Benefits of Using Liquid-Solid Separation with Dairy Manure Lagoons

1. Benefits of Using Liquid-Solid Separation with Dairy Manure Lagoons John P. Chastain, Ph.D. Professor and Extension Agricultural Engineer School of Agricultural, Forest, and Environmental Sciences April 2013 – CAMM Recertification Class

2. Purpose • Provide a summary of liquid-solid separation options • Discuss the benefits for dairy farms • Share some system layouts for dairy farms

3. Liquid-Solid Separation Options for Swine Farms Separation based on particle size – screens & presses. Separation based on density of the manure – gravity & cyclones

4. Mechanical Separation – Screens • Liquid manure flows through a screen. • Particles that are captured by the screen are removed from the liquid manure stream. • The liquids that flow through the screen go on to a lagoon or other treatment method. • Only pressure to drive separation comes from gravity or the flow of the manure.

5. Large particles in dairy can be easily removed by simple screens as compared with other species.

6. Some simple screen type separators

7. These are mostly used for dairy manure, but not swine manure because they use relatively large openings.

8. Issues with using simple screen separators with dairy manure • Large screen sizes needed to keep up with manure flow from barns. Flow matching is needed. • Fine screens turn liquid manure into slurry and liquid manure. • Separated solids are often too wet for optimal storage and handling as a solid. (Odor, flies)

9. Removal of solids, N, & P from dairy manure using a 0.059” (1.5 mm) stationary screen. Dairy solids removed by the screen had a solids content of 19% to 23%. Solids removed ranged from 23 to 51 lb /1000 lb/day.

10. Removal of solids, N, & P from dairy manure using a 0.030” (0.75 mm) rotating screen. Manure solids removed by rotating screen had a solids content of 6% to 11%. Too wet to handle as a solid. (Hegg et al.,1981)

11. Mechanical Separation – Presses • Applies pressure to force more liquids through a small screen. • Pressing can be provided by a screw, perforated belts, or filter plates. • Can be used with smaller screens than stationary screens. • Separated solids can be piled and handled as a solid. (Less odor and flies)

12. Some types of press separators

13. Issues with using press separators with swine manure • High pressure provides dry solids, but forces some large particles through screen. • Trade-off between particle capture and dryness of pressed cake. • Low process flow rate. • Tight tolerances can lead to screen replacement & higher maintenance costs.

14. Removal of solids, N, & P from dairy manure using a screw press. Separated solids ranged from 25% to 34%

15. Removal of solids, N, & P from dairy manure using a belt press with a 0.039” (1.0 mm) mesh belt. Separated solids 15% (Moller et al., 2000).

16. Trade offs that make use of mechanical separators difficult… • Presses can remove more total and volatile solids, N and P than simple screens, but need to process slurry not liquid manure. • Presses can yield drier solids than simple screens. • Presses are slower than simple screens. • Screens with small openings can remove a significant amount of solids & plant nutrients but yield wet solids (slurry) at high flow rates.

17. Combination of an in-channel flighted conveyor screen and a small screw press to treat liquid manure Screw Press

18. Liquid-solid separator that employs three techniques: fine stationary incline screen (0.020 in), screw press, and an inclined flighted conveyor screen (courtesy of US FARM Systems, Tulare, CA).

19. Removal of solids, N, & P from dairy manure using the combination machine (US FARM Systems). Flushed manure, stalls bedded with composted dairy solids, separated solids TS = 23% (Chastain, 2009).

20. Presses have also been used to remove solids from anaerobically treated manure – lagoon sludge and digester solids.

21. Treatment of anaerobically digested manure using a screw press with a 0.020” (0.50 mm) screen (dairy). Separated solids ranged from 24% to 25% TS and could be stacked (Gooch et al., 2005).

22. Liquid-Solid Separation by Settling

23. During gravity settling the fluid mixture separates into liquid and settled material layers. Cliquid Vliquid Liquid Layer CI VI Settled Material CSM VSM Before Settling After Settling

24. Factors that determine the effectiveness settling • Particles must be heavier than water. • There must be enough water in the mixture for the solids to separate and form a large liquid layer to form. • Want to provide sufficient settling conditions – very low flow velocity

25. Gravity settling can be used for… • Removing solids & nutrients from runoff from outdoor lots. • Flushed manure from freestall buildings and milking centers.

26. Gravity settling cannot be used to treat dairy manure with a TS greater than 3%. Gravity settling cannot be used to treat slurry manure.

27. Gravity settling can work for dilute dairy lagoon water and sludge mixtures.

28. Removal of solids, N, and P from liquid dairy manure by gravity settling. (Inflow TS = 1.7%) Gravity settling can greatly reduce the loading of solids and phosphorus on a lagoon. Volume of settled solids was 25% of flush volume (SVF = 0.25)

29. Solids and Nutrient Content of Liquid Dairy Manure Before & After Settling for 1 hour.

30. Change in ratio of PAN and P2O5

31. Gravity settling improves the balance of N to P2O5 for many crops for the liquid part while increasing the relative P2O5 content in the separated solids. Most grain crops want PAN:P2O5 = 2.2 to 2.5.

32. Main issues with gravity settling to take into account are… • Cost and permitting of settling basin or pond • Potential for increase in odor. • Cost of permeable cover that can greatly reduce odor. • Purchase and maintenance cost of agitation and pumping equipment. • Requires transport to fields.

33. Since the settled solids are slurry they can be used to load a press if dry solids are needed.

34. Addition of Polymers (PAM) and Metal Salts • These chemicals can be used to improve the performance of any method of liquid-solid separation. • Requires TS less than 6% • PAM, Alum, Iron Chloride, and others can be used alone or in combination at proper dose.

35. Chemicals can be used to remove 70% to 90% of the solids and P for most methods of liquid-solid separation Need proper dose Need proper mixing Need proper dilution Need $$$

36. Best Liquid-Solid Separation Options for Dairy Facilities • Presses: Slurry Systems • Combo Systems: Liquid Systems • Gravity Settling: Liquid Systems • Use chemicals? If more TS, VS, P removal needed. • Separation of lagoon sludge? Yes with right equipment and TS content.

37. Benefits of Liquid-Solid Separation for Manure Storages – not for recycle systems

38. Benefits of Liquid-Solid Separation for Storages • Remove large particles to reduce energy and time needed for agitation and pumping • Reduce storage volume by up to 20% if TS removal is on the order of 40%. • Remove large particles that could cause clogging of pipes and nozzles.

39. Benefits of Liquid-Solid Separation for Treatment Lagoons– best for recycle systems

40. Lagoon Sizing • Lagoon Volume = (Manure Volume + Treatment Volume + Sludge Storage Volume) • On top of these volumes add DEPTHS for Net Rain (P+R), 25 year – 24 hr storm + minimum of 12” of freeboard. • These depths are required for any manure storage.

41. Typical Lagoon System

42. Well treated recycled lagoon water needed for manure removal. • High loading rates = strong recycle water for flush freestall buildings. • Need well treated lagoon water to make recycle flush buildings function properly. • Maximum loading for recycle should be based on ASABE Standard.

43. Manure Storage Volume • Will include all manure, wasted water, and other solids added to manure per day (bedding and wasted feed) • Typically use a storage period ranging from 180 days in warm southern climates to 365 days in cold climates (e.g. Midwest) • Liquid-solid separation can reduce this volume by 10% to 25%. Best to be conservative.

44. Treatment Volume • Depends on VS loading rate , LR = lb VS/1000ft3/day. • TV (ft3) = 1000 (lb VS/day / LR) • Design loading rate depends on the climate. • Larger loading rates can be used in warm climates than in cold climates (ANSI/ASAE EP403.4, ASABE, 2011)

45. Variation of LR With Climate(ANSI/ASAE EP403.4, ASABE, 2011)

46. VS Removal Reduces TV, ft3 / 1000 lb of live animal weight, Dairy Cows (11.8 lb VS/1000 lb)

47. VS Removal Reduces TV, ft3 / 1000 lb of live animal weight, Finishing Swine (5.01 lb VS/1000 lb)

48. Sludge Storage Volume, ft3/1000lb /year (ANSI/ASAE EP403.4, ASABE, 2011) • Depends on TS loading rate , MTS = lb TS added per year. • Sludge accumulation rates: • Swine = 0.0219 ft3/lb TS Added • Dairy = 0.0729 ft3/lb TS Added

49. Liquid-solid separation will reduce sludge build up in a treatment lagoon – Critical for dairy! Solids Production: Swine = 6.5 lb TS/AU/day, Dairy = 14.4lb/AU/day

50. Odor Reduction? • Research has shown that most of the odor comes from particles that are smaller than 0.0098” (0.25mm). • Must have high-rate separation to greatly reduce odor production from liquid manure. • However lower VS loading rates have been shown to reduce frequency of odor from a lagoon.