These methods, instrumentation and/or protocols apply to all data in this dataset:| Methods and protocols used in the collection of this data package |
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| Description: | Construction of anaerobic digesters:
For the pilot study, a sample commercial biodigester of floating tank design was used as a model to build three identical digesters, whereby 500 L polyethylene tanks were used as the anaerobic reactors, and 300 L tanks were used as biogas holders. On top of the biogas holder tanks, gas valves were fitted with a recycled rubber material for an airtight seal. A small hole (diameter = 4 cm) was also drilled on top of these gas holders for inserting the pH/temperature and biogas probes, which were temporarily sealed with an aluminum foil tape in between readings. All digesters were placed under a shed, with the closest building (feed storage house) approximately 50 meters away.
| | Instrument(s): | 3 x 500 L polyethylene tanks, 3 x 300 L polyethylene tanks, 3 x gas valves, aluminum foil tapes, recycled rubber material |
| | Description: | Feedstock preparation and anaerobic digestion operation:
Fresh PM was collected from the farm a day before the commencement of an AD batch. It was essential to use fresh manure because past studies have shown that volatile content greatly reduces as lag period increases between feedstock collection and AD (Hilborn, 2011; Hills & Ravishanker, 1984). The cow manure utilized as inoculate, was obtained from privately owned cattle, while the kitchen waste (KW) and newspaper waste (NPW) were acquired from a nearby household. The KW comprised of mostly fruit and vegetable peelings. Mechanical pre-treatment only was applied to both the NPW and KPW, whereby the NPW was shredded to approximately 2 cm2 pieces, while the KPW were mashed up until a slurry consistency was achieved.
Two batches of AD were carried out, with digesters 1, 2 and 3 occurring simultaneously in the first batch, and digesters 4, 5 and 6 in the second batch. Digesters 1 and 2 acted as mono-digesters, containing poultry manure only, digesters 3 and 4 contained PM and KW, while digester 5 and 6 contained PM with NPW.
Out of the total 500 L digester tank, 70% or 350 L was filled and used as an active reactor. 20% of this active volume was filled up with the inoculum consisting of cow slurry that had a cattle manure to water dilution ratio of 1:1, as utilized by previous studies (Boysan, Özer, Bakkaloğlu, & Börekçi, 2015; Carlini, Castellucci, & Moneti, 2015). This inoculum volume was only used in the first batch of AD. For the second batch, half of its inoculum were from cow slurry, while the other half was obtained from the effluent of the mono-digesters in the first batch. The remaining active volume (280 L) of the digester were filled up with the main substrates under investigation. Digesters 1 and 2 acted as mono-digesters and had PM occupying its total active volume. For digesters 3 and 4, the percentage composition of PM was 75% against 25% of KW, while for digesters 5 and 6, PM made up 90% of the active volume with NPW making up the remaining 10%. All feedstocks were diluted with a substrate to water ratio of 1:2 and weighed accordingly.
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| | Description: | Operational measurements:
Temperature and pH readings were recorded daily for the first two weeks then on a weekly basis for the rest of the digestion period. A Hanna HI8314 model pH meter was used, which was calibrated before every measurement accordingly, to the manufacturer’s guide (Hanna Instruments, 2001). However, the pH/temperature readings for the second batch of feedstocks were measured for only the first half of its digestion period due to technical hitches.
The biogas content was measured with a Geotech Biogas 5000 analyzer daily, unless the occurrence of bad weather such as a tropical cyclone or heavy rain. The biogas volume was measured with markings on the biogas holders, with smallest divisions and an uncertainty of 10 L. As the biogas was collected and the tank rose, the readings were noted from the biogas holders and the gas was collected in a biogas storage bag.
The C/N ratio of the different feedstocks were computed using a comprehensive online calculator (Greer, 2021), according to the mass of each substrate component. The calculator was created by compiling other reliable and scientific literature, however, the C/N values generated may not be the exact amount as the results are based on average figures. Previous researchers that have measured C/N ratio utilized various elemental analysers such as the Vario MICRO Cube (Duan et al., 2018) or the LECO analyser (Farrow, 2016), while others measured the elements with an inductively coupled plasma mass spectrometry (Dahunsi, Osueke, Olayanju, & Lawal, 2019). However, employing such methods were out of the scope of the present study.
| | Instrument(s): | Hanna HI8314 model pH meter, Geotech Biogas 5000 analyzer, Online Carbon-to-nitrogen ratio calculator, graduated floater tank, biogas storage bag |
| | Description: | Physical Analysis:
Volatile solids suspension (VSS) test was carried for samples collected from all the digesters at the beginning and at the end of the digestion periods, i.e., two samples for each digester. The VSS test was conducted according to the American Public Health Association (APHA) standard methods (U.S. Environmental Protection Agency, 2001) as carried out by many researchers (de Oliveira Paranhos, Adarme, Barreto, de Queiroz Silva, & de Aquino, 2020; Duan et al., 2018; Ribeiro et al., 2018).
| | Instrument(s): | 12 x crucibles, drying oven, muffle furnace, desiccator, electronic weighing scale |
| | Description: | Full-scale design:
The results obtained from the pilot study were then used to design a full-scale anaerobic digestion system. The calculations and steps utilized to determine the potential biogas production and electricity usage were obtained from Anaerobic Digestion of Biowaste in Developing Countries by (Vögeli, Lohri, Gallardo, Diener, & Zurbrügg, 2014). Simple payback (SPB) time and levelized cost of energy (LCOE) approaches were used for the economic analysis of the proposed full-scale project to indicate its financial viability.
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