7 Del. Admin. Code § 7103-17.0
Current through Reigster Vol. 28, No. 6, December 1, 2024
Section 7103-17.0 - Characterization Parameters17.1 Generation Rate. The quantity of wastewater generated per year must be determined so annual generation rate of constituents can be calculated. Variability in rate must also be considered because this variability can affect storage, cropping systems and land requirements. Most municipal treatment plants have a constant flow. However, those in seasonal use areas such as beach resorts will have large seasonal fluctuations. Industrial waste flows may be constant but will vary during plant shutdown periods or if batch processes are used.17.2 Composition. The solids content of municipal wastewater does not pose a problem, however, screening may be necessary to remove trash introduced in ponds, storage lagoons, etc., so pumps and sprinklers are not damaged or clogged. Solids content of certain industrial wastewater may affect the selection of crops and the possible need to flush the system and the crop with clear water after irrigation.17.3 Plant nutrient content must be determined so wastewater rates may be applied to supply adequate nutrients for good crop production but to prevent excess rates which exceed the assimilative capacity of the soil-crop system.17.4 Salts are important from two standpoints. High concentrations of total dissolved salts can cause crop injury due to osmotic effect. High concentrations of Na in the absence of adequate Ca and Mg (expressed as sodium adsorption ratio [SAR]) will reduce soil permeability due to clay dispersion.17.5 The trace metal concentrations are important because of their effect on crop production and on animal or human health. High accumulations of copper, zinc and nickel will cause crop injury before concentrations in the crop are high enough to be toxic to consumers of the crop. Lead has never been shown to cause toxicity in crops; and since plants normally do not translocate high amounts of lead to their shoots, there is little danger of lead injestion by consumers of the crop unless it is present on leaf surfaces.17.6 However, in most crops cadmium can accumulate to concentrations that are not toxic to the crop but may be harmful to consumers of the crop. The most prevalent problems in humans due to excess cadmium ingestion are kidney and bone disorders.17.7 It is important to know the organic content of wastewater (usually measured as COD1). Excessive COD loadings can cause anaerobic conditions at the soil surface, greatly reduce infiltration, and cause unpleasant odors.17.8 Wastewater may contain specific organics that are resistant to decomposition or may be toxic or carcinogenic. Resistant organics such as chlorinated hydrocarbons, some halogenated insecticides, PCB's and PBB's may be present. These compounds are not absorbed from soil by plants, but irrigation may leave them on leaf surfaces which may be later ingested by animals fed hay from the site. Thus, if vegetation from the site is to be fed as hay and these constituents are known to be present, then the vegetation should be analyzed before use as livestock feed.17.9 Experience over many years has shown the health hazard associated with land treatment of wastewater to be very low. However, an analysis for fecal coliforms in wastewater is generally required. Normal sanitation practices by workers and prohibition of growing crops for direct human consumption help alleviate concerns about the health hazard. 17.10 Representative Sampling. It is important that the wastewater sample analyzed be representative of the entire flow; thus, a scheme of periodic or composite sampling should be used. After the land treatment system is in operation, a regular analysis program should be set up so land treatment can be modified if wastewater composition changes significantly.17.11 Wastewater Analysis Analysis of wastewater should be completed to determine essential plant nutrients, solids content, oxygen demand, important trace metals, pH and other critical constituents dictated by the type of industrial input. If it is suspected or known that inputs to the wastewater treatment system contain other potentially toxic substances or substances which would affect system design, the wastewater should be analyzed for these also. 17.12 1COD is more appropriate than BOD for land treatment system design.The microbial population in soil is much more diverse than the population in water and can bring about greater rates of organic matter decomposition.17.13 Pretreatment and Source Reduction. In general, the principal objectives of pretreating wastewater prior to land treatment are to reduce solids and any toxic substances associated with the solids (e.g. heavy metals), reduce pathogens, and minimize or control odors. Also, for nitrogen containing wastewaters, the pretreatment method that results in the lowest production of nitrate is the most preferred method.17.14 After wastewater analysis, one may find one or two constituents that reduce or limit the suitability of the wastewater for land treatment. Industries may find it economically feasible to make changes in their processes or increase the degree of pretreatment to reduce the concentration of the limiting constituent. 7 Del. Admin. Code § 7103-17.0