Three different methods are described for the determination of the initial inert particulate organics, measured in terms of COD. The methods involve experimental procedures using batch reactors and are designed to differentiate residual particulate products generated by metabolic activities during the treatment processes. In the first method, the final threshold value of the particulate COD is monitored in an aerated batch reactor fed by the initial total COD. The second method uses the threshold values of the total and soluble COD in two parallel batch reactors, one fed with unfiltered and the other with filtered wastewater. The third method involves running three batch reactors, two with the wastewater to be studied and the third with glucose. One method has been experimentally tested to assess the inert particulate fractions of domestic and textile wastewaters.