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Engineering data on N, P, K removal with manure treatment to make solids and liquids usable Read More ....
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MANAGEMENT ON A DAIRY FARM
Engineering data on N, P, K removal with manure treatment to make solids and liquids usable
by E. Paul Taiganides, Matthias Rabener, Bernie Sheff
Like the majority of the dairy farms of its size, [1500 milking cows], the Wagner brothers west of Madison, Wisconsin, do not have sufficient cropland adjacent to the farm to meet the promulgated limits on the amount of manure that can be applied per acre of land.
Like most dairy farms, the Wagner farm, too, has been operating at its location for decades and has been disposing its manure on the same cropland; result: soil phosphorus content has increased beyond the limits being set by local and state agencies. Like the majority of farms everywhere, it, too, has increased its numbers of cows. Like everywhere else, new residents have encroached on its rural domain; result: dairy farms have to reduce smell levels, control flies, and improve sanitation to remain in good standing with their neighbors and local environmental officials!
Scope of the technology demonstrated
The pictogram shows a mass-balance of the waste treatment system designed for the Wagner farm and tested over a period of several years to demonstrate the “best technology” to:
Process manure solids so they
can be re-used as bedding, instead of bringing-in tons of
into the farm and have the additional burden and associated cost for their disposal.
Make the excess solids compostable so as to
dispose them in distant areas without creating nuisance at
significant savings in transportation costs.
Ø Recycle the treated liquids for flushing so as to keep the alleys drier and cleaner, thus improving the hygienic condition within the barns and their appearance to the neighbors.
Ø Enhance the storage and treatment capacity of the lagoon and making it less smelly
Ø Reduce sufficiently the N, P, K content of the liquid stream so the lagoon liquids can be irrigated on the adjacent land without exceeding the current limits for nitrogen and phosphorus.
How the system works
First, the coarse particles in the slurry are separated mechanically by squeezing out the water with press screw separators [PSS]. This is the first module of the total treatment system. The second module is the removal of fine solids with centrifugal classifiers [CCS]. This is the mechanical Phase I of the system, and in most farms, it would be sufficient because it can achieve a removal of 45% of the solids in the slurry, 35% of the P, 30% of the N, and 25% of the K.
The solids, as separated, will have moisture content of 60% to 70%, which is optimal for the onset of composting. Expressing this number in engineering terms, the dry matter content is 30% to 40%, before composting, which is optimal for the material to be transported with regular trucks to adjoining lands at significant savings. Moreover, these solids do not attract flies or vermin and do not create public nuisance like liquid slurries do, so they can be disposed on neighbor’s lands.
Secondly, if the farm is required to reduce Phosphorus levels in the liquid stream by as much as 90%, then Phase II, third module, can be added as treatment of the liquids by dissolved air floatation [DAF] with the addition of chemicals to coagulate nutrients and make them float. The advantage of treating the liquids is that a clear effluent can be achieved with minimal solids content, thus making handling of the liquids with pumps though irrigation pipes and nozzles easier, besides reducing lagoon and barn odors significantly.
Pictures of the equipment used, in the sequence installed
for Phase I [mechanical] and Phase II [chemical],
are also shown in the pictogram. We added a picture showing a
barn alley of the Wagner dairy barn flushed clean and dry and a
picture of a pile of separated solids as they form a typical
cone when dropped from the solids separator installed on the
Stencil dairy, by
Performance of the system and engineering data
The data presented on the pictogram are based on the data collected over years of monitoring the operation for the 1500 milking cows of the Wagner farm. However, to make the data more usable to consultants and agricultural engineer who are preparing nutrient management plans for concentrated animal feeding operations [CAFO] as is required by EPA and state offices for the issuance of permits to operate a CAFO, the numbers given in the boxes of the pictogram are for a farm of 1000 milking cows. This way, it becomes easier to apply these data for farms of different size.
Wastes flushed out of the barns are collected in a homogenization tank before being pumped into screw separators to remove coarse solids. The coarse solids are used as bedding material. Of the 18 tons of solids separated mechanically, 7 tons are recycled as bedding, as is indicated in the pictogram [in a box on the upper left]. The bedding requirements are set at 14 lbs of 30% dry matter content material per milking cow per day. These quantities are added to the amounts of manure excreted by the cows in the barns. The volume of flushing is based on 150 gallons of lagoon liquids and 15 gallons of fresh water per milking cow per day.
The resulting slurry from these three sources, [as shown in the pictogram in the box before mechanical separation], has a volume of 763 tons [182,000 gallons, or 182 gpd per milking cow]. Only 14 percent [24 gpd per milking cow] of the wastewater volume needs to be in long-term storage in the lagoon, thus minimizing the size of a new lagoon or increasing the storage capacity of an existing lagoon.
The amounts of bulky solids that are exported from the farm amount to 11 + 19 = 30 tons [see upper right of the pictogram]; i.e., only a truckload per day.
Costing of the System for 1000-milking cow farm
Before this system was installed, the Wagner’s were paying around $100 per year per head to transport liquid slurries to dispose on distant farms. With mechanical separation and removal of nutrients from the liquid into the solids stream, these cost were reduced to $30 per cow or a savings of $70 per milking cow per year.
The cost of bringing in material for bedding and disposing it along with the slurry generated on the farm in this and other dairy farms is estimated at $30 to $100 per milking cow per year.
Thus, the estimated savings from the system are a minimum of $100 [70+30] to $170 [70+100] per milking cow per year.
The costing of the system is based on leasing the equipment with a 25% lease charge over the total purchase price over a 5-year period. Amortization and full operation costs of the equipment of separators and centrifugal separators for the mechanical Phase I of the system would amount to $100 per milking cow per year.
The operating cost of the Phase II in combination with Phase I, that is the mechanical plus chemical solids nutrient removal, would amount to $200 per milking cow per year with a 5-year amortization of the capital costs for the purchase and installation of the equipment and for the cost of the chemicals added to achieve 90% removal of phosphorus from the liquid stream.
The savings from the reuse of the dry solids for bedding and from cheaper costs for the disposal of the compostable solids without creating odor or fly nuisance would be equal or exceed the cash costs for the mechanical phase, which could be the only phase needed in most farms, and would be almost that of the total system, that is the combination of the mechanical and chemical for complete treatment of both the solids and liquid streams on the farm.
The system is a modular system: the first module would be the solids separation by screw separator only [in this case the costs would be half of the mechanical costs given above]; the second module, centrifugal classification may be added if required for removal of the fine solids and/or for tertiary treatment with dissolved air flotation, which would be the third module of the complete treatment.
Our MISSION is to help livestock producers assess the costs of practical potential systems of handling the wastes from their animal units with maximum recycle and minimum public nuisance.