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

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:

• You can estimate your monthly BOD5 treatment bill.

  A plant discharges to a city that charges $0.20 per pound of BOD5. BOD5 Treatment Bill = 114,675 lb BOD5/month x $0.20/lb BOD5

  BOD5 Treatment Bill = $22,935.00 per month

• You can estimate the amount of monthly lost product. A plant discharged 114,675 lb of BOD5 for the month. Flour has a BOD5 of 0.65 lb per pound. Thus, if we assume all the BOD5 came from flour, we can calculate the amount of flour lost to the drain. Flour lost to drains = 114,675 lb BOD5 = 176,423 lb 0.65 lb BOD5/lb flour

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:

• Make waste reduction a management priority.
• Adopt the attitude that waste load reduction is one of the best business decisions a manager can make.
• Establish waste load reduction goals for your plant.
• Train employees in the concept of pollution prevention and how to perform their jobs to maximize pollution prevention in your plant.

Table 4. Suggestions for Preventing Pollution in Bakeries

• Establish waste load reduction goals for all important processes and areas of the plant where waste can be monitored and controlled.
• Increase maintenance to prevent product leaks from valves, piping, and equipment.
• Reduce water use; water used in processing will be WASTEWATER and subject to sewer and surcharge costs.
• Thoroughly drain tanks, troughs, mixers, and kettles of products before cleaning.
• Scrape mixers and kettles before cleaning.
• Collect solids from floor and equipment by sweeping and shoveling into containers before wetting equipment or floors. DO NOT USE HOSES AS BROOMS.

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