Recovering humic substances from the dewatering effluent of thermally treated sludge and its performance as an organic fertilizer

Abstract

The biologic treatment of the dewatering effluent from thermally treated sludge is difficult due to the high concentration of refractory humic substances. On the other hand, humic substances are an important source of organic fertilizer. In this study, a novel process using ferric coagulant was developed to recover humic substances from dewatering effluent for use as an organic fertilizer. When ferric coagulant was applied to raw dewatering effluent, up to 70% of humic substances were enmeshed by hydrolyzed ferric ions at an optimum pH of 4.5. The proper mass ratio of iron ions to humic substances was 0.6. In the recovered material, humic substances accounted for 24.2% of the total dry solids, and the amount of phosphorus (equivalent phosphorus pentoxide) was 6.2%. Heavy metals and other components all met the legal requirements for organic fertilizer. When the recovered material was applied to soybeans, the germination and growth of the seeds was significantly improved.

Keywords

sewage sludge / humic substances / recovery / phosphorus / fertilizer

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Acknowledgements

Financial support for this project was obtained from the China Major Science and Technology Program for Water Pollution Control and Treatment (No. 2011ZX07302), the Natural Science Foundation of China (Grant No. 51478239), and Shenzhen Science and Technology Research and Development Fund (No. JCYJ20150320154458994).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg