Hello Detlef,Congratulations ...

Hello Detlef, Congratulations with your comprehensive post on which I fully agree. The academic world focuses primarily on publications, on prestige and on acquiring R&D funds. The business world focuses primarily on selling products and silver bullet "solutions". In most cases sustainability, water & carbon footprints are just buzz words to get funding resp. sales. Being an M.Sc. professional engineer like yourself, after 37 years of practice, I still look at each new application with an open mind as to configure the most sustainable (resources) and economic (capex + opex) treatment and select the most appropriate process technology with efficient equipment and process controls. For most organic wastewaters this results in high-rate AD converting typically 90% of the organics to methane to save fossil fuel. The AD effluent is treated by low energy advanced activated sludge (AAS) as to biodegrade recalcitrant compounds and colloids enabling very clear and clean water for recycling. In most cases (realized worldwide over the last 35 years) several times more energy is produced/recovered than needed for the complete treatment including water recycling. This is what I would call sustainable.