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Abstract
The unsafe disposal of wastewater and sludge in different areas of developing countries results in significant environmental pollution, particularly for groundwater, thus increasing the risk of waterborne diseases spreading. In this work, a two-phase anaerobic digestion process for post-treatment of partially acidified sewage sludge was investigated to evaluate its feasibility as a safe sludge disposal system. Pilot tests showed that an effective sludge stabilization can be achieved (total volatile solids content<65%, organic acid concentration<200 mg/L at flow rate=50 L/d and hydraulic residence time=18 d) as well as a relative low faecal coliform density (<1000 most probable number per g total solids), showing that land application of the sludge without restrictions is possible according to US Environmental Protection Agency criteria for safe sludge disposal. A biogas production as high as 390 L/d with a 60% methane content by volume was achieved, showing that energy production from biogas may be achieved as well.
Acknowledgements
The authors would like to thank the Federal Ministry of Education and Research (BMBF) as well as the European Union for the funding received through the ERASMUS exchange programme which allowed Dr Luca Passio to work for six months at the Karlsruhe Institute of Technology for his Master's thesis. Moreover, Dr Luca Passio would like to thank Dr Susanne Fach for her valuable advice and Dr Antonio Bottini for his technical support.