Relationships were developed to establish the theoretical basis for scale-up of a fixed-film continuous-flow tubular photobioreactor for removal of hydrogen sulphide from synthetic industrial wastewater and its conversion to elemental sulphur. These are based on experiments with a bench scale reactor where the active part of the reactor was sixteen 150 mm length Tygon tubes. Three different tube sizes (internal diameters of 6.4, 3.2 and 1.6 mm) were used to investigate the effect of tube size on reactor performance. In addition, the washout velocity (the velocity at which fixed-film biomass started to washout) for the 1.6 mm diameter tube reactor was determined. Three models were developed to predict reactor performance and establish the basis for scale-up of the process. All three models predicted reactor performance with a reasonable degree of accuracy.