Anaerobic sludge digestion is an effective biosolids treatment process at larger municipal wastewater plants. After anaerobic digestion, the sludge is dewatered, and the centrate/filtrate is recycled back to the head of the main plant for treatment. Unfortunately, the centrate/filtrate stream has very high concentrations of ammonia, typically between 800 mg/l and 1200 mg/l, and sometimes even higher if the plant adopts a thermal hydrolysis process (THP) upstream of the anaerobic digesters. The BOD and COD concentrations can be high as well with THP.

This recycle flow increases the ammonia and total nitrogen loading to the main plant treatment process by up to 25% while adding only about 1% to 2% to the plant influent flow.

The recycle flow can be detrimental to plant design/operations in several ways:

• The recycled nitrogen load not only increases the aeration requirement to achieve nitrification but also adversely impacts the stability of the treatment process.
• It requires more process tank volumes.
• It can require adding an external carbon source, such as methanol, to achieve low total nitrogen limits.
• The increased oxygen requirements and additional chemical consumption contribute significantly to facility energy consumption and operational costs.
• When the biological activity slows down in cold climates, the extra ammonia load can cause the treatment plant to exceed the NPDES permit limits, especially when the limits are stringent.

Veolia’s ANITA™ Mox Process

Veolia’s ANITA^™ Mox process effectively treats the recycle flow from anaerobic digesters with high ammonia concentrations and solves the problems of returning high ammonia concentrations to the main plant treatment process. In addition, it helps save energy and O&M costs by reducing the demand for aeration and chemicals.

Veolia/Kruger is a leader in providing the media-based deammonification process to the US municipal market. The ANITA^™ Mox process is available in two different configurations, MBBR (Moving Bed Biofilm Reactor) and IFAS (Integrated Fixed Film Activated Sludge), to attain a single-stage deammonification process using anammox bacteria. The process can achieve greater than 90% removal of ammonia and 75-85% removal of total nitrogen. Furthermore, it accomplishes these removals with considerably less energy than conventional nitrification-denitrification without needing an external carbon source.

Anammox Bacteria

The anammox bacteria, discovered in wastewater sludge in the early 1990s, exists naturally in marine and freshwater habitats. The word anammox was derived from ANoxic AMMonia OXidizing bacteria. They are unique in their ability to oxidize ammonia and reduce nitrite to produce nitrogen (N₂) gas.

The ANITA™ Mox process utilizes anammox bacteria to convert ammonia to nitrogen gas. It is performed in two steps: aerobic nitritation and anoxic ammonia oxidation. The use of anammox bacteria provides many beneficial advantages over traditional nitrogen removal processes, especially in treating ammonia-rich waste streams.

ANITA^™ Mox: MBBR Configuration

The two steps take place in a one-stage biofilm process in different biofilm layers on the carriers: nitrification (aerobic) in the outer layer and anammox (anoxic) in the inner layer. This is achieved within a single MBBR reactor tank. Temperature, pH, and oxygen levels are maintained within the reactor to allow the anammox bacteria to grow as a biofilm on AnoxKaldnes media carriers. Due to the biofilm being securely attached to the protected areas of the media carriers, long sludge ages are easily maintained to offset the slow growth rate of the anammox bacteria, making the ANITA™ Mox system a simple, stable and robust deammonification technology. All the system benefits of the proven MBBR technology apply to MBBR ANITA™ Mox, including easy retention of media carriers and critical biomass, maintenance-free SS air grids and media retention screens, and a simple flow-through process.

Benefits of MBBR ANITA^™ Mox include, but are not limited to, the following:

• Biofilm is resistant to flow and load variations and not prone to anammox washout.
• Simple and stable flow-through process
• Easy to operate and maintain
• The operator-friendly process that does not require a champion operator
• Media, aeration grids, and media retention screens are maintenance-free
• Easy to expand capacity by addition of media
• Tolerates high influent TSS influent without requiring pretreatment and therefore provides CAPEX savings
• Do not require micronutrients, antifoaming, or other special agents
• It can be put in an idle mode without feed for extended periods
• Recovers quickly from process upsets such as power shutdowns, overfeed, under aeration…etc
• The process is tolerant of temporary limitations or fluctuations in pH, temperature, and parameter concentrations.
• HDPE carriers last the life of the system
• The Anita Mox process is proven to withstand short-term or even pro-longed system shutdowns. The system can be placed into low-flow and/or low-loading mode. This allows the facility to have flexibility in dewatering schedules and perform routine or emergency maintenance to their digesters and/or dewatering equipment without significantly impacting system performance.
• Anita Mox is the best technology for treating centrate/filtrate. 

ANITA^™ Mox: IFAS Configuration

The IFAS (Integrated Fixed Film Activated Sludge) configuration of the ANITA Mox process combines biofilms attached to media carriers and mixed liquor suspended solids (MLSS) and offers distinct benefits.

In the ANITA™ Mox IFAS system with anammox biofilms attached to media carriers, the MLSS concentration is maintained using a small sludge settling zone. The nitritation step, or the conversion from ammonia to nitrite, occurs in the MLSS. The deammonification step occurs mostly in the biofilm attached to the media carriers. Nitrite production has been shown to be the limiting step in anammox conversion rates. Moving the nitritation step to the suspended phase increases nitrite production, thus providing an overall increase in anammox conversion and removal rates.

Added benefits of IFAS ANITA™ Mox include the following:

• Nitrogen removal rates are over two times higher
• Reduced footprint
• Lower dissolved oxygen levels are required, which further improves energy savings.
• Handles the presence of high influent and potentially recalcitrant COD and other toxic substances better
• Best suited for centrate/filtrate treatment from anaerobic digesters following THP and treating food waste

ANITA^™ Mox Carriers

A vital element of the ANITA™ Mox process is the AnoxKaldnes carriers. They provide a large protected surface area for the biofilm to attach and optimal conditions for biological activity when suspended in water. The design of the carriers maximizes oxygen and substrate transfer efficiencies by having an ideal media bed depth. Too shallow of a media bed depth would reduce biofilm protection and ease biofilm attachment. Too deep of a media bed depth would make liquid mixing and biofilm scouring more difficult, reducing oxygen and substrate transfer efficiencies and performance. The specially designed carriers allow for the retention of the anammox bacteria within the reactors. The carriers significantly lessen the potential for anammox washout compared to other suspended growth technologies.

Conclusion

Municipal wastewater treatment plants (WWTPs) must upgrade to cost-effective technologies to reduce ammonia and total nitrogen (TN) levels to meet their increasingly stringent effluent limits. With its distinct benefits and cost-saving capabilities, the ANITA Mox process is one of the fastest adopted deammonification technologies for treating centrate/filtrate from anaerobic digesters to reduce ammonia and total nitrogen (TN) loading recycled back to their main treatment process.

Veolia/Kruger is a leader in providing the media-based deammonification solution to the US municipal market. The Veolia US team (Kruger) works directly with Veolia Engineering and Research Institute in France and AnoxKaldnes AB in Sweden to incorporate the latest knowledge and developments in the design of the media-based deammonification technology.

OVER THE LAST TEN YEARS, the ANITA™ Mox process has been implemented at more than 35 full-scale facilities to treat centrate/filtrate/pressate from conventional anaerobic and anaerobic digesters following THP. 

Veolia’s ANITA™ Mox process is the market’s most reliable sidestream deammonification process that offers distinct benefits with different configurations.

For more information, brochures, or presentations, please get in touch with Envirep/TLC at sales@envirep.com or call 717-761-7884.

By Michael J. Gillespie, P.E., President of Envirep

Envirep/TLC is a manufacturer’s representative serving the municipal and industrial water and wastewater market in Pennsylvania, New Jersey, Maryland, Delaware, the District of Columbia, and Virginia.

We represent manufacturers of equipment used to pump, treat and dispose of wastewater and biosolids. We also represent manufacturers of equipment used to pump, treat, distribute, and store potable water.