A laboratory river model for the study of biodegradation kinetics of organic pollution in surface waters is presented. It enables an engineering - technological prediction of the impact of wastewater biodegradation on DO and TOC profile in a river downstream from the point of entry of wastewater effluent thus providing rapidly and inexpensively significant design information to an environmental scientist or engineer. The method was applied to the determination of degradation of pharmaceutical wastewaters. Biodegradation during adaptation and a comparative study on organic constituents, biodegradation rates in polluted and unpolluted river waters were simulated.