Industrial wastewater may contain pollutants which cannot be removed by conventional sewage treatment. Also, variable flow of industrial waste associated with production cycles may upset the population dynamics of biological treatment units, such as the activated sludge process. Thus, industrial wastewaters can pose serious hazardous to municipal systems because the collection and treatment systems have not been designed to carry or treat them.
Table 3.4 Examples of industrial wastewater concentrations for nonconventional pollutants.
| Industry | Pollutant | Concentration (mg/l) |
| Coke by‐product (steel mill) | Ammonia (as N) | 200 |
| Organic nitrogen (as N) | 100 | |
| Phenol | 2 000 | |
| Metal plating | Chromium (VI) | 3–550 |
| Nylon polymer | COD | 23 000 |
| TOC | 8 800 | |
| Synthetic textile | COD | 3 300 |
| Nitrogen | 40 | |
| Meat processing and packing | COD | 2 100 |
| Nitrogen | 150 | |
| Phosphorus | 16 | |
| Grease | 500 | |
| Temperature | 28 °C | |
| Plywood‐plant glue waste | COD | 2 000 |
| Phenol | 200–2 000 | |
| Phosphorus (as PO4) | 9–15 | |
| Chlorophenolic manufacture | Chloride | 27 000 |
| Phenol | 140 |
Highly regulated industrial effluent usually receives at least pretreatment, if not full treatment, at the factories themselves to reduce the pollutant load, before discharge to the sewer. Using proven treatment technologies and manufacturing practices that promote recycling, industries can remove or eliminate pollutants before discharge of wastewater. This practice is called industrial wastewater treatment or pretreatment.
The pretreatment program is a component of the USEPA (United States Environmental Protection Agency) national NPDES (National Pollutant Discharge Elimination System) program. It is a cooperative effort of federal, state, and local environmental regulatory agencies established to protect water quality. Similar to how USEPA authorizes the NPDES permit program to state, tribal, and territorial governments to perform permitting, administrative, and enforcement tasks for discharges to surface waters (NPDES program), EPA and authorized NPDES state pretreatment programs approve local municipalities to perform permitting, administrative, and enforcement tasks for discharges into the municipalities’ POTWs. A treatment works (as defined by CWA section 212) is owned by a state or municipality [as defined by CWA section 502(4)]. This definition includes any devices or systems used in the storage, treatment, recycling, and reclamation of municipal sewage or industrial wastes of a liquid nature. It also includes sewers, pipes, or other conveyances only if they convey wastewater to a POTW treatment plant.
The national pretreatment program identifies specific discharge standards and requirements that apply to sources of nondomestic wastewater discharged to a POTW. By reducing or eliminating waste at the industries (“source reduction”), fewer toxic pollutants are discharged to and treated by the POTW, providing benefits to both the POTWs and the industrial users. Oversight of the program is by the POTW, state, or the EPA. The control authority issues permits for discharge of industrial wastewaters to the POTW. The permits contain numerical limits for controlled pollutants and requirements for sampling, flow measurements, laboratory testing, and reporting.
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