Application of hydrothermal oxidation and alkaline hydrothermal gasification for the treatment of sewage sludge and pharmaceutical wastewaters

Abstract

Hydrothermal treatment involving the oxidation and gasification of sewage sludge and pharmaceutical wastewater samples has been carried out in batch autoclave reactor. The efficiency of the oxidation processes measured in terms of total organic carbon (TOC) and total solids (TS) removal showed that effective sample treatments were achieved at moderately low temperatures of 350–450°C. More than 90% TOC removal was achieved in all samples, with samples with lower organic contents reaching above 99% TOC removal. A maximum of 78% TS removal was achieved due to the high initial ash contents of the samples. Alkaline hydrothermal gasification of the samples with very high TOC contents yielded gas products rich in hydrogen gas and methane. Due to high concentrations of acetonitrile in some of the samples, the yields of methane were high, giving calorific values of the product gases of up to 35 MJ/m³ in some samples; however, the gasification process resulted in lower TOC destruction compared to the oxidation process.

Keywords:

• hydrothermal
• sewage sludge
• wastewaters

Acknowledgements

The authors are grateful for the financial support for this work by the UK Engineering and Physical Sciences Research Council under EPSRC Grant EP/D053110/1.