|
By Pio S. Lombardo
Unfortunately, the 2006 NOWRA Conference panel, “A More Holistic Watershed View on Nitrogen,” has created, through its distortions, a thick fog rather than providing illumination.
The premise—that “nitrogen reduction is the Achilles’ heel of the onsite wastewater treatment industry and a Trojan Horse for land use control”—is flawed technically. It is also an incorrect emotional response to what is not a threat but an unheralded opportunity for the distributed (aka decentralized) wastewater industry, herein defined as the use of onsite and cluster systems.
Let’s discuss how nitrogen removal can reliably be achieved rather than abandoning this market as proposed by the NOWRA Conference Panel. Let’s also encourage and professionally reward those distributed wastewater systems that can perform to the high nitrogen removal standards necessary to achieve water quality standards—and responsibly eliminate those that can’t. As stated in many state regulations, nitrogen removal systems that do not meet their performance requirements, generally greater than 70% of the time, would have permit approval in jeopardy with immediate scheduled corrective action required, or lose their permit. During the past few years, the failed attempts of some technology vendors to achieve nitrogen removal performance standards has caused a very conservative permitting approach by the regulatory community, and incorrect perceptions of industry capabilities have developed. We need to separate the wheat from the chaff.
From a wastershed perspective, when nitrogen removal systems are needed they would be in the following categories.
Situation 1
50% TN Removal
Or TN < 19 mg/
This level of treatment will generally be required in nitrogen-sensitive areas where the density and minimum lot size of development is currently and is planned to be such that dilution and reliable aquifer removal of nitrogen will achieve water quality standards. Aquifer removal of nitrogen can occur in areas where sufficient biologically available carbon and anaerobic conditions exist and/or where discharge to the hyporheic zone will occur in a consistent basis during the full range of seasonal and long-term anticipated aquifer conditions. Based upon my experience, this occurs in limited situations and limited TN removal occurs. In cases where the credit has been provided it does not significantly affect wastewater treatment requirements. It is no small challenge to understand aquifers to make these “natural” nitrogen removal determinations.
Situation 2
TN < 10 mg/l
This requirement is typically required in areas that are water supply recharge zones and in areas where water quality standards require higher levels of nitrogen removal than in Situation 1. Whether it is a requirement at the end of pipe or property line varies by state, with climatic conditions a factor; it is also a requirement in areas where the higher nitrogen removal requirements of Situation 3 should exist. Regulators, however, have not imposed Situation 3 requirements, due to hesitancy on the availability of technologies to achieve the requirements of Situation 3 or for political/economic reasons.
Situation 3
TN < 3 – 5 mg/l
This requirements exists in the many environmentally sensitive—especially coastal—watersheds where the maximum level of nitrogen removal is necessary to achieve water quality standards. The currently accepted limits of technology, even for sophisticated centralized wastewater treatment system, is 3 mg/l TN. For certain watersheds, even further than Situation 3, TN removal is necessary to achieve water quality standards. For these watersheds innovative (scientifically valid, but unproven in the field) technologies are available to achieve the desired goal.
However, it is known that, through the use of strategically located permeable reactive barriers, further TN removal can be achieved and the most stringent water quality goals achieved.
The public health drinking water standard is 10 mg/l NO3-N. In many areas, the environmental nitrogen level standard is more restrictive than the drinking water standard. In the New Jersey Pinelands the nitrogen level standard is 2 mg/l, in the Massachusetts Estuaries it is 0.3 mg/l, and Wekiva Springs, FL, has established the standard of 0.11 mg/l.
Now, let’s speak to the technologies that can achieve these three situations.
Technologies For Situation 1
TN < 19 mg/l
There are a variety of proprietary and nonproprietary distributed wastewater system technologies that can achieve these standards. Recirculating media filters reliably achieve this standard. Activated sludge (AS) and integrated fixed film-activated sludge (IFF-AS) systems have a checkered history of performance, especially in light of the benchmark requirement that the standard must be achieved > 70% of the sampling events.
Technologies For Situation 2
TN < 10 mg/l
The standard reliably, of permit adherence > 70% of the time has been achieved with single pass and recirculating media filters along with some type of active or passive carbon feed or electron donor system.
Generally speaking, the single pass (when sufficient alkalinity exists) or recirculating media filter pretreatment system must produce an effluent with a Total Kjeldahl Nitrogen (TKN) concentration of < 5 mg/l. Single-pass filters must have sufficient wastewater alkalinity to achieve this requirement. TKN is the sum of organic nitrogen and ammonia nitrogen, and does not get removed in the denitrification process. Consequently, it is imperative that the pretreatment system achieve TKN < 5 +/- mg/l for the entire system to reliably produce an effluent of TN < 10 mg/l.
AS and IFF-AS systems may be able to achieve TN < 10 mg/l. However, we are not aware of any data demonstrating that they consistently achieving the reliability benchmark of > 70% of the time.
Technologies For Situation 3
TN < 3–5 mg/l
To achieve this standard reliably, requires a pretreatment system that fully nitrifies, defined as TKN < 3 mg/l and a denitrification system that can achieve complete nitrate removal.
Again, single-pass (when sufficient alkalinity exists) and recirculating media filters and carbon-feed or electron-donor systems have successfully achieved this requirement.
Based upon my experience, AS and IFF-AS systems have a poor record in achieving this high standard, in part due to intense operator oversight requirements.
So, in my opinion, the evidence is clear that the reliable industry technologies are:
- Recirculating media filters and single pass filters, in areas with sufficient alkalinity, with carbon feed or electron donor systems can and have achieved the highest TN removal standard of TN < 3 – 5 mg/l.
- AS and IFF-AS have the capability, with required reliability still a concern, to achieve the TN < 19 mg/l removal standard.
This is what can be achieved. It would be helpful for the industry to have a centralized performance evaluation system. With the new database management systems being used by municipalities and better insights on industry technology capabilities, more statistical data will start to emerge.
That data needs to be “mined” and made as “live” as soon as possible, so that the performing and nonperforming systems can be clearly understood.
Given that the prospective size of the denitrification system market is huge, projected at $3 billion on Cape Cod alone, and could potentially dwarf the conventional septic systems market, the statements by the NOWRA nitrogen panel that “distributed wastewater systems for nitrogen removal are expensive and don’t work,” is not only wrong, it gives away the denitrification market to sewer advocates, who will laugh all the way to the bank.
Let us not dilute ourselves and not recognize the importance to treat the emerging contaminants, personal care products and endocrine disruptors, in drinking water aquifers. It can be done.
It is time for the industry to develop some discipline and reward the well-performing systems and eliminate the negative non-performers.
Pio S. Lombardo, P.E., D.E.E., is president of Lombardo Associates Inc., of Newton, MA.
OW - November/December 2006 |
