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
Purpose Provide a summary of liquid-solid separation
options
Discuss the benefits for dairy farms
Share some system layouts for dairy farms
Liquid-Solid Separation Options for Swine Farms1. Separation based on particle size – screens
& presses.
2. Separation based on density of the manure – gravity & cyclones
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.
Large particles in dairy can be easily removed by simple screens as compared with other species.
Some simple screen type separators
These are mostly used for dairy manure, but not swine manure because they use relatively large openings.
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)
Removal of solids, N, & P from dairy manure using a 0.059” (1.5 mm) stationary screen.
Influent TS
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P Removed
1.5% 19% 24% 13% 18%
-- 46% 50% 17% 11%
3.8% 60% 63% 49% 53%
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.
Removal of solids, N, & P from dairy manure using a 0.030” (0.75 mm) rotating screen.
Influent TS
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P Removed
0.5% 0% 3% --- ---
3% 14% 4% --- ---
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)
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)
Some types of press separators
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.
Removal of solids, N, & P from dairy manure using a screw press.
Influent TS
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P Removed
0.5 mm
2.6% 25% --- 8% 6%
0.75 mm
10% 70% 77% 24% 24%
2.38mm
10% 47% --- --- 29%
Separated solids ranged from 25% to 34%
Removal of solids, N, & P from dairy manure using a belt press with a 0.039” (1.0 mm) mesh belt.
Influent TS
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P Removed
7.1 32.4 --- 10% 15%
Separated solids 15% (Moller et al., 2000).
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.
Combination of an in-channel flighted conveyor screen and a small screw press to treat liquid manure
Screw Press
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).
Removal of solids, N, & P from dairy manure using the combination machine (US FARM Systems).
Influent TS
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P Removed
< 1.5% 50% 56% 23% 20%
Flushed manure, stalls bedded with composted dairy solids, separated solids TS = 23% (Chastain, 2009).
Presses have also been used to remove solids from anaerobically treated manure – lagoon sludge and digester solids.
Treatment of anaerobically digested manure using a screw press with a 0.020” (0.50 mm) screen (dairy).
Influent TS
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P Removed
7.5% 50% 56% 16% 24%
8.3% 47% 53% 17% 20%
Separated solids ranged from 24% to 25% TS and could be stacked (Gooch et al., 2005).
Liquid-Solid Separation by Settling
During gravity settling the fluid mixture separates into liquid and settled material layers.
Cliquid Vliquid
CI VI
CSM VSM
Liquid Layer
Settled Material
Before Settling After Settling
Factors that determine the effectiveness settling
1. Particles must be heavier than water.
2. There must be enough water in the mixture for the solids to separate and form a large liquid layer to form.
3. Want to provide sufficient settling conditions – very low flow velocity
Gravity settling can be used for… Removing solids & nutrients from runoff
from outdoor lots. Flushed manure from freestall buildings and
milking centers.
Gravity settling cannot be used to treat dairy manure with a TS greater than 3%.
Gravity settling cannot be used to treat slurry manure.
Gravity settling can work for dilute dairy lagoon water and sludge mixtures.
Removal of solids, N, and P from liquid dairy manure by gravity settling. (Inflow TS = 1.7%)
Total Solids
Removed
Volatile Solids
RemovedNitrogen Removed
P2O5
RemovedK2O
Removed
61% 66% 41% 45% 25%
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)
Solids and Nutrient Content of Liquid Dairy Manure Before & After Settling for 1 hour.
Flushed Manure
Liquid From Settling
Settled Solids
TS 1.7% 0.9% 4.1%
Pounds / 1000 gallons
VS 111.6 50.5 290.7
Org-N 3.8 1.4 10.7
TAN 6.3 6.5 6.4
P2O5 3.4 2.5 6.0
K2O 7.6 8.0 7.8
Change in ratio of PAN and P2O5
Flushed Manure
Liquid From Settling
Settled Solids
Pounds / 1000 gallons
Org-N 3.8 1.4 10.7
TAN 6.3 6.5 6.4
PAN- incorp 7.3 6.0 11.5
P2O5 3.4 2.5 6.0
PAN:P2O5 2.1 2.4 1.9
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.
Flushed Manure
Liquid From Settling
Settled Solids
PAN:P2O5 2.1 2.4 1.9
Most grain crops want PAN:P2O5 = 2.2 to 2.5.
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.
Since the settled solids are slurry they can be used to load a press if dry solids are needed.
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.
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 $$$
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.
Benefits of Liquid-Solid Separation for Manure Storages – not for recycle systems
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.
Benefits of Liquid-Solid Separation for Treatment Lagoons– best for recycle systems
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.
Typical Lagoon System
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.
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.
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)
Variation of LR With Climate(ANSI/ASAE EP403.4, ASABE, 2011)
LocationLoading Rate, lb VS/1000ft3/day
Southern Minnesota (Cold) 3.0
Iowa 3.5
Kansas 4.0
North Carolina 4.5
South Carolina & Georgia 5.0
Central Texas 5.5
Central Florida (Hot) 6.0
VS Removal Reduces TV, ft3 / 1000 lb of live animal weight, Dairy Cows (11.8 lb VS/1000 lb)
Loading Rate VS Removed by Liquid-Solid Separation
lb VS/1000 ft3-d 0% 20% 40% 60% 80%
3.0, MN 3936 3149 2362 1574 787.23.5, IA 3374 2699 2024 1349 674.74.0, KS 2952 2362 1771 1181 590.44.5, NC 2624 2099 1574 1050 524.85.0, SC 2362 1889 1417 944.6 472.35.5, TX 2147 1718 1288 858.8 429.46.0, FL 1968 1574 1181 787.2 393.6
VS Removal Reduces TV, ft3 / 1000 lb of live animal weight, Finishing Swine (5.01 lb VS/1000 lb)
Loading Rate VS Removed by Liquid-Solid Separation
lb VS/1000 ft3-d 0% 20% 40% 60% 80%
3.0, MN 1668 1335 1001 667.3 333.73.5, IA 1430 1144 858.0 572.0 286.04.0, KS 1251 1001 750.8 500.5 250.34.5, NC 1112 889.8 667.3 444.9 222.45.0, SC 1001 800.8 600.6 400.4 200.25.5, TX 910.0 728.0 546.0 364.0 182.06.0, FL 834.2 667.3 500.5 333.7 166.8
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
Liquid-solid separation will reduce sludge build up in a treatment lagoon – Critical for dairy!
TS Removed By Separator
SwineSludge Volume
Per Year
DairySludge Volume
Per Year
0% 52.0 ft3/AU 383.2 ft3/AU
20% 41.6 306.5
40% 31.2 229.9
60% 20.8 153.3
80% 10.4 76.63
Solids Production: Swine = 6.5 lb TS/AU/day, Dairy = 14.4lb/AU/day
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.
Effect of VS Loading Rate on Odor Frequency (adapted from Humenik, et al. 1981)
Well treated recycled lagoon water needed for manure removal. High loading rates = strong recycle water for
flushing. Increases odor and ammonia problems in and
around buildings. Need well treated lagoon water to make our
recycle flush buildings function properly. Maximum loading for recycle in SC
= 5 lb VS/1000 ft3-day.
Use of a mechanical separator (MS) to reduce loading on lagoon
Enhancing solids and nutrient removal by using chemicals slows the system down in this configuration.
Use of a mechanical separator (MS) to reduce loading on lagoon - Advantages
Small amount of space needed as compared to settling.
Can be added to existing systems in many cases.
Solids can be dry enough to stack or store in a small volume.
Need separator throughput rates of 150 to 200 gpm.
Use of a mechanical separator (MS) to reduce loading on lagoon - Disadvantages
Energy to operate system. Screens, drives, motors, belts, augers require
maintenance High solids removal requires small screens
and low throughput rates – often main problem.
High removal systems often generate wet solids.
Gravity settling can be used to make high-rate mechanical separation easier – also reduces chemical costs.
Add a settling basin or pond before the lagoon – basins drain dry, ponds do not.
Can use chemicals to enhance removal of solids and plant nutrients for a settling basin or pond.
Drain-dry basins…not many used in SC but could be.
Add a settling basin or pond before the lagoon – Advantages
Greatly reduces VS loading Greatly reduces or eliminates sludge build up Solids are in a semi-solid or slurry and plant
nutrients are more accessible than sludge on the bottom of a lagoon.
Size based on desired storage volume and period. Reduces organic-N mineralization in lagoon and
conserves N by reducing ammonia generation and loss.
Less maintenance than a mechanical separator
Add a settling basin or pond before the lagoon – Disadvantages
If solids are too dry the fly population could increase. A layer of water is needed to control flies.
May cause an increase in odor near settling pond/basin. Permeable cover could help.
Takes up more space than mechanical separation.
A reception pit/settling basin used with a mechanical separator to dewater lagoon sludge.
Summary Liquid-solid separation can be used to
significantly reduce treatment and sludge storage volumes.
Allows use of smaller structures to save money. Allows more economical use of lower loading
rates to improve recycle water quality. Can help reduce ammonia and odor production
Summary (2) Can allow use of anaerobic treatment lagoons
in colder climates. Can be used to remove a portion of VS and
Organic-N that would breakdown in the lagoon to yield methane, ammonia, and carbon dioxide.
Reduces cost of sludge management to maintain lagoon function.
Agricultural Mechanization &
Business
School of Agricultural, Forest, and
Environmental Sciences
Contact:
Christi Leard
864.656.3250
http://www.clemson.edu/cafls/safes/agmec/
