Technology Strengths, Weaknesses and Critical Indicators
Slope Screen technologies:
- Produces fiber for bedding, soil amendment and compost
- Used extensively on dairies across the country to reduce concerns associated with storage and application
- Do not significantly reduce nutrients from the manure stream
- Can utilize many types of technology like slope screen, screw press, rotary drum and others
- Used before many other technologies to remove coarse solids
- Minimal maintenance and operator time required
- Proven technology for nitrogen recovery, phosphorous recovery, storage reduction, GHG reduction, and odor control but with limited impact in all cases
- Slope screen solid-liquid separation is used to separate coarse solids from diluted raw dairy manure.
- Solid-liquid separation is generally performed as a pre-treatment for subsequent manure treatment processes, reduce organic matter loading to storages/lagoons, reduce GHG emissions from long-term storages, facilitate pumping to distant fields/storages, and/or use of separated solids for stall bedding/compost media.
- Slope screens fit on any dairy that can economically justify flush cleaning of barns and/or manure flume conveyance.
- Slope screens can be used with all bedding types, although they are not intended to separate bedding sand from manure.
- When located outside, slope screens are limited to temperate climates if intended for daily use year-round. In cool/cold climates, slope screens need to be in a climate-controlled space for use year-round.
Economic/Return on Investment Consideration
- The capital cost is low compared to other methods of primary separation.
- Operating costs are also low compared to other methods of primary separation with the main costs being electricity to run influent mixers and influent pumps.
- Optimized influent pit design reduces mixing equipment needs and corresponding operating costs.
- As with all forms of primary solid-liquid separation, there is the potential for reduction of soil health due to diverting separated organic matter away from recycle to the land base thus reducing the overall potential return on investment from a whole-farm system perspective.
- Another possible unintended consequence is increased odor emission from a long-term storage; removal of course solid organic matter results in little to no crust on the storage and this can affect daily farmstead odor emissions.
- Inclined screen solid-liquid separation has been used extensively by dairy farms that employ flush cleaning of barns located in temperate climates and somewhat by farms as part of an integrated manure treatment system.
- Flush systems generate large volumes of dilute dairy manure. Primary separation can best be achieved using sloped screen separators due to their ability to handle high flow rates.
- Slope screen separation of dilute manure is a mature technology.
- Slope screens are all basically the same with some variation in the screen size and slope.
- Removal of organic matter in theory can contribute to manure storage odor reduction overall but in practice daily odor emission can be more noticeable.
- Reduce organic matter loading to storages/lagoons.
- Reduce GHG emissions from long-term storages.
- Use of separated solids for stall bedding/compost media.
- Pre-treatment for subsequent manure treatment processes
- Nutrient separation – about 20% of the mass of the original manure nutrient mass is contained in the separated solids.
- Solid-liquid separation provides the opportunity for farms to more easily pump manure long distances thus reducing manure hauling with tanker trucks.
How it Works
- Sloped screen solid-liquid separation only works on very dilute manure slurries.
- Dilute slurry is aggregated from source barns in an influent pit.
- Agitators (pump or impeller) are used to homogenize pit contents.
- Submerged or shaft-driven centrifugal pumps convey pit contents to the top of the barn sloped screen separator. Slope screen separators are normally elevated, so the separated solids can drop by gravity and accumulate in a pile for a short time, up to a few days.
- Influent is evenly distributed over the slope screen using a distribution weir
- The included screen bar allows liquids to fall thru the screen while separated solids “cascade” to the bottom and drop off.
- The separated liquid gravity flows or is pump to long-term storage of next treatment step.
- Separated solids are removed from pile normally by a payloader.
Pre-treatment and/or Post-treatment Required
- No pre-treatment is required if the manure is very dilute.
- No post-treatment is required but many times is employed based on-farm goals/needs.
- Manure must be very dilute; sloped screen will not work with raw or slightly diluted manure slurries.
- Sloped screens work best with continuous flow as residual manure solids left on the screen tend to dry and cake between screen uses. A washing system can be used to combat this problem and if used, it can also aid in the separation process.
- Manure solids generated by sloped screen separation are very wet; attention is needed to ensure the meaningful leachate volume is collected.
- Additional solids dewatering can take place by installing a roller press after the screen.
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