The application of RNA assay and N-acetyloglucosamine determination in activated sludge wastewater treatment processes as well as biodegradation of organic solid waste suspension are presented. The conducted experiments proved that both methods can be successfully used for biomass determination in the samples containing much solid particles during waste and wastewater biodegradation. Relative Standard Deviation (RSD) for both measurements are similar and ranged from 0.73 to 4.6%.