Nitrification Denitrification

Overall Summary

Primary Application

• Dairy farms with surface/groundwater nitrogen-overload concerns as well as those with ammonia particulate matter/odor issues—needing reduction in total nitrogen and ammonia concentrations within their liquid manure.
• Dairy farms that use flush systems resulting in very dilute barn effluent; flush systems are generally employed by large farms.
• All stall bedding materials are acceptable – pre-treatment required to remove sand bedding.
• Open-air nitrification/denitrification systems are limited to dry and temperate climates for suitable operative conditions for microbes to work.

Economic/Return on Investment Considerations

• Capital costs for traditional NDN are high, use of earthworm-catalyzed trickling filter-based and/or modified lagoon systems reduce capital cost.
• Electrical operating costs for traditional NDN systems are higher than for earthworm-catalyzed trickling filter-based systems; the worms reduce the electrical energy demand associated with the aeration.
• Possible returns on investment are in the form of reduced manure application costs and with respect to worm-systems, possible sale of harvested worm casing.

Industry Uptake

• There are very few NDN systems operating on US dairies and a limited number employed world-wide on animal manure, specifically swine.
• Nitrification/Denitrification systems on-farm are located where flush cleaning of barns are employed (dry and tempered climates).

Technology Maturity

• Traditional NDN systems used in wastewater treatment are mature – earthworm-catalyzed trickling filter-based systems developed for treatment of dilute animal wastewaters is in an early adoption stage with the few operating systems reported to be operating successfully.

Primary Benefits

• Strong reduction in inorganic and ammonia nitrogen due to conversion and release of nitrogen gas. Some additional phosphorous reduction in liquid due to assimilation of phosphorous within the bacteria.
• Odors associated with the overall manure management system will be reduced by the system due to removal of ammonia nitrogen.
• Manure organic matter will be reduced to a small extent.
• Pathogen reduction occurs because of the sequencing of anaerobic and aerobic processing.
• GHG emissions can be significant due to some organic solids reduction, aeration of stored liquid to alleviate anaerobic methane emissions, and conversion of ammonia-N to nitrogen (N₂) gas, thus potentially avoiding potent downstream emissions of nitrous oxide (N₂O) gas.

Secondary Benefits

• Reduced organic matter accumulation in long-term storages, although organic matter accumulation occurs in the NDN vessel and thus will need to be cleaned out periodically.

How it works

• Barn effluent is processed by a sloped screen or other solid-liquid separator.
• In the case of the worm-system, separator liquid effluent is evenly distributed by a manifold pipe system over the worm earthworm-catalyzed trickling filter bed located on top of a porous media. As applied liquid infiltrates into the bed, aeration is used to keep the bed aerobic and is achieved by a blower forcing air through diffusers located at the bottom of the bed. Operative microbes convert ammonia-N to a series of intermediate N compounds and finally to N₂ gas. Liquid flows to the bottom of the vessel and is discharged by a point-source effluent pipe.
• In the case of more traditional NDN, solid-liquid separated liquid is pumped between anoxic and aerated zones for conversion of inorganic-N to a final N₂ gas. Control of temperature, feed rate, and recycle rates between the different zones, as well as settling/retention of bacterial solids, control the operation and performance.

Pre-treatment and/or Post-treatment Required

• Primary and even fine solid-liquid separation is required.
• For farms using sand bedding, sand-manure separation is required.
• No post-treatment is required of liquid effluent or gaseous emissions.

Limitations

• NDN cannot be used with raw or slightly diluted dairy manure as the solids and nitrogen loading interfere with the process. Solids-separated digested manure can be used however, increased ammonia-N concentrations and reduced availability of carbon complicate the process and its viability.
• Operative microbes only work in areas with dry or temperate climates.
• NDN does not appreciably reduce overall manure storage requirements.

Other Considerations

• Labor is required to manage and operate the system.
• NDN systems are appropriate to consider 1) in the case where a farm has a nutrient imbalance exists, i.e. more N is contained in manure than needed to grow field crops or 2) when farms have large distances between the farmstead and fields resulting in high manure transportation costs.
• Harvesting worm casings and processing for sale is labor intensive and requires specialized equipment.