Technology Type - Nitrification Denitrification
Technology Strengths,Weaknesses and Critical Indicators
- No saleable product produced in most systems
- Vermiculture and some other technologies do produce salable by-products (i.e. worms and worm castings)
- Traditional and modified forms exist with years of experience treating municipal wastewater
- Uses large, multiple reaction chambers seeded with both anaerobic and aerobic bacteria
- Traditional concerns are capital cost, requiring large dedicated tanks and large power consumption for aeration.
- Proven technology for phosphorous recovery, storage reduction, GHG reduction, odor control and pathogen reduction
- This technology loses nitrogen as non-reactive nitrogen gas
- 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.
- 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).
- 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.
- 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.
- 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.
- 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.
- 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.
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