Gulf of Mexico
Google Earth - The satellite image shows the elaborately “constructed wetland” around the Sewerage & Water Board’s pilot project at Bayou Bienvenue.

Big ‘green’ mistake: dumping sewage in wetlands carries hidden costs

There is a dangerous confusion at the core of the current debate over a seemingly “greenwashed” way to handle sewage and other kinds of effluent.

In essence, the mistaken idea is that dumping partially treated wastewater into our shrinking wetlands will somehow nourish and restore them.

It appears to be an error on the part of regulatory agencies looking for ways to cut costs and sidestep more stringent permit enforcement. Among environmentalists, the same error reflects an over-eager search for solutions that might seem to rely on natural processes.

In fact, wastewater assimilation is a flawed concept that comes with heavy economic and environmental liabilities.

The flawed thinking is dramatically apparent at Bayou Bienvenue in the Lower 9th Ward, where the New Orleans Sewerage & Water Board is building a stalled $9 million pilot project for  “wastewater assimilation,” the focus of informative articles recently published by The Lens.

Against the backdrop of New Orleans’ — and the nation’s — aged and outdated sewage treatment infrastructure and a growing recognition that our wetlands are in dire need of conservation and restoration, it’s quite understandable that a simple, thought-to-be-true solution to a complex problem would be appealing. Aggressively promoted, it is proclaimed to be a “win-win” concept that saves money and helps the environment.

Adding to the conceptual confusion and potential for environmental degradation is the claim that nutrient pollution is consistently beneficial to natural wetlands, that it somehow nourishes and restores them without harmful alterations.

A fundamental source of error lies in a sometimes deliberate conflation of the wastewater-assimilation concept, which is unproven as a way to restore wetlands, with the well-proven concept of using a constructed wetland to treat sewage. Both concepts latch onto the idea of wetland treatment, but one concept treats sewage while the other concept receives treated sewage. They are, in fact, very different concepts.

Constructed wetlands are basically horizontal trickling filters using aquatic vegetation to treat sewage. The carefully engineered process moves water above or below an artificial wetland and then releases it through defined outlets. The water movements in a constructed wetland allow for control of water depth  and amounts. The flow can be diverted into other treatment cells for clean-out maintenance or in the event of accidents, overloads, and the like.

Inflow material and pollutants along with plant debris from the aquatic vegetation inevitably build up in these constructed systems and reduce treatment efficiency. To restore that lost efficiency the pollutants and plant debris must be physically removed. Constructed treatment wetlands require regulatory permits and must be carefully monitored and managed.

Wastewater assimilation, on the other hand, refers to the discharge of treated or partially treated sewage into the natural environment, especially natural wetlands. The term “wastewater assimilation” implies that the wastewater accumulates and becomes transformed within a natural wetland, but this is not sewage treatment comparable to what occurs in a sewage treatment plant.

Environmental regulatory officials often relax water quality levels for permits associated with discharging treated sewage into natural wetlands. Once in the natural wetland, control over the discharge is lost and becomes loosely regulated. There are no constraining walls, the water fluctuations are subject to weather and tides, and monitoring is far less frequent.

By contrast with a constructed wetland facility, which is well defined, controlled and ends at the outfall of the discharge pipe, assimilation wetlands are largely uncontrolled and extend indefinitely into the natural receiving environment. There is very limited flexibility to control water flow at assimilation sites and there are no practical means for clean out (removal) of the soils/sediments that inevitably become saturated with pollutants.

Proponents of wastewater assimilation often claim that it entails “tertiary” treatment of water that has already been initially treated to some degree. This is misleading. Treatment occurs only in a treatment facility not in the natural environment.

Yes, rivers, lakes and wetlands interact with the effluent discharged into them and the effluent may eventually reach lower concentrations, but that is largely through dilution, not treatment. Part of the problem is that ballyhooing “tertiary treatment” directs focus away from negative impacts on the natural wetlands where the wastewater is discharged.

Support for wastewater assimilation ignores or minimizes hard truths:

The only way to solve this persistent problem is to treat sewage to advanced levels before it is discharged into the natural environment.

And we need more stringent regulations to minimize the potential, accumulation, regrowth and mutation of pathogens within the receiving wetlands where they find hospitable conditions for survival. Because assimilation wetlands are low in oxygen, rich with nutrients and have an abundance of decaying organic matter used for food and protection, they pose a health risk that has not been sufficiently evaluated and regulated. The assimilation wetland, in effect, becomes a giant petri dish for pathogens and therefore, increases health risks to people using these popular wetlands for recreation.

Adding to the conceptual confusion and potential for environmental degradation is the claim that nutrient pollution is consistently beneficial to natural wetlands, that it somehow nourishes and restores them without harmful alterations. This also is false. A constant discharge of unspecified and excessive levels of nutrients (nitrogen, phosphorus and other pollution constituents) usually produces more liabilities than benefits.

Continually inundating wetlands with waters bearing excessive nutrients, such as ammonia, tends to stress deep-rooted perennial vegetation. Instead it favors  floating vegetation with smaller and weaker roots, vegetation that dies back every year and is much less able to hold wetlands together.

Good environmental advocacy should be centered on improving sewage treatment to advanced levels before it is discharged, not on relaxing permit levels to save money or dilute pollution.

Another false equivalent is to compare the cost of a constructed treatment facility with the no-to-low-cost option of discharging wastewater into a natural wetland. The main cost savings of “wastewater assimilation” come with the relaxation of permitted pollution levels — which the Louisiana Department of Environmental Quality has unwisely allowed.

Reducing water quality standards may seem to cut costs, but cost are related to treatment methods not the receiving environment, which could incur costs in the form of impact and degradation. It’s all smoke and mirrors, but somehow these illusory “savings” have been cited over and over to justify wastewater assimilation projects and sell them to municipalities.

It is legitimate to evaluate the contrasting cost of approved treatment methods such as comparing the cost of a trickling filter to the cost of treatment in a constructed wetland. But it is very misleading to claim that what happens in the receiving wetland is equivalent to what takes place in a treatment facility. It is also misleading, if impact cost to the receiving ecosystems is not calculated.

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