A vast improvement on conventional biological nutrient removal could save the wastewater treatment industry untold millions.
If you’re thinking about setting up your wastewater treatment plant (WWTP) for biological nutrient removal (BNR), hold that thought. There is a new process that heralds a radical departure in how BNR is performed, according to Lauren Fillmore, senior program director at the Water Environment Research Foundation (WERF), and it drastically reduces the amount of energy and O&M that current BNR methods require.
The breakthrough is known as shortcut nitrogen removal because it eliminates a step in the BNR process. Instead of nitrifying ammonia and then denitrifying later, this revolutionary advancement replaces nitrification and denitrification with singlestep deammonification.
Used mainly for high-strength sidestream wastewater flows, shortcut nitrogen removal has been adopted at Hampton Roads Sanitation District (HRSD) in Virginia as a full-scale process — a first for North America — while DC Water is in the development phase of full-scale deammonification. Considering the savings potential involved (time, money, and carbon footprint), it’s an option that should be investigated by any WWTP operator on the verge of BNR implementation.
“We’re on the cusp of a major sea change in how people do nutrient removal in this country,” said Fillmore. “If you’re going to do a BNR upgrade, there’s a lot you need to be aware of before you design and build something that has a 40- or 50-year life. You may be designing it based upon technology that’s going to be outdated very quickly.”
The Deammonification Difference
Conventional nitrogen removal is performed in multiple stages. Wastewater ammonia (NH3) is oxidized to nitrite by autotrophic ammonia-oxidizing bacteria (AOB), and the nitrite is then oxidized to nitrate by nitriteoxidizing bacteria (NOB) under aerobic conditions. Two additional steps are required to convert the nitrate into inert nitrogen gas (N2). The overall process requires large amounts of dissolved oxygen (and energy) supplied by blowers, as well as a supplemental carbon source. It also produces high volumes of sludge that can be expensive to handle and discard.
With shortcut nitrogen removal, NOB are not used to convert nitrite to nitrate; instead, a different class of bacteria, labeled anammox (anaerobic ammonia oxidation), converts NH3 into N2 in two biological steps. The first step is called nitritation, in which AOB (the same used with conventional systems) convert about half of the ammonia into nitrite. This partial nitritation is common in wastewater treatment. The revelation comes with step two: anaerobic deammonification. The anammox bacteria, which use nitrite as an electron acceptor, convert about 89 percent of inorganic nitrogen (ammonia and nitrite) into N2, with 11 percent left over as nitrate.
Benefits Of Shortcut Nitrogen Removal
According to WERF, use of the above-described deammonication process “results in remarkable savings” in comparison to conventional nitrification/ denitrification. Cited benefits include:
- 55 to 60 percent reduction in aeration energy requirement
- No carbon requirement (or 90 percent reduction if carbon is used to eliminate leftover nitrate)
- Net consumption of carbon dioxide (CO2) versus CO2 release from carbon oxidation
- 45 percent reduction in alkalinity demand
- Reduced sludge production
Established Shortcut Technologies
Since the initial discovery of anammox bacteria in 1995, a number of variations on shortcut nitrogen removal have been developed to optimize performance and overcome inherent obstacles. The major shortcoming attributed to deammonification technologies is a long start-up period for slow-growing anammox bacteria (in comparison to AOB). Various commercial configurations include granular sludge reactors, suspendedgrowth sequencing batch reactors (SBRs), and moving-bed biofilm reactors (MBBRs) — all set out to better grow and retain the bacteria.
“We’re on the cusp of a major sea change in how people do nutrient removal in this country.”
– Lauren Fillmore, WERF senior program director
ANAMMOX® Granulated Sludge Reactor
Available as a single-step (one basin) or two-step arrangement, this process grows the anammox bacteria in gravity-separated granules. A high-rate clarifier is used to settle the granules in the reactor, which flushes out bacteria flocs while sustaining the sludge age required for existing bacteria.
DEMON® Sequencing Batch Reactor
The most widely employed of available shortcut nitrogen removal techniques, featuring 25-plus installations around the world, DEMON (DEamMONification) is also the first to be installed for full-scale use in North America. The process uses a hydrocyclone to separate floc from granular anammox bacteria under controlled dissolved oxygen (DO) and pH conditions to stabilize performance.
DEMON’s performance at HRSD has been exceptional since going online in 2013, saving the plant an estimated $200,000/year in chemicals, sludge-handling costs, and energy, in addition to reducing its carbon footprint. HRSD installed the system at its York River facility, a 15-MGD plant under the care of manager Charles Bott.
“With a lot of these processes that are emerging in Europe, they seem almost too good to be true,” said Bott. “But once you see them in action, you see that they are accomplishing exactly what they promise.”
In recognition of the bold move, Bott and HRSD received the American Association of Environmental Engineers and Scientists (AAEES) Honor Award for Environmental Sustainability.
Moving-Bed Biofilm Reactors
Three companies are doing shortcut nitrogen removal with MBBRs: Purac/Läckeby AB offers the DeAmmon® process, AnoxKaldness/Veolia has ANITA™ Mox, and the Terra-N® process comes from Clariant/Süd-Chemie AG. These systems were developed to handle highstrength, ammonium-rich plant recycle streams. They vary in design and support media, but each works by establishing AOB and anammox bacteria within a biofilm that collects on the media.
Sidestream MBBRs supported by anammox have been shown to reduce inorganic nitrogen by as much as 90 percent. The long start-up times associated with shortcut nitrogen removal, typically eight to 10 months, can also be reduced with MBBRs to as little as four months.[1]
Biological Double-Efficiency Process
Returning to full-scale (mainstream) wastewater treatment, the U.S. EPA reported in August 2013 on a technology it singled out as innovative and emerging — the biological double-efficiency process (BDP)® — calling it “the world’s first full-range simultaneous nitrification/denitrification (SND) process.[2]
According to the EPA, more than 20 full-scale operations in China utilize BDP, both for municipal sewage and industrial wastewater. The process achieves SND in a single bioreactor divided into aerobic and anoxic zones. Compared to conventional biological wastewater treatment, the EPA listed the following performance advantages for BDP:
- Increases efficiency by at least 100 percent for biological matter removal
- Reduces energy consumption by 50 percent or more
- Reduces carbon dioxide emissions by 50 percent or more
- Reduces sludge by at least 40 percent
- Reduces physical footprint by approximately 50 percent
- Reduces O&M costs by approximately 30 percent
BDP requires a carbon-to-nitrogen (C/N) ratio of just 0.17, which can be increased for higher nitrogen removal.
In China it has been implemented in new plant builds as well as retrofits, finding application in the petrochemical, oil refinery, textile, and pharmaceutical industries, to name a few. In short, BDP treats any waste stream with a high concentration of toxic chemicals.
The Path Forward
With agencies such as WERF and the U.S. EPA touting the benefits and potential of shortcut nitrogen removal practices, there is little doubt about the efficacy of simultaneous nitrification/denitrification. The true impact, however, is dependent on the rate of adoption. In an industry known to take the road more traveled, it remains to be seen if wastewater utilities will take advantage of this “shortcut” path that has been paved.
References
1.“Deammonification,” WERF, Dec. 2012
2. “Wastewater Treatment and In-Plant Wet Weather Management” (addendum), U.S. EPA, August 2013
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