| | Custom treatment with a portable plant | Permanent Snowfluent installation | Economic comparison of Snowfluent, direct injection, and conventional manure spreading
The ideal scenario for liquid manure is a treatment option that cost-effectively eliminates odours from both manure storage and manure spreading, separates water from solids, and concentrates the manure nutrients in the solids. The liquid fraction of the manure ideally would be clean enough for re-use for manure flushing in the barn, or discharge to surface water courses.
Snowfluent technology appears to fit into conventional liquid manure management systems without significant changes to the equipment and layout. Existing lagoons can be altered for runoff storage. An area for snowmaking next to the lagoons must be bermed, ditched, and compacted. Some additional pumping may be needed to return runoff water from the holding pond to the barns or to an irrigation system. Handling the solid residue can be done with conventional solid/semi-solid manure handling equipment (bucket loaders and manure spreaders)
Snowfluent meets three of these five criteria, which is more than conventional treatment can offer. It does not separate all nutrients with the solids, nor is the level of treatment achieved great enough that surface water discharge is an option. However, from the pilot test results some production scale treatment options can be visualized.
Custom Treatment with a Portable Plant
The custom treatment option using a portable plant is very similar to the pilot test. It also fits conventional sized operations that already use custom operators to empty lagoons and spread liquid manure.
The process would involve agitation of the lagoon to ensure that solids and liquid are well mixed so the lagoon can be emptied from one pump location. A snowmaking pad with compacted soil and gently graded slopes directing drainage to a runoff storage pond should be adjacent to the liquid manure lagoon(s). The size of the snowmaking area can be specified in detail by Northern Watertek Corporation. However, to avoid the problem of moving snowmaking towers with shifts in wind direction, an area 5 to 8 times the size of the lagoon would probably be sufficient. A runoff holding pond to collect meltwater should be approximately the same size as the liquid manure lagoon, and located adjacent to the snowmaking area.
A custom operation would involve four to five days of snowmaking to empty a lagoon storing two million gallons. Lagoon storage volumes can be minimized with two snowmaking operations, early and late winter. The snowmaking area may need a diversion drain to collect the first and last meltwaters and return them to the liquid manure lagoon. The initial snowmelt tends to have lots of colour and nutrients. The last snowmelt may pond and re-dissolve some of the precipitated nutrients. For operations with existing, permanent effluent-irrigation equipment in place, there may be an opportunity to apply the concentrated first and last runoff fractions to a crop.
The solids that remain behind in the snowmaking area can be allowed to dry out until they are dry enough to transport easily. Rainfall during the summer will determine how dry the solids get. A bucket loader and conventional manure spreader can then load, transport and spread the solids later in the summer. The window of opportunity to spread solids should be longer than with liquid manure since odour would not be an issue for transport and spreading.
The runoff will begin in April and finish flowing by July at the latest. Since the microbiology tests show a good reduction of faecal coliforms, the runoff water could be reused for manure flushing later in the summer. It could also be returned to the fields through a portable irrigation system. Additional treatment through a series of lagoons may bring the quality up to surface water discharge regulations.
Permanent Snowfluent Installation
For large operations where the flows to the liquid manure lagoons are large enough to make regular operation of snowmaking guns feasible, a permanent set-up may be more economical. Liquid manure storage would be sized to summer storage requirements. There are two options. The first option is to set the snowmaking towers up in a field and apply the snow to grow a crop. The area for snowmaking would be planted to forages and sized so that nutrient and salt loads from the snow are balanced with crop uptake and soil leaching requirements. Snowmelt runoff cannot leave the field so a buffer area outside the snow piles will be needed to intercept snowmelt. On some fields, some minor diking to prevent snowmelt from leaving the field may also be needed. The second option is to prepare an area similar for the custom operation scenario and opt for decantation of water from solids. This option avoids the problems of repeatedly applying manure to the same field.
There would be additional capital costs for permanent pumps, pipelines and snowmaking towers. However, Delta Engineering has developed automated control systems for these systems so the labour and time will be less for this option than a custom operation.
For field spreading, the water quality of snowmelt that infiltrates below the forage's root zone also may limit the depth of snow applied to the field. If large snowpiles result in significant recharge to groundwater, questions about leaching and salinity in addition to nutrient loading of groundwater will be raised.
Economic Comparison of Snowfluent, Direct Injection, and Conventional Manure Spreading
An economic analysis of Snowfluent for a mid-sized hog operation was performed so that a direct comparison could be made between Snowfluent, spreading, and direct liquid injection. Spreading was included because it is presently the most widely used method of disposing of liquid hog manure stockpiles. However, the strong odour associated with this method is one of the reasons for this investigation of Snowfluent as an alternative. Direct injection was also included in this comparison because it is a field application method that addresses the odour issue.
Surface application
The capacity of the lagoon at the Giebelhaus farm is 1.5 million gallons. Manure production from the farrow to finish operation is estimated at 2.8 million gallons per year. This results in two manure spreading operations per year (fall and spring). Both spreading operations are done by a custom operator. The farm supplies two 150 PTO horsepower tractors. The cost of the fall 1996 operation was estimated to be $11,000.00. The cost of the spring 1997 operation was $7, 000.00. The time required for the spring operation was approximately 20 hours. The fall operation required hauling the manure farther and took more time, approximately 32 hours. This results in a total hauling time of 52 hours. The cost of renting two 150 HP tractors for 52 hours is $3,588.00 (AAFRD, 1996). There is also a cost to incorporate the manure. To supply 70 lbs of nitrogen per acre, manure should be applied at 4100 gallons per acre. This requires approximately 640 acres of land for spreading. The cost of one tillage operation to incorporate the manure is $ 4, 160.00 (640 acres X $6.50/acre). This results in a total cost of $25, 748.00 to spread and incorporate the manure.
If the manure is not incorporated within 24 hours of spreading approximately 25% of the nitrogen in the manure is lost (Saskatchewan Agriculture and Food, 1997). Delaying incorporation adds an additional cost in lost plant nutrients. No incorporation of the manure results in odour, and as such is not comparable to Snowfluent or injection.
Not only is this method becoming less favourable with the public due to the odour associated with spreading, but it also requires year-round lagoon storage of liquid manure. This in itself can be a significant source of odour.
Direct injection into soil
Another method of manure application is injection. Injection also serves as a method of controlling odour during manure application. Based on rates obtained from custom manure injection operators, the cost of injecting 2.8 million gallons of liquid hog manure is approximately $22,400.00. It is also necessary to supply tractors to power the pumps during injection. If we assume that injection will use the same two tractors but will take approximately 20% longer than surface application, the cost of renting two 150 HP tractors for injection is $4, 305.00. This results in a total cost of $26, 705.00. If the manure needs to be hauled more than 2 miles away from the lagoon the cost of injection will increase. Little or no nitrogen is lost during injection.
Like spreading, this method also requires year-round lagoon storage, and the odours associated with it.
Snowfluent
Delta Engineering charges $1.60 per cubic metre to convert hog manure to Snowfluent. The volume of manure to be processed is 2.8 million gallons (12, 729 m3), for a total cost of $20,366.40. This cost does not include the value of the nitrogen and other crop nutrients lost during the Snowfluent process. The temperature must be -5C or colder to make Snowfluent. In order to compensate for down time Delta Engineering will charge up to $2.00/m3 during time periods with a higher risk of warm temperatures. This would increase the base cost of Snowfluent to $25, 458.00. Scheduling snowmaking for a high risk period significantly increases the cost of Snowfluent. The Snowfluent process leaves a residue of approximately 50% organic matter which must be spread. The amount of this residue is considerably less than the original amount of manure. This residue contains nitrogen and is valuable as a soil amendment which can help to improve soil tilth and organic matter. It may also be suitable for bagging and sale as an organic fertilizer.
The Snowfluent process costs less than surface spreading and injection. However, there is an additional cost to be considered with Snowfluent. The manure in the lagoon was tested for its nitrogen content at the time the Snowfluent was made. Based on this test, the approximate nitrogen fertilizer value of 2.8 million gallons of hog manure is $8, 597.00 (based on values given by AAFRD, 1995. Code of Practice for the safe and Economic Handling of Animal Manures.). As previously discussed, by not agitating the contents of the lagoon this Snowfluent test processed water containing approximately one four-hundredth of the solids content of typical hog manure. As such, the nitrogen content of the processed water was primarily in the form of ammonia, most of which was lost to the atmosphere via volatilization. In a worst-case scenario, with a loss of 100% of the nitrogen content of the raw liquid manure, the total cost of the Snowfluent process would be $28,963.40.
This loss of nitrogen and other plant nutrients represents an important cost of the Snowfluent process. The value of these nutrients is extremely variable, and will depend on fertilizer prices, the nutrient status of the soil the residue is applied to, and the way producers normally spread manure. If soil tests indicate that the levels of nitrogen and other nutrients in the soil are adequate for crop growth, the nutrients in the manure can be considered as "excess" nutrients and may be of little value. If fertilizer prices are low, the nutrients lost during the Snowfluent process are of less value. The longer manure is left on the surface of the soil the greater the amount of nitrogen lost. If most producers delay incorporation this may indicate that the nutrients in hog manure are not considered valuable. The nitrogen and other nutrients lost making Snowfluent may not be considered a significant cost in such a situation.
The cost of Snowfluent is similar to surface spreading and injection. Snowfluent is done during the winter, shifting this demand on labour and equipment away from spring and fall. It has the potential to reduce nitrate contamination of groundwater, which may be a concern with conventional spreading or injection on a limited land base. It is possible to reuse the water left by the melting Snowfluent for manure flushing in the hog barns. Based on these preliminary calculations, Snowfluent appears to be an economically viable method of odour control for hog producers. |
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