Can Wastewater from Scrubber Drain to Sewer?

Q. Due to a huge increase in production of our aluminum products, we are evaluating the installation of an anodize line into our plant in order to anodize the parts in house instead of shipping parts off-site. Currently, we do not have any process wastewater discharges to the sewer. The equipment supplier that we are working with has put together a concept whereby the rinse waters are recycled and do not go to drain. However, the scrubber water overflow does go to drain. Because this flow is very small, probably less than 100 gallons per day, the supplier says that this scrubber water can be discharged to the sewer “with no problem.” The scrubber does have pH control with caustic in order to remove the sulfuric acid mist; the pH of the scrubber water is supposed to be controlled between 7.0 and 9.0. K.J.

 

A. It all depends what the supplier means by “with no problem.” Because of the expected pH levels and very low metal concentrations of the scrubber water, there is a very high probability that the wastewater would not need further treatment. However, the wastewater would still need to be permitted for discharge. Because the scrubber water is directly associated with a metal finishing process (anodizing) and contains contaminants from the metal finishing process (mists from the anodizing tank), the scrubber water is considered regulated process wastewater under EPA’s Metal Finishing Point Source Category 40CFR433 and, therefore, subject to these regulations and standards.

Unfortunately, there is no “de minimis” quantity of wastewater that, below which, the wastewater is not regulated under the Metal Finishing standard. Hence, this very small amount of wastewater must be permitted and periodically monitored in the same way as large metal finishing operations. The following is a list of regulatory requirements:

A wastewater discharge permit application is needed from the sewer district or state EPA; typically, application needs to be submitted 60–180 days before discharge begins.
At least 90 days before discharge commences, a Baseline Monitoring Report (BMR) must be submitted to the sewer district and/or state EPA.
The wastewater discharge must comply with the Metal Finishing Pretreatment Standards for New Sources (40CFR433.17) for cadmium, chromium, copper, lead nickel, silver, zinc, total cyanide or cyanide amenable to chlorination, and total toxic organics (TTOs) or the local sewer district’s limits, whichever are more stringent. While unlikely, the local sewer district could even have limits on the discharge of aluminum.
The sewer district will require some type of sampling; due to its very small volume, you should be able to convince the sewer district that flow-proportional sampling is “infeasible”, and, hopefully, convince them that compositing a series of grab samples throughout the operating day is sufficient,
Sampling and analysis of the wastewater, at least, on a semi-annual basis.
The sewer district can require pH monitoring and recording, either continuous or grab sample, and
As an alternative to expensive total toxic organics analysis, develop and implement a Toxic Organic Management Plan to certify that you are not dumping concentrated toxic organics, such as solvents, into the sewer.
As you can see, there is a large amount of regulatory compliance effort and costs associated with such a small amount of wastewater. Our recommendation is either work with your process supplier to stop the scrubber discharge or install a small storage tank to collect this wastewater for off-site treatment/disposal as a likely non-hazardous waste. Let me know what your final solution is.