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Ultrasonic and Thermal Pretreatments on Anaerobic Digestion of Petrochemical Sludge: Dewaterability and Degradation of PAHs.

Zhou J, Xu W, Wong JW, Yong X, Yan B, Zhang X, Jia H - PLoS ONE (2015)

Bottom Line: Moreover, capillary suction time (CST) of sludge increased after pretreatment, and then reduced after 20 days of anaerobic digestion, indicating that sludge dewaterability was greatly improved after anaerobic digestion.The decrease of protein and polysaccharide in the sludge could improve sludge dewaterability during petrochemical sludge anaerobic digestion.This study suggested that thermal pretreatment might be a promising enhancement method for petrochemical sludge solubilization, thus contributing to degradation of the PAHs, biogas production, and improvement of dewaterability during petrochemical sludge anaerobic digestion.

View Article: PubMed Central - PubMed

Affiliation: College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing, China.

ABSTRACT
Effects of different pretreatment methods on sludge dewaterability and polycyclic aromatic hydrocarbons (PAHs) degradation during petrochemical sludge anaerobic digestion were studied. Results showed that the total biogas production volume in the thermal pretreatment system was 4 and 5 times higher than that in the ultrasound pretreatment and in the control system, and the corresponding volatile solid removal efficiencies reached 28%, 15%, and 8%. Phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene removal rates reached 43.3%, 55.5%, 30.6%, 42.9%, and 41.7%, respectively, in the thermal pretreatment system, which were much higher than those in the ultrasound pretreatment and in the control system. Moreover, capillary suction time (CST) of sludge increased after pretreatment, and then reduced after 20 days of anaerobic digestion, indicating that sludge dewaterability was greatly improved after anaerobic digestion. The decrease of protein and polysaccharide in the sludge could improve sludge dewaterability during petrochemical sludge anaerobic digestion. This study suggested that thermal pretreatment might be a promising enhancement method for petrochemical sludge solubilization, thus contributing to degradation of the PAHs, biogas production, and improvement of dewaterability during petrochemical sludge anaerobic digestion.

No MeSH data available.


Related in: MedlinePlus

Variation of the content of PAHs during petrochemical sludge anaerobic digestion in the thermal pretreatment system.
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pone.0136162.g006: Variation of the content of PAHs during petrochemical sludge anaerobic digestion in the thermal pretreatment system.

Mentions: PAHs pollution is a limiting factor in the subsequent treatment of petrochemical sludge, so elucidating the variation of PAHs during the sludge anaerobic digestion is important. The contents of PAHs during the anaerobic digestion with different pretreatments are shown in Figs 4, 5 and 6. The contents of phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene were 4.4678, 1.775, 12.632, 18.876, and 18.644 mg/kg TS in the original petrochemical sludge. The content of PAHs in the petrochemical sludge decreased during the anaerobic digestion. It was found that phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene contents were 2.532, 1.126, 8.7655, 10.765, and 10.863 mg/Kg TS at the end of 20 days of anaerobic digestion in the thermal pretreatment system. The removal rates in the thermal pretreatment system reached 43.3%, 55.5%, 30.6%, 42.9%, and 41.7%, repectively, which were much higher than those in the ultrasound pretreatment (28.5%, 25.9%, 16.0%, 22.0%, 18.5%) and the control system (24.2%, 25.5%, 6.58%, 15.4%, 16.4%). This observation proves that pretreatment not only helps improve biogas production, but also increases the removal rate of PAHs. It has been reported increase in PAHs biodegradation is caused by either transfer of PAHs from sorption sites with low desorption rates to those with high ones or transformation of slow-sorption sites into fast-sorption ones through thermal pretreatment [30]. In addition, pretreatment could help break down the sludge microbial cells and facilitate the decomposition reaction, and make more intracellular organic matter (protein, polysaccharide, etc.) release to the liquid phase of sludge (S1–S4 Figs) and increase the SCOD, and the SCOD maybe as cometabolism substrate for the biodegradation of more PAHs in the digester [31–32]. This phenomenon was also found in other studies [33–35]. Bernal-Martinez et al. [33–34] found that the PAH removal rate was about 20%-70%, and ozonation pre-treatment could led to the enhancement of PAH biodegradability through the enhancement of bioavailability, and Barret et al. [35] found that the total removal rate of low molecular weight PAHs reached 25%. However, a large amount of PAHs still remain in the sludge after anaerobic digestion. To enhance the mass transfer, and thus, PAH removals, various operating conditions, such as increasing the temperature and adding surfactant or methanol, need to be tested in future studies [36].


Ultrasonic and Thermal Pretreatments on Anaerobic Digestion of Petrochemical Sludge: Dewaterability and Degradation of PAHs.

Zhou J, Xu W, Wong JW, Yong X, Yan B, Zhang X, Jia H - PLoS ONE (2015)

Variation of the content of PAHs during petrochemical sludge anaerobic digestion in the thermal pretreatment system.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4556613&req=5

pone.0136162.g006: Variation of the content of PAHs during petrochemical sludge anaerobic digestion in the thermal pretreatment system.
Mentions: PAHs pollution is a limiting factor in the subsequent treatment of petrochemical sludge, so elucidating the variation of PAHs during the sludge anaerobic digestion is important. The contents of PAHs during the anaerobic digestion with different pretreatments are shown in Figs 4, 5 and 6. The contents of phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene were 4.4678, 1.775, 12.632, 18.876, and 18.644 mg/kg TS in the original petrochemical sludge. The content of PAHs in the petrochemical sludge decreased during the anaerobic digestion. It was found that phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene contents were 2.532, 1.126, 8.7655, 10.765, and 10.863 mg/Kg TS at the end of 20 days of anaerobic digestion in the thermal pretreatment system. The removal rates in the thermal pretreatment system reached 43.3%, 55.5%, 30.6%, 42.9%, and 41.7%, repectively, which were much higher than those in the ultrasound pretreatment (28.5%, 25.9%, 16.0%, 22.0%, 18.5%) and the control system (24.2%, 25.5%, 6.58%, 15.4%, 16.4%). This observation proves that pretreatment not only helps improve biogas production, but also increases the removal rate of PAHs. It has been reported increase in PAHs biodegradation is caused by either transfer of PAHs from sorption sites with low desorption rates to those with high ones or transformation of slow-sorption sites into fast-sorption ones through thermal pretreatment [30]. In addition, pretreatment could help break down the sludge microbial cells and facilitate the decomposition reaction, and make more intracellular organic matter (protein, polysaccharide, etc.) release to the liquid phase of sludge (S1–S4 Figs) and increase the SCOD, and the SCOD maybe as cometabolism substrate for the biodegradation of more PAHs in the digester [31–32]. This phenomenon was also found in other studies [33–35]. Bernal-Martinez et al. [33–34] found that the PAH removal rate was about 20%-70%, and ozonation pre-treatment could led to the enhancement of PAH biodegradability through the enhancement of bioavailability, and Barret et al. [35] found that the total removal rate of low molecular weight PAHs reached 25%. However, a large amount of PAHs still remain in the sludge after anaerobic digestion. To enhance the mass transfer, and thus, PAH removals, various operating conditions, such as increasing the temperature and adding surfactant or methanol, need to be tested in future studies [36].

Bottom Line: Moreover, capillary suction time (CST) of sludge increased after pretreatment, and then reduced after 20 days of anaerobic digestion, indicating that sludge dewaterability was greatly improved after anaerobic digestion.The decrease of protein and polysaccharide in the sludge could improve sludge dewaterability during petrochemical sludge anaerobic digestion.This study suggested that thermal pretreatment might be a promising enhancement method for petrochemical sludge solubilization, thus contributing to degradation of the PAHs, biogas production, and improvement of dewaterability during petrochemical sludge anaerobic digestion.

View Article: PubMed Central - PubMed

Affiliation: College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing, China.

ABSTRACT
Effects of different pretreatment methods on sludge dewaterability and polycyclic aromatic hydrocarbons (PAHs) degradation during petrochemical sludge anaerobic digestion were studied. Results showed that the total biogas production volume in the thermal pretreatment system was 4 and 5 times higher than that in the ultrasound pretreatment and in the control system, and the corresponding volatile solid removal efficiencies reached 28%, 15%, and 8%. Phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene removal rates reached 43.3%, 55.5%, 30.6%, 42.9%, and 41.7%, respectively, in the thermal pretreatment system, which were much higher than those in the ultrasound pretreatment and in the control system. Moreover, capillary suction time (CST) of sludge increased after pretreatment, and then reduced after 20 days of anaerobic digestion, indicating that sludge dewaterability was greatly improved after anaerobic digestion. The decrease of protein and polysaccharide in the sludge could improve sludge dewaterability during petrochemical sludge anaerobic digestion. This study suggested that thermal pretreatment might be a promising enhancement method for petrochemical sludge solubilization, thus contributing to degradation of the PAHs, biogas production, and improvement of dewaterability during petrochemical sludge anaerobic digestion.

No MeSH data available.


Related in: MedlinePlus