Abstract
Ammonia concentration is one of the key factors influencing the methanogenic community composition and dominant methanogenic pathway in anaerobic digesters. This study adopted a radiolabelling technique using [2-14C] acetate to investigate the relationship between total ammonia nitrogen (TAN) and the methanogenic pathway. The radiolabelling experiments determined the ratio of 14CO2 and 14CH4 in the biogas which was used to quantitatively determine the percentage of CH4 derived from acetoclastic and syntrophic acetate oxidation routes, respectively.This technique was performed on a selection of mesophilic digesters representing samples of low to high TAN concentrations (0.2–11.1gkg−1 wet weight). In high TAN digesters, the ratio between 14CO2 and 14CH4 was in the range 2.1–3.0; indicating 68–75% of methane was produced via the hydrogenotrophic route; whereas in low ammonia samples the ratio was 0.1–0.3, indicating 9–23% of methane was produced by the hydrogenotrophic route. These findings have been confirmed further by phylogenetic studies.
Highlights
Anaerobic digestion (AD) has gained popularity over the last decade as a waste management strategy with the added benefit of producing generation renewable energy in the form of methane (Mata-Alvarez, 2003)
It has been reported on a number of occasions and at different scales of operation that a characteristic build-up of volatile fatty acids (VFA) can occur when digesting food waste which can lead to process failure (Banks et al, 2008; Banks and Zhang, 2010; Neiva Correia et al, 2008)
The determination of the dominant acetate oxidation pathway is based on measuring the production of 14CH4 and 14CO2 from acetate radiolabelled on the methyl group (C-2 labelled)
Summary
Anaerobic digestion (AD) has gained popularity over the last decade as a waste management strategy with the added benefit of producing generation renewable energy in the form of methane (Mata-Alvarez, 2003). A wide range of prior research shows, that substrates including food waste and other farm waste streams which have high nitrogen concentration are prone to unstable digestion This is due to the inhibitory effect of free ammonia nitrogen (FAN) released during protein hydrolysis and the breakdown of urea in animal manure (Breure et al, 1986; Kayhanian, 1999; McCarty, 1964; Yenigün and Demirel, 2013). It has been reported on a number of occasions and at different scales of operation that a characteristic build-up of volatile fatty acids (VFA) can occur when digesting food waste which can lead to process failure (Banks et al, 2008; Banks and Zhang, 2010; Neiva Correia et al, 2008)
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