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

ccampb3@clemson.edu

http://www.clemson.edu/cafls/safes/agmec/