Preventing Pollution in Shrimp Processing

Prepared by:
Roy E. Carawan
Extension Food Science Specialist
North Carolina State University

Published by: North Carolina Cooperative Extension Service

Publication Number: CD-25

Last Electronic Revision: March 1996 (JWM)

Dry Cleanup and By-Product Recovery Can Eliminate 70 Percent of Your Plant's Waste Load!

The wastewater from most breaded shrimp plants is about ten times more concentrated than domestic sewage. It commonly contains large amounts of organic matter, including small particles of shrimp flesh, breading, soluble proteins, and carbohydrates. When these materials flow into drains, they become pollutants that must be removed before the water can be discharged into streams, rivers, or estuaries.

Most public wastewater treatment plants levy a surcharge to treat water containing excessive waste loads. These surcharges have increased greatly in recent years, and they promise to go even higher in the future. Thus it pays shrimp processors to cut waste loads by keeping as much waste as possible out of drains.

Waste concentration can be measured by a number of different methods. A common way to determine the amount of biodegradable organic matter present is to measure the biochemical oxygen demand, or BOD5, of the wastewater. The BOD5 concentration is measured in milligrams per liter (mg/l). When the level exceeds 250 to 300 milligrams per liter, most treatment plants apply a surcharge.

To see how much the waste load could be reduced -- and how much money could be saved -- by adopting waste control strategies, a study was conducted in cooperation with the managers of a shrimp processing plant in Georgia. Through the use of hydrosieve screening, dry cleanup methods, and by-product recovery, the plant was able to cut its BOD5 waste load by 60 percent, or more than 600,000 pounds per year. That's roughly equivalent to the amount produced by a town of 10,000 people.

Screening

Before the experiment began, plant managers had installed a hydrosieve screening system that removed particles larger than 0.02 inches in diameter from the wastewater. Tests showed that this system substantially reduced the BOD5 load, as shown in the table.

Screening reduced the BOD5 load from processing operations by 38 percent, from 117 pounds to 72 pounds per thousand pounds of green, headless shrimp processed. The BOD5 load resulting from cleanup operations was decreased 53 percent, from 104 pounds to 49 pounds. The total BOD5 load was reduced from 221 to 121 pounds per day. Thus, screening decreased the total raw waste load at this plant by 45 percent.

Dry Cleanup

Cleaning up production areas by dry methods before flushing them with water is another way to keep pollutants out of drains. Although screening had reduced waste loads greatly, plant managers and scientists wanted to see whether dry cleanup methods could cut the BOD5 load even further.

The answer was yes! The waste load resulting from cleanup operations was reduced further from 49 pounds of BOD5 per thousand pounds of shrimp processed to only 21 pounds, as Table 1 shows. This decrease of 57 percent in cleanup load meant a further 13 percent decrease in overall BOD5 load.

Before screening, the total BOD5 load was high: 221 pounds per thousand pounds of shrimp processed. After the change to screening and dry cleanup, the total BOD5 load dropped to only 92 pounds per thousand pounds, a decrease of almost 60 percent.

  
Effect of Screening and Dry Cleanup on 
BOD5 Loads in a Shrimp Processing Plant  
                              
                                                     With Dry
                                   With               Cleaning 
Operation         Before         Screening          and Screening 
                 (pounds of BOD5/1,000 pounds of shrimp processed*) 

Processing ....... 117              72                   71
Cleanup .......... 104              49                   21
Total ............ 221             121                   92
*Green, headless shrimp.

An Inexpensive Approach to Waste Treatment

Preventing wastes from reaching the drains by using dry cleanup methods is an economical way to cut waste loads and treatment surcharges. Savings in waste treatment costs will more than compensate for any extra time and expense incurred by plant personnel. The box on this page lists some cleanup practices that will help cut waste loads substantially.

Reducing waste within the plant may also make it possible to delay or avoid large capital expenditures for new waste treatment facilities. The engineering staff at the Georgia plant calculated that the company could save 90 percent in capital construction costs by removing wastes in the plant instead of providing end-of-pipe treatment for the entire waste load.

Dry cleanup does not require expensive equipment or changes in plant design. It does require cooperation from production and cleanup personnel and a strong commitment from top management.

Tips for Effective Dry Cleanup

Collect dripping batter by placing pans under breading tables.
Squeegee spilled batter into a pan from the floor so batter will not enter the drain during wet cleanup.
Empty batter tanks into barrels instead of pumping the batter down the drain.
Place trays under conveyor belts to catch particles of dry batter -- it’s a concentrated source of soluble and suspended BOD5.
Place trays under machines to help keep breading off the floor.
Remove leftover breading from machines such as sifters by hand, not with a hose or air gun, so that it will not enter the drain.
Clean and store dry cleanup tools and utensils separate from regular wet cleanup gear.
Use a stiff broom to sweep breading from the floor. Scraping and then brushing is the only effective way to recover breading from under equipment.
Place salvaged breading in barrels so it can be given away or sold for animal feeding; it is a good source of carbohydrates and energy.
Remove shrimp hulls by dry cleanup whenever possible. When left in contact with water, enzyme action turns them into a major source of pollution.
Install a hydrosieve to remove any shrimp hulls and particles that enter the floor drains during wet cleanup. Collect material in a dumpster to be disposed of in an approved manner.
Look for opportunities to make use of waste materials. Sieved wastes containing shrimp hulls, breading, and other particulate wastes can be rendered into meal for animal food if enough can be collected.

Savings and Benefits

At the Georgia plant, relying on municipal treatment for the entire waste load would have meant surcharges and construction of bigger sewer lines. If the plant operated 200 days per year, the surcharge savings from screening and dry cleanup could total more than $125,000 annually based on a surcharge rate of 20 cents per pound of BOD5.

Reducing the waste load has other advantages as well. Waste treatment plants may impose restrictions at any time on parameters such as BOD5, total solids, and total flow. Initiating good waste practices now could save many headaches later.

Help to preserve the quality of your environment by preventing as much unnecessary pollution as possible -- and save money at the same time. Protecting your environment will show others that your firm is a good corporate citizen, will protect its image, and may even help sales.

And remember that your raw material supply depends on coastal waters that are safe for shrimp.

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

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