Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
March, 2002

Pollution From Metal Finishing Operations

Q. Im a student in chemical engineering and Im studying pollution by heavy metals due to metal finishing operations. Have you got recent information about a review of metal finishing plants and survey of wastewater effluent discharges from these types of operations in USA?

A. Some information is available but keep in mind that many facilities do not meet reporting threshold limits and therefore do not show up in the databases. Also keep in mind that the US EPA definition of a metal finisher only applies to facilities that first meet the definition of the Electroplating source category. Therefore many facilities that do some metal finishing processes such as grinding, honing and polishing only do not show up at all in the data.

The Toxic Release Inventory (TRI) is a reporting system operated by EPA to track chemical releases from manufacturing operations. Companies with 10 or more employees that meet certain thresholds are required to submit TRI reports each year by July 1 that cover the previous calendar year. You can access the 1999 TRI data (latest available data) on the Internet at: http://www.epa.gov/enviro/html/tris/tris_query.html. The SIC code for electroplating is 3471. Keep in mind that the TRI data base includes only certain regulated chemicals and metals, has quantity reporting triggers, and includes all emissions to air, land and water. If a regulated facility uses more than 10,000 lbs per year of a zinc compound they are required to report even if 9999 lbs. leaves the facility as hot dip galvanizing on the parts they sell! If they only use 9,999 lbs. (i.e. if they have not exceeded the usage reporting limit) in the year and if they dump say 8,000 lbs of it in a properly permitted landfill they would not be required to report under the TRI!

National data on hazardous waste disposal and air emissions of heavy metals for a specific industry such as metal finishing will be much more difficult to nail down data on since many states now run those programs directly in their own state. You would need to get the data on a state by state basis and that is if they have it in a usable form. Even then they may have a hefty fee for the data.

For approximately 20 years, EPA has closely regulated the wastewater discharges of metal finishers. Wastewater discharges from electroplating and other metal finishing operations are currently regulated by federal standards 40 CFR 413 (http://www.access.gpo.gov/nara/cfr/waisidx_03/40cfr413_03.html) and 40 CFR 433 (http://www.access.gpo.gov/nara/cfr/waisidx_03/40cfr433_03.html). These are the base regulations for this industry sector. Local sewer districts often impose more stringent standards. Also note that EPA has proposed new federal standards called the Metal Products and Machinery (MP&M) effluent guidelines (see http://www.sterc.org/mpm.php) that are scheduled to be issued by the end of this year with final compliance deadlines in December 2005.

Since you are a chemical engineering student I would suggest that you look at the entire mass balance (in - out = accumulation) and consider air and solid waste issues as well as waste water. For instance chromium plating facilities must capture chromium metals from plating tank air ventilation systems and waste water discharges. While cleaning up the air and waste water discharges they frequently (depends on the process) produce a sludge byproduct that in the US is a listed hazardous waste. Some facilities recycle this by shipping it to metal recycling firms that extract, recover and recycle the metal (chromium, nickel, lead, silver, etc.). Other facilities dispose of the sludge in permitted hazardous waste landfills. Most of the non-product, non-recycled heavy metals disposal (probably 99.9%) ends up in hazardous waste double lined permitted landfills.

An interesting project would be to compare the quantity of metals shipped to consumers as product to the TRI reported landfilled metals and then compare the discharged metals by the metal finishing industry to the quantity discharged by households. You may discover that, overall; the metal finishing industry is discharging much less metal. Also keep in mind that some of the TRI reported quantities may be hydrated compounds (because of the reporting rules) and only a fraction of the mass balance may be the pure metal content for solid waste shipped to landfills.

I hope this is some help to you. Good luck with your project.