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Best Management Practices

for

Nitrogen and Phosphorus Control

in

Rendering Plants

October 11, 2001 Partial Draft, prepared by J. Willis Sneed of HDR, Inc.

• I. Introduction
• II. Description of production-related activities
• III. Typical nitrogen and phosphorus levels
• IV. Nitrogen and phosphorus sources
• V. Best management practices for nitrogen and phosphorus control
• VI. BMP monitoring
• Appendix
• References

I. Introduction

This document is intended to provide guidance for plant and corporate personnel in voluntarily establishing Best Management Practices (BMP) to control nitrogen and phosphorus in the wastewater from rendering operations. These nutrient control practices solely address in-plant waste minimization practices and do not include wastewater pretreatment or treatment methods.

This is one part of a three-part set of documents. This part addressed BMP for rendering operations. The other two documents discuss BMP for slaughter, cutting up the carcasses, and further processing the meat. If the rendering is conducted at an independent rendering facility, this is the only document required. However, if the rendering is conducted at a slaughter plant, it will be appropriate to use two or all three of these documents since they slaughter and may also cut up the carcasses and further process the meat.

II. Description of production-related activities

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III. Typical nitrogen and phosphorus levels

In 1975, the Environmental Protection Agency (EPA) published a Development Document for Renderers. Included within this document is a table showing waste characteristics for rendering. Table I shows data for total Kjeldahl nitrogen (TKN) from that Development Document.

TABLE I
RENDERING EFFLUENT NITROGEN AND PHOSPHORUS LEVELS

FROM 1975 DEVELOPMENT DOCUMENT

* Raw Material

All data in Table I represents plant effluents after physical pretreatment, i.e. no chemically-enhanced pretreatment. However pretreatment facilities were generally less extensive in the early 1970s than is presently typical.

IV. Nitrogen and phosphorus sources

A. Nitrogen.

Total nitrogen is comprised of TKN, nitrate nitrogen and nitrite nitrogen. TKN is the combination of organic nitrogen and ammonia nitrogen. Table I shows that essentially all of the nitrogen in rendering plant effluents is in the form of TKN, with very little nitrate or nitrite nitrogen present. By far the major source of nitrogen is from the protein in the meat particles and blood in the wastewater from rendering plants. Protein contains about 16 percent organic nitrogen. Other sources of nitrogen are the manure and partially-digested feeds from stomachs and gizzards and intestines, as well as urine. Fat contains no nitrogen, nor is any contained in carbohydrates such as sugars, starches and cellulose. The primary source of the small amount of carbohydrates in rendering plant wastewater is from animal feeds remaining in stomachs and intestines.

As protein is utilized by both aerobic and anaerobic saprophytic bacteria, organic nitrogen is broken down to ammonia. The longer the inedible material is held before rendering, the more the organic nitrogen will be converted to ammonia nitrogen. This is significant because organic nitrogen can be removed from the wastewater by physical pretreatment; such as fine screening, settling or flotation; but ammonia cannot because it is in solution. In fact, the condensate (condensed cooking vapors) from off-site renderers (renderers not located at a packing plant) is typically quite high in ammonia. TKN at these plants has varied from a low of 36 mg/l to a high of 1005 mg/l, while nitrates have varied from 14 mg/l to 750 mg/l, although nitrites have been negligible.

B. Phosphorus.

A significant source of phosphorus in rendering wastewater is also the proteins in the meat particles and blood. Lean meat contains approximately two percent [verify] organic phosphorus. Even without the red blood cells, the phosphorus content in blood plasma has been measured at approximately 3,500 mg/l. Carbohydrates and fat contain small amounts of phosphorus. The manure and partially-digested feeds from stomachs and gizzards and intestines contribute to phosphorus in packing plant wastewaters. If phosphate-bearing detergents are used for cleaning, these can be a source of a small amount of the phosphorus in the wastewater. Ranging from about 2.5 mg/l to 20 mg/l, total phosphorus in the condensate is relatively low. Boiler-water additives can also contribute small amounts of phosphorus in the wastewater.

V. Best management practices for nitrogen and phosphorus control

• A. Inedible Material Management
• B. Blood Handling
• C. Dry Cleanup
• D. Solids Removal
• E. Cleaning Chemical Management
• F. Water Conservation
• G. Product Loss Prevention
• H. Pollution Prevention Team
• I. Environmental Awards Program

A. Inedible Material Management:  

• Minimize Sluicing Inedible Material. Encourage raw material suppliers to minimize the use of water to sluice meat scraps to inedible rendering trucks. This water must be drained from the raw materials before the inedible material is rendered. This leaches blood and other soluble materials out of the inedible material and sends them to the sewer. Alternatives to sluicing include screw and belt conveyors, ram-type and other solids-handling pumps, blow tanks and vacuum systems.

Impacts:

1. Reduction of TKN, total P, BOD, TSS, and fat, oil and grease (FOG) in the wastewater.
2. More recovery of inedible material for rendering.

• Avoid Overfilling Cookers. Consider implementing procedures or provisions to avoid overfilling batch cookers, which results discharge of inedible material with the condensate.

Impacts:

1. Reduction of TKN, total P, BOD, TSS, and fat, oil and grease (FOG) in the wastewater.
2. More recovery of inedible material for rendering.

• Prevent Leaks and Spills. Prevent leaks and spills of raw material, whole blood, blood plasma, meat and bone meal, feather meal, blood meal, and oil and grease.

1. Review the design of equipment used for loading, unloading or transferring materials to prevent spills. For example, try to minimize or eliminate spillage when transferring materials from one screw conveyor to another.
2. Consider establishing a program of routine maintenance to reduce or eliminate leaks and spills.

Impacts:

1. Reduction of TKN, total P, BOD, TSS, and fat, oil and grease (FOG) in the wastewater.
2. More recovery of inedible material for rendering.

• Avoid carry-over of hydrolyzed product from batch cookers.

1. Provide and maintain traps in the cooking vapor lines.
2. Control pressure reduction rates after hydrolysis.
3. Stop or slow cooker agitation during pressure reduction after hydrolysis.

Impacts:

1. Reduction of TKN, total P, BOD, TSS, and fat, oil and grease (FOG) in the wastewater.
2. More recovery of hydrolyzed material for drying.

B. Blood Handling: 

• Blood Processing. Evaluate drying blood whole, or in combination with feather hydrolyzing, rather than saving the red blood cells and discharging the plasma to the sewer. Total phosphorus in blood plasma has been measured at approximately 3,500 mg/l.

Impacts:

1. Minimizes the discharge of blood plasma from blood processing/drying, thereby effecting nitrogen, phosphorus and BOD reductions.
2. The drying of the plasma can be profitable.
3. Adding protein value to feathermeal can be profitable.

• Routine Maintenance. Consider establishing a program of routine maintenance to reduce leaks and spills of whole blood or plasma.

1. Where possible, dry clean up blood spills.
2. Repair or replace pump and valve seals as required to minimize or eliminate leaks of whole blood or plasma.
3. Strive to continuously eliminate pipe and equipment blood/plasma leaks and spills.

Impacts:

1. Reduction in total P, nitrite and BOD in the wastewater.
2. Maximizes the capture of valuable blood and plasma.

C. Dry Cleanup:

a. Review the design of equipment to avoid creating difficulties with dry cleanup. For example, try to minimize numerous legs on equipment that inhibit use of a squeegee or shovel for dry cleanup.
b. Assign workers during the production shift(s) to dry cleanup materials from the floors for rendering.
c. Provide tools for dry cleanup, such as squeegees, shovels, dump carts, vacuums, etc.
d. Consider establishing and enforcing written standard operating procedures for dry cleanup, either at the end of the production shift or at the start of the sanitation shift

Impact:

1. Reduction of TKN, total P, BOD, TSS and FOG in the wastewater. Rapid removal of meat scraps and blood from the floors prevents the breakdown of organic nitrogen to the ammonia form, which cannot be removed through pretreatment.
2. More recovery of inedible material for rendering.

D. Solids Removal:  Investigate improving screening practices to physically remove solids from wastewater. Consider a two-tier screening system using the drain covers for coarse solids removal and fine drain basket screens or both coarse and fine screens. 

Impact:

1. Reduction of TKN, total P, BOD, TSS and FOG in the wastewater. Rapid removal of meat scraps and blood from the floors prevents the breakdown of organic nitrogen to the ammonia form, which cannot be removed through pretreatment.
2. More recovery of inedible material for rendering.

Comment: This may not be practical where large amounts of solids would quickly plug the baskets and require constant attention. In other areas, occasional plugging may force more frequent cleaning of the drains and baskets. Removal of the baskets or emptying them into the open drain must be prohibited for this to be effective.

E. Cleaning Chemical Management:  Consider switching to low-phosphorus or non-phosphorus cleaning compounds. Phosphorus-based cleaners can often be replaced with organic surfactants (butyoxyethanol) and caustic cleaners (NaOH or KOH).

Impact: This step alone reduced phosphorus in the effluent from a pork low-processing packinghouse by approximately 2 mg/l for a six percent reduction.

Comment:

1. Low or non-phosphorus cleaning compounds may be less effective and more costly.
2. Caustic cleaners can harm aluminum and copper equipment.

F. Water Conservation: Although there is no readily-apparent reason why water conservation would result in nitrogen and phosphorus reductions, the Development Documents all contain graphs showing that plants with lower water use per 1000 lb RM also had lower waste loads. Obviously less water is used, however, if a scrap of meat is picked up during dry cleaning than if it is hosed to a floor drain during sanitation, for example. This may also simply be an indication that better-run plants use less water and discharge less wastes versus poorer-managed plants in general.

• Use the appropriate pressure and volume of water for sanitation according to each application.

Impact: Reduced water requirements for cleanup.

• Consider installing water meters and monitor potable water usage during each shift.

1. Monitoring water use on a day-to-day, month-to-month, and year-to-year basis can detect daily excursions, as well as long-term trends.  Significant water flow during idle shifts and weekends may indicate water leaks.
2. Consider establishing baseline quantities and holding each shift manager responsible for water usage for his shift. Reward usage under budgeted amounts and condemn usage of excessive quantities.
3. Encourage competition for water reductions between shifts.

• Evaluate establishing a program to inspect all hose nozzles and equipment spray nozzles and measure flow rates, where possible, at least annually. Replace nozzles discharging excessive flow.

Impact: Less water usage; hence less pollutant discharge.

G. Product Loss Prevention: Consider establishing procedures to monitor wastewater pollutant loadings (TKN, total P, BOD, TSS, and FOG).

• Monitor pollutant loads on a week-to-week, month-to-month, and year-to-year basis can reveal daily excursions, as well as long-term trends.
• Consider establishing baseline quantities and holding each department manager responsible for loads from his department. Reward quantities under budgeted amounts and condemn discharge of excessive quantities.
• Encourage competition for waste reductions between shifts and between different departments

Impacts:

1. Reduced loadings for wastewater treatment, hence reduced waste treatment costs.
2. Problem areas are identified and corrected.
3. Allows measurement of the impact of waste reduction projects within the plant.

H. Pollution Prevention Team: Investigate establishing teams to identify methods to reduce water usage and plant waste, set goals, and monitor progress.

Impacts:

1. Reduced water usage and waste loads.
2. Recognition for employee efforts.

I. Environmental Awards Program: Consider participating in an industry-sponsored awards program or establishing corporate sponsorship of awards to plants, departments or individuals for both water and waste reduction. Plants could compete for awards with winners recognized by the industry or company management with a trophy or plaque.

Impacts:  Annual savings for water and waste reductions.

VI. BMP monitoring

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Appendix

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References

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