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 Small, out-of-date facilities have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.
