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Frontiers of Environmental Science & Engineering

Front. Environ. Sci. Eng.    2019, Vol. 13 Issue (3) : 43
Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline, thermal hydrolysis and ultrasonic pretreatments
Mengli Wang, Ruying Li(), Qing Zhao
School of Environmental Science and Engineering, Tianjin University, Tianjin 300350, China
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Sludge digestion is critical to control the spread of ARGs from wastewater to soil.

Fate of ARGs in three pretreatment-AD processes was investigated.

UP was more efficient for ARGs removal than AP and THP in pretreatment-AD process.

The total ARGs concentration showed significant correlation with 16S rRNA gene.

The bacteria carrying ARGs could be mainly affiliated with Proteobacteria.

Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.

Keywords Tetracycline resistance genes      Sulfonamide resistance genes      16S rRNA gene      Sludge pretreatment      Anaerobic sludge digestion     
This article is part of themed collection: Environmental Antibiotics and Antibiotic Resistance (Xin Yu, Hui Li & Virender K. Sharma)
Corresponding Authors: Ruying Li   
Issue Date: 18 June 2019
 Cite this article:   
Mengli Wang,Ruying Li,Qing Zhao. Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline, thermal hydrolysis and ultrasonic pretreatments[J]. Front. Environ. Sci. Eng., 2019, 13(3): 43.
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Mengli Wang
Ruying Li
Qing Zhao
SCOD (mg/L) 250 3630 6670 3480 350 1530 2950 1640 1245 1365 1730 1425
(10) (42) (85) (28) (14) (28) (42) (28) (64) (21) (57) (64)
SP (mg/L) 121.43 771.43 3150.00 1521.43 121.43 435.71 1621.43 721.43 978.57 1028.57 1157.14 1042.86
(2.15) (8.89) (12.73) (28.28) (4.24) (16.97) (28.55) (11.31) (0.00) (50.51) (10.10) (10.10)
VS/TS (%) 67.19 64.01 68.04 67.88 51.67 50.73 52.31 51.65 28.90 28.14 27.99 29.13
(0.01) (0.41) (0.73) (0.02) (0.36) (0.50) (0.01) (0.01) (0.07) (0.12) (0.09) (0.01)
Cumulative biogas (mL) 451.0 463.8 547.3 509.8
(3.9) (16.3) (2.1) (9.9)
Tab.1  Biogas production, VS contents and soluble organics concentration of various pretreatments and subsequent AD experiments a)
Fig.1  Variation of (a) absolute abundance and (b) relative abundance of total ARGs and the amount of 16S rRNA gene in RS and sludge samples in pretreatment and subsequent AD processes.
Fig.2  The absolute abundance of each subtype of ARGs and intI1 in RS and sludge samples after alkaline, thermal hydrolysis and ultrasonic pretreatments (tetB, tetM, tetO, tetQ and tetS for thermal hydrolysis were not detected).
intI1 Parameters Tet genes Sul genes
tetA tetB tetC tetG tetM tetO tetQ tetS sulI sulII
intI1 after pretreatments ra) 1.000** 0.903 0.982* 0.979* 0.960* 0.776 0.670 0.940 0.996** 0.828
pb) 0.000 0.097 0.018 0.021 0.040 0.224 0.330 0.060 0.004 0.172
intI1 after
AD experiments
r 0.953** 0.155 0.901** 0.935** -0.768* -0.664 -0.732* 0.633 0.979** 0.978**
p 0.000 0.714 0.002 0.001 0.026 0.073 0.039 0.092 0.000 0.000
Tab.2  Pearson correlation coefficients between the intI1 and ARGs
Fig.3  The absolute abundance of each subtype of ARGs and intI1 in feed sludge and digested sludge samples of AD process.
Fig.4  Principal Coordinates Analysis (PCoA) of Weighted UniFrac distances among the bacterial communities of the sludge samples during pretreatment and AD processes.
Fig.5  Taxonomic classification of bacterial DNA sequences from communities of pretreatment and AD processes at the (a) phylum level and (b) the class level.
Microbial community Total ARGs
ra) pb)
Predominant phyla Proteobacteria 0.731** 0.007
Bacteroidetes -0.698* 0.012
Firmicutes -0.652* 0.022
Predominant classes Betaproteobacteria 0.732** 0.007
Bacteroidia -0.667* 0.018
Clostridia -0.624* 0.030
Tab.3  Pearson correlation coefficients between the total ARGs and predominant phyla and classes
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