Enhanced volatile fatty acids (VFAs) production in a thermophilic fermenter with stepwise pH increase - Investigation on dissolved organic matter transformation and microbial community shift.
In this study, a mixture of primary and wasted activated sludge was fermented in a semi-continuous reactor aiming for enhanced volatile fatty acids (VFAs) production. The reactor was subjected to a stepwise pH increase from 7 to 10 during approximately 130 days of operation. The result revealed that the maximum acidification was obtained at pH 8.9 (21%) resulting in the maximum production of VFAs (423.22 ± 25.49 mg COD/g VSS), while the maximum hydrolysis efficiency was observed at pH 9.9 (42%). The high pH was effective in releasing dissolved organic matter (DOM) including protein, carbohydrate, building blocks and low molecular weight (LMW) neutrals. More LMW DOMs were released than high molecular weight (HMW) DOMs fractions at higher pH. pH 9.9 favored hydrolysis of HMW DOMs while it did not enhance the acidogenesis of LMW DOMs. The microbial community analysis showed that the relative abundance of phyla Actinobacteria and Proteobacteria increased with the increased pH, which may lead to the maximum hydrolysis at pH 9.9. At pH 8.9, class Clostridia (59.16%) was the most dominant population where the maximum acidification (21%) was obtained. This suggested that the dominance of Clostridia was highly related to acidification extent. The relative abundance of Euryarchaeota decreased significantly from 58% to 2% with increased pH.
Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026, People's Republic of China.
Yun
Y
Chen
Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore.
Xie
X
Jiang
Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore.
Keke
K
Xiao
Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore.
Nan
N
Shen
CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026, People's Republic of China.
Raymond J
RJ
Zeng
Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore, 637141, Singapore; School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore. Electronic address: ZhouYan@ntu.edu.sg.
Yan
Y
Zhou
D019149:Bioreactors; D005232:Fatty Acids, Volatile / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D012722:Sewage / Q000737:chemistry
D005232:Fatty Acids, Volatile; D012722:Sewage
Dissolved organic matter; Microbial community; Progressive pH increase; VFAs production