Free nitrous acid serving as a pretreatment method for alkaline fermentation to enhance short-chain fatty acid production from waste activated sludge.
Alkaline condition (especially pH 10) has been demonstrated to be a promising method for short-chain fatty acid (SCFA) production from waste activated sludge anaerobic fermentation, because it can effectively inhibit the activities of methanogens. However, due to the limit of sludge solubilization rate, long fermentation time is required but SCFA yield is still limited. This paper reports a new pretreatment method for alkaline fermentation, i.e., using free nitrous acid (FNA) to pretreat sludge for 2 d, by which the fermentation time is remarkably shortened and meanwhile the SCFA production is significantly enhanced. Experimental results showed the highest SCFA production of 370.1 mg COD/g VSS (volatile suspended solids) was achieved at 1.54 mg FNA/L pretreatment integration with 2 d of pH 10 fermentation, which was 4.7- and 1.5-fold of that in the blank (uncontrolled) and sole pH 10 systems, respectively. The total time of this integration system was only 4 d, whereas the corresponding time was 15 d in the blank and 8 d in the sole pH 10 systems. The mechanism study showed that compared with pH 10, FNA pretreatment accelerated disruption of both extracellular polymeric substances and cell envelope. After FNA pretreatment, pH 10 treatment (1 d) caused 38.0% higher substrate solubilization than the sole FNA, which indicated that FNA integration with pH 10 could cause positive synergy on sludge solubilization. It was also observed that this integration method benefited hydrolysis and acidification processes. Therefore, more SCFA was produced, but less fermentation time was required in the integrated system.
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China.
Jianwei
J
Zhao
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China; Advanced Water Management Centre, The University of Queensland, QLD 4072, Australia. Electronic address: w.dongbo@yahoo.com.
Dongbo
D
Wang
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China. Electronic address: xmli@hnu.edu.cn.
Xiaoming
X
Li
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China.
Qi
Q
Yang
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China.
Hongbo
H
Chen
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China.
Yu
Y
Zhong
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China.
Guangming
G
Zeng
D019149:Bioreactors; D005232:Fatty Acids, Volatile / Q000378:metabolism*; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009608:Nitrous Acid / Q000737:chemistry*; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology
D005232:Fatty Acids, Volatile; D012722:Sewage; D009608:Nitrous Acid
Alkaline fermentation; Cell envelope; Extracellular polymeric substances; Free nitrous acid; Short-chain fatty acid; Waste activated sludge