Effects of Iron Powder Addition and Thermal Hydrolysis on Methane Production and the Archaeal Community during the Anaerobic Digestion of Sludge

Abstract

The conventional anaerobic digestion of sludge has the disadvantages of long digestion time and low methane production. Pretreatment is often used to mitigate these problems. In this study, three pretreatment methods, namely, the addition of iron powder, high-temperature thermal hydrolysis, and a combination of these methods, were compared for application with conventional continuous anaerobic digestion reactors. The results showed that pretreatment improved methane yield by 18.2–22.9%, compared to the control reactor (conventional anaerobic digestion). Moreover, it was recognized that the archaeal community in the sludge underwent significant changes after pretreatment. Specifically, the addition of iron powder reduced the diversity in the archaeal community, but increased the abundance of hydrogenotrophic methanogens without changing the community composition. Thermal hydrolysis at high temperatures had the reverse effect, as it increased the diversity of the archaeal community but inhibited the growth of acetoclastic methanogens. In the case of the combined pretreatment, the thermal hydrolysis had a dominant influence on the archaeal community. By comparing the changes in functional gene content, it was found that the functional abundance of the archaeal community in the transport and metabolism of carbohydrates, lipids, and amino acids was higher after pretreatment than in the control group.

Effects of Iron, Lime, and Porous Ceramic Powder Additives on Methane Production from Brewer’s Spent Grain in the Anaerobic Digestion Process

“…As a result, the methane yield increased from 248 to 300 mL × g VS −1 (an increase of 21%), while hydrolysis did not change (0.083 d −1 ) [37]. Cao et al [38] tested the effects of zero valency iron powder (Fe 0 ) at a dosage of 30 mg × g VS −1 on the AD of sewage sludge. Fe 0 addition resulted in a small reduction in the diversity of the archaeal community that decreased from 1534 OTUs to 1493 OTUs, and a significant increase in the content of hydrogenotrophic methanogens (by 15.4%) was observed.…”

“…Fe 0 addition resulted in a small reduction in the diversity of the archaeal community that decreased from 1534 OTUs to 1493 OTUs, and a significant increase in the content of hydrogenotrophic methanogens (by 15.4%) was observed. Increased abundance of hydrogenotrophic methanogens helped to reduce hydrogen partial pressure, thereby increasing acetic acid content and methane production by 18.2% [38]. It is worth noting that hydrogenotrophic methanogens are a group of slow-growing microorganisms that convert dissolved CO 2 and H 2 (CO 2 + 4H 2 →CH 4 + 2H 2 O), which during normal AD are responsible for around 1/3 of total methane production [39].…”