumps the oxygen into the water below the surface at a high volume, 800 cubic feet per minute, and the paddle wheels help circulate it through the water.”
Each pond also has five emergency paddle wheels that don’t run constantly. They are tied to a separate 600-amp utility service. If the primary utility service (Florida Power & Light Co. at LaBelle Farm; Glades Electric Cooperative at Little Cypress Farm) has a hiccup, the paddle wheels on the 600-amp service immediately turn on and run for about five minutes, waiting for the primary service to return. If the primary service does not return, the generators come on in five to eight minutes, allowing full aeration to resume. If all power goes down, the backup generators kick in after eight to 10 minutes.
“The generators are a backup for the utility backup. They’re for force majeure—natural disasters and other major power outages,” Wilson says.
At both LaBelle Farm and Little Cypress Farm, OceanBoy has installed generators from Generac Power Systems Inc., of Waukesha, WI. LaBelle Farm has eight generators rated at 180 kilovolt amperes; Little Cypress Farm has seven generators rated at 230 kilovolt amperes.
One of the Little Cypress generators is for the hatchery. Each of the other six powers a 16-acre “quad”—four 4-acre ponds, enclosed within a perimeter dike and separated by internal dikes that form an X within the perimeter.
Little Cypress also has a 125-kilovolt-ampere mobile generator made by Multiquip Inc., of Carson, CA. “It’s used for backup to the backups,” Wilson says. “This unit is on a trailer that is moved into place under extreme emergencies or when one of the 230-kilovolt-ampere generators is down for service.”
Wilson says OceanBoy’s generators cost $40,000 to $55,000 apiece to purchase and another $25,000 apiece for installation and wiring. “We have well over $1 million of backup generation equipment that we own, operate, and maintain,” he says.
The generators run circulation pumps, purge pumps, and the aeration equipment that supplies the oxygen keeping the shrimp alive. “When the oxygen level drops, the ammonia level comes up because the ponds are lined, so the ammonia in the water has nowhere to go,” Wilson says.
Balancing the Ecosystem
OceanBoy’s zero-discharge, zero-exchange approach to water quality entails maintaining a balanced ecosystem in its shrimp ponds by simultaneously managing the shrimp growing in the ponds, the bacterial populations coexisting with the shrimp, and the chemical and physical water-quality parameters that shrimp and bacteria alike require for optimal growth. These include an adequate oxygen level (measured by dissolved oxygen and biological oxygen demand) and proper pH. Neutral pH is 7; natural seawater is slightly alkaline, with a pH of 8.3. “Shrimp like their pH in the 8-ish range,” says Michael Mogollon, OceanBoy’s senior vice president of science and technology.
The shrimp eat an organic high-protein feed containing specific amino acids that fulfill their nutritional requirements, with a different formulation for each life stage. The feed contains fish meal for some critical amino acids not contained in vegetable protein, plus soybean meal, wheat, vitamins, and minerals. It has no antibiotics, chemicals, hormones, pesticides, preservatives, or other additives.
Some of the bacteria in the shrimp ponds digest the solid wastes the shrimp produce. Other bacteria engage in nitrification, converting ammonia from the soluble portion of shrimp excretions to nitrite and then to nitrate. In this process, the ammonia loses hydrogen ions and gains oxygen atoms, while consuming alkalinity. “In aquaculture, it’s favorable to start with water that has high alkalinity,” Mogollon says, “so the nitrification that occurs in the ponds can be carried out effectively.”
OceanBoy’s installations have no industrial filters; the ponds themselves are biofilters. Ponds where nitrification occurs have AquaMats (Kevlar mats from Meridian Aquatic Technology LLC in Beltsville, MD) suspended in the water, providing a substrate on which the nitrification
bacteria grow.
The bacteria are 50% protein. As they break down the shrimp wastes, they grow and aggregate into colonies called floc, forming a nutritious particulate that shrimp can pick out of the water and eat. Thus, the bacteria convert the energy contained in the shrimp waste back into additional food for the shrimp.
Mogollon describes these bacteria as “probiotic,” because they participate in an association of two organisms that enhances the life processes of both. OceanBoy has cultured some of these probiotic bacteria and inoculated the pond water with them. Others are freeloaders indigenous to the atmosphere and the ponds’ natural surroundings.
“We encourage the types of probiotic bacteria that help break down the shrimp wastes by managing the available carbon and nitrogen in the water,” Mogollon says. “The nitrogen is in the water from excretions and undigested protein. These bacteria require a ratio of 15 parts carbon to one part nitrogen. To guarantee that the bacteria are in an ideal environment to proliferate, we add organic carbon to the water to attain that ratio.”
The organic carbon comes from sugars in molasses added to the shrimp feed. A commodity readily available from local sugar mills in the Clewiston area, the molasses is about 50% sugars.
High Power Density
The generators OceanBoy installed have turbocharged, aftercooled diesel engines with a high power density. “The combination of the turbocharger and aftercooler provides sufficient excess air to produce more power for the physical size of the unit,” says Allen D. Gillette, director of engineering for Generac Power Systems. “It’s a very cost-effective and reliable way to densify the power in a given liter size, which keeps the packaging cost down.
“Because these are very large, highly densified-power machines, they use a lot of fuel—but they use it efficiently for the kilowatts they’re producing, so they have superior specific fuel consumption [the amount of fuel consumed to produce a given power output, measured in grams of fuel per hour per kilowatt]. By blowing compressed air into the cylinders, you can create a more powerful internal explosion, which gives you more power output. Compared with a naturally aspirated diesel engine, you see fuel efficiency gains of at least 10%.”
In a normal engine, the exhaust would come out of the manifold into the muffler and then leave the engine. A turbocharger retrieves exhaust heat to compress ambient air into the intake of the engine, using a turbine on a common shaft to drive the compressor. The compressed ambient intake air goes through an aftercooler, then enters the intake manifold and the cylinders.
“These generators have modern digital control systems that provide proper protection of the equipment,” Gillette says. “An alarm will sound when necessary, and in the extreme, if some parameter is outside nominal limits and the equipment is in jeopardy, the controls will shut it down.”
Wilson says the ammonia buildup in the ponds would begin to affect the shrimp after an hour or so, but they can manage for a few minutes until the backup generators begin operating. Wilson and Gillette agree that OceanBoy doesn’t need an uninterruptible system, such as a hospital might install. Uninterruptible power would cost thousands of dollars more and require additional maintenance.
“In a true uninterruptible scenario,” Gillette says, “a battery pack takes over once the voltage starts to sag. The batteries will sustain operation for several minutes while the generator starts up and begins running. Then a handoff from the batteries to the generator occurs. The generator provides power until you no longer need it, while recharging the batteries.”
Fuel a Limiting Factor
At LaBelle Farm, Hurricane Wilma destroyed 70% of the hatchery. Only one of the in-ground ponds for juvenile shrimp survived, and its backup generator saved the shrimp there.
The corporate office just outside Clewiston was heavily damaged, having lost exterior siding, doors, and signage. The processing plant had roof damage but never shut down. By day’s end the roof was repaired, and shrimp processing resumed the next day.
When Hurricane Wilma struck, OceanBoy had harvested 90% of its shrimp crop. Only two ponds at LaBelle Farm and four at Little Cypress Farm were occupied. Backup generators came on in all of the ponds. As soon as the winds subsided to a safe level, electricians were dispatched to make sure all of the backup generators were operating, to fill their fuel tanks, and to place pumps in strategic locations.
Wilma’s heavy rains had filled the ponds to near overflowing. “We had to draw the water levels down 2 to 3 feet on some of the ponds. The drainage canals around Little Cypress Farm were all at their highest level, and we had standing water everywhere on that property,” Wilson says.
As soon as possible, the service staff at both farms shut down all nonessential generators. In the days that followed, as fuel supplies dwindled, the staff transferred fuel from the idle generators to the ones that were running—a maneuver that proved crucial to the survival of the remaining shrimp.
“After 11 days without primary power, we were within hours of our backup-generator power going down due to lack of fuel,” Wilson reports. “Our bulk fuel distributor in LaBelle had no power and couldn’t pump fuel into tankers, and the highway the tankers would use was blocked anyway. We put 55-gallon tanks in pickup trucks, went to the distributor to get fuel, and drove it to Little Cypress Farm using a roundabout route along back roads.”
Each of the generators at Little Cypress Farm has a 250-gallon tank that holds enough fuel for 12 hours of operation. OceanBoy keeps 6,000 gallons of backup diesel fuel at Little Cypress Farm, but that wouldn’t have been enough if the farm had needed to run all of its generators through the entire outage.
To move the fuel from storage to the generators, OceanBoy uses a trailer with a 250-gallon tank and an electric pump, hauled behind a 1-ton service truck with storage boxes containing repair parts for generators, pumps, and other farm equipment. The truck’s electrical system powers the pump on the fuel trailer.
“For 2006 we expanded our storage capacity to 15,000 gallons before the hurricane season began,” Wilson says.
Another Fuel Alternative
Although Gillette says OceanBoy’s best option is increasing its diesel-fuel storage, he also suggests that the firm consider acquiring a supply of compressed natural gas (CNG). “These generators won’t run completely on CNG, but they will run partially on it,” he says. “CNG is available in bottles and tanks. It’s a means of extending the diesel supply. Using bi-fuel technology would allow them to conserve diesel fuel, giving them a longer run time on both fuels. Ultimately, if they run out of CNG, they can operate on diesel alone. That scenario may make sense because diesel may be the harder fuel to get.”
Gillette also notes that CNG is cleaner than diesel fuel and less expensive. He suggests that OceanBoy determine the distance from its farms to the nearest natural-gas pipeline and explore the feasibility of extending a pipeline directly onto one or both properties.
“Generac offers four models of factory-designed bi-fuel generators, rated at 300, 375, 600, or 750 kilowatts of output,” Gillette says. “Their ability to operate on up to 90% natural gas and 10% diesel fuel allows them to run up to 10 times longer on a tank of fuel than diesel-only gensets of comparable output. The bi-fuel option costs about 15% more but can be invaluable during an extended outage.”
George Leposky is a science and technology writer based in Miami, FL.
[SIDEBAR] A Different Kind of Shrimp Farm
The concept of growing organic saltwater shrimp in low-salinity inland ponds originated with the founder and chief science officer of OceanBoy Farms Inc., David Z. McMahon.
“In the past 50 years, coastal shrimp farming has shared a great deal of the responsibility for destroying naturally growing mangroves along beaches worldwide, either by cutting them down to build shrimp ponds or by polluting or otherwise devastating their habitat, while ships fishing for wild shrimp destroyed reefs and seagrass beds,” McMahon explains.
In addition, many foreign countries feed antibiotics to their pond-raised shrimp to combat white-spot virus and other diseases of crustaceans raised in dense concentrations in a seawater habitat. Consumers could be ingesting residues of potentially harmful drugs in the shrimp they eat.
“I was determined to see if there was a way to move an operation away from the shore and not use marine waters,” McMahon says. “So now we raise marine shrimp inland in artesian freshwater ponds.”
Beginning in 1997, McMahon undertook a feasibility study of sustainable saltwater shrimp production at an inland location as a dissertation topic for his Ph.D. in oceanography and marine biology at the Nova Southeastern University Oceanographic Center in Dania Beach, FL.
After conducting geological studies to find the water best suited for raising shrimp, McMahon selected south-central Florida and raised money from a group of investors to fund land acquisition and development of facilities, first in the LaBelle area and later near Clewiston. OceanBoy Farms harvested its first crop in 2001 and incorporated in March 2002.
In 2001, McMahon purchased his initial batch of shrimp larvae from Florida Shrimp Improvement Systems (FSIS), a hatchery in the Florida Keys. There he met Michael Mogollon, a respected international aquaculturist who was FSIS’s operations manager. Mogollon had earned a bachelor of arts in biology from Harvard University and a master of science in fisheries and aquaculture from Auburn University in Alabama. He had worked in or consulted for shrimp operations in Central and South America, the Caribbean, and Florida.
After working briefly with McMahon and his team to help acclimate the larvae, Mogollon joined OceanBoy in 2002 to enhance the firm’s efficiency and expand its operations to a commercial scale.