Potential Areas of Research for Modification of the Fresh Fruit Packing General Permit
The intent of this talk is to increase dialogue about an area of the current Fresh Fruit Packing General Permit where changes are needed. Washington State Department of Ecology (DOE) officials have presented significant proposals regarding upcoming changes in the next 5-year permit cycle for the Waste Water General Permit. Proposed modifications including changes related to the disposal of pear float, and drencher water containing calcium chloride. However, as the current and future permit now stand, effluent limits (TDMs) for disposal to land application and percolation treatment will not be changed.
Current effluent limits for these TDMs unnecessarily put the industry in a defensive position, because it does not take into consideration the contribution made by the soil to the treatment of the wastewater. I will outline and summarize historical data regarding wastewater disposal via land application and percolation, as it relates to disposal limits set in the current Fresh Fruit Packing General Permit. This data strongly indicates that the current limits for total dissolved solids (TDS), biological oxygen demand (BOD), and total suspended solids (TSS), are set well below levels at which soil systems are able to adequately treat for the protection of groundwater.
Total dissolved solids removal by soils
Problem areas and wastewater composition
In 1996, most of the industry violations for both land application and percolation disposal were because of high levels of TDS. Most of the violations were from non-contact cooling water discharges from evaporative cooling towers. Evaporation in this water results in the concentration of minerals naturally present in the water. Predominant minerals in Eastern Washington well water are calcium and bicarbonates. Other minerals are present but in much smaller amounts. So most of the TDS content in this wastewater can be attributed to benign minerals which make up what is chemically named calcium carbonate, or lime.
dissolved solids removal in the soil
Many of the ions that make up the TDS of packinghouse wastewater are effectively renovated by spray irrigation or percolation treatments. The residence time in association with soil particles can be sufficient to achieve up to 75% removal of the cationic (positively charged ions) content of wastewater (Spyridakis and Welch, 1976). The soil components active in the removal or reduction of TDS are organic matter and colloidal clays. Organic matter has many reactive sites that have the ability to fix, in exchangeable form, both cations and anions (negatively charged ions). Clays are generally defined as mineral particles less than 2 microns in size. In most soils, clay is the most abundant and active component. Clays have tremendous surface area relative to their masses: even in sandy soils, 95% of the total surface area is associated with clay particles. Clays have an internal negative charge usually described in terms of cation exchange capacity. Divalent cations, such as calcium and magnesium, are strongly attracted to clay particles in the soil profile.
Retention of cations by clay particles facilitates their precipitation and mineralization in the soil. Major losses of TDS occur through precipitation of calcium and magnesium as carbonates. Acknowledgment of this phenomenon resulted in the development of the MINETEQA1 computer program for the US EPA to aid in the computation of aqueous speciation, absorption, and precipitation/dissolution of solid phases (USEPA, 1987). This model serves as a convenient means of estimating probable ion complexes that form in the ground water. If the mass of an ion is removed from solution due to precipitation, it remains in the soil profile and has reduced capacity to percolate downward to ground water.
This information has direct relevance to Eastern Washington fruit packers. As discussed above, cooling tower wastestreams of this region have high levels of calcium bicarbonate in the form of calcite (CaCO3). Their presence is commonly measured as total water hardness. Concentration of these waters by evaporation in non-contact cooling towers results in total hardness levels which may range from 300 to 800 mg/L, making up most of the total dissolved solids in the water (R. McLaughlin, personal data). At 1 atmosphere of pressure, calcite (100 mg/L) has very low water solubility. For wastewater having total hardness levels of 300 to 800 mg/L, precipitation of a significant proportion of the calcium and magnesium hardness can be predicted in the soil profile. As a result, a very large portion of the TDS will remain mineralized in an innocuous form in the soil profile.
BOD and suspended solids removal by soils
The capacity of the soil and its microflora as a physiobiological remover of BOD and suspended solids is enormous. Net BOD removal efficiency has been observed to be quite high even with the coarsest soil and highest infiltration rates studied (Spyridakis and Welch, 1976). A removal efficiency of 95 to 99% would be expected for aerobic soils. The soil acts as an effective filter in removing particulate and dissolved organic matter; most of the BOD, and all of the TSS, removal occurs in the upper 5 to 6 inches in the profile (Law, et al., 1969). Physical removal in this layer can account for as much as 30 to 40% of BOD.
Case histories illustrate the degree to which soil systems can effectively remove BOD. Industrial wastewater containing 1,150 mg/L BOD5 was sprayed on sand with high permeability and well covered with reed canarygrass and humus (Crawford, 1961). BOD5 removal was reported greater than 99% with a BOD5 loading of 138 lb/ac-day.
Elazar (1971) compiled several examples of wastewater treatment by application to soil which show that BOD5 removal efficiency for industrial wastewater is high even when loading is relatively high (Table 1). Two of the facilities were food processors (numbers 1 and 3) and one was a paper manufacturing company (number 2). A wide range of soil types (from glacial till to loamy sand) accomplished a minimum of 95% BOD removal at these sites. Note also that the data given for influent BOD levels is also expressed as weekly loadings per acre-week.
In order for BOD to be removed from soils, aerobic conditions must be maintained for efficient removal of BOD and TSS. Successful wastewater disposal sites allow for a drying period between applications. The perpetuation of anaerobic conditions in the soil surface layer leads to clogging and ponding. Clogging usually occurs in the top few inches of soil and is more a function of the organic mat that is largely independent of soil texture (Law and Thomas, 1969; Laak, 1971; Jones and Taylor, 1965).
Application of wastewater using "on-off" cycling allows for drying and re-establishment of aerobic conditions in the soil. This method of wastewater application should be feasible for most fresh fruit packers to achieve, since most packing lines generate wastewater from 8 to 16 hours per day, so there is a 8 to 16 hour rest period. Multiple wastewater application points can also be used to increase the rest period between application cycles.
Opportunities exist for modification of the existing Fresh Fruit Packing General Permit in the areas mentioned above. There is ample documented evidence that disposal limits currently in the Permit are too conservative. These limits ignore the treatment capacity of the soil and characteristics of the wastestreams that would facilitate disposal of TDS, BOD and TSS at significantly higher rates without causing harm to the ground water. Modification of the limits, or changing of the limits in terms of allowable loading rates per day, may require some research and documentation by the fruit packing industry.
For establishing higher TDS effluent limits, research data could be obtained to establish the wastewater characteristics from cooling tower wastestreams for organic and hardness mineral content in respect to total TDS. Testing of specific wastestreams with various soils used by fruit packers in Eastern Washington could be done to evaluate the range of TDS loss that can be expected in the soil profile.
For establishing higher BOD and TSS effluent limits, industry wastewater could be applied to various soil types at different rates to determine allowable loading rates. BOD loading rates of up to 200 lb/acre-day should be allowed at most packing facilities. The limiting factor should be whether or not the soil has the ability to percolate the wastewater. General Permit guidance as it now stands, is more than adequate in allowing only for discharges that do not cause ponding or overland flow.
Perhaps the most important type of change for future permits should encompass expression of effluent discharges as loading rates per surface area. Simple effluent limits, as found in the current permit, ignore the treatment aspect of the land application and percolation disposal methods. Modified disposal limits, based on the surface area to which the wastewater is applied, is a reasonable approach for factoring in the treatment capacity of the soil. This approach to establishing limits should be adopted in future permits.There is some indication that DOE officials are acknowledging surface area in their proposals for the next permit. For calcium chloride disposal, they are factoring in surface area and annual rainfall to arrive at a "dilution to extinction" of chlorides in the soil profile. For SOPP (sodium orthophenylphenate, or Steri-Seal D) disposal, increased land area is being proposed for disposal of ligninsulfonate pear float water when SOPP levels exceed a concentration of 1000 mg/L
The industry should be encouraged that permit changes are being proposed. It should, however, expect additional changes that make sense from a historical standpoint for industrial wastewater treatment. I have outlined two very specific areas where changes can, and should, be implemented. I believe that applied research on this issue will help implement such changes and will, simultaneously, help maintain the important goal of protecting Washington State's groundwater resource.
Crawford, S. C. 1961. Spray irrigation of certain sulfate pulp mill wastes. Sewage Indust. Wastes 30:1266.
Elazar, D. J. 1971. Greenland - Clean Streams. The Beneficial Use of Waste Water through Land Treatment. Temple Univ. Press, Philadelphia, PA.
Laak, R. 1971. Influence of domestic wastewater pretreatment on soil clogging.
J. Water Poll. Control Fed. 42:1495.
Law, J. P., Jr., Thomas, R. E., and Myers, L. H. 1969. Nutrient removal from cannery wastes by spray irrigation of grassland. U. S. Dept. Interior, FWPCA, 16080-11/69.
Spyridakis, D. E., and Welch, E. B. 1976. Treatment processes and environmental impacts of waste effluent disposal on land. Pages 45-83 in: Sanks, R. A., and Asano, T., eds. Land Treatment and Disposal of Municipal and Industrial Wastewater. Ann Arbor Science Publishers, Ann Arbor, Michigan. 310 pp.
U.S. Environmental Protection Agency (EPA). 1987. MiNTEQA1, an equilibrium metal speciation model: User's Manual. Environmental Research Laboratory, Athens, GA. EPA/600/3-87/012. . U. S. Environmental Protection Agency, Cincinnati, OH.
Dr. R. McLaughlin
Columbia Technical Associates, L.L.C.
14th Annual Postharvest Conference,
March 10-11, 1998