Influence of process variables on the modelling and design of a rotating biological surface

An investigation of the Rotating Biological Surface (RBS) process variables to determine the efficiency of BOD₅ removal from wastewater is presented.Operating parameters including influent substrate concentration, liquid retention time, stage temperature, flow rate, disk surface area, hydraulic loading, disk rotational speed, disk sizes, number of disks, fractional submergence, were evaluated.The process parameters were obtained from a pilot scale RBS plant constructed and applied to the treatment of municipal and industrial wastewater and from the literature.The data were employed to determine a kinetic equation of general application, whch tends to the well-known Michaelis-Menten equation for municipal wastewater and easily degradable substrates.The study shows that influent BOD₅ concentration, the type of substrate, hydraulic loading, stage number and wastewater temperature are the most significant variables predicting the RBS system performance.The model presently developed was verified by field data concerned with the treatment of domestic and low strength industrial wastewater.The obtained model for urban wastewater cannot be applied to high strength industrial wastewaters where poorly biodegradables substrates are present together with easily degradable substrates.The situation has been verified by treating straw paper and tannery wastewaters.For those substrates a more complex equation has been obtained that becomes the Michaelis-Menten type equation at high values of a BOD fraction in the effluent.