November 1, 2002

Disclaimer

The Pennsylvania Department of Environmental Protection does not endorse or recommend any of the technologies described herein. The technical articles are provided for informational purposes only. Persons seeking additional information about the described technologies should contact the parties listed in the article.

The ability of the conventional activated sludge process to nitrify is highly temperature- dependent. At low winter temperatures, nitrification can be sustained only if the activated sludge process is operated at relatively high solids retention time (SRT) values. (For example, at least 15 to 18 days SRT is used for designing nitrification at temperatures around 10°C if an effluent ammonia concentration of 2.0 mg/l is required.) If the activated sludge process is operated at substantially lower SRT values, the growth rate of nitrifying bacteria (nitrifiers) becomes lower than the daily wasting rate of nitrifiers (discharged in the excess activated sludge) and nitrifiers are washed-out of the system causing nitrification to cease. To upgrade existing activated sludge plants for winter nitrification usually requires substantial enlargement of the aeration tank to allow operation at higher SRT values.

InNitri® ("Inexpensive Nitrification") is a new, side-stream nitrification process offered by Mixing & Mass Transfer (m²t) Technologies, Inc. that allows nitrification at short SRT values, even at low winter temperatures and provides nitrification in a substantially smaller aeration tank than is currently required for conventional nitrification design. The InNitri® process was developed to provide an inexpensive alternative for plants in the northern climates that need to upgrade their air or pure oxygen activated sludge process for year-round nitrification or nitrogen removal. The system is designed to treat the high TKN internal plant recycle streams, which may represent 30% of the plant TKN load. (The InNitri® system is designed to treat the nitrogen load generated by the internal sidestream (i.e., digester supernatant and dewatering liquid) which is typically 20-30% of the total influent nitrogen load. The sidestream reactor generates nitrifier seed to assist the mainstream activated sludge tankage nitrification. This seed supplement reduces the required volume of the mainstream reactor by approximately 40%.), while also generating a nitrifier seed to supplement the main stream activated sludge system. The process is suited as a retrofit and can also be used for new plants.

In general, the InNitri® process consists of supplemental nitrifiers being added constantly to the main stream activated sludge process (aeration tanks) to replenish nitrifiers removed with the wasted activated sludge. The supplemental nitrifiers are grown in a separate small side-stream aeration tank using either ammonia available in the digested sludge dewatering liquid and in the digester supernatant or commercial ammonia.

A conventional secondary treatment plant may consist of primary sedimentation, an aeration tank, secondary clarification, sludge thickening followed by anaerobic digestion and sludge dewatering. The upgrading of this type of conventional plant to provide year-round nitrification using the InNitri® (short SRT nitrification) process requires the addition of a small aeration tank and clarifier for growing nitrifiers. In the process, the warm (typically 30 to 35°C) dewatering liquid containing a high ammonia content (between 300 to 900 mg/l) is mixed with a small portion of primary effluent (to adjust the temperature and provide BOD), and nitrified in the side-stream nitrification aeration tank. A portion of the resulting biological sludge – containing a high percentage of nitrifiers - is discharged into the main aeration tank and provides the main activated sludge process with supplemental nitrifiers. This results in the plant being able to provide year-round nitrification.

The same process can also be applied in plants without digesters. In this case, commercial ammonia is used instead of the dewatering return stream.

In-Plant Sludge Treatment

• Low capital cost
• Low operating cost
• Ability to implement future flow increases
• Minimal site excavation needed for implementation
• Amenability of construction sequencing to current plant operations
• Operational simplicity
• Replacement protection for nitrifiers

• No long-term data is available

To demonstrate the difference between the conventional nitrification process (The conventional nitrification system/process consisted of a complete mix-steady state aeration tank with 6 hr. hydraulic detention time, operating at 10°C and receiving an influent containing 25 mg/L of TKN and 25% of TKN is in the side-stream dewatering liquid.) and nitrification with supplemental nitrifiers (InNitri® process), Dr. Peter Kos - an independent wastewater researcher - presented theoretical equations and results of modeling for a typical wastewater treatment plant (1998). Mathematical modeling was conducted and results showed that, for conventional nitrification at 10°C, as the operating SRT is decreased, the concentration of nitrifiers also decreased while ammonia nitrogen in the effluent increased. For the InNitri process approach, results indicated that nitrifiers are present in the main aeration tank at all SRT values. Nitrifiers cannot be washed-out from the aeration tank even if operated at lower SRT values and so partial nitrification takes place even at extremely low SRT values. In other words, the InNitri® process does not have minimum SRT under which nitrification would not occur. Therefore, it will be much more stable and may not need as high a safety factor as conventional nitrification. The modeling was repeated at other temperatures from 7.5 to 20°C. Results showed the InNitri® process allowed for significantly lower design SRT than the conventional nitrification to achieve the same effluent ammonia concentration. For the case where the design effluent ammonia concentration is 2.0 mg/l, the minimum required design SRT for the InNitri® process is only about 60% of that required for conventional nitrification. A comparison of the sludge retention time necessary for nitrification using InNitri® versus conventional nitrification showed significant reductions in costs for low temperature wastewaters using the InNitri® process.

Subsequent research by the University of Manitoba indicated that the transport of nitrifying sludge from a warm side-stream reactor to a cold mainstream reactor should pose no process problems. Also, the evaluation of the process to upgrade an existing facility showed significant cost savings using the InNitri® system versus using conventional and other advanced nitrification processes.

In June of 2000, Brinjac, Kambic and Associates completed a Feasibility Analysis for upgrading the Harrisburg City Advanced Wastewater Treatment Facility (Harrisburg, Pennsylvania) for nutrient control. This facility was considered to be typical of many of the plants designed to meet the effluent requirements of the Federal Clean Water Act. The facility is located in the colder climate in Northeastern United States and is a principal point source contributor of nitrogen to the Susquehanna River. The river flows to the Chesapeake Bay where efforts are underway to improve water quality by reducing the nutrient load to the Bay. The facility is site-constrained with little room available for flow or process expansion. Due to the results of the Feasibility Study (see Exhibit A), Brinjac, Kambic and Associates recommended that the facility proceed with implementing the InNitri® process. (As of this date, the City has not yet proceeded with the project.)

Currently, there are no full-scale InNitri® installations. Capital and O&M costs for the system vary by the type and size of facility. For site-specific unit design and costs, it is recommended to contact the manufacturer directly.

Sources of Additional Information about the InNitri® system can be obtained from m²t Technologies, Inc., P.O. Box 315, State College, PA 16804, (888) 715-9600, by e-mail at Kimm@m2ttech.com, or by web site at www.m2ttech.com.

ACKNOWLEDGEMENTS

Information for this Technology Review was obtained from publications and/or work by:

Dr. Peter Kos (independent researcher in wastewater process technology),
Melanie A. Head (student) and Dr. Oleszkiewicz (Professor) of the University of Manitoba,
Mr. Al Warakomski (m2t Technologies), and
Brinjac, Kambic and Associates (Engineering Feasibility Study)
Thomas P. Gilligan (m²t Technologies)

This report has been prepared and submitted by Renee Bartholomew, PA Department of Environmental Protection, Bureau of Water Supply and Wastewater Management, Division of Municipal Financial Assistance, Innovative Technology Section, at (717) 787-3481 or e-mail at rebartholo@state.pa.us.

Exhibit A
Summary of Costs For Total Nitrogen Control

¹Cost per pound of nitrogen removed is based on an assumed 1 mg/l residual ammonia-N in the effluent. Design flow with loading assumed to be 18 mg/l as TKN to secondaries provided removal calculations. Values are based on the annual amortized cost for the capital expenditure plus the annual O&M cost, divided by the pounds of nitrogen removed per year.

Evaluation Criteria:
Construction contingency @ 20% of construction cost
Engineering cost @10% of construction cost
Present Worth Period: 20 years
Interest rate: 8.75% 

Definition Of Evaluated Systems