Significance of mineral elements characterization for anaerobic digestion substrates: The case of avocado oil processing by-products

Mineral elements effects on anaerobic biogas production (AD) were reviewed and inferences made for avocado oil processing by-products. Mineral elements in these by-products were measured using ICP-OES methods. It was noted that there is no consensus among researchers on absolute mineral requirements for optimal digester performance and only ranges stating lowest and highest mineral requirements could be found from different studies. These ranges vary for each element depending on analytical methods used, substrate type and digester operating conditions. Mineral elements exceeding certain limits in digesters can be toxic to the AD microorganisms, a situation which negatively affect the efficiency and stability of substrate biodegradation to biogas. Other mineral elements, such as arsenic, despite their concentration in the digester, are naturally toxic to microorganisms. These toxic minerals must therefore be removed or detoxified if detected in substrates. Researchers choose to perform substrate mineral elemental analysis depending on their pre-existing knowledge of the substrate, recommendations from standards adopted in the research and objective of their studies. The bioavailability of minerals in substrates require further investigation to accurately correlate mineral elements concentration in avocado oil processing by-products by ICP-EOS methods to the expected AD performance when using these substrates. The current study revealed mineral elements related to avocado oil processing by-products that may need possible attention for optimal biodegradation of these substrates to biogas.