Liam Christian
Age 14 | Red Deer, AB
Canada-Wide Science Fair 2019 Finalist
DOI: 10.18192/csfj.v2i1.20191720
Rural landscapes in Alberta are changing. The number of small acreages is growing, and these new rural residents often need, and benefit from, resources on how best to manage their land and animals. Rural residents have a direct impact on the natural environment and should, therefore, practice land stewardship. Land stewardship is the act of taking care of the land you own in a way that benefits the natural environment. Proper manure management is one example of how small acreage owners can practice land stewardship, because poorly managed manure piles can negatively affect water quality (Warren & Sweet, 2003). For example, runoff from manure piles can carry excess nutrients, pathogens, and organic material into groundwater (Warren & Sweet, 2003). In addition, manure piles can become a breeding ground for flies and other insects (Warren & Sweet, 2003). Considering that the average 450 kg horse produces 16.65 kg of feces per day (Westendorf, 2019), knowing what to do with the manure and understanding the potential benefits of feces (i.e. biogas production) can go a long way in helping the environment.
PURPOSE
The purpose of this two-part study was to determine the usability of horse feces as a suitable feedstock for biogas production. The preliminary phase involved designing a bench scale biodigester and then running three trials to determine if feces from a single horse can produce enough energy from biogas to power a small electric fencer (108 Watts). The digestate from this initial phase was used as an inoculant in the second phase of the study, which involved testing the effects of different inoculant treatments on start-up time1 and methane (CH 4 ) production for a bench scale biodigester.
HYPOTHESIS
It is hypothesized that start-up time will decrease and initial CH4 production will increase with higher amounts of inoculant.
MATERIALS AND METHODS
Phase 1 of the study began with designing and testing a bench scale biodigester. Any design flaws concerning biogas capture (i.e. gas collection system) and start-up time (i.e. use of an inoculant) were addressed during this phase. The digestate from Phase 1 was used to inoculate trials in Phase 2. The materials used in the final biodigester design were: an 18.9 L PVC bucket with airtight lid, a 1.25 x 5 cm PVC hole adapter, a 1.25 x 7.5 cm threaded PVC adapter, a 1.25 cm PVC ball valve, a 1.25 cm PVC nipple, a 3.6 L plastic bag, a stainless steel clamp ring, Teflon tape, and electrical tape (Figure 1).
Figure 1. Biodigester components (left), assembled gas collection system attached to the lid (centre), and a close-up of the plastic bag attachment (right).
The bench scale biodigester was a simple design in which biogas produced in the 18.9 L PVC bucket was forced into the 3.6 L plastic bag. Once the plastic bag was full, the biodigester was taken outside and the biogas was released via the pour spout in the top of the bucket lid.
In Phase 2, 12 bench scale biodigesters were assembled and weighed. Horse feces was collected over a one-week period. Each biodigester received 3.5 kg of feces in addition to 4 L of potable water. Digestate from Phase 1 was used as the inoculant —the purpose of which is to improve biodigester productivity— and divided into weighed amounts of 2.25 kg (Treatment 1), 1.5 kg (Treatment 2) and 0.75 kg (Treatment 3). Each treatment had four replicates. The 12 biodigesters were placed in random order in an experiment room with a heater and a regulated ambient temperature of 25 o C as shown in Figure 2.
Figure 2. Layout of experiment room.
Phase 2 ran for 21 days and the biodigesters were checked at specific intervals (8:00 h, 14:00 h and 20:00 h) each day. At 8:00 h and 20:00 h, all 12 biodigesters were agitated by gently shaking them, and their position within the experiment room was rotated clockwise. Temperature readings and biogas production were recorded at each time interval. Full bags of captured biogas were released outdoors except for three bags, one from each treatment, that were analyzed for biogas composition using a Sewerin Multitech 545 hand-held analyzer. Only three samples were used, because the samples were analyzed in Lethbridge at Lethbridge Biogas using their analyzer, and only one trip to Lethbridge was feasible during the study. Each of the three inoculant treatments were evaluated in five different categories. These categories were: start-up time, length of peak production, CH4 produced during peak production, average amount of CH4 produced per hour during peak production, and total CH4 produced.
RESULTS
In Phase 1 of the study, it was found that start-up time was 39 days without the use of an inoculant, and Phase 2 showed that start-up time can be decreased to as low as 3.5 days when an inoculant is employed. As shown in Table 1, Treatment 1 reached peak production 1.5 days before Treatment 2, and 1.25 days before Treatment 3.
Table 1. Comparisons of start-up time, peak production, and total production of methane.
Treatment 1 also had the longest peak production of 14.25 days, which exceeded Treatment 2 by 2.75 days and Treatment 3 by four days. The amount of CH4 produced during peak was also highest for Treatment 1, exceeding the second highest treatment by 1 L. Treatment 1 had the lowest total production of CH4 over the 21 days of the experiment and Treatment 2 had the highest. Total production of CH4 in Treatment 2 exceeded that in Treatment 1 by 1.35 L and in Treatment 3 by 0.56 L. Figure 3 shows that all three rates had similar CH4 production over the 21 days of the experiment. Treatment 1 produced the highest amounts of CH4 in the first 12 days of the experiment, but by Day 14 Treatments 2 and 3 had surpassed Treatment 1 and continued to out-produce Treatment 1 for the remainder of the experiment. The hand-held gas analyzer that was used to test the three different biogas samples suggested that the average composition of the biogas was as follows: methane (CH4) at 45.1%, hydrogen sulphide (H2S) at 37%, carbon dioxide (CO2) at 14%, and other gases made the remainder 3.9%.
Figure 3. Average cumulative methane production by treatment.
Treatment 1 also had the longest peak production of 14.25 days, which exceeded Treatment 2 by 2.75 days and Treatment 3 by four days. The amount of CH 4 produced during peak was also highest for Treatment 1, exceeding the second highest treatment by 1 L. Treatment 1 had the lowest total production of CH 4 over the 21 days of the experiment and Treatment 2 had the highest. Total production of CH 4 in Treatment 2 exceeded that in Treatment 1 by 1.35 L and in Treatment 3 by 0.56 L. Figure 3 shows that all three rates had similar CH 4 production over the 21 days of the experiment. Treatment 1 produced the highest amounts of CH 4 in the first 12 days of the experiment, but by Day 14 Treatments 2 and 3 had surpassed Treatment 1 and continued to out-produce Treatment 1 for the remainder of the experiment.
The hand-held gas analyzer that was used to test the three different biogas samples suggested that the average composition of the biogas was as follows: methane (CH 4 ) at 45.1%, hydrogen sulphide (H 2 S) at 37%, carbon dioxide (CO 2 ) at 14%, and other gases made the remainder 3.9%.
DISCUSSION
Horse feces is rarely used as a feedstock for biogas production (Hadin & Eriksson, 2016), which means that its potential as a source of energy is not being realized. In addition, using a waste product such as horse feces to produce energy has the added benefit of improving horse manure management, because feces left in stockpiles can cause environmental issues if not managed properly (Warren & Sweet, 2003).
The results of this study show that the use of inoculants decreased start-up time from 39 days to as low as 3.5 days, with Treatment 1 decreasing start-up time the most. Using an inoculant not only decreased start-up time, but also increased the duration of peak production of CH 4 , as well as initial CH 4 production. Interestingly, Treatment 2 decreased start-up time the least, but produced the highest amount of total CH 4 . It appears that the longer the start-up time, the more CH4 produced overall. This result was also observed in Treatment 3. The results from the three biogas samples (CH 4 at 45.1%, H 2 S at 37%, CO 2 at 14%, and other gases at 3.9%) are uncertain because the hand-held gas analyzer had not been recalibrated at the time of measurement; however, the values are within expected biogas composition (E. Mulder, personal communication, March 26, 2019).
CONCLUSIONS
According to this study, horse feces is a suitable feedstock for biogas production, and using an inoculant reduces start-up time and increases initial CH 4 production in bench scale biodigesters. In this experiment, start-up time is inversely related to the amount of inoculant used, while initial CH 4 production is positively related. Among the three inoculant treatments tested, Treatment 1 (2.25 kg) is preferred, because it had a shorter start-up time and showed a greater initial production of CH 4 . In a continuously fed biodigestion system the biodigester never stops producing, therefore reducing start-up time and improving initial CH 4 production is most important, whereas overall CH 4 production is less important. An inoculant of 2.25 kg should therefore be employed when using horse feces as a feedstock for producing biogas with a bench scale biodigester.
ACKNOWLEDGEMENTS
Thank you to Ike Edeogu, Alberta Agriculture & Forestry, for his guidance and support. Thank you also to Stefan Michalski and Ed Mulder of Lethbridge Biogas for giving me a tour of their facility and for analyzing my biogas samples. Thank you to Lynette Esak of Esak Consulting Ltd. for her advice and support. Thank you EQUS, Innisfail & District Agricultural Society, Central Alberta Co-op, and Home Depot for your financial support. Finally, thank you to my family for their continued support throughout my project.
REFERENCES
Hadin, S., & Eriksson, O. (2016). Horse manure as feedstock for anaerobic digestion. Waste Management, 56, 506-18. https://doi.org/10.1016/j.wasman.2016.06.023
Mulder, E. (2019, March 26). Personal Interview.
Warren, L., & Sweet, C. (2003). Caring for Alberta’s rural landscape: Manure and pasture management for horse owners. Alberta Agriculture, Food and Rural Development, Edmonton, AB.
Westendorf, M. (2019). Stall waste production and management. Livestock and Poultry Environmental Learning Community. Retrieved from https://lpelc.org/stall-waste-production-and-management/
BIBLIOGRAPHY
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Liam Christian
Liam is 14-years old and lives on a cattle ranch southwest of Red Deer, AB. He is homeschooled, which allows him time to pursue a variety of interests outside academics, such as hockey, camping, and fishing. In addition, Liam is an Intermediate member of the Knee Hill Valley 4-H Beef Club and runs his own business, Haywire Art and Design. Liam is passionate about agriculture and the environment, and recently won the junior category of Red Deer County’s Youth for Agriculture Award for his essay on land conservation. In addition, Liam was a finalist at the 4-H Canada Science Fair in Truro, NS where he was selected as a member of the 2019 4-H Canada Science Team. His current project idea came from his observation that, in Alberta, many small acreages with horses have large stockpiles of manure, but not the land base to utilize it.