Introduction. An industrial wastewater survey should gather enough information so professionals can develop a wastewater management plan. Such data include identification of the wastewater sources, and corresponding chemical compositions, quantities, variations, distribution, and discharge frequencies and durations of all process wastestreams. The data are used to describe the facility's wastewater, develop or model potential management strategies, and provide a baseline for evaluating the effects of changes in production, water conservation, or regulations [1].
Purpose of the study. The best way to collect such information is to discuss and diagram facility operations with the production manager and shift supervisors. The result should be accurate facility drawings showing the locations of various processing units and their relationship with water supply and wastewater generation and associated collection systems.
To develop an effective strategy, wastewater management professionals need to fully understand how each manufacturing process uses water and generates wastes. Then, each wastestream should be analyzed to determine its frequency, duration, flow rate, and pollutant types and concentrations. If possible, flows should be measured and samples collected via permanent monitoring stations; otherwise, temporary data-collection points should be used. The frequency, extent, and type of monitoring and sampling needed depend on each wastestream's nature and variability. To ensure that each wastestream is characterized appropriately, a sampling and analytical plan shouldbe prepared[2-4]. nce all wastestreams have been fully characterized, they can be sorted based on pollutant types or concentrations, or applicable EPA categorical effluent standards.
Materials and methods. Surveyors also should obtain environmental reports, community right- to-know reports or discharge monitoring reports), as well as monthly and annual records of chemical and raw material use and production. This information helps wastewater management professionals correlate material use and waste generation.
Results and discussion. Identifying Categorical Wastestreams. The standard industrial classification (SIC) code is typically used to determine applicability to industrial categorical effluent standards. Any wastestreams covered by federal categorical effluent standards should further be identified as subject to concentration limits, raw mate- rials-based standards, or production-based standards. Production-based standards, for example, directly relate the allowable mass rates of specific pollutants to the appropriate process's production rate. If categorical and noncategorical wastewater sources are combined before compliance sampling, the combined wastestream formula is used to determine compliance with the categorical limits. (For more information on this subject, see U.S. EPA, 1985.)
Identifying Wastewater Generators. The in-plant survey should identify wastestreams from both production processes and pollution-control efforts (e.g., wet air scrubber blowdown, sludge dewatering, product change washouts, site cleanup, yard drainage, noncontact cooling water, boiler blowdown, or secondary containment spillage). Although some of these wastestreams may be small and discharged infrequently (e.g., slugs), they could seriously affect the overall wastewater's treatability. Many industrial facilities consider treating hazardous wastes onsite because of the restrictions and costs associated with offsite disposal.
Surveyors should categorize wastestreams according to pollutant types. Doing so may reveal incompatibilities that must be resolved before the wastestreams can be combined. For example, plating shops may generate both acidic and cyanide-laden wastestreams that would be dangerous to combine until after the cyanide has been removed. Categorizing wastestreams also may reveal some that only contain conventional pollutants (e.g., BOD and suspended solids) and so may simply be discharged to a publicly owned treatment works (POTW) or a biological treatment plant onsite without additional treatment.
Conclusions. Some wastewaters—especially high-strength, complex industrial wastewaters— exhibit inhibited results when the BOD analysis involves a minimum number of dilutions and unacclimated seed (e.g., seed from a local POTW or commercial laboratory). The COD test is not subject to the effects of inhibition and can also be used to characterize industrial wastewaters. Chemical oxygen demand may be used to approximate BOD if the compounds contributing to BOD are consistent enough for a typical COD-to-BOD ratio factor to be applied. Chemical oxygen demand analyses may be run onsite in 2 to 3 hours, while BOD analyses, because of the incubation period, take 5 days in a laboratory to complete. When using COD to characterize a wastewater's organic strength, analysts must account for any inorganic, oxidizable components (e.g., ferrous, nitrite, sulfide, and sulfite) that may contribute to the COD concentration.
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