Engineering realization of processes of disinfection and treatment of wastewater and its sludge, as well as waste treatment in biotechnological processes, has considerable variability. Therefore, in this section, the basic technical methods and schemes of realization of such processes and an introduction to such biotreatment are given. Examples of biological wastewater treatment realisation in aerobic and anaerobic conditions are considered. Design solutions of biogas plants for recycling various organic wastes and their prevalence in different countries are considered.