Trace elements on influence of anaerobicfermentation in biogas projects

Abstract: The anaerobic digestion of biomass is a multi-stage process involving different types of microorganisms. Biogas projects employing anaerobic digestion and aiming at waste resource utilization are now becoming the most effective and promising techniques used for the treatment of urban waste，industrial wastewater, poultry excreta, and excess sludge from wastewater plants，and so on．In the process, in addition to macronutrients such as carbon (C), nitrogen (N), phosphorus (P), and sulphur (S), trace elements play a crucial role in the growth and metabolism of anaerobic microorganisms. Trace elements such as micro-nutrients are necessary for the metabolism of anaerobic microbes and important components in the anaerobic fermentation enzyme system, which can activate the activity of enzymes in methanogenic systems. Trace elements, such as iron (Fe), cobalt (Co), nickel (Ni), and so on, could promote the growth of the methanogens known to be crucial to the activity of enzymes in methanogenic systems, and to further speed up the biosynthesis of methane. The stimulation and antagonism of trace elements plays a very signi?cant role in the performance and stability of biogas digesters, which are operated with energy crops, animal excreta, crop residues, organic fraction of municipal solid wastes, and other types of organic waste. The deficiency or unavailability of these elements in biogas digesters is probably the ?rst reason of poor process efficiency (fermentation system operation instability and declining gas production) without any other obvious reason, despite proper management and control of other operational and environmental parameters. This paper reviews the biological effects of trace elements, methanogens demand for trace elements and the role of trace elements in methane synthesis on one hand, and the research status at home and abroad about the influence of trace elements such as iron (Fe), cobalt (Co), nickel (Ni), and so on, on anaerobic fermentation on the other hand. Trace elements Fe, Co, and Ni can improve the efficiency of conversion of volatile fatty acids (VFA) and eliminate the phenomenon of the accumulation of VFA. They also could antagonize the inhibitory effect induced by sodium ions, ammonia nitrogen, and increase the methane yield and keep the stability of anaerobic digestion process. Through review, the effects of trace elements on anaerobic fermentation may help to maintain the operational stability of the biogas project. Further, such knowledge is indispensable for a rational dosage of these metals to ensure maximum, high solid substrate conversion rates and to prevent disturbances in reactor performance using a minimum amount of metals. Additionally, understanding the potential environmental risks due to adding trace elements is currently insufficient.