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With EPA proposed Iron and Steel and Metals Products & Machinery (MP&M) Effluent Limitation rule coming effect, the subjected discharger facilities need to have a plan to comply with the proposed requirements and its financial impact. EPA estimates 63,000 facilities will be subject to the MP&M that includes 18 industrial sectors. Compared to today's Effluent Guideline limits, the proposed limitation has much lower metal limitation and more additional parameters. In certain sectors, the mass-based limits (i.e., lbs per 1000 lbs or per day) will be set instead of a concentration base (i.e., mg/l or ppm). Most of today's industrial wastewater treatment systems will face a challenge to meet these proposed limits. The type of treatment technologies and the options available will need to be considered in dealing with this upcoming, more stringent discharge limit.

Today's heavy metal wastewater treatment systems are commonly equipped with neutralization, flocculation, and clarifier to settle the metal hydroxide. Then, the clear effluent can be discharged and the dewatered sludge cake is ready for disposal. To meet the proposed sub-ppm discharge limits, the heavy metal bearing wastewater needs to be treated more efficiently to achieve compliance. EPA considers two Best Available Technologies (BAT), one is inclined gravity settling clarifier (e.g., lamella clarifier) and the other is microfiltration (e.g., membrane filtration).

In the metal-related production process metal comes in contact with lubricant and hydraulic fluid. The oily wastewater commingled with metals will need to be treated. Pre-treatment of oil and grease pollutants are necessary prior to the metal treatment. The available techniques to remove oil include oil-water separator, oil skimmer, dissolved air floating, or ultrafiltration.

Instead of the end of pipe treatment, facility pollution prevention and process waste minimization cannot be overlooked. Several pollution prevention (P2) practices include reduction of water usage, extending the life of process chemicals, or recycling/reuse technologies. Several successful cases for each area are listed below:

Flow reduction: Rinse water control, airknives to reduce chemical drag-out, wetting agent, temperature, lower concentration and others.

In-process P2 technologies are used to reduce the pollutant loading to wastewater treatment which in turn reduces treatment cost, such as filtration, waste segregation, evaporation, ion exchange/RO, electrodialysis, centrifugation, carbon adsorption and chemical substitution or elimination.

Recycling or reuse: Closed-loop recycling, acid regeneration, spent acid beneficial reuse, precious metal reclamation and electrolytic recovery.

In addition to these technologies, operator training and production planning also play a critical part in facility waste management and wastewater treatment. P2 needs to be incorporated into the wastewater treatment operation and should be evaluated before the commitment to costly capital improvements and the expenditure of a treatment system.

Document Type: Research Article


Publication date: January 1, 2002

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