Internit – Activated Sludge Process Operating System

Activated Sludge process operating system

EnviDan is at the forefront of advanced treatment systems for high treatment efficiencies for COD, nitrogen, and biological phosphorus removal at low operational costs.

The INTERNIT (INTERmittent NITrogen removal) system is one of EnviDans Activated Sludge (AS) operating systems that can be used for control of any type of activated sludge tank coupled with a clarifyer.

In the INTERNIT tank the wastewater treatment processes are all conducted  within one process volume as the intermittent (”ON/OFF”) aeration control philosophy allow for alternating aerobic and anoxic environments within the INTERNIT tank volume.

The treatment system is designed to give optimal conditions for Advanced Online Control (AOC) of biological treatment processes. Using the online signals from nutrient sensors the operating system can adjust the aeration according to the current load and process conditions. The optimised aeration control means that aeration energy will be minimised while the effluent concentration of nitrogen and phosphorus also will be minimised.

The continuous influent and effluent flow gives a stable hydraulic system that maximises the hydraulic capacity as well as the efficiency of the aeration system. The simple INTERNIT operating system minimises the capital investment of the process volumes needed, operational cost and, the maintenance requirements while maximizing the treatment efficiency and robustness against load variations.


  • Simple configuration for low capital investment (CAPEX) and maintenance requirement
  • Optimal condition for Advanced Online Control ensure high treatment efficiencies at low operational costs (OPEX)
  • Effective nitrogen and phosphorus removal system
  • Flexible operation for operational safety
  • Can operate without internal recirculation of nitrate
  • Continuous influent and effluent to each INTERNIT tank for a stable hydraulic load on the secondary clarifiers
  • Easy implementation
  • The INTERNIT operating system can be constructed as new units or existing AS systems can be upgraded for INTERNIT operation

About author

EnviDan is a full service environmental company offering professional solutions within the drinking water, wastewater, biogas and environment.

Primary contact
Gitte Nabe Kristensen

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