Biological wastewater treatment processes

Obrada otpadnih voda ključna je tehnologija za zaštitu i ponovno korištenje vodnih resursa. Opskrba vodom i odvodnja se stoljećima sastojala od transporta svježe, čiste vode do gradova i korištenja te vode za transport otpada iz grada i njegovo ispuštanje u prirodni okoliš. Međutim, s porastom broja stanovnika u gradovima, takva se praksa više nije mogla održavati pa se potaknuo razvoj postrojenja za obradu otpadnih voda. Otpadnu vodu stvaraju industrije tijekom procesa proizvodnje (tehnološke otpadne vode) kao i domaćinstva u njezinom svakodnevnom korištenju (kućanske otpadne vode). Otpadna voda narušava kvalitetu rijeka, mora, jezera i podzemnih voda što može negativno utjecati na zdravlje ljudi. Kako bi se zaštitili prijemnici (recipijenti), otpadne vode moraju se pročistiti prije ispuštanja u okoliš. Postupci pročišćavanja otpadnih voda mogu se podijeliti na fizikalne, kemijske i biološke postupke i u većini slučaja se ovi postupci kombiniraju. Biološki postupci obuhvaćaju djelovanje mikroorganizama koji razgrađuju otopljenu organsku tvar, anorganske tvari te zaostale suspendirane čestice nastale nakon primarne obrade. Primjenjuju se biološki aerobni ili anaerobni postupci koji se temelje na različitom odnosu mikroorganizama prema otopljenom kisiku.Sewage treatment is the key technology for the protection and re-use of water resources. For centuries, sanitation largely consisted of transporting fresh, clean water to the cities, and using this water to transport the waste out of the city and discharge it into the natural environment. However, with the increase in human population in cities, such practices could no longer be maintained, and thus facilitated the development of wastewater treatment plants. Wastewater is generated by industry through the production process (technological wastewater) as well as households in its everyday use (household wastewater). Wastewater deteriorates the quality of rivers, seas, lakes and groundwater, and causing negative effects on human health. In order to protect natural recipients, wastewater must be treated before being discharged into the environment. There are several methods for wastewater treatment such as physical, chemical, and biological wastewater treatment processes. In most cases these processes are combined. Biological procedures include the action of microorganisms that break down dissolved organic matter, inorganic substances and suspended particles formed after primary processing. Biologically aerobic or anaerobic procedures are based on the different affinity of microorganisms to dissolved oxygen