Cut Waste to Reduce Wastewater Surcharges for Your Bakery


Prepared by:
Roy E. Carawan
Extension Food Science Specialist

Consulting Technical Writer: Teri Houck
Graphic Artist: Karl E. Larson


Published by: North Carolina Cooperative Extension Service

Publication Number: CD-42

Last Electronic Revision: March 1996 (JWM)


Did you know that your bakery may be producing a waste load of 800,000 pounds of Biochemical Oxygen Demand (BOD5) per year-equivalent to the load from a city of 13,000 people.

Wastewater from most bakeries is discharged to publicly owned treatment works where the majority of the pollutants are removed before the water is discharged to various water bodies in our communities. Treating this water costs money, and most treatment works charge according to the amount of wastewater treated. In addition, they commonly apply a surcharge if the waste load exceeds certain specific levels because it costs more to treat wastewater that contains more pollutants.

In recent years, discharge limits have been imposed on bakeries. Meeting these limits demands rigid waste management or the installation of expensive pretreatment technologies; for example, grease traps, pH control, dissolved air flotation systems, and even extended aeration.

Treating wastewater is becoming costly for food processing plants and is burdening our environment. This publication describes how your bakery can save money, increase profits, and protect the environment by cutting waste.


Waste Loads in Bakeries

Waste load can be determined by a number of different tests. Biochemical oxygen demand (BOD5) is the test most often used for monitoring wastewater from bakeries. The BOD5 test is a biological test used to indicate the amount of oxygen needed to degrade the organic matter carried by the wastewater.

This test is widely used because 1) the use of oxygen is often the greatest expense in wastewater treatment, and 2) oxygen deficiency is usually the cause of polluted water and fish kills.

The BOD5 concentration in wastewater is usually measured in milligrams per liter (mg/l) or parts per million (ppm). When the level exceeds 250 to 300 mg/l, many treatment plants apply a surcharge.

The level of BOD5 in bakery wastewater is directly related to the types of food products in the wastewater. More than 90 percent of a plant's total waste load comes from ingredients that are lost and flow into floor drains during processing and cleaning. Flour, sugar, yeast, and shortening are the major components. The wastewater may also contain cleaning agents, lubricants, and solids removed from equipment and floors.

The BOD5 concentration can be estimated by measuring the fat, protein, and carbohydrates in a bakery's wastewater and using the following conversion factors: Some bakeries discharge as much as 12 pounds of BOD5 per thousand pounds of bakery products produced.

Waste Load Can Affect Profits

In the past, most bakery managers were not concerned about reducing their plant's waste load because treatment costs were minimal and restrictions were few. However, municipal water and sewer charges have increased from four to ten fold in the past 25 years, and BOD5 surcharges now exceed 30 cents per pound in some cities. Pretreatment ordinances and plant-specific permits in some localities may limit the level of wastes that can be discharged into the sewers. In that case, the waste load must be reduced by pretreatment systems before the wastewater leaves the bakery.

Wastewater Costs

When bakeries dispose wastewater to publicly owned treatment works (POTW), there are three types of costs incurred: the cost of pretreatment, the cost of residual or sludge disposal, and the cost of discharge. Discharge costs include sewer and surcharge costs. Currently sewer costs average about $1.50 per thousand gallons but can range from $0.20 to about $8.00 per thousand gallons. Surcharges are levied for waste loads discharged above the prescribed limit.

Surcharges for BOD5 range from $0.025 to almost $3.00 per pound of excess. (Surcharges are also sometimes levied for waste load concentrations of the following: COD, chemical oxygen demand; TSS, total suspended solids; TKN, total Kjeldahl nitrogen; and FOG, concentrations of fats, oils, and grease.)

To determine the BOD5 waste load produced by your plant, use the formula below:

Waste Load (lb)   = 8.34 (CONC) (FLOW)
                   --------------------
                       1,000,000
	CONC  = concentration (mg/l or ppm)
        FLOW  = volume of wastewater (gal)
Example:  A bakery processes 20 days per month with a wastewater  
          discharge of 250,000 gal/day and BOD5 = 2,750 mg/l. 
          What is the monthly waste load?
	  For One Month:
	  FLOW   = 250,000 gal/day x 20 days
 		 = 5,000,000 gal
	Waste Load    =  8.34 (CONC) (FLOW)
                         ------------------
  	                    1,000,000
	BOD5 (lb/month) = 8.34(2,750)(5,000,000)
                         -----------------------
 	                      1,000,000
	BOD5  = 114,675 lb/month

Knowing your plant’s BOD5 waste load provides you with information that can save money on treatment costs and lost product. For example:

Of course, we know that all of the BOD5 did not come from flour. However, most of it came from lost ingredients (flour, shortening, etc.) or from lost products — each of which costs a bakery money.

The cost of wastewater treatment, coupled with the cost of lost ingredients or product, have become important considerations for every manager. At today’s rates, a bakery’s waste load can have a significant effect on profits. Realizing this, some bakery managers have been able to cut waste discharges to as little as 1 pound of BOD5 per thousand pounds of bakery products produced.

Saving Money by Reducing Waste Load: An Example

How much money could a bakery save by reducing the BOD5 load to only 1 pound per thousand pounds of bakery products processed? To find out, consider two bakeries that each process 250,000 pounds of products per day. Both pay a BOD5 surcharge of 20 cents per pound. Processor A discharges 1 pound of BOD5 per thousand pounds of products pro-cessed, while Processor B discharges 5 pounds of BOD5 processing the same amount of bakery products.

Table 1 shows the daily and annual surcharge costs for the two plants. The operators of Plant A save $6.40 per thousand cases of products processed. That means they can bank an extra $200 per day or $50,000 annually if the plant operates 250 days each year. In effect, Processor B is pouring that amount of money down the drain.

It is also important to remember that the excess waste load reflects product lost during processing, and the cost of this lost product must be added to the surcharge to find the true cost of a higher waste load.

To estimate the potential savings for your plant, determine the sewer surcharges in your community and the current waste load produced by your plant per thousand pounds of products processed. Then calculate the amount you think the waste load could be decreased by improved operating practices. Enter the values in the following work sheet to compute your savings (Table 2).


Table 1. Potential Surcharges for Two Bakeries Producing 250,000 Pounds of Bakery Products Per Day

         	               Processor A    Processor B     Advantage
Waste Load (lb BOD5/1,000 lb        1             5               4
of products processed)
Daily Surcharge1	           $50	         $250	        $200
Annual Surcharge1	       $12,500	      $62,500	     $50,000              
Cost/1,000 cases2 processed	 $1.60    	$8.00	       $6.40
1Surcharge on BOD5 at $0.20 per pound of BOD5.
2One Case = 8 pounds of product.


Table 2. Sewer Surcharge Savings for Your Bakery

	                                             Current  	 Target
Enter current and target waste load in 
pounds of BOD5 per thousand pounds of
products processed
	
Enter daily production in thousands of pounds
Multiply current and target waste 
loads by daily production to find daily 
waste load in pounds
	
Enter your BOD5 surcharge 
cost per pound   $
Multiply the daily waste load by the 
surcharge cost to find your daily
surcharge cost 
                                                	$	  $
Enter the number of days 
your plant operates each year
Multiply the daily surcharge cost by the
number of days your plant operates 
annually to find the annual surcharge cost
                                                        $         $
Subtract the annual surcharge cost for 
the target waste load from the annual 
cost for the current waste load to find your 
annual savings 	$


You Can Reduce Waste Load and Save Money in Your Plant

You can take positive steps to reduce the waste load produced by your plant. Suggested priority steps for managers are given in Table 3. To keep tabs on your progress, use the work sheet to calculate your plant’s waste load. Specific suggestions for reducing pollution from bakeries are given in Table 4.

You will not only help to protect the environment, you will also show the people in your community that your firm is a responsible corporate citizen.

AND...you will send more money to the bank instead of down the drain.


Table 3. What Can You Do to Reduce Waste Load at Your Bakery?

Positive steps must be taken to reduce waste load in a bakery. You can make the difference at your plant:


Table 4. Suggestions for Preventing Pollution in Bakeries


Other publications of interest to bakers include:
Liquid Assets for Your Bakery (CD-41)
Dissolved Air Flotation Systems (DAFs) for Bakeries (CD-43)


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.


CD-42