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An evaluation of solar thermal heating to support a freeze-thaw anaerobic digestion system for human waste treatment in subarctic environments
Citation:
Krause, M., N. Detwiler, A. Schwarber, AND M. McCauley. An evaluation of solar thermal heating to support a freeze-thaw anaerobic digestion system for human waste treatment in subarctic environments. Renewable Energy. Elsevier B.V., Amsterdam, Netherlands, 198:618-625, (2022). https://doi.org/10.1016/j.renene.2022.08.055
Impact/Purpose:
In Alaskan villages, freezing temperatures and remote locations issues make installation and operation of typical wastewater treatment systems impossible. This manuscript investigates the technical feasibility of anaerobic digestion of synthetic human feces after freezing. Multiple freezing conditions and incubation temperatures were investigated. Following positive results (methane generation) from the laboratory experiments, thermal modeling was conducted to estimate heat energy demands for hypothetical anaerobic digesters located in several Alaskan towns/villages. Solar radiation and air temperature data from other sources were used to perform the modeling assessment. Academic audiences would be interested to understand the resiliency of anaerobic microbes. Government entities or public groups may be interested in the prospect of anaerobic digestion in cold climates but many technical and social challenges for implementing a system need to be further addressed.
Description:
Remote locations, small communities, and extreme weather conditions prevent the installation or operation of piped sanitary sewers in many Alaska Native Villages (ANVs). Research was conducted to understand the technical feasibility of installing anaerobic digesters (ADs) in remote ANVs which would be heated by solar thermal collectors. Biochemical methane potential (BMP) assays were conducted to understand the effect of freezing and thawing on methanogenic activity of synthetic human feces. To encompass the range of expected winter temperatures, BMPs were frozen at -20 or -80 °C for 7 days and then incubated at psychrophilic (20 °C) or mesophilic (37 °C) conditions. Psychrophilic BMPs frozen at -20 or -80 °C yielded 453 ± 119 and 662 ± 77 mL CH4/g volatile solids (VS), respectively. Mesophilic BMPs frozen at -20 or -80 °C yielded 337 ± 59 and 495 ± 63 mL CH4/g VS, respectively. Freezing caused a lag period, but ultimately many of the assays reached yields similar to or even greater than the baseline, unfrozen psychrophilic and mesophilic assays (575 ± 96 and 596 mL ± 98 CH4/g VS, respectively). Monthly solar radiation and air temperature data were then used to identify the number of solar thermal collectors that would be required to supplement heat energy to operate the ADs in several subarctic and one arctic location. It was determined that Alaskan subarctic locations receive enough solar thermal energy in spring and summer months to support seasonally operated, psychrophilic ADs. The results of the research posit a new waste management scenario where human waste is collected in winter months, allowed to freeze, and then thawed and digested in the spring and summer months.
URLs/Downloads:
DOI: An evaluation of solar thermal heating to support a freeze-thaw anaerobic digestion system for human waste treatment in subarctic environments
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