Transcript Mass Balances: Application of the law of conservation of

Fundamentals of Liquid-Solid
Separation of Animal Manure
Feb. 27, 2008
John P. Chastain, Ph.D.
Professor
Department of Agricultural and
Biological Engineering
Objectives




Key characteristics of animal manure as
impacted by manure handling and facility
management.
Impact of facility design and management on
separator performance.
Measures to evaluate liquid-solid separation
performance.
Overview of screening and settling.
Animal manure is…

A complex mixture of compounds.

Some compounds are soluble and others are
insoluble (organic).

However, we are often interested in removal
of specific elements, such as P.

Elements of interest are always removed in a
compound.
What is the first thing that we must
understand before we select and
implement a liquid-solid separator on
a farm?
What is the first thing that we must
understand before we select and
implement a liquid-solid separator on
a farm?
Answer — Define all sources of solids and
plant nutrients that will be included in the
manure for the farm in question.
This is often overlooked!
No two swine or dairy farms are exactly the
same.
What are the sources
of solids and plant
nutrients in the waste
stream from this
swine finishing farm?
Wait – first we need
to find the answer
to another question.
What method is used to
remove manure from
these swine barns?
Flush?
Pit-recharge?
Gravity drain gutter?
Liquid-solid separation can be used with one of
three collection methods.

Flush – common where treatment lagoons are
used.

Pit-recharge – common where treatment
lagoons are used.

Gravity drain gutter – most common in colder
climates.
Flush (TS ≈ 0.5% to 2%)




Manure collects in a shallow pit below slotted
floors.
Manure is flushed at a sufficiently high
velocity to remove manure from the building.
Manure is removed from buildings 2 to12
times per day depending on design and
control.
Typically use recycle lagoon supernatant.
Pit-Recharge (TS = 1.5% to 3%)





Pit is located below slotted flooring and has a
depth ranging from 24 to 30 in.
Bottom of pit is sloped 0.5 in /10 ft toward
outlet.
Pit is filled with treatment lagoon supernatant to
a set volume.
Excess liquid decants as manure accumulates.
Emptied by gravity every week by pulling a
“plug”.
Gravity Drain Gutter (TS = 5% to 8%)






Shallow pit is located below slotted flooring.
May or may not be divided as a “hair pin”.
Bottom of pit is often flat.
Pit is filled with 2 to 3 in of fresh water.
Manure accumulates for 5 to 7 days.
Emptied by gravity every week by pulling
a “plug”.
Comparison of Waste Volumes

Gravity drain gutter (TS = 5%)
16.5 gal/AU/day

Pit-recharge (TS = 2%)
51 gal/AU/day

Flush (TS = 1%)
80 gal/AU/day
What does this have to do with defining the
waste stream?



Obviously extra water impacts the throughput
requirements of the separator (gal./hr).
Extra dilution sometimes decreases separator
performance.
Using treatment lagoon water will add solids
and plant nutrients that cannot be treated by
simple separation.
Sources of solids & nutrients…



Manure from hogs
Wasted feed
Solids and nutrients
in recycled lagoon
water used to
remove manure.
A real example from a swine finishing farm
using pit-recharge buildings.
Removed from Pit
Added from Lagoon
lb/1000 gal
lb
lb/1000 gal
lb
TS (2%)
166.9
7177
41.7
1434
TKN
19.9
856
6.3
217
Org-N
6.1
262
2.0
69
P2O5
14.8
636
3.6
124
(43,000 gal/wk; VS/TS = 0.687; 80% of pit volume is recycled lagoon water)
A high percentage of the TS, N and P removed from
a pit-recharge building was recycled.
30
25
26
Recycled from Lagoon (%)
25
20
19
20
15
10
5
0
TS
TKN
Org-N
P2O5
Recycled solids and nutrients generate
the following problems…




Solids and nutrients recycled from the lagoon
cannot be removed by screening or settling.
They cause an increase in the influent
concentration and mass.
Will confound field validation by decreasing
the observed removal by the separator.
Must estimate amount added from recycle to
get a true picture of effectiveness.
Flush systems can add
much more!
80
71
Pit-Recharge
Recycled from Lagoon (%)
70
Flush
60
46
50
40
34
30
25
30
26
20
19
20
10
0
TS
TKN
Org-N
P2O5
The sources of solids and plant nutrients on dairy
farms are varied.







Manure
(un-collectable?)
Bedding – organic or
dried separated solids
Sand bedding
Waste feed
Milking center waste
Soil tracked into barn
Recycled lagoon water
Solids production from a flushed dairy
MTS = MTSMANURE + MTSMILK + MTSBED
+ MTSFEED + MTSSOIL + MTSLAGOON
Impact of organic bedding on solids produced by
an inclined screen treating flushed dairy manure.
TS of Flush
Water
Organic Bedding
3.82%
≈ 2.5% NR
≈ 3.4 lb
TS /AU-day
≈ 0.5 to 1 lb
TS /AU-day
≈14.4 lb TS/AU-day
Manure
Mass of dry
solids produced
10.4
5.3
lb SDM/AU-day lb SDM/AU-day
Screen was 1.5 mm or 0.059 in both cases.
Measures to evaluate liquidsolid separation performance
1. Concentration reduction
2. Mass removal efficiency
Concentration Reduction (CRC)
Difference in the influent (IN) and effluent (EFF)
concentrations in percent.
CIN
Separator
CEFF
Separated
Solids
Concentration Reduction (CRC)
CRC = 100 x [(CIN – CEFF) / CIN]
CIN
Separator
CEFF
Separated
Solids
Mass Removal Efficiency - MREC
The mass of solids or plant nutrients removed and
deposited in the separated solids. More accurate.
CIN QIN
Separator
CEFF QEFF
CSS MSS
Separated
Solids
MREC – Based on influent and effluent
MREC = 100 x [(CINQIN – CEFFQEFF) / CINQIN]
CIN QIN
Separator
CEFF QEFF
CSS MSS
Separated
Solids
MREC –
Based on influent and separated solids
MREC = 100 x [CSSMSS / CINQIN]
CIN QIN
CEFF QEFF
Separator
CSS MSS
Separated
Solids
MREC –
Based on effluent and separated solids
MREC = 100 x [CSSMSS / (CEFFQEFF + CSS MSS)]
CIN QIN
CEFF QEFF
Separator
CSS MSS
Separated
Solids
In some cases, the mass of the separated
solids is tough to measure.
SSVF = separated solids volume fraction
= [Vol. SS/ Vol. IN] = [QEFF / QIN]
CIN QIN
Separator
CEFF QEFF
CSS MSS
Separated
Solids
Alternative MREC formula using SSVF
MFRC = 100 x [ CIN - CEFF (1 – SSVF)] / CIN
CIN QIN
Separator
CEFF QEFF
CSS MSS
Separated
Solids
Separation is accomplished by exploiting
differences in

Size 

Density 

Solubility

Electrical charge
Separation by Size: Screening
Two major factors that determine the
effectiveness of screen type separators
1.
2.
Particle size in the waste stream – larger is
easier to remove.
Total solids content of the waste mixture.
In general, screen separators increase
in effectiveness as [TS] increases.
Why do high [TS] wastes often screen
better?

Some thicker slurries contain a greater
proportion of “large” particles.

A “mat” of larger particles will form on the
screen and will catch particles that are smaller
than the screen opening size.

This capture of small particles by a mat of
large particles is called entrainment.
Large amounts of organic bedding increases proportion
of screen-able solids and promotes entrainment.
Heavily Bedded
Average Amount of
Bedding
Stalls
Solids Prod.= 10.4 lb SDM/AU-d 5.3 lb SDM/AU-d
CRTS =
CRVS =
CRTKN =
60.9%
62.8%
49.2%
45.5%
50.1%
17.1%
CRP =
53.1%
11.0 %
Same brand, screen was 1.5 mm or 0.059” in both cases.
In Western states, some dairy
producers use composted and/or
dried manure solids as bedding.
Adds 1.5 to 3 lb TS / AU-day to flush water.
 Composting and drying decreases particle
size.
 Adds many solids and nutrients that cannot be
screened.

Impact of bedding type and screen size on MRE for
an incline screen treating flushed dairy manure.
Solids Prod.=
MRETS =
MREVS =
MRETKN =
MREP =
SC: wood shavings, CA: dried separated
fresh flush
solids, recycle flush
0.059 in Screen
0.020 in Screen
10.4 lb SDM/AU-d 11.7 lb SDM/AU-d
63%
52%
64%
58%
52%
0.07%
56%
0.06%
SSVF ≈ 0.05
Dairy manure screens best - swine screens
the worst.
Percent of TS Passing Through Screen
100
0.25 mm = 0.010 in
90
1 mm = 0.039 in
80
70
60
Dairy Cows
Beef
Poultry
Swine
50
40
0.5 mm = 0.020 in
30
Data from Meyer et al. (2007), Chang and Rible
(1975), and Masse et al. (2005).
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
Screen Size (mm)
1.4
1.6
1.8
2
2.2
Screening Swine Manure - Examples
[TSIN] =
Screw Press
(0.020 in screen)
5.5%
Incline Screen
(0.039 in screen)
1 – 4.5%
CRTS =
CRVS =
CRTKN =
17.8%
23.4%
14.1%
6 to 31%
5 to 38%
3 to 6%
CRP =
17.8%
2 to 12%
New types of separators and combinations
can provide better results for swine manure.
Screw Press +
Tangential Flow (TF)
[TSIN] =
0.81%
Tangential Flow
0.77% – 1.13%
CRTS =
CRVS =
CRTKN =
30.7%
47.1%
7.2%
25.8 to 31.7%
35.1 to 47.4%
15%
CRP =
56.6%
40 to 41%
Applicability of Screen Separators

Most screens can be implemented for [TS] in
the range of 1% to 5% solids.

Effectiveness increases as [TS] increases.

Presses can be used for slurries with [TS] up
to about 10%.
Separation by density: sedimentation
(gravity settling) and centrifuge.
During gravity settling the fluid mixture separates
into supernatant and settled material layers.
CSUPER VSUPER
CI VI
Supernatant
Layer
Settled Material
CSM VSM
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 for a large
supernatant layer to form.
Want to provide sufficient quiescent settling
conditions.
(Volume of Settled Solids / Initial Volume)
Settling requires dilution. (Dairy)
1
TS = 6.5%
0.9
0.8
TS = 4.3%
0.7
TS = 3.3%
0.6
0.5
TS = 2.2%
0.4
Range
0.3
MC, TS = 1.7%
TS = 1.2%
0.2
0.1
MC, TS = 0.7%
0
0
1
2
3
4
Settling Time (hr)
5
6
7
We have similar results for swine.
Settled Volume/Initial Volume
1.00
Fresh Swine Manure
TS = 2.6%
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0
4
8
12
16
Time (hr)
20
24
28
Solids CR for Swine & Dairy
TS Concentration Reduction (%)
70
60
50
40
Swine
Dairy
30
20
10
0
0
0.5
1
1.5
2
2.5
influent Total Solids Content (%)
3
3.5
Settling of Dairy Wastewater: TS = 1.7%
TS
Concentration
Reduction
47%
Mass Removal
Efficiency
61%
VS
TKN
P2O5
55%
21%
26%
66%
41%
45%
SSVF ≈ 0.25
Settling of Swine Waste: TS = 2%
TS
Concentration
Reduction
54%
Mass Removal
Efficiency
66%
VS
56%
67%
TKN
22%
41%
P2O5
72%
79%
SSVF ≈ 0.25
Gravity settling works well
for both dairy and swine
systems.
We probably should be using settling more in
treatment system design in many cases.
Polymers, aluminum, and iron can enhance liquidsolid separation by screening and gravity settling.
1.
2.
3.
Use of a variety of chemicals can increase
concentration reductions of TS, VS, P to
70% to 90%.
Cost of chemical and proper injection are
main concerns.
Land and containment cost should be
considered in the economics.
Summary
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Take the required time to understand the facilities on
the farm and the waste generated.
Practices on a given farm can greatly alter
performance.
Have realistic expectations for screens and presses.
Best for dairy – getting better for swine.
Sedimentation is effective for dairy and swine.
Chemical enhancement cost should be weighted
against other costs (e.g. land, containment).
Sources of more information


Several reports have been posted with this
presentation to provide details on specific
systems.
A NRCS Tech Note is being written and will
be ready for publication by Dec. 2008.
Contact information
John P. Chastain, Ph.D.
Professor
Department of Agricultural and
Biological Engineering
[email protected]
864-656-4089