Prepared by:
Wayne A. Bough
Manager, Environmental Affairs
Formulated Dairy Foods Group
Mid-America Dairymen, Inc.
Roy E. Carawan
Extension Food Science Specialist
North Carolina State University
Publication Number: CD-39
Last Electronic Revision: March 1996 (JWM)
As a result, more and more food processing plants are facing the decision of whether to install wastewater pretreatment facilities and implement other methods for saving water and reducing waste. Intelligent decisions on water conservation, waste reduction, and pretreatment programs must be based on adequate information. By monitoring water use, raw waste loads, biomass (sludge) production from pretreatment facilities, and unit treatment costs, managers can obtain the data they need.
To gain the information needed, Mid-America's managers began monitoring their plants to measure water use, waste load discharged, biomass (sludge) produced by the pretreatment facility, and costs.
Seven of these plants, the products processed, the type of pretreatment facilities used, and the average daily wastewater flow rates are shown in Table 1. Annual wastewater discharges and raw waste loads for these plants are given in Table 2. The waste load in the water discharged from the production facility before pretreatment is referred to as the raw waste load to distinguish it from the waste load in water discharged after pretreatment. Raw waste load was calculated from measurements of the biochemical oxygen demand (BOD5) and wastewater flow rate.
The effectiveness of the pretreatment systems used at plants 2, 3, 4, and 6 was assessed by measuring the amount that it reduced BOD5 in the wastewater.
The volume of biomass (residue recovered during pretreatment) was tabulated, and the amount of biomass produced per unit of BOD5 removed was calculated. (See Table 3.)
Table 1. Pretreatment Facilities, Products, and Daily Wastewater Flow of the Dairy Plants Monitored
Average Plant Wastewater Number Products Pretreatment Facilities Flow Rate (gal/day) 1 Infant formulas, butter pH equilibration 234,000 2 Nutritional and infant Trickling filter (plastic), 467,000 formulas clarification, lime coagulation 3 Cheddar curd, Anaerobic, aerated basins, trickling electrodialyzed whey, filter (plastic), clarification 353,000 dried condensed milk 4 Yogurt, sour cream, Clarification, lime coagulation 103,000 whipping cream 5 Cottage cheese, Flow equalization 197,000 dried cheese coatings 6 Cheddar, dried whey Trickling filters (rock), 204,000 clarification 7 Milk receiving and None 8,000 shipping
Pretreatment costs were calculated by totaling costs for interest, depreciation, maintenance, labor, biomass disposal, power, and management. These computations were simplified by entering the data into a computer spreadsheet program that calculated loads, removal rates, efficiencies, running averages, and ratios.
To obtain total waste treatment costs, municipal sewer charges and surcharges were added to the pretreatment costs. Costs for the seven plants are presented in Table 4.
Pretreatment costs at Plant 3 were 22 cents per pound in 1987, 17 cents per pound in 1988, 19 cents per pound in 1989, and 31 cents per pound in 1990. Costs at plant 2 were 24, 24, 22, and 31 cents per pounds of
Annual Wastewater Discharge Raw BOD5 Load Plant (million gallons per year) (million pounds per year) Number 1987 1988 1989 1990 1987 1988 1989 1990 1 154 86 84 48 1.0 0.7 0.8 0.6 2 157 169 184 153 1.0 1.1 1.2 1.0 3 116 146 123 110 2.5 3.2 3.1 2.6 4 44 30 38 54 1 1 0.5 0.8 5 74 78 63 62 0.6 0.7 0.8 1.0 6 74 77 72 82 1.3 1.3 1.2 1.4 7 1 3 3 1 1 0.05 0.4 1
Volume of Biomass Biomass Ratio Plant (million gallons per year) (gallons per lb of raw BOD5) Number 1987 1988 1989 1990 1987 1988 1989 1990 2 1.7 1.9 1.8 2.3 1.75 1.69 1.47 2.20 3 4.1 2.0 1.6 6.2 1.62 0.63 0.53 2.33 4 0.6 0.6 0.8 0.9 N/A N/A 1.72 1.09 6 2.4 3.2 1.9 2.3 1.86 2.52 1.56 1.62
BOD5 removed in 1987, 1988, 1989, and 1990, respectively. Costs at plant 4 were 0.34 in 1989 and 0.29 in 1990.
Although costs have been contained through good maintenance and care-ful management, the costs for the three plants (2, 3, and 6) with com-plete data indicate cost increases of 29, 40, and 83 percent, respectively, over this four-year period. The large increase at plant 6 was due to reduced loads and decreased efficiency resulting from a city-mandated curtailment in lime coagulation.
Comparing the BOD5 removal costs to data published in 1986 by the U.S. Environmental Protection Agency (USEPA) shows that the pretreatment plants were operating efficiently. The removal costs were decidedly less than the USEPA figure of 35 cents per pound for small municipal systems (those handling 0.38 to 3.3 million gallons per day) and approximated the 18-cent-per-pound predicted costs for large municipal systems (25 million gallons per day).
Table 4 compares total treatment costs for the four processing plants that have pretreatment systems with the costs for the three plants that discharge raw wastes to municipal systems. Plant 5 clearly had the lowest cost, 3 cents per pound. However, costs can escalate dramatically in a short period of time. Because of a new sewer ordinance, the surcharge increased by a factor of 10; plant 5 will pay 30 cents per pound in future years. Plant 1, located in a much larger town and paying over $250,000 per year in sewer bills, had total treatment costs of 26 cents per pound in 1987, 21 cents per pound in 1988, 20 cents per pound in 1989, and 21 cents per pound in 1990. These costs were similar to the pretreatment costs alone at plant 2 during those years. Thus treatment costs per unit of raw BOD5 discharged were no greater when all BOD5 removal was done by a large municipal treatment system than when the wastewater was pretreated and then discharged to the municipal system.
The amount of raw waste load affects pretreatment costs. For ex-ample, compare the raw BOD5 loads for plant 3, shown in Table 2. The treatment costs at plant 3 dropped from 23 cents to 18 cents per pound of BOD5 from 1987 to 1988 (Table 4), primarily because of production increases that generated more BOD5 load for the pretreatment plant without any increase in operating costs. Actually, biomass hauling costs decreased at plant 3 in 1988 because the waste treatment operators learned how to manage wasting of aerobic biomass to the anaerobic reactor. They were able to reduce the volume of biomass hauled from over 4 million gallons to 2 million gallons (Table 3). However, this practice may have contributed to severe operational problems with the anaerobic reactor experienced during the fall of 1989. The anaerobic reactor was removed from service and the treatment accomplished by the aerobic system. These changes are reflected in the biomass ratio, which was 1.62 in 1987, 0.63 in 1988, and 0.53 in 1989, and 2.33 in 1990 (Table 3). The biomass hauling cost (1 to 2 cents per gallon) dramatically affected costs, as shown in Table 4.
Pretreatment systems remove pollutants from the wastewater and concentrate them in the biomass produced in the pretreatment process. The disposal of this biomass is becoming more costly, and regulations governing how this material is stored, transported, and used are becoming stricter. Plant managers find that their biomass disposal costs range from 1 to 10 cents per gallon. It is less costly, better for the environment, and easier for plant managers if the biomass can be marketed as a by-product instead of being disposed of as waste material.
To address the biomass disposal
problem, Mid-America participated in a five-year research program with the University of Missouri. The research explored the application of biomass to agricultural land for the production of crops such as fescue, alfalfa, and red clover. The program demonstrated the beneficial effects on these crops and established application rates. Many of the benefits stem from the quicklime (calcium carbonate) added to the biomass. The biomass ratio ranges from about 0.5 to 2.5 gallons per pound of raw BOD5, with an expected average of approximately 1.5 gallons per pound. The biomass ratio for BOD5 removed ranges from 0.6 to 3.0 gallons per pound of BOD5 removed, with an expected average of approximately 2.0 gallons per pound of BOD5 removed. The cooperatives named the biomass "Dairygro" to help promote its use on cropland. The use of this name helps differentiate the dairy pretreatment biomass from municipal sludges, septic tank septage, poultry litter, and other materials that are sometimes spread on the land.
This process of comparing treatment costs and calculating cost ratios raised the plant managers' awareness of water and waste management and encouraged them to find ways of reducing waste. It prompted the vice-president of manufacturing and engi-neering to establish a waste reduction program. He created an environmental waste committee composed of midlevel managers and department heads from the division staff and assigned the environmental manager to chair the committee.
Table 5 shows the results of spring and fall surveys in 1988 and the savings in flow observed. Water use and loss were categorized according to the way in which they could be reduced. For example, the training category includes water wasted by leaving hoses running or faucets open, problems that could be corrected by better training of workers. The preventive maintenance category includes water wasted because of leaking valves and dripping faucets that could easily be repaired. The projects category includes opportunities to save water by installing tanks, controllers, or other pieces of equipment.
Division-wide reductions of 60 percent were observed in the training category. In the preventive maintenance category, an overall reduction of 81 percent was achieved. Because efforts in the waste reduction program in 1988 were devoted primarily to the training and preventive maintenance categories, it was not surprising that a reduction of only 7 percent was realized in the projects category. Management decided that the training and preventative maintenance activities were so successful that they should be repeated about every five years. They have already been scheduled for 1993.
This process of comparing treatment costs and calculating cost ratios raised the plant managers' awareness of water and waste management and encouraged them to find ways of reducing waste. It prompted the vice-president of manufacturing and engi-neering to establish a waste reduction program. He created an environmental waste committee composed of midlevel managers and department heads from the division staff and assigned the environmental manager to chair the committee.
Table 5 shows the results of spring and fall surveys in 1988 and the savings in flow observed. Water use and loss were categorized according to the way in which they could be reduced. For example, the training category includes water wasted by leaving hoses running or faucets open, problems that could be corrected by better training of workers. The preventive maintenance category includes water wasted because of leaking valves and dripping faucets that could easily be repaired. The projects category includes opportunities to save water by installing tanks, controllers, or other pieces of equipment.
Division-wide reductions of 60 percent were observed in the training category. In the preventive maintenance category, an overall reduction of 81 percent was achieved. Because efforts in the waste reduction program in 1988 were devoted primarily to the training and preventive maintenance categories, it was not surprising that a reduction of only 7 percent was realized in the projects category. Management decided that the training and preventative maintenance activities were so successful that they should be repeated about every five years. They have already been scheduled for 1993.
Managers of the dairy cooperative found that by monitoring water use, raw waste load, biomass production, and wastewater treatment costs they could improve operations and reduce costs. They found that pretreatment costs are not necessarily less than the charges levied for direct discharge to publicly owned treatment works. Based on their ability to track costs, water use, and waste load, they established a successful waste reduction program. They found it far more economical to reduce water use and waste in the plant than to operate pretreatment facilities or pay surcharges. Other dairy and food plants could benefit by implementing similar monitoring and waste reduction programs.
problem, Mid-America participated in a five-year research program with the University of Missouri. The research explored the application of biomass to agricultural land for the production of crops such as fescue, alfalfa, and red clover. The program demonstrated the beneficial effects on these crops and established application rates. Many of the benefits stem from the quicklime (calcium carbonate) added to the bio-mass. The biomass ratio ranges from about 0.5 to 2.5 gallons per pound of raw BOD5, with an expected average of approximately 1.5 gallons per pound. The biomass ratio for BOD5 removed ranges from 0.6 to 3.0 gallons per pound of BOD5 removed, with an expected average of approximately 2.0 gallons per pound of BOD5 removed. The cooperatives named the biomass “Dairygro” to help promote its use on cropland. The use of this name helps differentiate the dairy pretreatment biomass from municipal sludges, septic tank septage, poultry litter, and other materials that are sometimes spread on the land.
Table 5. Spring and Fall Water Use, 1988
Preventive
Training Flow Maintenance Flow Projects Flow
Plant (gal/min) (gal/min) (gal/min)
Number Spring Fall Spring Fall Spring Fall
1 39 11 12 3 182 189
2 25 22 197 21 413 405
3 0 0 7 5 22 7
4 31 1 15 15 23 24
5 6 6 10 2 36 32
6 0 0 0 0 205 165
Total 101 40 241 46 881 822
Waste Reduction Program Established
Conclusions
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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