Abstract
Fish offal and other high protein substrates are generally not suitable for anaerobic digestion because of the high levels of ammonia produced as a result of their biodegradation. In order to efficiently use these types of substrates to produce methane, co-digestion is used to balance the amounts of carbon and nitrogen in the feedstock. In this experiment an optimization procedure for maximizing the methane potential of fish offal, using river tamarind as the co-substrates was developed. Our experimental design tested the effects of substrate to substrate mixtures, as well as overall substrate to inoculum combinations, on the methane potentials. This was performed using batch style biochemical methane potential assays, which employed a methodology developed in our laboratory. The optimum of the 25 combinations tested was 50% fish offal to 50% river tamarind at a substrate to inoculum ratio of 0.03, with a specific methane yield of 144 ± 6 NmL/gFM (330 ± 14 NmL/goDM). This gave much improvement when compared with the fish offal alone, which reached 63 ± 4 NmL/gFM (317 ± 20 NmL/goDM) at maximum. These results indicate that with the correct mixture, rivertamarind is a suitable co-substrate for anaerobic co-digestion of fish offal.
Highlights
Anaerobic digestion is the biochemical process by which bioorganic degradable material, through a series of biochemical reactions mediated by a consortium of micro-organisms, is converted into biogas [1,2]
Co-digestion of substrates aids in nutrient balance and can increase the overall methane yield or rate of methane production from a bioreactor
A total of 25 substrate combinations were tested and it was determined that the river tamarind alone had the potential to give a high yield of methane (155 ± 2 NmL/gFM; 355 ± 5 NmL/goDM)
Summary
Anaerobic digestion is the biochemical process by which bioorganic degradable material, through a series of biochemical reactions mediated by a consortium of micro-organisms, is converted into biogas [1,2]. Anaerobic co-digestion is the mixing of two or more feedstocks in the anaerobic bioreactor in order to improve the efficiency of the anaerobic digestion process [3] The advantage of this is that the drawbacks of single substrate digestion, such as unfavorable carbon–nitrogen (C/N) ratios, high ammonia content, high volatile acid production, or even inadequate amounts of a particular substrate can be overcome [1,3,4]. A highly variable range of C/N ratios has been reported as suitable for stable bioreactor performance, including ratios of 20 and 70, and lower values, in the 6–9 range
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