Final Report

to

Dr. C. Mike Williams, Director NCSU Animal and Poultry Waste Management Center

Project Title: Ambient Temperature Anaerobic Digester and Greenhouse for Swine Waste Treatment and Bioresource Recovery at Barham Farm

Investigators: Dr. Jiayang Cheng Department of Biological and Agricultural Engineering

North Carolina State University Raleigh, NC 27695 Phone: (919) 515-6733; Fax: (919) 515-7760 E-mail: jay_cheng@ncsu.edu Dr. Daniel H. Willits

Department of Biological and Agricultural Engineering North Carolina State University Raleigh, NC 27695 Phone: (919) 515-6755; Fax: (919) 515-6719 E-mail: dan_willits@ncsu.edu Dr. Mary M. Peet

Department of Horticultural Science North Carolina State University Raleigh, NC 27695 Phone: (919) 515-5362; Fax: (919) 515-2505 E-mail: mary_peet@ncsu.edu

Collaborator: Mr. Julian Barham Barham Farm Zebulon, NC Project Duration: January 1, 2001 through December 31, 2003 Reporting Date: May 20, 2004

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EXECUTIVE SUMMARY The goal of this project was to evaluate an integrated system of anaerobic digestion, biofilter nitrification, and greenhouse tomato production for swine waste management and bioresource recovery for its potential as an “Environmentally Superior Technology” at Barham Farm, Zebulon, North Carolina. The system consists of an ambient-temperature anaerobic digester (ATAnD), cogeneration of electricity and heat through combustion of biogas produced in the digester, a storage pond, nitrification biofilters for ammonia emission control, and tomato production greenhouses for nutrient recovery. The specific objectives of the evaluation were to:

1. Determine swine manure treatment efficiency in the ATAnD; 2. Monitor biogas production in the digester and energy production from the biogas; 3. Determine nutrient (N, P, and minerals) removal/recovery in the digester, the nitrification

biofilters/denitrification pits, and the tomato production greenhouses; 4. Determine ammonia removal efficiency in the nitrification biofilters; 5. Develop protocols for the utilization of treated swine wastewater in the production of high-

quality greenhouse tomatoes; 6. Monitor tomato production in the greenhouses; 7. Model waste heat and CO2 utilization in the greenhouses; and 8. Provide technical data for economical analysis of the integrated waste treatment system.

Barham farm is a farrow-to-wean swine operation with approximately 4,000 sows. An ambient-temperature anaerobic digester was installed in late 1996 for the primary treatment of the swine waste. The digester has worked properly since mid-1998. A 28,000 ft2 greenhouse was installed to utilize nutrients and water from the treated swine wastewater for tomato production in 1999. A second greenhouse of the same size was added in 2001. Trickling nitrification biofilters were installed in 2002 to convert ammonia in about half of the effluent from the anaerobic digester to nitrate and to provide nitrified water to recharge the pits in the pig houses where nitrate was expected to be denitrified to odorless nitrogen gas. The pits were drained to release the wastewater and recharged with the nitrified water every eight days. Our evaluation results indicate that the wastewater flow from the pig houses was 36,720 gallons per day (gpd) including 20,420 gpd of fresh swine waste and 16,300 gpd of recycled nitrified effluent of the anaerobic digester. Organics destruction efficiency was over 92% and biogas production rate was 1,383 ft3/h with methane content of 63.7% in the anaerobic digester. The trickling nitrification biofilters achieved almost 90% nitrification efficiency in the summer but a low efficiency in the winter. Complete denitrification was observed in the pits. Based on Mr. Barham and his workers’ observations, the air quality inside the pig houses has been significantly improved since the nitrified water was used to recharge the pits. Average tomato production was 920 lb/day of large-fruited cultivars and 92 pints/day of grape tomatoes during the production period in 2003. The tomatoes were sold at a price of $1.99/lb for the large-fruited cultivars and $1.50 per pint for the grape tomatoes. The tomato plants utilized 4.08 lb N, 0.53 lb P, 7.81 lb K, and 1,716 gallon waster from the treated swine wastewater per day. The evaluation suggests that as much as 55% of the heating needs of a 2,600 m2 greenhouse might be met by utilizing the waste heat produced by the electrical generator engine. Tomato yield increases of up to 5% might be possible if the CO2 in the engine exhaust could be successfully utilized in the greenhouse; however, we were unable to verify that hypothesis in this study.

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I. INTRODUCTION Animal production has experienced a transition from family-style small-scale farms to large-scale concentrated animal feed operations in the last two decades in the United States. The transition has improved the efficiency of animal production and resulted in a tremendous growth of animal industry in many states (USDA 1999). In North Carolina, swine production has increased from 2 million in 1987 (NCDA 1988) to 10.1 million in 2001 (NCDA 2002). The growth of animal industry has created revenue and job opportunities, but it has also caused environmental concerns regarding to animal waste management practice. Currently, swine waste is usually washed out of the confinement houses, treated in open anaerobic lagoons, and applied to cropland through spray irrigation for nutrient utilization. Anaerobic stabilization of swine manure in the lagoons generates ammonia, methane, and other greenhouse gases that emit to atmosphere and cause air pollution. Incomplete degradation of organics in the manure produces odorous compounds such as volatile fatty acids. Excess nutrients in lagoon liquid may cause contamination in the receiving water courses if leaked to surface or ground waters. In order to maintain the sustainability of the swine industry, there is a great interest in developing innovative and cost-effective waste management systems to address these environmental concerns. Hog production and a clean and safe environment are important to the farming community and economy of North Carolina. With the support from the Agreement between the Attorney General of North Carolina and Smithfield Foods, researchers have been developing or evaluating candidate Environmentally Superior Technologies to eliminate the discharge of animal waste to surface waters and groundwater, to control atmospheric emissions of ammonia and odor, to remove pathogens from the waste streams, and to restrain nutrient and heavy metal contamination of soil and groundwater. The goal of this project was to evaluate an integrated system of anaerobic digestion, biofilter nitrification, and greenhouse tomato production for swine waste management and bioresource recovery for its potential as an “Environmentally Superior Technology” at Barham Farm, Zebulon, North Carolina. The system consists of an ambient-temperature anaerobic digester (ATAnD), cogeneration of electricity and heat through combustion of biogas produced in the digester, nitrification biofilters for ammonia emission control, and tomato production greenhouses for nutrient recovery. The specific objectives of the evaluation were to:

1. Determine swine manure treatment efficiency in the ATAnD; 2. Monitor biogas production in the digester and energy production from the biogas; 3. Determine nutrient (N, P, and minerals) removal/recovery in the digester, the nitrification

biofilters/denitrification pits, and the tomato production greenhouses; 4. Determine ammonia removal efficiency in the nitrification biofilters; 5. Develop protocols for the utilization of treated swine wastetater in the production of high-

quality greenhouse tomatoes; 6. Monitor tomato production in the greenhouses; 7. Model waste heat and CO2 utilization in the greenhouses; and 8. Provide technical data for economical analysis of the integrated swine waste management

system.

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II. SYSTEM DESCRIPTIOIN Barham farm is a farrow-to-wean swine operation with approximately 4,000 sows in six houses: two farrowing houses and four gestation houses. Pigs are housed on elevated partially slatted floors under which there are pits to collect manure from the pigs. Table 1 shows standing pig population in each house. Table 1. Standing pig population in each house at Barham farm.

House Type

Sows

Wean

Gestation 1 (Breed)

600

0

Gestation 2

1,080

0

Farrow 1

320

1,500

Farrow 2

320

1,500

Gestation 3

1,080

0

Gestation 4 (Breed)

600

0

Total

4,000

3,000

A. Ambient-Temperature Anaerobic Digester Figure 1 shows a diagram of the waste management system at Barham farm. A pit-recharge system has been used to remove manure from beneath slatted floors with recycled treated wastewater. The pits are drained and recharged every eight (8) days. Swine wastewater drained from the pig houses flows by gravity to an ambient-temperature anaerobic digester for primary treatment. The digester was built according to the Natural Resource Conservation Service (NRCS) Interim Standard No. 360 for Covered Anaerobic Lagoon. The digester has a surface area of 265 ft x 265 ft and a fixed operating depth of 20 ft with a side slope of 3:1. The volume of the digester is approximately 864,500 ft3. The digester had a three-foot clay liner at the bottom. A 40 mil high density polyethylene (HDPE) cover was installed to completely cover the digester. A rain water pump is used to remove rain water from the top of the cover. Biogas produced in the digester is utilized for electricity and heat production through an internal combustion engine, a 120 kW electricity generator, a 400,000 BTU boiler, and a 10,000 gallon water tank. An odor control flare was also installed to burn excess biogas. The digester has been working consistently since August 1998. Effluent from the digester is stored in a storage pond (former anaerobic lagoon before the anaerobic digester was installed) that has a total volume of approximately 1,850,000 ft3, a surface area of about 256,800 ft2 (1,070 ft x 240 ft), and a depth of about 8 ft. In order to control ammonia emission from the digester effluent stored in the pond, four nitrification biofilters were installed to convert ammonium in the liquid to nitrate. The nitrified effluent is then used to recharge the pits inside the pig houses. In 2002the storage pond was partitioned into two parts:

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east storage and west storage. The east storage (105 ft x 240 ft and about 181,500 ft3) next to the digester is used for collecting effluent from the digester. The effluent is pumped to the biofilters for nitrification. The nitrified effluent is stored in a HDPE storage bag (capacity: 40,000 gallons) floating in a corner of the west storage (965 ft x 240 ft and about 1,668,500 ft3). The nitrified effluent in the storage bag is then pumped to fill the pits where nitrate is denitrified to odorless nitrogen gas (N2).

Swine House

WestStorage W

aste

Col

lect

ion

Ambient-TAnaerobic Digester

Hot Water Tank

HeatExchanger

Engine

Electricity

Hot Water

Tomato Greenhouse I

NitrificationBiofilter

Exha

ust G

as ( C

arbo

n D

ioxi

de)

Tomato Greenhouse II

NitrificationBiofilter

Tomatoes

TomatoPacking

Biogas

Drainage

StorageBag

Irrigation to Cropland

EastStorage

Sand Filter

Figure 1. A layout of the integrated system for swine waste management, renewable energy production, and nutrient removal and recovery at Barham farm, Zebulon, North Carolina.

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B. Nitrification Biofilters Four trickling biofilters with floating polystyrene beads was built for biological nitrification to convert the NH4

+ to NO3- in the anaerobic effluent in 2002. Each biofilter is 10 ft or 3 m in

diameter and 10 ft in height with a water depth of 5 ft or 1.5 m. Approximately 78.5 ft3 (or 1 ft in depth) of 2 mm polystyrene beads float on top of the wastewater in each biofilter. The density and specific surface area of the beads were 0.77 kg/m3 and 1,000-2,000 m2/m3, respectively. About 49% of the digester effluent was pumped to the biofilters from the east storage, distributed onto the beads, trickled through them, and nitrified by the bacteria attached on the beads. The remaining effluent from the anaerobic digester went from the east storage to the west storage by overflow through the floating baffle. Some nitrified water is recycled back to the top of the bead bed and mixed with the influent wastewater to avoid NH4

+ shock loading to the nitrifying bacteria attached on the beads. The ratio of recycled water to the incoming water is 10:1. The hydraulic retention time in the trickling biofilters is 12 hours. The four biofilters were operated in parallel. A diagram of a trickling nitrification biofilter is shown in Figure 2. A photograph of the biofilters is shown in Figure 3.

Trickling Nitrification Biofilter

Polystyrene Beads

Water Distributor

Ana

erob

i c E

fflu

ent f

r om

Ea

st S

tora

g eTo Storage Bag

Rec

ycl e

Ground Level

Water Level

Open to Air

Figure 2. A schematic diagram of a trickling filter with plastic beads as media for biological nitrification of anaerobically treated swine wastewater.

C. Tomato Production Greenhouses Two 28,000 ft2 (2,600-m2) greenhouses were constructed on the farm to utilize the nutrients in the stabilized swine wastewater. The stabilized wastewater from the west storage is used for fertigation (fertilization and irrigation) for tomato production in the greenhouses. There are

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Figure 3. Nitrification biofilters at Barham farm. approximately 7,200 tomato plants grown in 3,600 pots filled with perlite (an inert growing media) in each house. Before being applied to 14,400 tomato plants in the greenhouses, the stabilized wastewater is treated in a nitrification biofilter that is similar to the other nitrification biofilters mentioned previously to convert NH4

+ into NO3- because Dr. Mary Peet’s previous

studies indicate that tomato plants prefer nitrate as the nitrogen nutrient instead of ammonium that is the dominant nitrogen form in the stabilized swine wastewater. The nitrified water is pumped through a sand filter to remove solids and then applied to the plants with a drip irrigation system. All fertilization treatments were monitored, recorded and controlled by the Harrow Fertigation Manager® (HFM, Climate Control Systems Inc., Leamington, Ontario). Excess water from the plant pots flows back to the biofilter through a drainage system. The temperature and moisture inside the greenhouses are controlled with a GEMLink computer program (Version 2.05.00). Greenhouse I was built in 1999 and greenhouse II was built in 2001. Harvested tomatoes go through a water bath chlorine disinfection system before they are ready for sale. Figures 4 and 5 show photographs of the tomato production greenhouses. A aerial photograph of the whole Barham farm is shown in Figure 6.

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Figure 4. Tomato production greenhouses (from left to right: greenhouse I, tomato disinfection and packing house, and greenhouse II) at Barham farm.

Figure 5. Drip irrigation and drainage systems in tomato production greenhouses at Barham farm.

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Greenhouse II

Tomato Disinfection & Packing House

Greenhouse I

Nitrification Biofilter

Pig Houses

West StorageAmbient-T Anaerobic Digester

East Storage

Storage BagNitrification Biofilters

July 3, 2002

An Integrated System of Swine Production, Anaerobic Digestion of Swine Manure for Energy Production, and Greenhouse Tomato Production for Nutrient Recovery from Stabilized Swine Wastewater at Barham Farm, Zebulon, North Carolina

Figure 6. An aerial view of Barham farm, Zebulon, North Carolina. III. EVALUATION PROTOCOLS Performance of the integrated swine waste management system at Barham farm has been evaluated for its efficiencies of organics destruction, solids removal, nutrient reduction and recovery, ammonia reduction, water reclamation, and generation of value-added products such as biogas, energy, and tomatoes. A. Sampling and Measurement Flow Rate: Flow rate of the following wastewater streams have been measured: 1. Influent and effluent of the ATAnD (The flow rate of raw swine wastewater from the pig

houses to the digester should be the same as that of the effluent of the ATAnD because the digester is closed and continuous-flow.)

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2. Influent, effluent, and recirculation of the nitrification biofilters 3. Nitrified water recycled to the pig houses for pit recharge 4. Nitrified water utilized in the greenhouses 5. Irrigation water from the storage pond to the nearby cropland Biogas Production: Biogas production rate from the ATAnD at Farms 1 and 2 has measured with a gas meter recorded every day. Sampling: Biweekly samples have been taken from raw swine wastewater, effluent from the ATAnD, influent and effluent of the nitrification biofilters, treated wastewater sent to greenhouses, and biogas. B. Sample Analysis Wastewater samples are analyzed for chemical oxygen demand (COD), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), NH4-N, NO3-N, NO2-N, total phosphorus (TP), o-PO4-P, total solids (TS), volatile solids (VS), pH, K, Cu, and Zn. Biogas was analyzed for methane content. The analyses were performed in Environmental Analysis Laboratory of Biological & Agricultural Engineering Department at North Carolina State University (NCSU), Raleigh, NC, USA. Standard methods (APHA, 1995) and EPA methods (1983) were used for the analyses. C. Protocols for the Utilization of Treated Swine Wastewater in the Production of High-

Quality Greenhouse Tomatoes In spring 2002, studies were conducted at the NCSU Horticultural Field Laboratory (HFL) in support of greenhouse operations at Barham Farm. Protocols for the utilization of treated swine wastewater in the production of high-quality greenhouse tomatoes at Barham were developed based on the studies at the NCSU-HFL. Tomato, Lycopersicon esculentum Mill. cv. ‘Trust’, seedlings were transplanted, two plants per Bato® bucket filled with 1:1 peat/pine bark, in February 2002. Bato® buckets were selected because they can be configured to drain into PVC pipes and the leachate recycled or disposed of properly. At Barham Farm, leachate is returned to the biofilter, thus maintaining a closed cycle in terms of nutrient discharge. Experimental design was a randomized complete block with 4 replications of 38 plants each. Plants within each replication were randomly assigned to one of four fertilization treatments: 1.) CONVENTIONAL-modified Steiner solution; 2.) LAGOON-untreated effluent from the Barham farm secondary lagoon; 3.) BIOFILTER-lagoon effluent after nitrification in a trickling biofilter; 4.) OPTIMIZED BIOFILTER-nitrified effluent with adjustments made to approximate the conventional treatment by dilution, acid injection and nutrient addition. Nutritional and other characteristics of the treatments are described in Table 2. Conventional and optimized biofilter fertilization treatments were monitored, recorded and controlled by the HFM. Lagoon and biofilter treatments were fed directly to the plants. Plants were fertigated via drip irrigation using two 3.78 l h-1

emitters per pot. Fertigation treatments were initiated 36 days after transplant. All plants were trellised and hand pollinated. Fruit were thinned after fruit set to four per cluster. Water management was based on solar set points.

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Breaker stage fruit were harvested weekly until July 2002. Fruit were identified by plant and cluster location. Fruit were weighed and evaluated for blossom-end rot (BER) and other defects. Ripe fruit, free of defects, from all four treatments at each harvest were frozen to await fruit quality analysis. At that time, the samples of fruit from each treatment were homogenized and pH, Brix and EC values recorded. Data were analyzed using General Linear Models (GLM) and the Waller-Duncan K-ratio T-test. Table 2. pH, EC (dS cm-2) and nutrient composition (ppm) of fertilizer treatments.

Conventional Optimized

Biofilter Biofilter Lagoon

pH 5.16 6.34 7.53 8.11

EC 1.94 2.78 3.82 4.77

Total N 136 196 275 228

NH4 – N 24.0 27.3 55.7 223

NO3 – N 121 168 219 4.94

Urea – N 1.89 7.16 10.2 1.78

P 63.7 50.4 34.4 34.0

K 254 406 646 615

Ca 147 81.5 50.5 49.7

Mg 49.0 56.4 13.8 13.8

Fe 2.37 2.92 0.23 0.33

Mn 1.45 1.48 0.03 0.02

Zn 1.01 0.97 0.11 0.04 Cu 0.50 0.55 0.06 0.02

IV. EVALUATION RESULTS A. Ambient-Temperature Anaerobic Digester Flow Rate: A profile of average daily flow rate of the influent and effluent of the ATAnD at Barham farm from March to November 2003 is shown in Figure 7. Fluctuation of flow rate is mainly caused by rain storms. During and right after a rain event, rain water collected on top of the cover pushes the wastewater under the cover out of the digester, resulting an observed high flow rate of the anaerobic effluent. After the rain event, the rain water on top of the cover is normally pumped off, leaving some space under the cover in the digester and resulting in a low observed flow rate. The average flow rate from March to November 2003 was 25.5 gpm

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(gallons/min) or 36,720 gpd. The raw swine wastewater from the pig houses to the anaerobic digester consists of fresh waste generated by the pigs and the recycled water to recharge the pits. The rate of recycled nitrification biofilter effluent to recharge the pits in the pig houses was 16,300 gpd. Therefore, the fresh swine waste generation rate was 20,420 gpd (36,720 gpd – 16,300 gpd).

Figure 7. Average Daily Flow Rate of Swine Waste Water at Barham Farm, Zebulon, NC

0.0

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Rat

e, g

allo

ns /

min

Treatment Efficiency: The average concentrations of organics, nutrients, and solids in raw swine wastewater and anaerobic digester effluent observed at Barham farm in the entire year of 2003 are listed in Table 3. The efficiencies of organics destruction and nutrient reduction are also listed in the table. About 28% TKN was removed from the swine wastewater in the anaerobic digester. The removal mechanism probably includes bacterial assimilation and precipitation such as struvite. A slight increase of ammonia-N should be a result of the biodegradation of organic nitrogen in the raw swine wastewater. A significant removal of TP and o-PO4-P was observed in the anaerobic digester, 80.6% and 72.0%, respectively. Phosphorus removal is probably due to the precipitation of metal phosphates. A high organics destruction efficiency has

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Table 3. Results of sample analyses for raw swine wastewater and anaerobic digester effluent at Barham farm in 2003.

Raw Swine Wastewater

Anaerobic Digester Effluent

Removal Efficiency

TKN, mg/L 2,156 + 826* 1,546 + 233 28.3%

Ammonia-N, mg/L 1,354 + 396 1,401 + 117 -3.4%

Nitrate-N, mg/L 0.05 + 0.11 0.00 + 0.01

Total-P, mg/L 514 + 290 100 + 25 80.6%

o-Phosphate-P, mg/L 279 + 134 78 + 15 72.0%

COD, mg/L 27,670 + 14,480 2,035 + 776 92.6%

TS, mg/L 19,380 + 17,190 4,679 + 470 75.9%

VS, mg/L 12,200 + 1,255 1,464 + 26 88.0%

K, mg/L 996 + 267 798 + 179 19.9%

Cu, mg/L 1.46 + 1.82 0.15 + 0.10 89.4%

Zn, mg/L 14.2 + 12.8 1.89 + 1.89 86.7%

pH 7.00 + 0.28 7.82 + 0.25 * Mean + Standard Deviation of 25 samples. been observed in the anaerobic digester at Barham farm. COD, TS, and VS removal efficiency in 2003 was 92.6%, 75.9%, and 88.0%, respectively, which is very close to our previous observation from 1998 to 2002. This indicates that the ambient-temperature anaerobic digester has had a consistent and very stable performance since the installation of the current cover in July 1998. Typically, COD reduction in stable anaerobic digesters is approximately 70-80%. A high COD removal in the anaerobic digester at Barham farm is a result of a high hydraulic retention time (approximately 150 days) in the digester. Heavy metals such as copper and zinc have also been significantly removed in the digester. Copper and zinc were removed by 89.4% and 86.7%, respectively. Like the phosphorus removal, the heavy metals were most probably removed from the aqueous wastewater but ended up in the sludge at the bottom of the digester through precipitation such as metal phosphates. The values of pH in both raw swine wastewater and the anaerobic effluent were very stable. Although the nutrient concentrations in the raw swine wastewater were fluctuating because the wastewater consists of swine manure from both farrowing and gestating houses at different stages, much less fluctuation of the nutrient concentrations was observed in the effluent of the anaerobic digester. Biogas Production: Biogas production in the ambient-temperature anaerobic digester at Barham farm in 2003 is shown in Figure 8. The annual average biogas production rate in 2003 was 1,383 ft3/hour. Methane content in the biogas was consistently at 63.7 + 4.7%. The biogas was burned in an internal combustion engine to generate electricity, most of which was utilized on farm. Waste heat from the engine can be collected and used in the greenhouses or farrowing houses.

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Figure 8. Biogas Production in the Ambient-Temperature Anaerobic Dgester at Barham Farm.

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gas P

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ctio

n, ft

3 /h

B. Nitrification Biofilters The purpose of installing the nitrification biofilters was to control ammonia emission by converting ammonium in the anaerobically treated swine wastewater to nitrate. A hypothesis was proposed that the nitrate could be denitrified to nitrogen gas in the pits collecting fresh swine manure if the nitrified water was used to recharge the pits. Rationale to support such a hypothesis was that the nitrified water would stay in the pits for eight days and conditions, including anaerobic (or anoxic, to be exact) environment and rich organic carbon source, in the pits would be just right for denitrification. Flow rate: The measured flow rate of the anaerobically treated swine wastewater from the east storage or influent to the biofilter was 12.4 gpm or 17,860 gpd. In other words, approximately 49% of the effluent from the anaerobic digester was pumped to the nitrification biofilters. The capacity of the nitrification biofilters was designed based on the need of recycled water for pit recharge. The remaining effluent from the anaerobic digester went from the east storage to the

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west storage by overflow through the floating baffle. The main reason for not to nitrify the whole effluent from the anaerobic digester was to avoid nitrate accumulation in the storage pond. The effluent flow rate of the biofilters should be the same as the influent and all the effluent flows to the plastic floating bag at a corner of the west storage as shown in Figures 1 and 6. Out of 17,860 gpd effluent from the nitrification biofilters, 16,300 gpd was recycled to recharge the pits in the pig houses and the rest (1,560 gpd) overflowed from the storage bag to the west storage. Treatment Efficiency: The annual averages of nutrient concentrations in the east storage, the effluent from the nitrification biofilters, and the west storage are listed in Table 4. We have observed a significant difference between ammonia and TKN concentrations in the digester effluent and in the east storage. When the storage pond was partitioned into east and west storage ponds in 2001, the old wastewater stayed in the ponds. The decrease in ammonia concentration from the digester effluent to that in east storage pond was due to both dilution in the east storage pond and volatilization from the water surface. The efficiency of nitrification Table 4. Results of sample analyses for wastewaters in the storage pond and effluent from the nitrification biofilter at Barham farm in 2003.

Wastewater in East Storage

Effluent from Nitrification Biofilters

Wastewater in West Storage

TKN, mg/L 389 + 120* 307 + 167 285 + 106

Ammonia-N, mg/L 322 + 93 253 + 152 237 + 104

Nitrate-N, mg/L 1.0 + 1.8 94.2 + 85.0 4.3 + 6.5

Total-P, mg/L 38.3 + 13.9 33.9 + 5.0 36.7 + 18.3

o-Phosphate-P, mg/L 28.2 + 5.7 27.6 + 5.9 25.6 + 5.8

COD, mg/L 672 + 98.5 764 + 127 642 + 203.6

TS, mg/L 2733 + 263 2863 + 263 2590 + 248.8

VS, mg/L 669 + 11.1 773 + 8.6 601 + 12.7

K, mg/L 581 + 113 600 + 109 546 + 109

Cu, mg/L 0.03 + 0.04 0.02 + 0.04 0.03 + 0.04

Zn, mg/L 0.30 + 0.19 0.28 + 0.19 0.25 + 0.15

pH 8.15 + 0.15 8.05 + 0.48 8.14 + 0.26 * Mean + Standard Deviation of 25 samples. (calculated as the total nitrate-N production divided by the initial total ammonia-N) in the biofilters varies in different seasons because the growth rate of nitrifying bacteria is highly dependent on temperature. The seasonal effect on nitrification efficiency of the trickling biofilters is demonstrated in Figure 9. As shown in the figure, nitrification efficiency was quite low in the winter at low temperatures and it reached almost 90% in the summer at high temperatures. The annual average of nitrification efficiency was about 29%. Because 49% of

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the effluent from the anaerobic digester went through the trickling biofilters for nitrification, TKN and ammonia-N levels in the west storage were 36% lower than that in the east storage; thus, ammonia emission from the open storage pond could be reduced. Nitrate in the raw swine wastewater from the pig houses was negligible (Table 3), indicating that the nitrate in the recycled nitrified water for pit-recharge was completely denitrified. The trickling nitrification biofilter system is simple, very easy to operate, and effective at warm temperatures. However, winter performance of the biofilter system needs improvement to develop a year-round efficient nitrification system.

Figure 9. Seasonal Effect on Nitrification Efficiency of the Trickling Biofilters at Barham Farm.

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ate-

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L

Nitrification Efficiency, %Nitrate-N in Effluent

Discussion: Before the trickling nitrification biofilters were installed, Mr. Barham had used the liquid in the storage pond that contained high ammonium to recharge the pits. Based on Mr. Barham and his workers’ observations, the air quality inside the pig houses has been significantly improved since the nitrified water was used to recharge the pits. Some solids had been left and accumulated at the bottom of the pits after the drainage of the pits when the storage pond water was used to recharge the pits. However, the accumulated solids were gradually disappearing since the use of nitrified water. Moreover, Mr. Barham also observed that the drain pipe clogging problem caused by struvite was greatly alleviated after the nitrified water was used for pit recharge. Odor and ammonia emissions were measured by the OPEN team in 2002 before the biofilters’ operation was stabilized. Thus, the measured data might not reflect the effect of the biofilters on odor and ammonia emissions from the storage pond and the swine houses.

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C. Tomato Production Greenhouses NCSU-HFL Studies in Spring 2002: One month after harvest began, all plants received no fertigation water for 72 hours due to an undetected system failure initiated by a water main break. It should be noted that conventional treatment plants exhibited visible wilting and desiccation, while all other treatment plants appeared to recover quickly once fertigation resumed. For reporting purposes, data have been analyzed for fruit harvested prior to that system failure. Total yield per plant varied significantly between treatments. No difference was seen between the conventional (1348 g/plant) and optimized biofilter (1306 g/plant) treatments; however, biofilter only (958 g/plant) and lagoon (710 g/plant) treatments showed greatly decreased yields. Differences between treatments were seen in fruit size, as well, with all treatments different. Mean weights per fruit (g) were: conventional, 175; optimized biofilter, 141; biofilter, 97; and lagoon, 85. Yield and fruit size reductions in the effluent treatments could have been caused either by the low calcium and magnesium or by high salinity levels (Table 2). Also, pH was above optimal for tomato in all three treatments utilizing lagoon effluent, which may have also reduced yields. Blossom-end rot (BER) incidence was calculated as a percentage of the total number of fruit harvested in a treatment and was significantly different for all treatments. The conventional treatment had no BER fruit (0.0%) prior to the fertigation system failure, which was significantly less than the optimized biofilter (6.5%). Biofilter and lagoon irrigated plants in turn had significantly higher BER incidence (10.9% and 15.3%, respectively). In the biofilter and lagoon treatments, high BER rates could be attributable to both low calcium and high salinity compared to the conventional treatment (Table 2). The higher proportion of BER fruit in the optimized biofilter, where the EC was only 2.78 dS m-1 can be explained in part by the limitations imposed by our fertigation unit (equipped with only six injectors), which resulted in lower calcium levels than in the conventional treatment. The irrigation system failure that occurred a month after harvest began confounded interpretation of fruit quality data. Significant differences in Brix (p=0.015, F=4.45) and pH (p=0.066, F=2.80) were seen among treatments (Table 5), taking into account only data before the system failure. Effluent treatments had higher Brix and lower pH than the conventional treatment, both of which are considered indicators of better tasting tomato fruit. Differences in fruit EC were not significant. Including data from all harvests showed an increase in Brix throughout the season. It is not clear, however, if this trend is due to naturally occurring events such as increased day length or greater nutrient assimilation or if it was artificially imposed by the 72-hour lack of fertigation water. Based on the studies at NCSU-HFL, we were able to recommend that Barham Farm utilize a biofilter to convert the ammonium-N to nitrate-N. We also recommended: 1) the raw effluent, which we had initially hoped to use directly, should be acidified to reduce pH; 2) the nutrient content should be increased by addition of Ca and Mg; and 3) wastewater should be diluted to lower the EC. We recommended installation of a fertigation system (the Harrow Fertigation Manager) and software with sufficient flexibility to control salts, nutrient concentrations and pH

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in the irrigation water, which varied over time. In addition, we assisted with on-farm diagnosis of pests and diseases, and troubleshooting of initial irrigation issues, such as clogged emitters and low pump pressure. Table 5. Brix, EC (dS cm-2) and pH of processed fruit samples from fertilizer treatments. (Values with the same letters are not significantly different at p < 0.05, Waller - Duncan test) Brix EC pH

Conventional 4.75 B 2.85 ns 4.42 A

Optimized Biofilter 5.42 BA 3.07 4.38 AB

Biofilter 6.57 BA 3.19 4.33 AB

Lagoon 6.83 BA 3.19 4.25 AB

Tomato Production at Barham Farm: There are two 28,000 ft2 or 2,600 m2 greenhouses with 14,400 tomato plants at Barham farm. Tomato seeds were sown in the third small greenhouse and then transplanted to the production greenhouses. It took approximately two months between the transplant date and the first harvest. The tomato production at Barham farm are now scheduled so that the down times between transplant and first harvest in the two houses do not coincide. In other words, the schedule guarantees that there will be tomato production in both greenhouses or at least in one of the greenhouses any time of the year to maintain a consistent tomato supply to the customers. In 2003, average tomato production was 920 lb/day of the large-fruited cultivars and 92 pints/day of the grape tomatoes during the production period. The tomatoes were sold at a price of $1.99/lb for the large-fruited cultivars and $1.50 per pint for the grape tomatoes. Nutrient Utilization: A trickling nitrification biofilter that is the same as those mentioned previously is used to convert ammonium to nitrate. Treated wastewater from the west storage is pumped to the biofilter. Effluent from the biofilter goes through a sand filter to remove solids and then pumped to the greenhouses for fertigation. An average flow rate of the wastewater from the west storage to the biofilter was observed at 1,716 gpd. Nutrient concentrations in the wastewater are: TKN, 285 + 106 mg/l; NH3-N, 237 + 104 mg/l; NO3-N, 4.29 + 6.51 mg/l; TP 36.7 + 18.3 mg/l; o-PO4-P, 25.6 + 5.8 mg/l; K, 546 + 109 mg/l; Cu, 0.03 + 0.00 mg/l; and Zn, 0.25 + 0.15 mg/l. In addition to the treated wastewater, fresh water is also added for the irrigation of the tomato plants. An average addition of the fresh water was measured at 1,784 gpd. The overall water flow to the greenhouses was 3,500 gpd. The average utilization rates of nutrients and water from the stabilized wastewater by the tomato plants in the greenhouses were: N, 4.08 lb/day; P, 0.53 lb/day; K, 7.81 lb/day; Cu, 0.0004 lb/day; Zn, 0.0036 lb/day; and water, 1,716 gallon/day.

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Discussion: The greenhouses used about 8.4% of the wastewater generated on the farm. The value of the greenhouses as a part of the swine waste management system is to recover nutrients from the wastewater and make a value-added product. The greenhouses would obviously create environmental and social benefits to the farm, the swine industry, and the community. The economics team should determine the cost-effectiveness of the greenhouses. We have learned from this project that marketing of the value-added product is very important for the successful application of a new technology. Based on our evaluation data, utilizing nutrients and water from the treated swine wastewater for greenhouse tomato production is technically feasible. Quality tomatoes have been produced in the greenhouses. The system is environmentally friendly. It took Mr. Barham quite some effort to develop a market for the tomatoes produced in the greenhouses. This is a typical problem for produce operations, particularly during the establishment period. At this point, however, on-farm and wholesale markets have been established and are stable or increasing. Matching production to demand is also challenging for most growers, but Mr. Barham also seems to have achieved some equilibrium in this facet of his operation. D. Cropland Irrigation Our evaluation indicates that the greenhouses used about 8.4% of the wastewater generated on the farm, creating some flexibility of effluent applications to the sprayfields. Application of treated swine wastewater as irrigation/fertilization water to the greenhouses reduced the amount of effluent application to the sprayfields. During the years of 2001-2003 after the installation of the greenhouses, the total volume of effluent application to the sprayfields was 9,472,481 gallons with an average of 3,157,494 gallons per year. V. OPERATION AND MAINTENANCE A. Ambient-Temperature Anaerobic Digester The first modular polyethylene cover for the anaerobic digester was installed in early 1997 and it failed because of leaking. The manufacturer replaced the cover in late 1997 and the second cover failed again for the same problem. A third bank-to-bank cover was installed by a different manufacturer in mid-1998. This cover has been working well since its installation. Rain water on top of the cover needs to be pumped off after each heavy rain event. Mr. Barham usually starts the engine every morning when he arrives at the farm and turns the engine off before he leaves in late afternoon. Oil change for the engine was contracted to a local engine company. The operation of the engine is quite simple. B. Nitrification Biofilters Nitrification biofilters are in continuous operation. Some technical advice is needed to start up the biofilters. Once the biofilters are in operation, no operator is needed. Maintenance is basically to check the pumps, especially the submersible influent pump, the pipeline, and the

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tanks periodically, and make sure that the pumps are not clogged by the solids and the pipelines and tanks are not leaking. C. Greenhouses The irrigation system for the greenhouses is computerized and automatic. A manager who is knowledgeable of growing and marketing tomatoes is required for running the greenhouses. No certificate is required. Maintenance is needed for the greenhouse structure, the irrigation system, pumps, and pipelines.

VI. PUBLICATIONS A list of publications based on the results obtained from this project is as follows: Cheng, J., T. E. Shearin, M. M. Peet, and D. H. Willits (2003) Utilization of Treated Swine Wastewater for Greenhouse Tomato Production. Proceedings of the 4th

International Symposium on Wastewater Reclamation and Reuse, November 12-14, 2003, Mexico City, Mexico. Cheng, J., M. M. Peet, and D. H. Willits. (2003) Ambient temperature anaerobic digester and greenhouse for swine waste treatment and bioresource recovery at Barham farm. Proceedings of the 2003 North Carolina Animal Waste Management Workshop, October 16-17, 2003, Durham, NC, USA. Harlow, C., M. M. Peet, A. K. Ponce, J. Cheng, D. H. Willits, and M. Casteel. (2003) Utilizing a greenhouse tomato crop to recover bio-resources from swine waste. Proceedings of the ASHS-2003 Centennial Conference, October 3-6, 2003, Providence, RI, USA. Ponce, K.H., M.M. Peet, C.D. Harlow, J. Cheng, and D.H. Willits. (2004) Assessment of Swine Waste Bioremediation Using Greenhouse Tomatoes. Acta Hort. (ISHS) 633:415-423. Shearin, T. E., J. Cheng, M. M. Peet, and D. H. Willits. (2003) Utilization of nutrients in anaerobically-pretreated swine wastewater for greenhouse tomato production. Proceedings of the Ninth International Symposium on Animal, Agricultural and Food Processing Wastes (ISAAFPW), October 12-15, 2003, Durham, NC, USA. Willits, D. H., J. M. Marbis, J. Cheng, M. M. Peet, and T. Shearin. (2003) Waste heat utilization in a greenhouse used for the removal of nutrients from a swine waste stream. Proceedings of the ASAE Annual International Meeting, 27- 30 July 2003, Las Vegas, Nevada, USA. (Paper No. 034043) VII. REFERENCES

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APHA. (1995) Standard Methods for the Examination of Water and Wastewater, 19th ed. Washington, D.C.: American Public Health Association, American Water Works Association, and Water Environment Federation. Cheng, J., J. Pace, M. Peet, D. Willits, and T. Shearin. (2001) Using a greenhouse tomato crop to recover the nutrients from swine wastewater. Animal and Poultry Waste Management Center International Symposium on Agricultural Production and Environmental Issues. Oct. 3-5, RTP, NC. Danielson L.E., Cox V. (1994) Agriculture and the Coastal Non-point Pollution Control Program. Raleigh, Department of Agriculture and Resource Economics. EPA. (1983) Methods for Chemical Analysis of Water and Waste. United States Environmental Protection Agency, Cincinnati, OH. Gurjer, Y.R. (2001) Use of heat pumps for heating and night cooling of greenhouses. MS thesis, Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC. Kimball, B.A. (1986) A modular energy balance program including subroutines for greenhouses and other latent heat devices. U.S. Dept. Of Agriculture, Washington, D.C., Agricultural Research Service Publication ARS-33. Marbis, J.M. (2001) CO2 enrichment and hot water heat in a greenhouse as a means of recovering bioresources from swine waste. MS thesis, Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC. Marion, W. and K. Urban. (1995) User manual for TMY2s. National Renewable Energy Laboratory, Golden, CO. NCDA. (1988) North Carolina Agricultural Statistics Division, North Carolina Department of Agriculture, Raleigh, NC. NCDA. (2002) North Carolina Agricultural Statistics Division, North Carolina Department of Agriculture, Raleigh, NC. Peet, M.M., K. Ponce, D.H. Willits and J. Cheng. (2001) Bioremediation of Swine Waste using Greenhouse Tomatoes: A Systems Approach. 98th Conference of the American Society for Horticultural Science. July 22-25, 2000, Sacramento, CA. HortScience 36:472 (poster presentation #465 at ASHS and also presented at Sustainable Ag. Conference, Rock Hill, SC, Nov. 2-4). USDA. (1999) National Agricultural Statistics Service, United States Department of Agriculture, Washington, DC.

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VIII. ACKNOWLEDGEMENT We would like to acknowledge: Mr. Julian Barham for his collaboration and assistance during the conduction of this project; Smithfield Foods Inc., North Carolina Attorney General’s office, and North Carolina State University-Animal & Poultry Waste Management Center for funding the project; and the Environmental Analysis Laboratory of the Biological and Agricultural Engineering Department at North Carolina State University for sample analyses.

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APPENDIX: Waste Heat and CO2 Utilization Models 1. Waste Heat Utilization Model a) Model Development Kimball’s modular energy balance (MEB) model (Kimball, 1986) was chosen for the basic model because it is flexible, comprehensive and the investigator has had some experience using it. The greenhouse (Tomato Greenhouse I) is divided into ten bays, each containing two exhaust fans (9.5 m3 sec-1, 3.6 kW) and one LP gas heater (58,563 W output). There were 30 horizontal airflow (HAF) fans (0.25 kW) installed for air circulation. The floor space was divided into 38 rows, each row containing 95 bags with two tomato plants in each bag. A micro-tube was placed in each bag for irrigation purposes. Additional detail about the configuration of the model can be found in Marbis (2001). Waste Heat Subroutine: The waste heat subroutine tracked the waste heat produced by the engine and the transfer of that energy into the greenhouse. Water temperature in the storage tank was calculated at the end of each time step based on the energy added by the engine or removed by the greenhouse. Manufacturer's data for operation of the G3406NA engine on natural gas states that 193 kW of heat is available from the cooling jacket water and 117 kW from the exhaust gas, if the temperature were reduced to 120 C. These figures were modified by a factor of 2/3 to account for the approximate methane content of the biogas (~2/3 of the content of the biogas), yielding an estimated 128.9 kW of heat from the water jacket and 78 kW from the exhaust. The engine was assumed to run from 700 h in the morning until 1900 h in the evening, patterned after the normal operation at Barham Farm. When the water temperature in the storage tank reached 90 C the energy was assumed to be rejected to the atmosphere through an liquid-to-air heat exchanger (radiator) to protect the engine and to avoid the use of a pressurized storage tank. Heat loss from the storage tank was calculated at each time step and subtracted from the total energy available at any point. When the water temperature dropped below 50 C, use of the waste heat system was discontinued. The waste heat system was given priority for all heating needs with the LP heaters being added as needed to make up the difference. The exit temperatures of the air and water from the hydronic heater(s) in the greenhouse were calculated at each time step based on manufacturer's data for the heater (see below) and the inlet conditions established from the previous time step. Water flow rate to each heater was assumed to be constant at 1.26 kg/s.

Validation: The data for validation were collected during the period of January 11th through May 15th of 2001 and the details of the methods used are provided in Gurjer (2001) and Marbis (2001). Both inside and outside data were collected as 30-minute averages of 1-minute readings collected by a QCom GemLink environmental control system (Irvine, CA). Outside meteorological conditions (solar radiation, outside air temperature, relative humidity, wind speed and wind direction) were measured using a weather station mounted at the top of the greenhouse consisting of a LI-200SB

23

LiCor pyranometer, a Davis wind speed and direction unit (industrial model) and a RTD temperature sensor mounted in an aspirated housing. In March, a HyCal relative humidity sensor was added. Inside greenhouse temperature, relative humidity and CO2 levels were measured using a Vaisala 50Y temperature/humidity sensor mounted in an aspirated housing and a Vaisala GMP 111E CO2 sensor. The greenhouse used two stages of heating with separate set points for day and night heating. Day set points were used when the solar radiation (on an outside horizontal surface) was greater than 250 W m-2 while the night set points were used when the solar radiation was below 50 W m-

2. The night set points were 16°C and 16.5°C while the day set points were 20.5°C and 21.1°C. When solar radiation was between 50 W m-2 and 250 W m-2 the heating set points were determined by linear interpolation. Both model and greenhouse used five stages of cooling, the first three being exhaust fans only while the last two were combining exhaust fans with evaporative pads. The air moving capacities of the five stages were 22.3, 66.8, 111.4, 167.1 and 222.8 kg/s. Cooling set points were 24.4°C, 25°C, 25.5°C, 26.1°C and 26.6°C for both day and night. Humidity control in the validation greenhouse was via exhaust fans (2 fans running 5 minutes every 15 minutes) whenever the relative humidity exceeded 90%. To simulate this, the model ran 1/10 of the total fan capacity whenever the relative humidity was above 90%. Greenhouse temperature, relative humidity, combined heating periods and combined cooling periods predicted by the model were compared to the observed data. The simulations were run for the period between January 11th and May 15th. A root mean square error (RMSE) and the average absolute percentage difference (AAPD) were computed for the greenhouse temperature and relative humidity for comparison purposes. For the combined heating and cooling periods, an average percentage difference (APD) was calculated, as we were only concerned about the total heating and cooling. RMSE, AAPD and APD were calculated using

RMSE 1N (Voi Vpi)

2

i 1

N

(1)

NV

VV

AAPD oi

pioin

i100

)(

1

⋅−

=∑= (2)

NV

VV

APD oi

pioin

i100

)(

1

⋅−

=∑= (3)

where RMSE is the root mean square error, AAPD is the average absolute percentage difference, APD is the average percentage difference, Voi and Vpi are the observed and predicted values, respectively and N is the number of observations.

Simulations: Simulations were carried out for various scenarios and compared to the base condition. The base condition represented a conventional greenhouse equipped with conventional heating and cooling equipment. LP gas usage was determined assuming a combustion efficiency of 80%. The heating value of LP gas was taken as 25.37 GJ per m3. The simulations were conducted using TMY2 data (Marion and Urban, 1995) for Raleigh, North Carolina (latitude: 35° 52.7′ N; longitude: 78° 47.2′ W; elevation: 132.6 m) and Wilmington, North Carolina (latitude: 34° 16.2′ N; longitude: 77° 54.1′ W; elevation: 9.8 m).

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Since waste heat utilization is dependent upon the availability of heat and the rate of delivery, the simulation scenarios considered both. Availability was manipulated by considering waste heat production from one of two sources: 1) the engine cooling jacket only, which is required for basic operation of the engine, or 2) from the cooling jacket plus an optional exhaust heat recovery heat exchanger. For the purposes of this study, it was assumed that sufficient biogas was available to run the engine each day for the full 12 h period. The water tank was assumed to hold 45,460 liters based on the size of the tank at Barham Farm. Rate of heat delivery to the greenhouse was varied by changing the number of hydronic heaters available from 1 to 7 in steps of 2. The heaters were assumed to be Reznor Model 300/350, capable of delivering 80.8 kW at a water flow rate of 105.4 lpm and water temperature of 93 C. b) Model Prodiction

Validation: RMSE’s for greenhouse temperature varied from 1.29°C to 1.86°C and AAPD’s varied from 4.51% to 6.22% (table 6) over the period from January 12th to June 7th. RMSE’s for relative humidity varied from 7.85% to 9.89% and AAPD‘s varied from 8.42% to 11.91% (table 6). On average, temperatures were under-predicted by 1.6% and relative humidities by 2.4%.

Table 6: Comparison of predicted and observed greenhouse temperatures and relative humidities.

Temperature Relative Humidity Period

RMSE °C

AAPD %

RMSE %

AAPD %

1/12 to1/31 1.82 6.22 8.69 8.42 2/1 to 2/28 1.70 5.18 7.85 8.11 3/1 to 3/31 1.86 5.96 8.70 9.75 4/1 to 4/30 1.71 5.84 9.71 11.91 5/1 to 5/31 1.45 5.19 9.89 11.33 6/1 to 6/7 1.29 4.51 8.27 8.84

A summary of the predicted and observed heating and cooling activity is presented in table 7. Over the entire period, heater run times were under-predicted by 12.5% and the energy consumed by the cooling equipment was over-predicted by 3.1%. For simplicity, run time was selected for comparison of heating activity since both the LP gas usage and the electrical power consumed by the heaters are linear functions of the run times. For cooling, however, the energy used is not linear since the evaporative pad is employed for cooling stages 4 and 5. The pads required about 1 kW of additional electrical power for the pumps. The results of this validation suggest that the model performed quite well and that the output can be considered valid over an extended period of time.

Simulations Tables 8 and 9 present the simulation results for Raleigh and Wilmington, respectively, illustrating the interactive effect of increased heat delivery rate vs increased heat generation rate. In both locations, adding heaters reduced the consumption of LP gas, therefore increasing the

25

savings; however, the increased savings per additional heater declined as the number of heaters increased. Adding exhaust heat to the water jacket heat reduced mitigated decline.

Table 7: Comparison of predicted and observed heating times and cooling energy. Heating Times Energy for Cooling*

Period Obs h

Pred h

APD %

Obs kWh

Pred kWh

APD %

1/12 to 1/31 343 280 18.4 148 152 -2.72/1 to 2/28 373 364 2.4 511 415 18.93/1 to 3/31 424 377 11.3 706 810 -14.74/5 to 4/30 174 147 15.7 3649 3867 -6.05/1 to 5/31 46 23 51.3 5976 6300 -5.46/1 to 6/7 0 1 - 2881 2752 4.5 ______ ______ _____ ______ ______ ______Totals 1362 1191 12.5* 13,872 14,296 -3.1*

*Includes evaporative pad pump. **APD (absolute percentage difference) values calculated from the totals. Table 8. LP gas usage and percentage savings compared to the baseline for Raleigh, NC, as a function of the number of hydronic heaters, for waste heat taken from: 1) water jacket only or 2) water jacket plus exhaust. Baseline gas usage was 135.6 m3.

Water Jacket Only Water Jacket + Exhaust No. of Htrs LP Gas

m3Savings

% LP Gas

m3Savings

% 1 112.6 17.0 112.7 16.9 3 88.2 35.0 78.6 42.1 5 80.5 40.6 64.0 52.8 7 78.6 42.0 61.2 54.9

Table 9. LP gas usage and percentage savings compared to the baseline for Wilmington, NC, as a function of the number of hydronic heaters, for waste heat taken from: 1) water jacket only or 2) water jacket plus exhaust. Baseline gas usage was 103.6 m3.

Water Jacket Only Water Jacket + Exhaust No. of Htrs LP Gas

m3Reduction

% LP Gas

m3Reduction

% 1 85.1 17.9 85.0 18.0 3 63.8 38.5 57.2 44.8 5 57.7 44.3 44.4 57.2 7 56.9 45.1 41.9 59.6

Although in every case the percentage savings in LP gas usage was greater in Wilmington than in Raleigh, the actual amount of LP gas saved was greater in Raleigh. This is because Raleigh is generally cooler than Wilmington and thus provides more opportunity for the waste heat to be used. Despite the fact that the annual heat produced by the engine was 3.47 TJ and the baseline heating needs of the greenhouse were 3.46 TJ in Raleigh and 2.64 TJ in Wilmington, the waste heat did

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not displace more than 59.6% of the baseline fuel consumption. Efforts to increase the savings by allowing the water temperature to rise above 90 C and fall below 50 C (to reduce the amount of heat rejected to the atmosphere) were marginal, at best, producing increases in savings of only a few percent. Although this increased the thermal storage capacity of the tank, it was not enough to offset the mismatch between waste heat availability and the heating demand of the greenhouse. The bulk of the waste heat produced by the engine during the warm months was rejected to the atmosphere whereas during the colder months the supply of waste heat was inadequate. Increasing the overall production of waste heat would not sufficiently help the situation unless the production could be shifted from the warmer months to the colder months. This would have to be done with some care, however, since the primary purpose of the engine is to produce electrical energy. Only by consider the total demand for electrical energy and waste heat can appropriate decisions be made about how best to shift production. Despite the limitations of using waste heat, the advantages seem clear. Using data from a typical meteorological year (TMY2), a 40% savings in LP gas usage would save $14,000/yr in Raleigh for LP gas prices of $0.264 per liter ($1.00 per gal) using water jacket heat alone. The estimated cost of a single heater would be about $1500. If $5,000 were allowed for plumbing and installation, the total investment would run about $12,500 for five heaters, leading to a payback period of less than one year. If heat were reclaimed from the exhaust as well as the water jacket, the number of heaters could be reduced to three; however, an additional cost would have to be incurred for the exhaust gas heat exchanger. All of this assumes, of course, that the ATAnD, electrical generator and greenhouse are already in place as a part of the waste disposal system and that waste heat utilization is being added to increase the viability of the system. These calculations also assume that the rate of biogas production is constant year round, which may not be a very good assumption. It may be possible to store biogas from the warmer months to the colder months to offset the decline in production with temperature; however, the extent to which the biogas could be stored and the production of waste heat leveled over the year has not been studied in detail. Conclusions: The results presented here suggest that waste heat utilization can be an effective means of increasing the viability of the anaerobic-digestion/greenhouse swine waste management system under study at Barham Farm, Zebulon, NC. The study suggests that as much as 55% of the heating needs of a 2,600 m2 greenhouse in Raleigh might be met by utilizing the waste heat already being produced by the electrical generator engine. Before economic viability can be determined, however, a more comprehensive study is needed to consider the effect of biogas production rates on waste heat utilization. 2. CO2 Utilization for CO2 Enrichment of the Greenhouse Preliminary Analyses: The suitability of the exhaust gas for CO2 enrichment is dependent upon the presence of pollutants in the gas and the ease with which they can be scrubbed from the exhaust stream. To assess this, measurements had been made in the summer and fall of 1999 by Dr. Viney Aneja (Dept of Marine, Earth and Atmospheric Science) measure ozone and NOy (NOx = NO + NO2; NOy = NOx + oxidized N) using his mobile lab. In addition, hand measurements of ozone, SO2,

27

and NOx were made using Draeger tubes. To facilitate both sets of measurements, a heat exchanger was constructed from stainless steel tubing and galvanized pipe, with the gas passing through the inside of the stainless steel tubing and well water passing through the annulus created between the tubing and the pipe. In this manner, the temperature of the exhaust gas could be reduced prior to entering the instrumentation. Measurements with the Draeger tubes on 11/8/99 showed levels of ozone in the exhaust of about 0.02 ppm, SO2 levels > 25 ppm (the limits of the indicator) and NOx levels of 300 to 475 ppm. Measurements made by Dr. Aneja on 12/16/99 indicated about 10 ppm of ozone with NO and NOy running about 0.1 to 2.3 ppb. Subsequent measurements with Draeger tubes on 1/20/00 again showed SO2 > 25 ppm, ozone levels approximately 0.7 ppm and NOx levels greater than 500 ppm. Considering the design dilution ratio of 1533 to 1 to achieve a CO2 level in the greenhouse of 1000 ppm, the measurements made by Dr. Aneja indicated no need to clean the exhaust. On the other hand, the Draeger tube measurements suggested that levels of NOx in the greenhouse might be as high as 325 ppb, too high for extended exposure to plants. It was decided to pipe the gas over to the greenhouse and retest the greenhouse NOx levels before allowing plants inside, implementing a scrubbing procedure if necessary. CO2 Utilization in the Greenhouses: Although the plumbing was in place for conveying the gas, the decision was made in the spring of 2000 to delay the construction of the CO2 enrichment system until additional funds could be obtained. During the summer and fall of 2000, Mr. Barham applied for and received funds from Smithfield. Construction of Tomato Greenhouse II was finished in the late summer of 2001 and plants were introduced in September. Completion of the CO2 enrichment and waste heating systems (see above), however, was not accomplished until October, after the plants had been growing for about six weeks. After the CO2 enrichment system was completed, Mr. Barham conducted a brief (15 min) test of the enrichment system to make sure the plumbing was operational. No provisions were made to protect the plants. The result of the brief test run was severe leaf burn on about 1/3 of the crop in Greenhouse I. The symptoms suggested NOx burn, which led to the conclusion that NOx levels may have been higher than either set of measurements had predicted. In an attempt to confirm that NOx was responsible, on 11/16/01 an IMR 1400 exhaust gas analyzer (Environmental Equipment International, Inc.) was used to measure the levels of NOx in the exhaust. The NO levels were found to be in excess of 1000 ppm (the limit of the analyzer) and NO2 was on the order of 1500 ppm. O2 readings were about 6%. Since these readings were considerably higher than any of the previous readings, a second set was made on 1/9/02, shortly after the engine had undergone a routine tune-up. On this occasion, NO2 was considerably lower (approximately 200 ppm) but NO was still greater than 1000 ppm. O2 readings had dropped to around 4%. To see if ethylene in the exhaust was a problem, on 12/18/01 six samples of the exhaust gas were collected using three glass vials and three glass syringes. The vials were placed into the exhaust stream at the exit of the exhaust and tilted slightly to allow the force of the exhaust gas to push the contents of the vials out and replace them with the exhaust gas. After filling the three vials, three samples were withdrawn from the same location using the syringes. The samples were transported back to the lab of Dr. Sylvia Blankenship, HS, on that same day and tested using gas

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chromatography. The ethylene levels were found to be 1.6 ppm in the vials and 3 ppm in the syringes. The higher values translate to 9 ppb in the greenhouse, less than the threshold for injury to tomato plants. The IMR 1400 readings better explained the results of the brief operational test in October than did the earlier measurements in the fall and winter of 1999, but the fact that the readings for NO exceed the limits of the analyzer made it impossible to determine how much cleanup would be needed to utilize the gas. Arrangements were then made to use an analyzer in the lab of Dr. Bill Roberts (MAE) and to have one of his students take the measurements. Before the could be made, however, the engine malfunctioned and remained inactive for about two months. When the engine came back on-line, exhaust gas tests were conducted using an Ipex 1 analyzer (Protech Systems Co., Ltd.), which had a NOx range of 0-5000 ppm. Measurements were made at the engine exhaust and at the greenhouse. At the greenhouse, ducting was added to the system to divert the gas outside the house to a point a safe distance away from the air intake. NO levels ranged from 600 ppm to 2500 ppm, but more importantly the O2 readings were negative. Attempts to resolve the negative O2 readings were to no avail, so the manufacturer was contacted for an explanation. The apparent cause was that the meter was unstable in the presence of high levels of SO2, and the measurements were therefore not reliable. Arrangements were made for another analyzer, and provisions were made to scrub some of the SO2 so that the Ipex 1 analyzer could be retested. Before the tests could be repeated, however, the engine went down again. The engine was down until November 2002, at which time the analyzers were no longer available. The cost of cleaning the gas will be very much dependent upon the level of NOx in the exhaust (which dictates the size of the scrubber) and the level of SO2 (which dictates the process). The platinum catalytic converter process is the cheapest technology; however, very low levels of sulfur will ‘poison’ the converter reducing its efficiency dramatically. An alternative process injects urea into the exhaust stream at a very high temperature, removing both NOx and SO2 simultaneously; however, this process cannot function in the presence of more than 0.5% O2. The measurements using the IMR 1400 indicated O2 levels > 4%. Quotes for scrubbing the exhaust were obtained from two companies. The technology that would be effective depends upon the presence (or absence) of SO2. An installed cost $6,000 was obtained for platinum converter technology, which is effective only in the absence of SO2. An installed cost of $11,000 was obtained for a urea process which is capable of removing NOx and SO2. Manufacturer's specifications suggest that either process would be capable of removing sufficient NOx for the exhaust gas to become usable with the urea process also removing the sulfur at the same time. To assess the probable concentration of SO2 in the exhaust, the biogas was tested on 5/23/2003. The switch from testing the exhaust stream to testing the biogas was prompted by the fact that operation of the engine was unreliable and Mr. Barham was attempting to make arrangements for another engine, thus rendering exhaust gas measurement usefulness questionable. A sample of the biogas was drawn into an evacuated container provided by Enthalpy Analytical, Inc., Durham, NC. Analysis of the gas was via GC/FPD and FTIR. The results showed nitrogen at

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0.906%, methane at 63.3% and CO2 at 23.9%. H2S was found to be 2,003 ppm. Ammonia levels were not detectable. The presence of 2,003 ppm of sulfur in the biogas will require that the biogas be scrubbed of sulfur or that the urea process be used for scrubbing NOx and SO2 from the exhaust. Alternatively, an engine with a lower combustion temperature could be used to reduce the NOx output. A Sterling engine was investigated but was not pursued. The manufacturer of the engine claimed NOx output of less than 20 ppm. Using the design dilution ratio of 1533 to 1, that translates into a greenhouse NOx level of about 1.3 ppb, well below the 200 ppb threshold for damage to tomato plants. NOx specifications for a Capstone micro-turbine ranged from about 3.0 to 6.6 ppm, suggesting an even better choice for a CO2 source. Either of these engines could probably be used without resorting to scrubbing.

Conclusions: Investigation into the utilization of the CO2 in the engine exhaust was not as successful as had been hoped. Preliminary projections indicated yield increases of 5% might be possible; however, several problems prevented the testing of this hypothesis. A few things did become clear during the course of the investigation, however. Scrubbing the gas did appear to be a viable option, based on the estimated levels of pollutants in the gas and the design thresholds to be maintained in the greenhouse. The cost would have been higher than anticipated, but not prohibitive. If the engine had been purchased with CO2 enrichment in mind from the beginning, a lower overall cost would probably have been achieved. The use of a Sterling engine, or perhaps a micro-turbine, would have resulted in lower NOx levels and therefore lower scrubbing costs.

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