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March 5, 2019March 20, 2019

Early Stage Economic Modeling of Gas-permeable Membrane Technology Applied to Swine Manure after Anaerobic Digestion

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Purpose

The objective of this study was to conduct cost versus design analysis for a gas-permeable membrane system using data from a small pilot scale experiment and projection of cost versus design to farm scale.

What did we do?

This reported work includes two major steps. First, the design of a small pilot scale batch gas-permeable membrane system was scaled to process effluent volumes from a commercial pig farm. The scaling design maintained critical process operating parameters of the experimental membrane system and introduced assumed features to characterize effluent flows from a working pig farm with an anaerobic digester. The scaled up design was characterized in a spreadsheet model. The second step was economic analysis of the scaled-up model of the membrane system. The objective of the economic analysis was to create information to guide subsequent experiments towards commercial development of the technology. The economic analysis was performed by introducing market prices for components, inputs, and products and then calculating effects on costs and on performance of changes in design parameters.

What have we learned?

First, baseline costs and revenues were calculated for the scaled up experimental design. The commercial scale design of a modular gas-permeable membrane system was modeled to treat 6 days accumulation of digester effluent at 16,300 gallons per day resulting in a batch capacity of 97,800 gallons. The modeled large scale system is 19,485 times the capacity of the 5.02 gallon experimental pilot system. The installation cost of the commercial scale system was estimated to be $903,333 for a system treating 97,800 gallon batches over a 6 day period.

At $1/linear ft. and 7.9 ft./gallon of batch capacity, membrane material makes up 86% of the estimated installation cost. Other installation costs include PVC pipes, pumps, aerators, tanks, and other parts and equipment used to assemble the system, as well as water to dilute the concentrated acid prior to initiating circulation. The annual operating cost of the system includes concentrated sulfuric acid consumed in the process. Using limited experimental data on this point, we assume a rate of 0.009 gallons (0.133 pounds) of acid per gallon of digester effluent treated. At a price of $1.11 per gallon ($0.073/lb) of acid, acid cost per gallon of effluent treated is $0.010. Other operating costs include electric power, labor, and repairs and maintenance of the membrane and other parts of the system estimated at 2% of investment cost for non-moving parts and 6% of investment for moving parts. Potential annual revenue from the system includes the value of ammonium sulfate produced. Over the 6 day treatment period, if 85% of the TAN-N in the digester effluent is removed by the process, and if 100% of the TAN-N removed is recovered as ammonium sulfate, and given the TAN-N concentration in digester effluent was 0.012 pounds per gallon (1401 mg/l), then 0.01 pounds of TAN-N are captured per gallon of effluent treated. At an ammonium sulfate fertilizer price of $588/ton or $0.294/pound and ammonium sulfate production of 0.047 pounds (0.01 pounds TAN-N equivalent), potential revenue is $0.014 per gallon of effluent treated. No price is attached here for the elimination of internal and external costs associated with potential release to the environment of 0.01 pounds TAN-N per gallon of digester effluent or 59,073 pounds TAN-N per year from the system modeled here.

Several findings and questions, reported here, are relevant to next steps in experimental evaluation and commercial development of this technology.

1. Membrane price and/or performance can be improved to substantially reduce installation cost. Membrane material makes up 86% of the current estimated installation cost. Each 10% reduction in the product of membrane price and length of membrane tube required per gallon capacity reduces estimated installation cost per gallon capacity by 8.6%.

2. The longevity and maintenance requirements of the membrane in this system were not examined in the experiment. Installation cost recovery per gallon of effluent decreases at a declining rate with longevity. For example, Cost Recovery Factors (percentage of initial investment charged as an annual cost) at 6% annual interest rate vary with economic life of the investment as follows: 1 year life CRF = 106%, 5 year life CRF = 24%, 10 year life CRF = 14% . Repair costs are often estimated as 2% of initial investment in non-moving parts. In the case of the membrane, annual repair and maintenance costs may increase with increased longevity. Longevity and maintenance requirements of membranes are important factors in determining total cost per gallon treated.

3. Based on experimental performance data (TAN removal in Table 1) and projected installation cost for various design treatment periods ( HRT = 2, 3, 4, 5, or 6 days), installation cost per unit mass of TAN removal decreases and then increases with the length of treatment period. The minimum occurs at HRT = 4 days when 68% reduction of TAN-N in the effluent has been achieved.

4. Cost of acid relative to TAN removal from the effluent and relative to fertilizer value of ammonium sulfate produced per gallon of effluent treated are important to operating cost of the membrane system. These coefficients were beyond the scope of the experiment although some pertinent data were generated. Questions are raised about the fate of acid in circulation. What fraction of acid remains in circulation after a batch is completed? What fraction of acid reacts with other constituents of the effluent to create other products in the circulating acid solution? What fraction of acid escapes through the membrane into the effluent? Increased efficiency of TAN removal from the effluent per unit of acid consumed will reduce the cost per unit TAN removed. Increased efficiency of converting acid to ammonium sulfate will reduce the net cost of acid per gallon treated.

5. Several operating parameters that remain to be explored affect costs and revenues per unit of effluent treated. Among those are parameters that potentially affect TAN movement through the membrane such as: a) pH of the effluent and pH of the acid solution in circulation, b) velocity of liquids on both sides of the membrane, and c) surface area of the membrane per volume of liquids; effluent and acid solution, in the reactor. Similarly, the most profitable or cost effective method of raising pH of the digester effluent remains to be determined, as it was beyond the scope of the current study. Aeration was used in this experiment and in the cost modeling. Aeration may or may not be the optimum method of raising pH and the optimum is contingent on relative prices of alternatives as well as their effect on overall system performance. Optimization of design to maximize profit or minimize cost requires knowledge of these performance response functions and associated cost functions.

6. Management of ammonium sulfate is a question to be addressed in future development of this technology. Questions that arise include: a) how does ammonium sulfate concentration in the acid solution affect rates of TAN removal and additional ammonia sulfate production, b) how can ammonium sulfate be removed from, or further concentrated in, the acid solution, c) can the acid solution containing ammonium sulfate be used without further modification and in which processes, d) what are possible uses for the acid solution after removal of ammonium sulfate, e) what are the possible uses for the effluent after removal of some TAN, and f) what are the costs and revenues associated with each of the alternatives. Answers to these questions are important to designing the membrane system and associated logistics and markets for used acid solution and ammonium sulfate. The realized value of ammonium sulfate and the cost (and revenue) of used acid solution are derived from optimization of this p art of the system.

7. LCA work on various configurations and operating parameters of the membrane system remains to be done. Concurrent with measurement of performance response functions for various parts of the membrane system, LCA work will quantify associated use of resources and emissions to the environment. Revenues may arise where external benefits are created and markets for those benefits exist. Where revenues are not available, marginal costs per unit of emission reduction or resource extraction reduction can be calculated to enable optimization of design across both profit and external factors.

Future Plans

A series of subsequent experiments and analyses are suggested in the previous section. Suggested work is aimed at improving knowledge of performance response to marginal changes in operating parameters and improving knowledge of the performance of various membranes. Profit maximization, cost minimization, and design optimization across both financial and external criteria require knowledge of performance response functions over a substantial number of variables. The economic analysis presented here addresses the challenge of projecting commercial scale costs and returns with data from an early stage experimental small pilot; and illustrates use of such preliminary costs and returns projections to inform subsequent experimentation and development of the technology. We will continue to refine this economic approach and describe it in future publications.

Corresponding author, title, and affiliation

Kelly Zering, Professor, Agricultural and Resource Economics, North Carolina State University

Corresponding author email

kzering@ncsu.edu

Other authors

Yijia Zhao, Graduate Student at BAE, NCSU; Shannon Banner, Graduate Student at BAE, NCSU; Mark Rice, Extension Specialist at BAE, NCSU; John Classen, Associate Professor and Director of Graduate Programs at BAE, NCSU

Acknowledgements

This project was supported by NRCS CIG Award 69-3A75-12-183.

March 5, 2019July 13, 2020

On-Farm Comparison of Two Liquid Dairy Manure Application Methods in Terms of Ammonia Emission, Odor Emission, and Costs

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Abstract

* Presentation slides are available at the bottom of the page.

Ammonia and odor emissions from land application of liquid dairy manure, and costs associated with manure land application methods are serious concerns for dairy owners, regulators, academic, and the general public. Odor and ammonia samples from agricultural fields receiving liquid dairy manure applied by surface broadcast and subsurface injection methods were collected and analyzed. Costs associated with both of the manure application methods were estimated. The test results showed that subsurface injection reduced both the odor and ammonia emissions compared with surface broadcast; therefore, applying liquid dairy manure by subsurface injection could be recommended as one of the best management practices to control ammonia and odor emissions. The estimated costs associated with subsurface injection were higher than surface broadcast. However the higher costs could be partially compensated by the higher nitrogen fertilizer value captured in the soil by the deep injection method.

Why Study Air Emissions from Dairy Farms?

A floating self-propelled mixing pump and a remote controller (yellow)

Agriculture is the single most important economic sector in Idaho. Dairy production currently stands as the single largest agricultural pursuit in Idaho. Currently, Idaho ranks as the third largest milk production state in the US. Idaho has roughly 550 dairy operations with 580,000 milk cows. Over 70% of milk cows are located in the Magic Valley in southern Idaho (Idaho Department of Agriculture-Bureau of Dairying, 1/22/2013). A number of dairies in the Magic Valley use flushing systems resulting in huge amount of lagoon water which is applied to crop lands near the lagoons via irrigation systems during the crop growing seasons. The volatilization of ammonia (NH₃) from the irrigated lands and lagoons is not only a loss of valuable nitrogen (N), but also causes air pollution. Concentrated dairy production in a limited area such as the Magic Valley has caused air and water quality concerns. Controlling odor and capturing N in dairy manure are big challenges facing the southern Idaho dairy industry.

Direct injection incorporates manure directly beneath the soil surface and thus minimizes odor and NH₃ emissions during application. Injecting manure decreases soluble phosphorus (P) and N in runoff relative to surface application. Some common types of direct injection applications are liquid tankers with injectors and drag-hose systems with injectors. Manure can be successfully injected in both conventional tillage and non-till systems with currently available equipment. The manure direct injection has been proven in other regions, such as the Midwest, to effectively manage odors and manure nutrients. The purpose of this research was to demonstrate, evaluate, and encourage the widespread adoption of the manure direct injection method in southern Idaho for mitigating odors and managing manure nutrients.

Subsurface injection with drag hose system

What Did We Do?

A manure application field day was held on October 31, 2012 on a dairy in Buhl, Idaho, to demonstrate and evaluate dairy manure land application via a drag-hose system and manure mixing equipment. The dairy had approximately 3,500 milking cows managed in a free-stall and open-lot mix set-up, with about 60% of the cows housed in free stalls. Waste is flushed from lanes running under the feeding alleys and from the milking parlor. The wastewater passes through solids removal equipment and basins and then into three lagoons in series. Manure used for this demonstration study was from the last lagoon, which had about 9 million gallons of manure at the beginning of the demonstration field day and its sludge had been not cleaned for 5 years.

Soil after manure subsurface injection

The on-farm manure application trials conducted at two sites were comprised of two manure application methods: surface broadcast and subsurface injection. At each of the sites, a square plot of approximately 3,600 m² in the western portion of the site was used for surface broadcast and the rest of the land was used for subsurface injection. The western portion of the site was chosen because the prevailing winds were from the north during the test period. The previous crop at the two sites was corn; both sites had been disked after harvest.

The manure lagoon was agitated before and during application with a floating mixing pump. Manure was pumped from the lagoon directly to the application field via drag hoses. The two manure application methods were demonstrated with the same equipment. Subsurface injection placed manure behind the shank in a band approximately 20 cm (8 inches) deep. Surface broadcast was realized by lifting the shanks above ground so manure was applied on the soil surface. Manure was applied from east to west and back again until the site was finished. The equipment shanks were lifted only when the equipment was in the designated 3,600 m² square plot for surface application. After manure application in the site, three towers, each 1.5 m high, were placed in a north-to-south orientation with approximately 15 m spacing. The middle tower was placed at the center of the manure surface applied plot. Three towers were placed in the manure subsurface injected field parallel to the ones in the manure surface broadcasted plot and approximately 200 m apart to avoid or minimize cross-contamination between the two manure application methods.

Passive NH₃ samplers (Ogawa & Co. USA Inc., Pompano Beach, FL) were installed on each tower at a height of 0.5 and 1 m to determine the NH₃ concentration at each location. Ammonia samplers were changed approximately every 24 hours over a two-day period after manure application. Right after collection of NH₃ samplers in field, samplers were placed into airtight containers and then shipped back to the U-Idaho Twin Falls Waste Management Laboratory where the NH₃ sampler filters were carefully removed from the samplers and transferred into 15-mL centrifuge tubes. Five mL of 1 M KCI was added to each of the centrifuge tubes to extract NH₃ trapped in the filters. The extractant was transported to the USDA Northwest Irrigation and Soils Research Laboratory (NWISRL) located in Kimberly, Idaho where it was analyzed for NH₄-N using a flow-injection analysis system (Quickchem 8500, Lachat Instruments, Milwaukee, WI). Background concentrations of NH₃ were determined by placing three towers 50 m upwind (north) of the site following the same procedure described previously. Concentrations from passive samplers are time-average concentrations for the amount of time the sampler was exposed to the air and were calculated with the following equation:

[NH₃-N]_air (mg/m³) = 1,000,000 *[NH₄-N]_extractant (mg/L)/200/time deployed (min)/31.1 (cm³/min)

In this, [NH₃-N]_air is the concentration of NH₃-N in the air, [NH₄-N]_extractant is the concentration of NH₄-N in the extractant, and 31.1 cm³/min is a constant used to calculated diffusion to the trap (Roadman et al., 2003; Leytem et al., 2009). Details regarding the design and calculation of NH₃ concentrations can be found in Roadman et al. (2003) and Leytem et al. (2009).

Air samples were collected from the first test site right after manure application using Tedlar bags. One air sample was collected at 1 m above ground from each of the three towers located in the surface broadcast plot, subsurface injection, and background, respectively. A total of nine air samples were collected and then sent via UPS over-night service to Iowa State University Olfactometry Laboratory for odor analysis. The nine air samples were analyzed within 24 hours based on ASTM E679-04 (ASTM, 2004).

For each test site, a grab sample (about 1 L) of liquid manure was collected and transported to a commercial lab (Stukenholtz Laboratory, Inc., located in Twin Falls, Idaho) for pH and total nitrogen analysis. The manure pH, total N, and calculated total N application rates are shown in Table 1. The liquid manure application rate was approximately 20,000 gallons per acre on both the test sites.

Table 1. Manure pH and total N concentrations and application rates of total N at the two test sites

Site and Application Method	Manure pH	Manure total N concentration (mg/L)	Manure total N Application Rate (kg/acre)
Site 1	7.4	3433	257
Site 2	7.3	3519	265

A soil temperature probe with data logger (HOBO U23 Pro v2 2x external temperature data logger-U23-003) was placed 3 cm below the soil surface to record soil temperature data in 15-min increments. Wind speed, temperature, and relative humidity data were obtained from local Buhl Airport, located six miles from the test sites, due to failure of the mobile weather station set on the test sites. The ambient weather conditions and soil temperature at the test sites over the test period are shown in Table 2.

Table 2. Ambient weather conditions and soil temperature at the test sites

	Site 1		Site 2
Item	Day 1	Day 2	Day 1	Day 2
Average wind speed, m/s	5.0	4.2	4.2	3.1
Air temperature, average(minimum, maximum),˚F	61 (42, 78)	49 (45, 63)	49 (45, 63)	47 (38, 61)
Average relative humidity, %	28	53	53	51
Soil temperature, average(minimum, maximum), ˚F	50.9 (51.1, 56.1)	47.3 (51.1, 51.2)	46.5 (51.5, 52.1)	66.7 (51.6, 69.1)

Cost analysis was carried out for four different manure land application systems as shown in the “What Have We Learned?” section below. Cost calculations are based on 500 hours annual use for the tractor and 200 hours annual use for the injection system. Tractor operator labor is figured at $11.70/hour, diesel is figured at $4.00/gallon. Equipment costs were determined using the MACHCOST program from the University of Idaho’s department of Agricultural Economics and Rural Sociology. The program is available on the AERS web page at https://www.uidaho.edu/cals/idaho-agbiz/resources/tools. Equipment data was provided by John Smith at Smith Equipment Co. Rupert, ID 83350. Some machinery data was taken from “Costs of Owning and Operating Farm Machinery in the Pacific Northwest” PNW 346 available on line at: https://www.extension.uidaho.edu/publishing/pdf/PNW/PNW0346/PNW0346.html.

What Have We Learned?

Odor results from test site 1

T-test for Odor showed there was no significant difference between the background and subsurface injection (P=0.41), there was significant difference between the background and surface broadcast (P=0.03), and P value was 0.08 for the t-test of mean difference between the subsurface injection and surface broadcast. The field day attendees felt there was significant difference in odor perception between the subsurface injection and surface broadcast methods.

Test site 1

First day ammonia sample results from test site 1.

Second day ammonia sample results from test site 1.

The NH₃ concentration data from test site 1 showed significant difference between surface broadcast and subsurface injection based on P<0.05. The NH₃ concentration data from test site 1 showed 82% and 64% reduction in NH₃ concentration for first and second sampling day, respectively when liquid dairy manure was applied by subsurface injection vs. surface broadcast.

Test site 2

First day ammonia sample results from test site 2.

Second day ammonia sample results from test site 2.

The NH₃ concentration data from test site 2 showed significant difference between surface broadcast and subsurface injection based on P<0.05. There were 64% and 41% decrease in NH₃ concentration for first and second sampling day, respectively when manure was applied by subsurface injection compared with surface broadcast.

The NH₃ concentration data from both the test sites showed lower NH₃ concentration in the air from the subsurface injected soil vs. surface applied land which means higher nitrogen fertilizer value captured in the soil by the subsurface injection method.

Cost analysis results:

*Fuel and Lubricant Costs are assigned to the Power Unit.

The above fact sheet summarizes probable costs of operation for a 7,400 gallon tank with a 2,000 gpm discharge rate and a 15 foot wide broadcast unit. A 180 PTO HP tractor is needed to pull this unit at an average ground speed of 8 mph. Up to 10 acres per hour can be covered with the unit. The tank is discharged in approximately 4 minutes. Time and equipment to refill the tank is not included in these calculations.

*Fuel and Lubricant Costs are assigned to the Power Unit.

The above fact sheet summarizes probable costs of operation for a 7,400 gallon tank with a 2,000 gpm discharge rate and a 12 foot wide broadcast unit. A 215 PTO HP tractor is needed to pull this unit at an average ground speed of 7 mph. Up to 7 acres per hour can be covered with the unit. The tank is discharged in approximately 4 minutes. Time and equipment to refill the tank is not included in these calculations.

*Fuel and Lubricant Costs are assigned to the Power Unit.

The above fact sheet summarizes probable costs of operation for a 7,400 gallon tank with a 2,000 gpm discharge rate and a 12 foot wide broadcast unit. A 225 PTO HP tractor is needed to pull this unit at an average ground speed of 7 mph. Up to 7 acres per hour can be covered with the unit. The tank is discharged in approximately 4 minutes. Time and equipment to refill the tank is not included in these calculations.

*Fuel and Lubricant Costs are assigned to the Power Unit.

The above fact sheet summarizes probable costs of operation for a system utilizing 5,280 FT of 8 inch hose and 1,320 FT of 5 inch hose. The pump unit capacity is 1,500 gpm to a 16 foot knife injection unit. A 250 PTO HP tractor is needed for the injection unit operating at 75% field efficiency and at an average ground speed of 3.5 mph. The lagoon pump is a 270 HP unit and operating efficiency assumed at 70%. Beyond 2 miles a booster pump would be necessary. Up to 4.75 acres per hour can be covered with the unit. Operation is continuous as no tank refill is needed.

Based on the estimated costs above, the subsurface injection method has higher costs mainly due to the need of larger tractor and lower operating speed. However, we did not include the time and equipment costs associated with refilling the tank for the tank application system. Due to the short time to discharge the tank on the tank broadcast and tank injection systems additional equipment to refill the tank in a timely fashion would be desirable. This would increase the investment in equipment and also would reduce the number of acres that could be covered per hour due to down time while the tank is refilled.

In summary, subsurface injection can reduce both the odor and NH₃ emissions compared with surface broadcast; therefore, applying liquid dairy manure by subsurface injection could be recommended as one of the best management practices to control NH₃ and odor emissions. The estimated costs associated with subsurface injection were higher than surface broadcast. However, the higher costs could be partially compensated by the higher nitrogen fertilizer value captured in the soil by the subsurface injection method.

Future Plans

We will finish development of educational videos to demonstrate the manure subsurface injection technique and disseminate results from this study to our stakeholders.

Authors

Lide Chen, Waste Management Engineer and Assistant Professor, Biological and Agricultural Engineering Department, University of Idaho lchen@uidaho.edu

Mario de Haro Marti, Extension Educator

Wilson Gray, District Extension Economist and Extension Professor

Howard Neibling, Extension Irrigation and Water Management Specialist and Associate Professor

Mireille Chahine, Extension Dairy Specialist and Associate Professor

Sai Krishna Reddy Yadanaparthi, Graduate student, University of Idaho

Acknowledgements

This project was supported by the USDA Natural Resource Conservation Service through a Conservation Innovation Grant. We would also like to thank Dr. April Leytem and Mr. Myles Miller (USDA Northwest Irrigation and Soils Research Laboratory (NWISRL) located in Kimberly, Idaho) for their help with analysis of ammonia samples.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

On farm comparison of two liquid dairy manure application methods from LPE Learning Center