Regular articleA novel parameter for evaluating the influence of iron oxide on the methanogenic process

- A novel parameter (R) was defined to evaluate the goethite influence on methanogenesis.
- R represented the ratio of available surface site of iron oxide to the acetate in reactor.
- Goethite facilitates methanogenesis at −3 to 0 and suppressed it at 1.7-3 of R values.
- R can also be used to evaluate and predict the influence of other iron oxides on methanogenesis.

The influence of iron oxide on anaerobic methanogenesis has been researched for several decades. Both promotion and inhibition effects have been reported under various conditions. In the current study, the effect of goethite on the methanogenesis of acetate was investigated in batch experiment for a period of 105 days. With the increasing dosages of goethite from 0.45 to 90 mM, the methane yield increased from 0.72 to 0.91 mM-CH4 mM-Ace−1, which was significantly higher than the methane yield of the control without goethite supplementation as 0.56-0.64 mM-CH4 mM-Ace−1, indicating that the added goethite had facilitated methanogenesis. The solid in culture was analyzed by electron microscopy. The tight binding of goethite and microbial cells indicated that the promotion of methanogenesis might be caused by the enhancement of syntrophic effect of methanogenic microorganisms through the electron transfer mediated by the (semi)conduct iron oxide goethite. Based on the analysis of the data from various reports, a novel parameter of iron influence factor (R) was proposed, which represented the ratio of available surface site of iron oxide to the concentration of acetate in reactor, and showed that the methanogenesis was facilitated at goethite lgR values of −3 to 0 and suppressed at goethite lgR values of 1.7-3. This study provided novel insights for the evaluation of iron oxides influence on methanogenesis in anaerobic digestion.