title: Bioaugmentation of anaerobic sludge digestion with iron-reducing bacteria: process and microbial responses to variations in hydraulic retention time.
abstract: Although anaerobic digestion (AD) is a widely used option to manage waste activated sludge (WAS), there are some drawbacks related to its slow reaction rate and low energy productivity. This study examined an anaerobic WAS digester, augmented with an iron-reducing microbial consortium, relative to changes in microbial community structure and process performance at decreasing hydraulic retention times (HRTs) of 20 to 10 days. The enhanced methanation performance (approximately 40 % increase in methane yield) by the bioaugmentation was sustained until the HRT was decreased to 12.5 days, under Fe(3+)-rich conditions (ferric oxyhydroxide, 20 mM Fe). Enhanced iron-reducing activity was evidenced by the increased Fe(2+) to total Fe ratio maintained above 50 % during the stable operational phases. A further decrease in HRT to 10 days resulted in a significant performance deterioration, along with a drop in the Fe(2+) to total Fe ratio to <35 %, after four turnovers of operation. Prevailing existence of putative iron-reducing bacteria (IRBs) was identified by denaturing gradient gel electrophoresis (DGGE), with Spirochaetaceae- and Thauera-related organisms being dominant members, and clear dominance shifts among them with respect to decrease in HRT were observed. Lowering HRT led to evident shifts in bacterial community structure likely associated with washout of IRBs, leading to decreases in iron respiration activity and AD performance at a lower HRT. The bacterial community structure shifted dynamically over phases, and the community transitions correlated well with the changes in process performance. Overall, the combined biostimulation and bioaugmentation investigated in this study proved effective for enhanced methane recovery from anaerobic WAS digestion, which suggests an interesting potential for high-rate AD.
authors.affiliation: School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan, 689-798, Republic of Korea.
authors.forename: Gahyun
authors.initials: G
authors.lastname: Baek
authors.affiliation: School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan, 689-798, Republic of Korea.
authors.forename: Jaai
authors.initials: J
authors.lastname: Kim
authors.affiliation: School of Environmental Science and Engineering, POSTECH, Pohang, Gyungbuk, 790-784, Republic of Korea.
authors.forename: Seung Gu
authors.initials: SG
authors.lastname: Shin
authors.affiliation: School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan, 689-798, Republic of Korea. cslee@unist.ac.kr.
authors.forename: Changsoo
authors.initials: C
authors.lastname: Lee
mesh_terms: D000693:Anaerobiosis; D001419:Bacteria / Q000378:metabolism*; D057919:Biological Oxygen Demand Analysis; D019149:Bioreactors; D058645:Denaturing Gradient Gel Electrophoresis; D007501:Iron / Q000378:metabolism*; D059013:Microbial Consortia / Q000502:physiology*; D012722:Sewage / Q000382:microbiology*; D013143:Spirochaetaceae / Q000378:metabolism; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000382:microbiology
chemical_list: D007501:Iron; D012722:Sewage; D062065:Wastewater
keywords: Anaerobic digestion; Bioaugmentation; Ferric oxyhydroxide; Iron-reducing bacteria; Microbial community structure