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By Mike Corry
Nitrogen reduction is the Achilles heel of the onsite wastewater treatment industry and the Trojan Horse for land use and development control. “Achilles’ heel” because it is expensive and difficult to achieve the nitrogen reduction levels required by some regulatory agencies at the single family and small cluster system scale. Single home site influent variability coupled with the traditional regulatory failure to create and enforce management requirements will result in the perceived failure of the technology. This, coupled with high costs, will reduce the value of onsite relative to central treatment systems. “Trojan Horse” because rural land use and development control objectives can be incorporated into onsite regulation.
This is not to suggest that nitrogen pollution management is not important. Our environment is being overloaded with nitrogen compounds. The point here is that society would benefit more if scarce resources were directed to more efficient and effective measures. Targeting onsite systems as the solution is not a reasonable approach except in a narrow range of conditions discussed later in this article.
Onsite Challenges
There are five key reasons to challenge nitrogen pretreatment for sites otherwise suitable for conventional systems.
Nitrogen contribution to the environment in most watersheds is very minor compared to agricultural activities, atmospheric deposition, nonagricultural fertilizer use and municipal treatment systems.
The pounds of nitrogen reduced per dollar spent are small compared to other nitrogen management op-
portunities.
Advanced treatment systems require electric power, the production of which can create more nitrogen pollution in the form of NOx air pollutants than is reduced in the treatment system. Atmospheric deposition of this nitrogen vies with agriculture for top contributor to surface water pollution in most watersheds.
Advanced treatment systems are more complicated than conventional systems and require significantly more maintenance. While there are stellar exceptions, the onsite regulatory industry as a whole has a poor record of ensuring maintenance is performed. Where strict nitrogen standards are deployed, maintenance is critical to the operation. If not maintained, the significant investment can be wasted.
There will be many areas where the migration of liquid from a soil system through groundwater and to a diffuse discharge point in a receiver environment requires the liquid to pass through a “hyporheic” zone. The biological activity in this area is significant and tremendous nitrogen loss results.
Adding nitrogen reduction components to sites already utilizing pretreatment devices is less problematic because the marginal increases in cost and added pollution from power plants is smaller. Still the opportunity costs and the cost/benefit relationship need examination.
Development And Land Use Control
There is a sixth reason to question many regulatory mandates for onsite nitrogen reduction—the motive to limit rural development by strict nitrogen treatment standards, limiting access to treatment technology in prescriptive codes, mandating larger lots than necessary, and raising the cost and aggravation of owning and operating an onsite system.
The State of Florida is taking action to regulate systems under requirements of the EPA Region 4 Total Maximum Daily Load (TMDL) nitrogen standard published in December 2005 for springs in the Orlando area. The TMDL standard calls for a reduction of between 90% and 95% of existing nitrate-nitrogen reaching the springs from all sources to 0.11 mg/L, the estimated predevelopment level. This standard is so strict that, if enforced, all human-caused sources need to be eliminated, by definition, to achieve predevelopment levels, and pollution trading is not possible. It is unlikely that the TMDL standard can be achieved. The standard, however, does create a basis, even an obligation under nondegradation standards of the EPA rules, to deny any application for a new or renewed operational permit of any source that contributes any nitrogen to a watershed that is already exceeding standards. This practice keeps homeowners, developers, farmers, power plant operators, car owners, and the like in persistent violation of the standard and subject to case by case and selective enforcement
practices.
Housing and commercial development control by limiting access to wastewater treatment is politically less painful than zoning and is often the tool of choice in many jurisdictions. The methods include limiting access to treatment technology and strict nitrogen standards. Nitrogen reduction for single home systems is often more about land-use control than public health and environmental protection.
An example of this practice occurred in Wisconsin when the department attempted to update the code to allow treatment systems in addition to conventional and Wisconsin Mound systems. The changes increased the area suitable for a treatment system from about 57% to about 80%. The remaining areas were allowed to use holding tanks. A strong coalition of urban governments and environmental interests opposed the code on the basis of land-use effects and sued to block implementation. Their issue was urban out-migration as rural residential lots that “didn’t perc” under the old code became buildable under the new code. The legal issue was settled when the Wisconsin Supreme Court refused to hear the cities’ appeal of previous adverse court decisions.
Nitrogen reduction standards had a major role in the 12-year struggle. In the mid ’80s the state adopted a groundwater nitrogen standard of 10 mg/L of nitrate nitrogen at the lot line or point of drinking water use. In the early ’90s the department introduced a 10-year phase in of the requirement. A strong public backlash on cost and effectiveness of the requirement resulted in a new law that removed onsite systems from the groundwater nitrogen standard. The public argued that it was foolish to require a rural resident to install an expensive nitrogen-reducing system to remove 10-15 pounds from the septic system when the neighboring farmer was applying 150 pounds per acre to the corn fields. The public discounted the “blue baby” argument because very few cases had been identified over a 10-year study period.
The Nitrogen Cycle And Conservation of Matter
The nitrogen cycle transforms nitrogen-containing compounds in nature. It involves the fixation of atmospheric nitrogen to compounds critical for life, followed by reduction by bacteria to nitrogen gas to complete the cycle. While many nitrogen compounds such as ammonia and nitrate are valued assets in agriculture, many nitrogen compounds are considered pollutants in water because they can affect health and alter the natural environment in significant ways. Humans play a major role in altering the nitrogen cycle by fixing nitrogen and by releasing nitrogen compounds from long term storage in coal and petroleum deposits. Scientists maintain that humans now fix more nitrogen than nature. These human interventions occur for the purpose of growing food, making industrial products, producing electricity, heating buildings and driving our vehicles.
Nitrogen is neither created nor destroyed in the nitrogen cycle; it just changes form. Some suggest that recycling wastewater in the lawn or garden solves the onsite nitrogen problem. Not so. It just shifts the problem. Vegetative nitrogen goes through the same reduction cycle as wastewater nitrogen and poses a similar threat to water bodies. Nitrate is nitrate, regardless of the source.
Recycling
Recycling nutrients is useful if replacing manufactured nitrogen; however, accomplishing this at the single-family home is problematic for several reasons.
Onsite wastewater applications occur 365 days a year. The growing season is much shorter and varies from place to place. Application of fertilizer during other periods can harm the grass and leach to groundwater.
The amount of nitrogen delivered to the plant needs to equal the plant’s demand and be delivered evenly to the target area to reduce the homeowner’s unmanaged addition of manufactured fertilizer. The amount effectively delivered is a function of the actual occupancy, the extent of pretreatment reduction, the size of the area applied and the season.
The homeowner needs to manage the application of manufactured nitrogen to adjust for effluent nitrogen. The operating assumption should be that this management will not occur.
The nitrogen in the grass clippings needs to be removed from the lot and transported out of the watershed or deployed in lieu of commercial fertilizer.
The human body does not produce nitrogen. It only processes the nitrogen consumed in food. The onsite system further processes this nitrogen. The same amount of nitrogen would be in play in the nitrogen cycle if the food were left on the plate. The average person processes approximately 9 pounds of nitrogen in a year’s time.This is not to say that the 9 pounds enters the groundwater or the surface water. Like other sources, much of it never reaches the surface or groundwater.
The primary sources of nitrogen pollution in surface water are identified in the pie chart, developed from a 2003 study of the sources of nitrogen loads to Chesapeake Bay. While the mix or sources will be different in each watershed, this profile is a good example of a watershed with mixed urban and agricultural land uses.
Consolidating these categories shows the relative contributions by major activity source. If a ban were placed on nonagricultural use of fertilizer, the benefit to surface water would be 2.5 times greater than installing pretreatment devices that remove 100% of wastewater nitrogen. The cost to the homeowner is less lush gardens and lawns, but the monetary savings are significant.
An example of a rural state’s nitrogen budget is provided for the Iowa in the 2004 DNR report, “Nitrogen and Phosphorus Budget for Iowa and Iowa Watersheds.” While Iowa’s population is low and agricultural activity high relative to the area around Chesapeake Bay, the pie charts reinforce the minimal contribution of onsite nitrogen in a major watershed.
Farm Activity
Four major farm activities contribute to the nitrogen problem: application of manufactured fertilizer, manure, erosion of organic soil nitrogen, and the cultivation of nitrogen-fixing legumes.
Manufactured fertilizer—Fertilizer use contributes to surface water pollution through leaching to groundwater, being transported in stormwater runoff and volitization of ammonium to the atmosphere. Atmospheric nitrogen pollutants are reintroduced to the surface water environment in the form of wet and dry atmospheric deposition.
The International Fertilizer Industry Association reports North American nitrogen fertilizer consumption at 12.57 million tonnes or 27.7 billion pounds annually. The US share is 90% of the total. This computes to 84 pounds per capita per year.
Manure—Manure nitrogen content varies by animal species. Cow manure contains 11 pounds per ton with poultry at 83 pounds per ton. The average cow process 250 pounds of nitrogen each year within the nitrogen cycle. There are currently about 97 million cattle in the US processing about 24.3 billion pounds of nitrogen a year or about 81 pounds per capita. Manure affects surface water in several ways: volitization of ammonia and subsequent deposition, leaching to ground water and stormwater runoff.
Agricultural legumes—Most nitrogen fixation in nature is accomplished by plants that utilize nitrogen-fixing bacteria to provide nutrients to the plant. Legumes and other plants like the Adler tree are capable of fixing nitrogen. Scientists estimated that 70 million tons are fixed annually in agriculture, or 467 pounds per capita. Lightening and weathering of nitrogen-bearing rocks also contribute.
Atmospheric deposition—There are a number of nitrogen pollutants in the air that pollute surface waters in the form of wet and dry deposition: NOx (nitrogen monoxide and dioxide), ammonia and ammonium, nitrate and nitric acid. The source of NOx pollution is combustion of fossil fuels, mostly in cars and power plants, but also from decomposition of organic material. The primary source of airborne ammonia and ammonium is the volatilization of nitrogen from fertilizers and animal wastes. EPA estimates that a half a million metric tons of ammonia are released into the atmosphere from fertilizer annually (3.7 pounds per person). Three times as much was emitted annually from animal waste (11 pounds per person). Total NOx emissions have been estimated by EPA at 20,728,000 tons for 2003 or 142 pounds per capita. Each air shed has a different profile.
Atmospheric deposition varies by region. The deposition of 6 kilograms (kg) per hectare (ha), common in the Midwest and Northeast, is equal to 6.23 pounds/acre.
Onsite Nitrogen Reduction
As indicated earlier, the average human processes about 9 pounds of nitrogen from food. A portion is treated within the conventional treatment system and more is treated within the groundwater before it reaches surface water. According to planners for the Chesapeake Bay Program, an average of 40% reaches surface waters. The number will vary with location and soil conditions. Conventional systems can reduce most all nitrogen in the right circumstance—aerobic soil that nitrifies the wastewater is underlain by shallow groundwater with root intrusion or other carbon source to denitrify the flow. This site condition is considered unsuitable for systems in many states.
Problematic Issues
Nitrogen reduction systems are subject to frequent upset, and nitrogen reduction follows a two-step process. First, organic nitrogen must be oxidized to nitrate (nitrification). Then the nitrate is denitrified to atmospheric nitrogen.
Nitrogen treatment is accomplished by bacteria that are very sensitive to environmental conditions including source water characteristics such as low alkalinity, which limits nitrification potential. Following are some examples, recorded on the La Pine, OR, field study Web site, of situations that can upset the small-scale treatment process:
- “Owner started using a toilet bowl deodorizer approximately 6 months.”
- “Effluent creamy color, may have been painting.”
- “Effluent coming out top of tank, pump broke again?”
- “Leaking drastically in filter box.”
- “Added garbage disposal 3/8.”
- “Installer ordered new compressor 1-2 weeks ago, has not arrived.”
- “Antibiotic 10 days.”
Onsite Pretreatment
Nitrogen pretreatment devices require electricity to operate pumps and blowers. Data provided in EPA’s Environmental Technical Verification (ETV) program reports daily electrical demand of 1.3-8.4 kWh for tested pretreatment units. This translates to a range of .47 to 3 MW per year. Assuming power line loss of 7%, the power plant must produce .51 and 3.2 megawatts respectively to power these units.
Assuming a 2-MW annual demand, the Texas State Energy Conservation Office Electrical Power Pollution Calculator reports annual production of NOx atmospheric pollution at 11.6 pounds for power plants burning western coal and 8.8 and 2.2 pounds respectively for eastern coal and gas.
The mix of power plant fuel source varies from place to place. In Florida, the mix produces about 3.8 pounds NOx per megawatt year. This means that the 2-megawatt Florida onsite treatment system produces 7.6 pounds of NOx per year.
In addition to NOx, power plants release other atmospheric pollutants. A two- megawatt per year demand at a generating plant powered by western coal will also produce 4,000 pounds of CO2 a year.
Many suspended-growth treatment units use the same amount of power with 1 or 6 inhabitants in the home. Damann Anderson, in a report on onsite nitrogen treatment found on the Florida Department of Health Web site (http://www.doh.state.fl.us/environment/ostds/wekiva/damannandersonreview.pdf), reports that the typical nitrogen reducing systems will remove 10% in the septic tank, and 25% in the soil component (he does not account for further reduction in the groundwater). Assuming 9 pounds of nitrogen per person per year, the nitrogen effluent amounts to 6 pounds per year per person from a conventional system with no power use.
Anderson estimates a marginal decrease of 5 pounds per average home of 2.6 persons with pretreatment devices over that reduced by the conventional system. This translates to 1.92 pounds per person gain with a single occupant.
Pretreatment installed in 100 homes increases the total nitrogen pollution in the environment by 55% over use of conventional systems. With power demand at 3 MW per year, the NOx pollution increases to 1,140 pounds per year. At .51 MW per year, the pretreatment unit produces 194 pounds.
Conclusion
We are awash in naturally occurring and manmade nitrogen compounds within the nitrogen cycle. In most watersheds, the onsite nitrogen is a minor source relative to human-produced nitrogen that is generated to feed the population or as a byproduct of operating vehicles, generating electricity and heating our homes.
Some would argue that all human-induced nitrogen sources should be treated or reduced at the source. This is a reasonable position if society is willing to forgo the benefits associated with the source, if the technology is available to resolve the issue, and if resources are unlimited.
In reality, resources are scarce and should be concentrated where most effective. More resources could be devoted to the management of existing onsite systems for both environmental and health reasons. A switch to nuclear power plants would cause the largest drop in nitrogen pollution without a major shift in life style. Cars could be operated and homes and factories heated and operated with non-air-polluting electricity.
Reductions in noncritical uses of fertilizer would also be useful. The fact is, however, that those who want to return to the pristine environment that existed before extensive human intervention in the nitrogen cycle are likely out of luck.
The TMDL standards of the EPA Region 4 for the central Florida springs and rivers are more about government control of development and land use than actually achieving algae-free springs.
The massive injection of nitrogen compounds into the watershed’s nitrogen cycle/budget from agricultural activities alone will make the TMDL standard unachievable.
Based on the Chesapeake Bay data, it would be greater than 2.5 times more effective to eliminate nonagricultural use of fertilizer than to reduce 100% of onsite nitrogen. In contrast, Anderson reports, it costs $445 marginal dollars for each additional pound reduced relative to conventional treatment. This is without consideration of new nitrogen pollution generated by operating pretreatment units and without additional reductions occurring in the groundwater.
In the future, onsite regulation should be focused on the interests and needs of citizens by the reasonable management of the risk of decentralized wastewater dispersal to the human and natural environments. “Reasonable management of risk” means that regulation provides value to citizens by balancing benefits and costs. Costs include monetary costs, added time and attention, and land-use opportunity loss.
Watershed regulation of nitrogen sources needs to be approached based on reasonable goals, with an accounting of all sources and the costs of reducing each source. Only then can reasoned decisions be made about the most effective method to manage nitrogen.
We should abandon the idea of areawide nitrogen reduction requirements for single family and small cluster systems where soil conditions allow the use of conventional treatment systems—with some exceptions. Conditions that might lead regulators to reasonably require nitrogen reduction where conventional systems are suitable include:
- Nitrogen in water is a demonstrated environmental or health problem in a specific environment.
- Nitrogen from onsite systems has been determined to be a leading contributor based on a watershed analysis of all sources.
- Reduction of onsite nitrogen will resolve the problem.
- Additions of power plant generated atmospheric deposition are of less concern than the benefits of local reduction of nitrogen pollutants.
- The regulatory agency establishes and enforces maintenance requirements.
- Society is willing to pay the price for the benefit.
Mike Corry is senior regulatory consultant at Infiltrator Systems Inc.
OW - September/October 2006 |
