For sewage treatment, the design of reactor at higher loading rate is not possible due to limitations of upflow velocity, and maximum loading of about 2 to 3 kg COD/m3.d can be adopted for design. Similarly, for high strength wastewater, such as distillery, satisfying minimum velocity criteria and maximum HRT limit is difficult. Therefore, categorization of wastewater based on COD concentration was observed to be necessary for generalizing the design procedure of UASB reactor to meet the recommended operating conditions to the maximum extent. Thus, the COD concentration of the wastewater is suitably divided in four categories.