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. 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 Removed Nitrogen 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 Removed Nitrogen 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 Removed Nitrogen Removed P Removed 0.5 mm 2.6%25%---8%6% 0.75 mm 10%70%77%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 Removed Nitrogen Removed P Removed %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 Removed Nitrogen 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 Removed Nitrogen 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. C liquid V liquid C I V I C SM V SM Liquid Layer Settled Material Before SettlingAfter 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 Removed Nitrogen Removed P 2 O 5 Removed K 2 O 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 TS1.7%0.9%4.1% Pounds / 1000 gallons VS Org-N TAN P2O5P2O K2OK2O

Change in ratio of PAN and P 2 O 5 Flushed Manure Liquid From Settling Settled Solids Pounds / 1000 gallons Org-N TAN PAN- incorp P2O5P2O PAN:P 2 O

Gravity settling improves the balance of N to P 2 O 5 for many crops for the liquid part while increasing the relative P 2 O 5 content in the separated solids. Flushed Manure Liquid From Settling Settled Solids PAN:P 2 O Most grain crops want PAN:P 2 O 5 = 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/1000ft 3 /day.  TV (ft 3 ) = 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 Loading Rate, lb VS/1000ft 3 /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, ft 3 / 1000 lb of live animal weight, Dairy Cows (11.8 lb VS/1000 lb) Loading RateVS Removed by Liquid-Solid Separation lb VS/1000 ft 3 -d 0%20%40%60%80% 3.0, MN , IA , KS , NC , SC , TX , FL

VS Removal Reduces TV, ft 3 / 1000 lb of live animal weight, Finishing Swine (5.01 lb VS/1000 lb) Loading RateVS Removed by Liquid-Solid Separation lb VS/1000 ft 3 -d 0%20%40%60%80% 3.0, MN , IA , KS , NC , SC , TX , FL

Sludge Storage Volume, ft 3 /1000lb /year (ANSI/ASAE EP403.4, ASABE, 2011)  Depends on TS loading rate, MTS = lb TS added per year.  Sludge accumulation rates: Swine = ft 3 /lb TS Added Dairy = ft 3 /lb TS Added

Liquid-solid separation will reduce sludge build up in a treatment lagoon – Critical for dairy! TS Removed By Separator Swine Sludge Volume Per Year Dairy Sludge Volume Per Year 0%52.0 ft 3 /AU383.2 ft 3 /AU 20% % % % 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 ” (0.25mm).  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 ft 3 -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