Since the last century, aerobic biological trickling filters have been used for the treatment of wastewater. At first, a filter medium normally consisted of stones of different sizes, but recently, this medium has been replaced by plastic. Originally, the plastic media was for treatment of industrial wastewater with higher concentrations of organic matter than municipal domestic sewage.
Biological trickling filters filled with our preferred plastic media have shown a great stability towards fluctuating supply of organic matter and flows. The reason for this is the larger population of micro-organisms which adhere to this type of media than usually found in conventional types. It is therefore extremely resistant to occasional occurrences of toxins within the wastewater and it recovers much quicker from these types of event as well as from extreme cold snaps during winter months.