Co-digestion of Algae from Algal Turf Scrubbers in Farm-based Digesters to Increase Profitability and Reduce Nutrients to the Chesapeake Bay Watershed

Progress report for GNE20-231

Project Type: Graduate Student
Funds awarded in 2020: $14,978.00
Projected End Date: 07/31/2022
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Graduate Student:
Faculty Advisor:
Stephanie Lansing
University of Maryland
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Project Information

Summary:

Maryland farmers can install algal turf scrubbers (ATS) to generate nutrient trading credits. In an ATS, pond or river water is pumped across a flow-way which allows algae to seed and grow in a contained “bloom” on land that traps nitrogen and phosphorus in the algal turf for easy harvest. An ATS allows for upstream removal of nutrients to improve water quality downstream, while generating nutrient credit payments for farmers. Installation and operational costs of an ATS may be partially offset by using the weekly algae harvest to create value-added products for the farm. This experiment will use anaerobic digestion (AD) to process ATS algae into methane (CH4)-enriched biogas and fertilizer via co-digestion with traditional agricultural AD feedstocks (dairy manure, food waste, and poultry litter). The biogas can be used on-farm for electricity production to increase farm income. Fertilizer will be produced from AD effluent, which is commonly land applied on-farm. Thus, the nutrients trapped by the algae will be recycled for farmers to use again.

Two phases of experimentation will be performed. In Phase I, a batch-scale AD test will measure the volume and quality of CH4 produced from co-digestion reactors over a 45-day period. In Phase II, the effluent from the batch reactors will be used to fertilize potted lettuce to assess the quality of this fertilizer compared with commercial fertilizer. These experiments will demonstrate how farmers utilizing AD can supplement their digesters via co-digestion with algae and improve the economic benefits provided by both ATS and AD.

Project Objectives:

Objective 1. Quantify the volume and quality of biogas produced from co-digestion of ATS algae with traditional agricultural AD feedstocks: dairy manure, poultry litter, and food waste.

Hypotheses:

-Ha1.1: Co-digestion of ATS algae will yield a higher volume of CH4 than produced from AD of algae or the agricultural feedstocks alone.

-Ha1.2: Co-digestion of ATS will yield biogas with a lower concentration of H2S, and thus be of higher quality, than biogas produced from the agricultural feedstocks alone.

These hypotheses will be addressed using a batch-scale AD reactor experiment. ATS algae grown in Maryland will be digested alone and via co-digestion with dairy manure, poultry litter, and food waste over 62 days. It is expected that biogas from reactors containing algae will experience elevated biogas production, and a corresponding increase in CH4 production, due to the introduction of more complex substrates for AD bacteria to utilize. Additionally, it is expected that this biogas will have lower H2S than reactors without algae due to the iron content of algae bonding with sulfur to produce iron sulfide precipitates instead.

Objective 2. Determine how co-digestion of ATS algae with traditional feedstocks affects the quality of fertilizer produced from the digester’s effluent.

Hypotheses:

-Ha2.1: Lettuce seeds fertilized using effluent from co-digestion of algae will produce biomass equal to or greater than seeds fertilized using commercial fertilizers or effluent from AD systems utilizing agricultural feedstocks alone.

-Ha2.2: Lettuce grown using effluent from co-digestion will not contain a higher concentration of sodium or heavy metals than lettuce grown using commercial fertilizers or effluent from AD systems utilizing agricultural feedstocks alone.

These hypotheses will be addressed using a lettuce growth experiment carried out after the reactor experiment described in Objective 1. Effluent from the reactors will be used to fertilize buttercrunch lettuce seeds to compare its effectiveness with commercial fertilizers. It is expected that co-digestion will dilute any salts or heavy metals present in the algae sufficiently to prevent them from interfering with lettuce growth or increasing their concentration in the lettuce biomass, and thus verify the utility of the co-digestion AD effluent for land application.

Introduction:

The purpose of this project is to improve the economic viability of algal turf scrubber (ATS) technology for Maryland farmers interested in installing them to generate nutrient trading credits for their farm. This will be achieved by using anaerobic digestion (AD) to process algal biomass from an ATS into value-added products, specifically CH4-enriched biogas and fertilizer.

The Chesapeake Bay Watershed covers much of the northeastern United States, stretching hundreds of miles from the Atlantic Ocean in Maryland to the source of the Susquehanna River in Upstate New York. Farms present throughout the watershed are critical to the agricultural economy of this region, yet runoff from their fields could contribute to nutrients and sediments accumulating downstream in the Bay. To help increase the Bay’s water quality, all states within the watershed must develop Watershed Implementation Plans (WIPs) to set goals for their runoff management. Critical to Maryland’s WIP III plan is the use of economic incentives, such as nutrient credit trading, to reduce discharge of nutrients into the Bay watershed. Nutrient credit trading encourages research and development of nutrient abatement technology by allowing farms that install extra or novel systems to generate credits that can be sold to businesses unable to meet their discharge requirements.

ATS technology is an approved nutrient trading credit technology in Maryland. The ATS was developed in the 1980s to mimic algal growth patterns on coral reefs using land-based flow ways. Pumps are used to replicate the natural wave action in a coral reef by sending timed pulses of water from a river or pond across a textured surface on land, allowing time for algal cells naturally present in the water to settle and grow during the lull between pulses (Adey et al. 2011). The algae metabolize nitrogen and phosphorus dissolved in the water into its biomass as it grows, and traps sediments in its turf. In this way, dissolved nutrients and sediments can be removed from water and converted into an algal “crop” that may be harvested on a weekly basis during the growing season.

The algal crop may then be processed into value-added products, which can help offset the costs of ATS installation. Processing via AD will be the focus of this research due to the established use of AD systems on US farms to manage wastes, such as manure, wastewater sludge, and food waste. The non-selective nature of AD allows for algae to easily be incorporated as a co-digestion feedstock with these wastes. AD converts carbon in the feedstocks into CH4-rich biogas and a nutrient-rich effluent. The biogas is used for on-farm electricity production or sold to the grid, while the AD effluent may be separated into a solid fraction for bedding, composted, or sold off-site. The nearly odor-free liquid effluent may be disposed of as wastewater or land applied as fertilizer. It is expected that by using a combined ATS-AD system, the algae can increase farm income through 1) increased electricity production, 2) nutrient trading credits, and 3) continued sales of off-farm fertilizer or bedding.

Research

Materials and methods:

Objective 1: Energy production via anaerobic digestion                                  

Co-digestion feedstocks

A 71 x 168 cm (1.2 m2) ATS sited on the Anacostia River at Bladensburg Waterfront Park in Bladensburg, Maryland was used to supply algae for this project (Figure 1). This ATS was constructed in 2018 by the UM Student Chapter of the American Ecological Engineering Society and run by the UMD Algal Ecological Technology. For this experiment, it was activated on September 25, 2020 and run for three weeks with harvests every ten days to allow the biofilm to establish itself. The culture used in the Phase I experiments was collected during the third harvest on October 23, 2020, tested for total solids (TS) and volatile solids (VS), and frozen until needed. Microscopy was used to find that the dominant species in this algal culture were the diatom Melosira sp. (~70%) and the green alga Spyrogyra sp. (~30%) (Figure 2).

Figure 1: Small-scale ATS system on the Anacostia River used to supply algae for Phase I, before (left) and after (right) 10 days of biofilm growth. Photos taken on September 25 and October 5, 2020.

Figure 2: Microscope images of Spyrogyra sp. (left) and Melosira sp. (right) taken from samples of the algal biofilm from the Bladensburg Waterfront Park ATS system.

Poultry litter (PL) was collected from a poultry farm on the Eastern Shore of Maryland on August 27, 2020 and frozen until needed. Dairy manure (DM) was collected from the scrape system at the United States Agricultural Department’s Beltsville Agricultural Research Center (USDA BARC) dairy farm in Beltsville, Maryland on October 27, 2020 and refrigerated until needed. Artificial food waste (FW) was also prepared on October 27, 2020 using the methods described in Yarberry et al. (2019), consisting of 506 g of white bread, 907 g of pork and beans, and 176 g of potato flakes, homogenized via blending and refrigerated until needed.

The inoculum culture was a mixture of lab-grown liquid inoculum started from a dairy manure digester on a farm in Maryland and dewatered solid inoculum produced by an AD reactor at municipal wastewater treatment facility in Washington DC. Each batch of mixed inoculum culture was prepared by combining 1110 g of lab-grown inoculum with 390 g of BLOOM to achieve a final VS of ~5% (Table 1).

Table 1: Total solids (TS) and volatile solids (VS) of inoculum and co-digestion feedstocks used in the Phase I lab-scale reactor experiment. Values given are mean % wet weight ± standard error (n=3). DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Material

TS (%)

VS (%)

Algae

4.82 ± 0.02

0.61 ± 0.00

BLOOM Inoculum

33.8 ± 0.4

17.7 ± 0.2

Lab-grown Inoculum

1.11 ± 0.00

0.71 ± 0.00

Mixed Inoculum

8.48 ± 0.09

4.53 ± 0.04

Dairy Manure (DM)

15.4 ± 0.0

13.3 ± 0.1

Food Waste (FW)

45.3 ± 0.3

43.6 ± 0.2

Poultry Litter (PL)

71.0 ± 0.1

50.0 ± 0.3

Lab-scale AD reactor experiment

The AD reactors were loaded, and the Phase I experiment started on November 5, 2020. Six ratios of algae:co-digestion feedstock were tested (0:1, 1:10, 1:5, 1:2, 1:1, 1:0, by mass), with 1:0 and 0:1 ratio used as controls to measure the biogas produced from AD of algae-only and each feedstock-only, respectively. Furthermore, an inoculum-only control treatment was used to account for biogas production from the organic material in the inoculum used to seed the digesters. This baseline level of biogas production was subtracted from the biogas production data presented in the results. Each treatment was prepared with four replicates, three of which were incubated for 62 days, while the fourth was harvested immediately after preparation to provide a sample of pre-digestion reactor fluid.

The reactors used in the batch-scale experiments were set up in 250 mL and 500 mL glass bottles. The bottle size used for a given treatment was determined by the expected final volume of the reactors’ digestate, which varied due to the high range of the initial TS and VS content of the algae and co-digestion feedstocks. Inoculum and feedstocks were loaded based on a 2:1 inoculum to feedstock ratio. Treatments whose inoculum+substrate volume exceeded 220 mL were placed in 500 mL bottles to keep at least 30 mL of headspace for biogas accumulation in the reactor and prevent excessive pressure accumulation. Each bottle was loaded with 5 g total VS, and thus 2 parts (3.333 g VS) were supplied by the inoculum and 1 part (1.667 g VS) was supplied by the experimental co-digestion substrate (Table 2).

Table 2: Experimental Setup of the Phase I lab-scale reactor test. DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Reactor #

Treatment

Inoculum (g)

Algae (g)

Dairy Manure (g)

Food Waste (g)

Poultry Litter (g)

Total (g)

1-3

Mixed Inoculum

73.648

73.648

4 – 6

Algae

73.648

264.228

337.875

7-9

DM

73.648

12.542

86.190

10-12

FW

73.648

3.848

77.496

13-15

PL

73.648

3.332

73.648

16-18

Algae+DM 1:1

73.648

132.114

6.271

212.033

19-21

Algae+DM 1:2

73.648

88.076

8.361

170.085

22-24

Algae+DM 1:5

73.648

44.038

10.452

128.138

25-27

Algae+DM 1:10

73.648

24.021

11.402

109.070

28-30

Algae+FW 1:1

73.648

132.114

1.924

207.686

31-33

Algae+FW 1:2

73.648

88.076

2.565

164.289

34-36

Algae+FW 1:5

73.648

44.038

3.207

120.893

37-39

Algae+FW 1:10

73.648

24.021

3.498

101.167

40-42

Algae+PL 1:1

73.648

132.114

1.666

205.762

43-45

Algae+PL 1:2

73.648

88.076

2.221

161.724

46-48

Algae+PL 1:5

73.648

44.038

2.777

117.686

49-51

Algae+PL 1:10

73.648

24.021

3.029

97.668

After adding the inoculum and co-digestion substrates, the bottles were flushed with nitrogen gas (N2) for 30 seconds to displace oxygen in the headspace and create an anaerobic environment. They were then capped quickly with self-healing rubber septa, which provided an airtight seal. The total of 51 AD reactors were then incubated in the dark at mesophilic temperatures (35°C) with continuous agitation (120 RPM) for 62 days.

Biogas volume was measured using a 50 mL glass syringe to pierce the septa and release pressure from the headspace. This was performed every 4-6 hours during the first 48 hours of incubation, every 12 hours during the next 48 hours, and daily between Days 5-9 and 11-17. Sampling frequency was further reduced after Day 17 until the end of the experiment, as biogas production declined. The digestion experiment concluded on January 6, 2021.

After the gas volume measurement was taken, a small sample (0.5 mL) of the gas left in the headspace after pressure release was fed through an Agilent 7890A gas chromatograph (GC) to determine the concentration of CH4, carbon dioxide (CO2), and H2S in the biogas according to the lab’s published protocols (Achi et al. 2020; Lisboa and Lansing, 2013; Witarsa et al., 2020). After gas analysis, each bottle was capped with silicone to reinforce the self-healing septum and minimize the chance of the leaks.

Analytical methods

The pH of the reactor fluid was tested on pre- and post-digestion samples using an Accumet Basic AB15 meter. The TS and VS concentrations were measured according to APHA Methods 2540B and 2540E, respectively (APHA et al., 2005). The TS concentration was determined by drying samples at 105°C overnight and comparing sample weight before and after drying. Dried samples were then incinerated at 550°C to determine the VS by comparing the ash weight to the TS weight. Pre-digestion TS and VS values were calculated based on the ratios of the inoculum, algae, and co-digestion feedstocks in the reactors. Post-digestion TS and VS values were measured directly from each reactor.

Organics were further analyzed via a chemical oxygen demand (COD) test using spectrophotometry with HACH high-range COD digestion kits. Soluble COD (SCOD) was measured using the same kits, but with a filtering pre-treatment step to remove particulates. The specific organic acids present were determined via volatile fatty acid (VFA) analysis using the FID column within an Agilent 7890A GC.

Pre- and post-digestion ammonia (NH4) was analyzed using a Lachat Quickchem analyzer. Other nutrients, metals, and inorganic components of these samples will be analyzed in January 2021 at an external laboratory, Agrolab (Harrington, DE) that specializes in agricultural samples and supplies a variety of analysis services. Frozen samples will be sent to Agrolab for nitrogen (N), phosphorus (P), nitrate (NO3), iron (Fe), sulfur (S), C:N ratio, mineral, and fertility analysis to obtain a complete chemical profile of trace materials present in the influent and effluent.

Statistical analysis

Statistical analysis will be performed in Spring 2021 and will be used to support or reject the hypotheses in Objective 1. First, results from biogas and CH4 production will be normalized by g VS fed to each reactor. For Ha1.1, ANOVA will be used to find if there is a significant difference in CH4 volume produced between each of the different reactor loads. For Ha1.2, multiple linear regression will be used to determine if a statistically significant relationship exists between the Fe and S content of the algal influent and H2S content of the biogas in each reactor.

Objective 2: Fertilizer production from digester effluent

Lettuce growth experiment

Now that the batch-scale AD reactor tests has concluded, digested effluent from each treatment will be used in an indoor plant growth experiment in Spring 2021. This will be performed to verify the effectiveness and safety of land application of effluent from co-digestion. While AD effluent in MD is typically used to fertilize corn fields in Maryland, buttercrunch lettuce will be used as a model organism in this experiment due to its rapid growth and ability to grow in the small, controlled environment of a laboratory.

Fifty-one 6” clay pots will be filled with potting soil and seeded with two buttercrunch lettuce seeds. Triplicate pot be fertilized using the reserved effluent from the 17 composite samples resulting from the Phase I experiments. A separate control set of triplicate pots will be established with commercial fertilizers to provide comparison with the reactor effluents. Another triplicate set of pots will a be set up without any fertilization to account for trace nutrients that may be present in the potting media for a total of 57 growth pots.

The seeds will be germinated and grown indoors to allow better control over potential growth variables, such as temperature, light availability, and pest interference. The plants will be allowed to grow for 5 weeks under growth lights that have previously been used to successfully grow lettuce in a hydroponics experiment (Hassanein et al. 2019). The lights will be set on a 12-hour timer to provide a constant 12 hours of light and darkness in a consistent cycle.

Collection and analysis of soil and lettuce samples

At the end of the growth period, the above ground (shoots) and below-ground (roots) lettuce biomass will be harvested and soil substrate samples will be collected. For harvesting, the above ground biomass will be cut from within 1 cm of the soil surface of each pot, and the roots will be shifted from the soil substrate and washed. The above ground and below ground biomass will be dried and at 70°C for several days and then weighted to total dried biomass values. Subsamples will be sent to Agrolab for NO3, Fe, S, mineral, metal, and soil fertility analysis.

Statistical analysis

The results of this experiment will be statistically analyzed to determine if the results support the two hypotheses tested in Objective 2. For Ha2.1, t-tests will be used to analyze mean lettuce biomass growth across treatments. Additionally, the nutrient content of the reactor pots will be compared to the commercial fertilizer pots via ANOVA to determine if the chemical components of the fertilizers have a significant effect on plant growth. For Ha2.2, the results of Agrolab’s analysis of lettuce biomass will be compared between treatments using ANOVA to determine if there is a significant difference between the analytes tested in the reactor pots compared to the commercial fertilizer pots. This will verify the safety of crops grown with reactor effluent by determining if the lettuce has elevated levels of analytes of concern, such as heavy metals.

Research results and discussion:

Phase I

Biogas Production

Cumulative CH4 volume was lowest in the algae reactors (109 ± 4 mL CH4/g VS), although, the concentration of CH4 in the algae reactors was consistently amongst the highest in the study (>% 70 CH4). The algae+FW 1:10 and algae+FW 1:5 reactors had the highest cumulative CH4 production (398 ± 9 and 398 ± 22 mL CH4/g) respectively, followed by FW-only mono-digestion reactors (384 ± 23 mL CH4/g). It should be noted, however, that these reactors took more time to begin generating CH4 compared to the other treatments, with % CH4 in the biogas from these reactors during Days 1-7 (8.95-32.8%, 6.46-31.6%, and 7.60-24.4%, respectively) remaining consistently below that of the inoculum-only control reactor during the same time period (2.89-33.3%).

Reactors with DM and PL followed similar trends to each other, with the highest cumulative CH4 volume observed in the mono-digestion reactors (299 ± 8  and 302 ± 8 mL CH4/g VS, for DM and PL respectively) and progressively lower CH4 production in co-digestion reactors as the quantity of algae used increased (Figures 3 and 4).

Figure 3: Cumulative methane (CH4) production in the Phase I lab-scale reactor experiment, with methane (CH4) production normalized by g volatile solids (VS) of the substrates. The standard error of the triplicate reactors is shown in the error bars. DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Figure 4: Methane (CH4) concentration in biogas collected from the triplicate feedstock reactors and inoculum reactors in the Phase I lab-scale experiment. The standard error of the triplicate reactors is shown in the error bars. DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

The pH was consistently neutral or slightly basic in all reactors, except the pre-digestion FW reactors, which were slightly acidic (6.32 – 6.85), but the pH in those reactors rose to slightly basic levels by the end of the experiment. The final pH in reactors holding larger proportions of algae were consistently the lowest, with the reactor digesting algae-only exhibiting almost neutral pH after 62 days of incubation (7.02 ± 0.03) (Table 3).

Table 3: pH of lab-scale reactors before and after 62 days of incubation. Initial pH was n=1, while the final pH is shown as the mean ± standard error of the triplicate reactors (n=3). DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Treatment

Initial pH

Final pH

Mixed Inoculum

7.47

7.59 ± 0.03

Algae

7.31

7.02 ± 0.04

DM

7.27

7.40 ± 0.03

FW

6.58

7.57 ± 0.02

PL

7.38

7.58 ± 0.04

Algae+DM 1:1

7.38

7.07 ± 0.02

Algae+DM 1:2

7.30

7.20 ± 0.01

Algae+DM 1:5

7.38

7.34 ± 0.02

Algae+DM 1:10

7.38

7.34 ± 0.01

Algae+FW 1:1

6.85

7.11 ± 0.01

Algae+FW 1:2

6.62

7.26 ± 0.03

Algae+FW 1:5

6.58

7.42 ± 0.03

Algae+FW 1:10

6.32

7.47 ± 0.01

Algae+PL 1:1

7.45

7.16 ± 0.02

Algae+PL 1:2

7.40

7.26 ± 0.01

Algae+PL 1:5

7.33

7.48 ± 0.02

Algae+PL 1:10

7.34

7.54 ± 0.01

Solids and Organics Analysis

The algae-only reactor had the lowest initial TS and VS due to the high moisture content of the algae. There was a high initial solids concentrations in the mono-digestion reactors with DM-only (9.49% TS, 5.80% VS), FW-only (10.3% TS, 6.47% VS), and PL-only (11.7% TS, 6.79% VS). The  algae co-digestion reactors had lower TS and VS values than the individual substrate reactors, with the lowest solids content in algae+DM 1:1 (6.40% TS, 2.35% VS), algae+FW 1:1 (6.49% VS, 2.40% VS), and algae+PL 1:1 (6.70% TS, 2.42% VS). The algae-only reactors had the lowest initial TS and VS values (5.62% TS, 1.47% VS).

Post-digestion, similar trends were observed in the final TS and VS values, with the highest solids concentrations in the DM-only (08 ± 0.19% TS, 4.25 ± 0.09% VS), FW-only (7.41 ± 0.97% TS, 3.17 ± 0.92% VS), and PL-only (9.45 ± 0.23% TS, 4.85 ± 0.13% VS) reactors. The algae+DM 1:1 reactors had the lowest solids concentrations post-digestion (3.04 ± 2.67% TS, 0.94 ± 0.81% VS), followed by the algae+FW 1:1 (3.35 ± 1.55% TS, 1.01 ± 0.45% VS), and algae+PL 1:1 (5.99 ± 0.30% TS, 1.83 ± 0.09% VS) reactors. The algae+DM 1:2 yielded the greatest decline in TS (-70.0%) and VS (-74.3%). Analysis of VS post-digestion in the algae-only reactors is currently being analyzed and will be included in the next report (Table 4).

Table 4: The total solids (TS) and volatile solids (VS) of the lab-scale reactors before and after 62 days of digestion. The initial TS and VS values were calculated based ratios used in each reactor, while final the TS and VS values are shown as the mean ± standard error of the triplicate reactors (n=3). DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Treatment

Initial TS (% wet weight)

Final TS (% wet weight)

Initial VS (% wet weight)

Final VS (% wet weight)

Mixed Inoculum

8.48

8.15 ± 0.53

4.53

3.99 ± 0.24

Algae

5.62

-*

1.47

-*

DM

9.49

8.08 ± 0.19

5.80

4.25 ± 0.09

FW

10.3

7.41 ± 0.97

6.47

3.17 ± 0.92

PL

11.7

9.45 ± 0.23

6.79

4.85 ± 0.13

Algae+DM 1:1

6.40

3.04 ± 2.67

2.35

0.94 ± 0.81

Algae+DM 1:2

6.93

2.08 ± 1.55

2.93

0.75 ± 0.54

Algae+DM 1:5

7.79

5.71 ± 1.05

3.90

2.34 ± 0.43

Algae+DM 1:10

8.40

4.06 ± 1.71

4.58

1.90 ± 0.81

Algae+FW 1:1

6.49

3.35 ± 1.55

2.40

1.01 ± 0.45

Algae+FW 1:2

7.09

5.83 ± 0.27

3.04

1.94 ± 0.12

Algae+FW 1:5

8.12

6.84 ± 0.13

4.14

2.68 ± 0.05

Algae+FW 1:10

8.88

7.16 ± 0.16

4.95

3.08 ± 0.09

Algae+PL 1:1

6.70

5.99 ± 0.30

2.42

1.83 ± 0.09

Algae+PL 1:2

7.46

6.23 ± 0.11

3.08

2.10 ± 0.07

Algae+PL 1:5

8.79

7.61 ± 0.23

4.24

3.11 ± 0.11

Algae+PL 1:10

9.78

8.70 ± 0.31

5.12

3.76 ± 0.08

*Analysis ongoing, values will be provided in the next report.

Acetic acid was the VFA present in the highest concentration in all reactors pre-digestion, which indicated that the reactors could produce CH4, as acetic acid is the primary organic acid used by methanogenic bacteria. While each reactor had the same quantity of VS added, there was a wide range of VFA concentrations due to dilution by the high moisture content of the algae. The algae-only reactor had the lowest concentration of acetic acid (249 ± 4 mg/L) and lowest overall concentration of VFAs (497 mg/L). Valeric acid was notably lacking from most of the reactors having PL, except for the PL-only reactor (94.0 ± 1.63 mg/L) and algae+PL 1:10 reactors (79.6 mg/L), with valeric acid only detected in a single replicate for the latter. The co-digestion treatments with the lowest volume of algae (algae:DM 1:10, algae:FW 1:10, and algae:PL 1:10) had the highest concentration of VFAs within their respective co-digestion treatment groups. The highest overall VFA concentrations were observed in the DM-only and PL-only reactors, which exceeded 1200 mg/L VFAs. The highest concentration of acetic acid was observed in algae+FW 1:10 (1046 mg/L), which was the only co-digestion treatment to exceed 1200 mg/L total VFAs (1219 mg/L) (Figure 5).

Figure 5: Results of the volatile fatty acid (VFA) analysis on pre-digestion samples from Phase I lab-scale reactor experiment. DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Results from SCOD and post-digestion VFA analysis will be completed in January 2020 and included in the next report.

Nutrient Analysis

Pre-digestion, the highest NH4 content was observed in the PL-only reactors (1650 ± 25 mg/L), followed by the mixed inoculum (1500 ± 29 mg/L) and algae+PL 1:5 (1500 ± 67 mg/). Reactors containing PL generally had the highest NH4 concentration (682 – 1650 mg/L), followed by the DM reactors (623 – 1390 mg/L), and FW reactors (493 – 1320 mg/L), with the algae-only reactror having the lowest concentrations (325 ± 3 mg/L). The concentration of NH4 decreased as the volume of algae in the reactor increased, with algae+DM 1:1 (623 ± 11 mg/L), algae+FW 1:1 (493±8 mg/L) and algae+PL 1:1 (682 ± 10 (mg/L) having the lowest concentration of NH4 within their respective co-digestion groups (Table 5).

Table 5: Pre-digestion ammonia (NH4) from the Phase I lab-scale reactor experiment (n=3). Values given are as mean ± standard error. DM=Dairy Manure, FW=Food Waste, and PL=Poultry Litter.

Treatment

Pre-Digestion NH4 (mg N/L)

Mixed Inoculum

1500 ± 29

Algae

325 ± 3

DM

1390 ± 13

FW

1320 ± 30

PL

1650 ± 25

Algae+DM 1:1

623 ± 11

Algae+DM 1:2

684 ± 4

Algae+DM 1:5

850 ± 21

Algae+DM 1:10

1030 ± 37

Algae+FW 1:1

493 ± 8

Algae+FW 1:2

668 ± 8

Algae+FW 1:5

983 ± 22

Algae+FW 1:10

1080 ± 23

Algae+PL 1:1

682 ± 10

Algae+PL 1:2

940 ± 48

Algae+PL 1:5

1500 ± 67

Algae+PL 1:10

1450 ± 48

Post-digestion NH4 analysis will be completed in January 2021 and included in the next report. Frozen samples will be sent to Agrolab in January 2021 for analysis of other nutrients, including TN and TP, metals, and minerals, and the results will be included in the next report.

 

Phase II

No results have been collected for Phase II as of January 15, 2021. Results of Phase II will be included in the next report.

 

Education and Outreach

After the conclusion of Phase II, the results from both Phases will be used to prepare educational and outreach materials for farmers in Maryland. The goal of this project will be to give information to farmers on the effect of combining ATS with AD, which could allow for nutrient trading credits for farmers through ATS use, plus energy production from AD systems. The graduate student involved in this project has previously worked with the Port of Baltimore to explore the use of ATS-AD in an urban environment, but the applicability of ATS-AD to agricultural environments is a new area of research. The results of this study will help fill this gap. The study’s results will be communicated with Maryland’s farmers.

One method for delivering results to farmers will be a lay language Fact Sheet. The Fact Sheet will include basic information about ATS, including how ATS functions, AD and ATS installation and maintenance methods, and how the technologies can be used to generate credits for the nutrient trading program. It will also provide information about MDE’s resources detailing the program, including how credits are calculated and generator requirements for participation in the program. The Fact Sheet will also include how value-added products made from AD processing of the ATS algae affect the profitability of the system and return on investment.

This information can also be shared with eXtension, Maryland Department of Agriculture, and MDE to increase the visibility of the project results to the broader public. In addition, the results will be posted on Dr. Lansing’s website. They will build upon her work done on AD and ATS as profiled in videos on the Big Ten Network (https://today.umd.edu/articles/double-helping-ba2021aa-9a89-4c25-8e66-feb924c1e662) and Voice of America (https://www.voanews.com/a/4691150.html) by adding a co-digestion and fertilizer component, which has not been previously quantified as relevant information to farmers interested in this technology. It is expected that in the future a video can be created once the results go from the lab to the demonstration scale in future efforts. Results will also be presented to the scientific community at an academic conference and published in a journal, such as Bioresource Technology or Ecological Engineering. The results will also be available as part of my dissertation, freely available online.

All publications, educational deliverables, and outreach work will be completed after both Phase I and II are complete and will be included in a future report.

Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

Participation Summary

Education/outreach description:

Education and Outreach

After the conclusion of Phase II, the results from both Phases will be used to prepare educational and outreach materials for farmers in Maryland. The goal of this project will be to give information to farmers on the effect of combining ATS with AD, which could allow for nutrient trading credits for farmers through ATS use, plus energy production from AD systems. The graduate student involved in this project has previously worked with the Port of Baltimore to explore the use of ATS-AD in an urban environment, but the applicability of ATS-AD to agricultural environments is a new area of research. The results of this study will help fill this gap. The study’s results will be communicated with Maryland’s farmers.

One method for delivering results to farmers will be a lay language Fact Sheet. The Fact Sheet will include basic information about ATS, including how ATS functions, AD and ATS installation and maintenance methods, and how the technologies can be used to generate credits for the nutrient trading program. It will also provide information about MDE’s resources detailing the program, including how credits are calculated and generator requirements for participation in the program. The Fact Sheet will also include how value-added products made from AD processing of the ATS algae affect the profitability of the system and return on investment.

This information can also be shared with eXtension, Maryland Department of Agriculture, and MDE to increase the visibility of the project results to the broader public. In addition, the results will be posted on Dr. Lansing’s website. They will build upon her work done on AD and ATS as profiled in videos on the Big Ten Network (https://today.umd.edu/articles/double-helping-ba2021aa-9a89-4c25-8e66-feb924c1e662) and Voice of America (https://www.voanews.com/a/4691150.html) by adding a co-digestion and fertilizer component, which has not been previously quantified as relevant information to farmers interested in this technology. It is expected that in the future a video can be created once the results go from the lab to the demonstration scale in future efforts. Results will also be presented to the scientific community at an academic conference and published in a journal, such as Bioresource Technology or Ecological Engineering. The results will also be available as part of my dissertation, freely available online.

All publications, educational deliverables, and outreach work will be completed after both Phase I and II are complete and will be included in a future report.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.