For wastewater purposes, most finishers are “indirect” dischargers and, as such, deal with publicly owned treatment works (POTW) as a regulatory authority. The rules that govern indirect discharge are somewhat different than those for direct dischargers, and they involve both federal and local requirements. Federal regulations for indirect dischargers, because of dramatic variability of intervening POTW systems, tend to function rather arbitrarily. Whereas, local requirements typically reflect the specifics of the POTW’s capabilities and the character of industrial discharges. Since indirect dischargers are first responsible to the municipality, finishers need to understand the operations and regulatory motives of their POTW.

A direct discharge has immediate impact on public waters. Federal regulations are intended to protect these rivers and streams. “Indirect” simply means that wastewater is not discharged directly to a receiving stream. Indirect discharges pass through POTWs, which provide some degree of subsequent treatment. The degree of treatment and ability to handle industrial volumes of wastewater vary between POTWs. Many issues affect POTW capabilities. In some cases, federal pretreatment regulations form a reasonable base for local regulation. In others, however, the federal regulations of the industrial discharge have little or no relation to protection of the receiving stream. POTWs themselves have extensive discharge permits (NPDES) that are very specific to the health of the receiving water.

The extremes in POTW capabilities overshadow federal requirements. In some cases, a given industrial waste stream may be inconsequential to the POTW, and it may enforce federal regulations as a minimum, albeit arbitrary standard. In others, the local limits of the POTW may be more stringent than federal limits. In the former situation, the industrial discharge may be small in comparison to the overall flow of the POTW and/or the treatment system of the POTW may be very effective at removing the pollutants. In the latter, the POTW may be relatively small, old or with limited capabilities. Small, out-of-date facilities have problems meeting basic domestic sewer demands. Industrial discharge may simply present the POTW with unwanted volumes of material or the character of the discharge might disturb the balance of the activity in the plant.

The primary job of a POTW is to treat human sewage, first for health reasons and second for environmental purposes. Other jobs, such as treating storm runoff and industrial wastewater, have been added to the mix. However, the primary job remains the same. To further frame the discussion, it’s helpful to understand that overall water quality in the U.S. has improved dramatically during the past 40 years, and reduced industrial pollution has been the principal contributor. However, because of population growth and other factors, pollution from non-industrial sources has improved very little. Undersized and outdated treatment systems mean domestic sewage remains a health and pollution predicament. As industrial issues have diminished, other factors like agriculture and urban runoff have become the big issues. (Almost all of the hundreds of beach closing annually are related to sewage overflows from POTWs.)

While the problems associated with the treatment of domestic waste are easily manageable in theory, they are expensive. Capital costs of POTW expansion and improvement are enormous, and operating costs are among the largest expenses paid by municipalities. Nationally, tens of billions of dollars will be spent addressing this over the next 20 years, but on a day-to-day basis the problems loom large.

Modern POTWs can easily treat a range of industrial pollutants. In many ways, treating industrial wastewater is a comparatively lucrative sideline for POTWs, since it is easier and cheaper to treat than domestic waste. Industrial discharges can offer large economies of scale to a municipal project, providing considerable flexibility and opportunity for long-term growth in the service area. There are other issues to be considered, but suffice it to say that industrial discharges can serve as a substantial subsidy to the primary mission of a POTW.

As an example, an aluminum anodizer will generate a significant amount of aluminum in its waste stream. Other than the aluminum, the discharge flow is relatively clean and dilute. Aluminum is a pollutant only to the extent that it clouds water and builds up as unwanted sediment. Just as naturally occurring clay or silt, aluminum sediment can choke the aquatic life at the bottom of a river. However, aluminum is relatively easy to remove, and an adequately sized POTW can accomplish this almost effortlessly in the process of removing other solids from its system. While there is some cost involved in handling the solids, the wastewater is cheaper to treat than domestic sewage because it does not contain carbonaceous waste and organic nitrogen. Aluminum is also believed to contribute to the removal of soluble phosphates, another pollutant coming mostly from domestic sources.

It should be clear from this discussion that potential synergies exist within the POTW for treating industrial and domestic wastes together. In truth, the potential is even greater. Modern POTWs are capable of producing extremely clean water, particularly when compared to many of the old systems operating today. Synergies with industry pose the opportunity for vast environmental improvement while offering better costs to taxpayers and local business. It can be a win-win situation for a community and the rivers that flow through it.

POTW improvements are very expensive, long-term projects. In many communities, improvements are mandated by EPA or the state. Local government may be overwhelmed by the challenges. Still, an opportunity may exist for industry to become involved in this process and to become part of a winning combination. A large industrial discharger, relative to the size of the community, has the greatest potential for impact. However, smaller industries—particularly as a united front—can also move things in a positive direction.

EPA has some natural reservations about such industry-utility partnerships, but there are significant precedents. Another factor in the equation is that POTW and sewer infrastructure typically last upwards of 50 years. Long-term planning and flexibility become vital for long-term success. Again, industrial flows can offer large economies of scale and associated flexibility when looking ahead.

Getting to know your community’s situation and problems is an important first step. In the process, you may also discover additional things that can assist you in handling your regulatory burden. Understanding the future needs of the community and surrounding area is another step, as is learning more about the characteristics of overall industrial discharges and of the local receiving waters. In general, regulators should consider anything that will result in quicker, sustainable improvement to the environment, despite any biases about industrial discharges. Industry can be a genuine part of the solution, in a cooperative cost-saving effort where everyone, especially the environment, comes up a winner.

HOW A POTW WORKS ­– A Non-stop 24/7 Operation

Primary Treatment:
Initially, liquids flow or are pumped to the treatment station where they are screened for coarse solids, perhaps baseball sized or larger. Next, the flow is channeled to a large tank where the velocity slows and smaller solids settle.

Secondary Treatment:
The critical element of modern treatment systems, commonly called “activated sludge.” This is a vast area of tanks where oxygen and nutrients may be added to encourage decay by microorganisms (the bugs.) The bugs are absolutely critical to the POTW, and they will defend it like a mother bear and her cubs. (If the bugs are killed or damaged, the plant will begin to send under-treated sewage into the river.) The bugs decay organic material, remove ammonia and create a relatively inert sludge which can be land filled or land applied (as fertilizer.)

The secondary processes have intensive energy inputs, primarily pumping and aeration. Nutrient balances are important. Some pollutants, like cyanide, silver, etc., can have a toxic effect on the “bugs” and are scrupulously controlled in the industrial discharge.

The large activated sludge tanks are followed by large clarifiers where even more sludge settles. At this point, the water is now relatively clear and clean.

Tertiary Treatment:
The most modern part of the system, not found in many older systems. Very fine solids and microbiologicals are removed via fine filtration and chlorination.