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 Farms
1.
2.
Separation based on particle size – screens
& presses.
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.
Total
Volatile
Influent
Solids
Solids Nitrogen
P
TS
Removed Removed Removed 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.
Total
Volatile
Influent
Solids
Solids Nitrogen
P
TS
Removed Removed Removed 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
0.5 mm
2.6%
0.75 mm
10%
2.38mm
10%
Total
Solids
Removed
Volatile
Solids
Removed
Nitrogen
Removed
P
Removed
25%
---
8%
6%
70%
77%
24%
24%
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.
Total
Volatile
Influent
Solids
Solids
Nitrogen
P
TS
Removed Removed Removed 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).
Total
Volatile
Influent
Solids
Solids
Nitrogen
P
TS
Removed Removed Removed 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).
Total
Volatile
Influent
Solids
Solids
Nitrogen
P
TS
Removed Removed Removed 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
Liquid Layer
CI VI
Settled Material
CSM VSM
Before Settling
After Settling
Factors that determine the effectiveness settling
1.
2.
3.
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
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
Volatile
Solids
Solids
Nitrogen
P2O5
K2O
Removed Removed Removed Removed 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.
TS
VS
Org-N
TAN
P2O5
K2O
Flushed
Manure
1.7%
111.6
3.8
6.3
3.4
7.6
Liquid From
Settled
Settling
Solids
0.9%
4.1%
Pounds / 1000 gallons
50.5
290.7
1.4
10.7
6.5
6.4
2.5
6.0
8.0
7.8
Change in ratio of PAN and P2O5
Flushed
Manure
Org-N
TAN
PAN- incorp
P2O5
PAN:P2O5
3.8
6.3
7.3
3.4
2.1
Liquid From
Settled
Settling
Solids
Pounds / 1000 gallons
1.4
10.7
6.5
6.4
6.0
11.5
2.5
6.0
2.4
1.9
Most grain crops want PAN:P2O5 = 2.2 to 2.5.
PAN:P2O5
Flushed
Manure
2.1
Liquid From
Settling
2.4
Settled
Solids
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.
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)
Location
Southern Minnesota (Cold)
Iowa
Kansas
North Carolina
South Carolina & Georgia
Central Texas
Central Florida (Hot)
Loading Rate, lb
VS/1000ft3/day
3.0
3.5
4.0
4.5
5.0
5.5
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
3.5, IA
4.0, KS
4.5, NC
5.0, SC
5.5, TX
6.0, FL
3936
3374
2952
2624
2362
2147
1968
3149
2699
2362
2099
1889
1718
1574
2362
2024
1771
1574
1417
1288
1181
1574
1349
1181
1050
944.6
858.8
787.2
787.2
674.7
590.4
524.8
472.3
429.4
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
3.5, IA
4.0, KS
4.5, NC
5.0, SC
5.5, TX
6.0, FL
1668
1430
1251
1112
1001
910.0
834.2
1335
1144
1001
889.8
800.8
728.0
667.3
1001
858.0
750.8
667.3
600.6
546.0
500.5
667.3
572.0
500.5
444.9
400.4
364.0
333.7
333.7
286.0
250.3
222.4
200.2
182.0
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
0%
20%
40%
60%
80%
Swine
Sludge Volume
Per Year
52.0 ft3/AU
41.6
31.2
20.8
10.4
Dairy
Sludge Volume
Per Year
383.2 ft3/AU
306.5
229.9
153.3
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
ccampb3@clemson.edu
http://www.clemson.edu/cafls/safes/agmec/