Lettinga, G. and Hulshoff Pol, L.W. (1991) UASB process design for various types of wastewater. Water Sci. Technol. 24(8), 87-107.

Mahmoud, N., 2002. Anaerobic pre-treatment of sewage under low temperature (15 oC) conditions in an integrated UASB-digester system PhD thesis, Department of Environmental Technology, Wageningen University, Wageningen, The Netherlands.

Zeeman, G., Lettinga, G., 1999. The role of anaerobic digestion in closing the water and nutrient cycle at community level. Water Sci.Technol., 39 (5), 187-194.