Effect of ferrous chloride on biogas production and enzymatic activities during anaerobic fermentation of cow dung and Phragmites straw

Abstract

The effect of ferrous (added as FeCl2) on the anaerobic co-digestion of Phragmites straw and cow dung was studied by investigating the biogas properties, pH values, organic matter degradation (COD) and enzyme activities (cellulase, protease and dehydrogenase) at different stages of mesophilic fermentation. The results showed that Fe(2+) addition increased the cumulative biogas yields by 18.1 % by extending the peak period with high daily biogas yields. Meanwhile, the methane (CH4) contents in the Fe(2+) added groups were generally higher than the control group before the 15th day. The pH values were not significantly impacted by Fe(2+) concentrations during the fermentation process. The COD concentrations, cellulase, protease and dehydrogenase activities varied with the added Fe(2+) concentrations and the stages of the fermentation process. At the beginning stage of fermentation (4th day), Fe(2+) addition increased the biogas production by improving the cellulase and dehydrogenase activities which caused a decline in COD. At the peak stage of fermentation (8th day), Fe(2+) addition enhanced the cellulase and protease activities, and resulted in lower COD contents than the control group. When the biogas yields decreased again (13th day), the COD contents varied similar with the protease and dehydrogenase activities, whilst cellulase activities were not sensitive to Fe(2+) concentrations. At the end of fermentation (26th day), Fe(2+) addition decreased the cellulase activities, led to lower COD contents and finally resulted the lower biogas yields than the control group. Taking the whole fermentation process into account, the promoting effect of Fe(2+) addition on biogas yields was mainly attributed to the extension of the gas production peak stage and the improvement of cellulase activities.

A Preliminary Study of the Effect of Bioavailable Fe and Co on the Anaerobic Digestion of Rice Straw

“…An analysis of the enzymatic activity would also offer an elegant way to better evaluate the effects of TE addition on the activity of the microbial enzymes, including cellulases that are responsible for the hydrolysis of the cellulose contained in the rice straw [41]. Zhang et al [42] and Tian et al [43] showed a positive effect of Fe and Ni in enhancing the biogas production yields from cow dung and Phragmites straw, respectively, ascribing this also to a stimulation of the cellulase activity. Ni has also been reported to be an essential co-factor for enzymes involved in both the acetoclastic and hydrogenotrophic pathways for methanogenesis [44].…”

Hydrogen sulfide removal via appropriate metal ions dosing in anaerobic digestion

“…Iron also improved overall microbial activity, suggested by the increasing CO 2 generation with the increasing Fe concentration. Combined with above results on methane production, it is possible that Fe addition stimulated substrate hydrolysis of lignocellulosic biomass , and the hydrolysate further provided substrates for both CO 2 and methane generation.…”

Biodegradability during Anaerobic Fermentation Process Impacted by Heavy Metals

“…The COD were generally lower in Fe-added groups than in the control group [46]. Fe addition induced a stable and excellent COD conversion rate suggesting a more efficient utilization of soluble organic components in the fermenter that consequently improves biogas yields [47].…”