Variation in humic and fulvic acids during thermal sludge treatment assessed by size fractionation, elementary analysis, and spectroscopic methods

Abstract

Thermal pretreatment can be applied to sludge anaerobic digestion or dewatering. To analyze the variation in humic substances during thermal sludge treatment, sludge humic and fulvic acids were extracted before and after 30-min thermal treatment at 180°C, and then their contents, molecular weight distributions, elementary compositions, and spectral characteristics were compared. The results showed that the total contents of humic and fulvic acids in the sludge almost remained constant during thermal treatment, but 35% of humic and fulvic acids were dissolved from the sludge solids. Moreover, both humic and fulvic acids were partly decomposed and 32% of humic acids were converted to fulvic acids. The median value of the molecular weights of humic acids decreased from 81 to 41 kDa and that of fulvic acids decreased from 15 to 2 kDa. Besides the reduction in molecular size, the chemical structures of humic and fulvic acids also exhibited a slight change, i.e. some oxygen functional groups disappeared and aromatic structures increased after thermal sludge treatment.

Keywords

sludge / thermal treatment / humic acids / fulvic acids

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Acknowledgements

This project was financially supported by the China Major Science and Technology Program for Water Pollution Control and Treatment (No. 2011ZX07302), the Natural Science Foundation of China (Grant No. 51008174), and the Joint Research Center of Urban Resource Recycling Technology of Graduate School at Shenzhen, Tsinghua University and Shenzhen Green Eco-Manufacturer High-Tech Co. Ltd. (Grant No. URRT2013005).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg