A city in South East Asia has a sewage treatment plant which uses a cascade activated sludge process. Originally the plant was designed only for BOD removal at a capacity of 58,000 m3/day.  The plant utilizes eight trains of cascades having individual capacity of 7,250 m3/day.  Each train is designed with four cascades of 10 m x 10 m x 5.7 m size having 570 m3 active volume for suspended growth based treatment.  The plant is designed to cater to the cold winter conditions of the region for BOD removal.


The plant is receiving TKN to the tune of 70 ppm, however due to new discharge standards for municipal wastewater treatment, the Ammonia in the outlet is required to be brought down to < 5 ppm and TN < 30 ppm.  With the treatment facility being situated in an island country, the plant has severe space restrictions.  Therefore a solution which helps them to achieve a desired level of nitrification within the same infrastructure without additional civil construction or an additional land requirement is highly sought after.

  • Existing BOD removal plant
  • Having high TKN load of 70 ppm
  • Requires outlet Ammonia < 5 ppm and TN < 30 ppm
THE SOLUTION – Upgrading activated sludge results

Based on the Levapor engineer’s extensive experience with cold weather nitrification using the Levapor IFAS process, a solution was proposed to utilize two of the first reactors of the cascade as suspended growth reactors while the last two reactors would be converted in to Levapor carriers based IFAS reactors with 11% media filling in it.

Proposed Solution:

  • Use the first two reactors of the cascade as suspended growth reactor
  • Utilize the last two reactors to be upgraded to Levapor IFAS reactor by adding carriers at 11% filling.

The solution was tested in a pilot process configuration and the results were confirmed on site for its efficacy to achieve desired level of nitrification as per client’s requirement.

Full scale plant modification with two IFAS reactors. After successful trials, the project was implemented on site with minimal modifications of:

  • Retention screen placement at the IFAS reactors
  • Rearrangement of diffuser grid to meet air requirement for nitrification and IFAS reactor mixing requirement.