ReviewImpacts of trace element supplementation on the performance of anaerobic digestion process: A critical review
Introduction
Anaerobic digestion has been one of the most yearning and promising biological technologies for treating a wide variety of organic wastes with high treatment efficiency. This is because it enables by-production of biogas as a potential renewable energy source while managing the waste sustainably at the same time. These advantages not only have greatly encouraged the practice of anaerobic digestion worldwide, but also attracted the attention of researchers to further improve the digestion efficiency with less problems encountered during the process. This is because anaerobic digestion is a sensitive multi-stages process (hydrolysis, acidogenesis, acetogenesis and methanogenesis) which depends on susceptible microorganisms to carry out the digestion job (De Vrieze et al., 2012). One of the influential factors is the presence of trace elements in the digestion system which mainly function as the micronutrients. The trace elements must be adequate for supporting the metabolism of microorganisms in order to maintain the effective digestion process. Otherwise, the performance of anaerobic digestion will significantly deteriorate (Osuna et al., 2003a).
Besides basic macronutrients such as carbon (C), nitrogen (N), phosphorus (P) and sulphur (S), the anaerobes also require the growing factor of trace elements at relatively lower concentration. This aspect has been highlighted by researchers and many studies have been carried out to demonstrate the importance of trace elements in anaerobic digestion. For example, the strategy of supplementing iron (Fe), nickel (Ni), cobalt (Co), molybdenum (Mo) etc. in the digestion system had successfully manifested a promotion in the anaerobic digestion performance with different substrates including maize silage (Pobeheim et al., 2010), wheat stillage (Schmidt et al., 2014), food waste (Wei et al., 2014), and so on. In addition, Fermoso et al. (2009) indicated the fundamental role of trace elements by summarizing the knowledge of interactions between trace elements and microbe cells. Due to the natural characteristics of low trace element content, special attention had been paid by Demirel and Scherer (2011) on the solid organic substrates such as energy crops, crop residues, and organic fraction of municipal solid waste (OFMSW) by reviewing trace element requirements in their anaerobic digester.
The interest on anaerobic digestion for biogas production is continuously growing nowadays. Therefore, more substantial and relevant knowledge should be well documented for future references. However, despite the vital aspect of trace elements in the anaerobic digestion system that have been well established, the detail information on their roles and impacts are still scattered in the literature. Hence, this review paper will firstly introduce the roles of trace elements in anaerobic digestion, especially from the aspect of methanogenesis for the fundamental understandings and justifications. Furthermore, this work aims at compiling the information on impacts of supplementing trace elements on the performance of anaerobic digestion process based on the researches which had been done previously and discuss them critically.
Section snippets
Trace element composition of methanogens
Methanogenesis is the final and most critical stage of anaerobic digestion process ultimately produces biogas, and it is completed by the strict group of anaerobes called methanogens under the Archaea domain. Besides of the major elements i.e. C, H, N, P and S, microbes also highly depend on the content of trace elements to survive and carry out various cell metabolisms. Therefore, it is important to have an anaerobic digestion system with sufficient level of trace elements to ensure the
Iron (Fe)
Among various of trace elements, Fe is the most commonly studied element for the supplementation impact on the anaerobic digestion due to its high requirement based on the fundamental knowledge. First and foremost, Park and Novak (2013) demonstrated the direct addition of Fe (III) at 1.25% (by weight) into a sewage sludge digestion system to remove the odour-causing byproducts. They observed that the problematic and corrosive hydrogen sulphide (H2S) which had been reduced by more than 65%. H2S
Impacts of multiple trace elements supplementation on anaerobic digestion performance
By comparing the impact levels of single trace element addition, the synergism of multiple trace elements supplementation can be observed with a better performance of anaerobic digestion (Facchin et al., 2013, Zhang et al., 2015b). Besides that, the collaborative supplementation might be needed, otherwise the digestion performance could be affected negatively. This situation has been reported by Moestedt et al. (2016) in which Co addition alone caused a higher acetogenesis rate than
Crucial consideration: Trace element bioavailability
The trace elements characterization is the first screening procedure to analyze the nutrients fulfilment in the digester. For this, most of the studies had characterized the substrates in term of total metal concentration (Evranos and Demirel, 2015, Qiang et al., 2013, Zhang and Jahng, 2012). However, the total element contents can no longer be representative as the bioavailable fraction which can be utilized along the anaerobic digestion process. This is because there are complex interactions
Research outlook
The global effort to strengthen the energy security requires the support of the relevant scientific researches. Same goes to the anaerobic digestion, in order to further mature this promising renewable energy production technology. In this paper, the aspect of trace elements is discussed and regarded. The role of trace elements in anaerobic digestion had been well understood for the stages of acetogenesis and methanogenesis, but not for the hydrolysis and acidogenesis process. For fundamental
Conclusions
The measure of trace elements supplementation is effective to improve the performance of anaerobic digestion process by applying necessary (sub)optimum dosage. The positive impacts include the longer term digester stability with greater organic matter degradation, low VFA level, and higher biogas production. However, these impacts are uncertain, but can be affected by many factors. Fe, Ni, and Co are the most desirable trace elements. Single and multiple trace element(s) addition have presented
Acknowledgements
The authors gratefully acknowledge Universiti Sains Malaysia’s Research University Individual (RUI) Grant (1001/PTEKIND/814239) for the financial support.
References (75)
- et al.
Trace element requirements for stable food waste digestion at elevated ammonia concentrations
Bioresour. Technol.
(2012) - et al.
Effect of additives on process stability of mesophilic anaerobic monodigestion of pig slaughterhouse waste
Bioresour. Technol.
(2012) - et al.
High-rate iron-rich activated sludge as stabilizing agent for the anaerobic digestion of kitchen waste
Water Res.
(2013) - et al.
Methanosarcina: the rediscovered methanogen for heavy duty biomethanation
Bioresour. Technol.
(2012) - et al.
Trace element requirements of agricultural biogas digesters during biological conversion of renewable biomass to methane
Biomass Bioenergy
(2011) - et al.
Effect of trace element supplementation on the mesophilic anaerobic digestion of foodwaste in batch trials: the influence of inoculum origin
Biochem. Eng. J.
(2013) - et al.
Metal supplementation to UASB bioreactors: from cell-metal interactions to full-scale application
Sci. Total Environ.
(2009) The chemical biology of methanogenesis
Planet. Space Sci.
(2010)- et al.
Effect of cobalt on the anaerobic degradation of methanol
J. Ferment. Bioeng.
(1993) - et al.
Bioavailability of cobalt and nickel during anaerobic digestion of sulfur-rich stillage for biogas formation
Appl. Energy
(2013)