Abstract
Anaerobic co-digestion provides a promising solution for converting inexpensive carbon from wastes to biogenic methane. We used microalgae (Nannochloropsis oculata) with cow manure and sludge to produce a better quantity and quality of biogas. To further improve the gas production, microalgae were pretreated with ultrasonication, hot water, and a combination of both. Interestingly, the results showed that the pretreatment of microalgae decreased biogas production by 5 to 30%. The no-pretreatment runs produced a maximum of 118 L of biogas. The relative content of biogenic methane was higher in the pretreated feedstock (48 to 52%) in comparison with the no-pretreatment runs (44%). The conversion of volatile suspended solids present in the feedstock to total biogenic methane production was highest in hot-water-treated runs. The carbon content in the gas produced by the pretreated microalgae peaked (38%) in the middle of the experiment (i.e., at 45 days), whereas for no-pretreatment runs, the content remained constant from the start to the middle and declined (from 36 to 34%) at the end of the experiment (i.e., at 90 days). We also report the chemical structure of microalgae with and without pretreatments.
Highlights
Biogenic methane is a carbon-based gas primarily resulting from biological reactions by microorganisms taking place in the absence of oxygen through a process called anaerobic digestion.Anaerobic digestion takes place when bacteria convert carbon-rich biomass to different organic products, out of which the major product is a mixture of carbon dioxide and methane, regarded as biogas
The effects of pretreatment on the structural composition of microalgae were determined using the analytical protocols developed at the National Renewable Energy Laboratory (NREL) of the US
Of the components of cow manure and microalgae, carbon was present in the maximum quantity, with sulfur as the minimum
Summary
Biogenic methane is a carbon-based gas primarily resulting from biological reactions by microorganisms taking place in the absence of oxygen through a process called anaerobic digestion. Due to the lesser content of biogenic methane or poor quality of resulting biogas, many researchers have attempted to mix various feedstocks [4]. In a recent study [14], a thermal-ultrasonication pretreatment of manure helped increase the production of biogenic methane by 41%. This is because physical pretreatments trigger cell lysis and overcome the hindrances of lignin and cellulose [15]. The pretreatment of feedstock helps in improving hydrolysis and methanogenesis during the digestion process, resulting in an increase of biodegradability and enhancement of biogas production [16]. This study will help in understanding the chemical changes in the feedstock and products due to pretreatments
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