THE PROJECT
A city in southeast Asia has a sewage treatment plant based on cascade activated sludge process. Originally the plant was designed only for BOD removal at a capacity of 58,000 m3/day. The plant has eight trains of cascades having an individual capacity of 7250 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 PROBLEM
The plant is receiving TKN to the tune of 70 ppm and due to new discharge standards for municipal wastewater treatment, the Ammonia in the outlet should be brought down to < 5 ppm and TN < 30 ppm. Due to the island country, the authorities operating the plant have severe space restrictions, and thus a solution that helps them to achieve the desired level of nitrification within the same infrastructure without additional civil construction and land requirements is highly sought after.
- Existing BOD removal plant
- Having a high TKN load of 70 ppm
- Requires outlet Ammonia < 5 ppm and TN < 30 ppm
THE SOLUTION - Upgradation of activated sludge
Based on our 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 to be converted into Levapor carriers based IFAS reactors with 11% media filling in it.
Proposed Solution:
- Use the two first reactors of the cascade as suspended growth reactors.
- Two last reactors are to be upgraded to Levapor IFAS reactor by adding carriers at 11% filling.
The above solution was tested in a pilot process configuration and the results were confirmed at the site for its efficacy in achieving the desired level of nitrification as per the client’s requirement.
After successful trials, the project was implemented at the 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.
THE RESULTS
The plant is achieving consistently nitrification to Ammonia < 5 ppm level and COD < 30 ppm at the outlet with much lower downtime for the process start-up and upgradation.
Summary of results achieved:
| Parameter | Value |
|---|---|
| Total Flow of the plant | 58000 m3/day |
| Inlet COD | 170-200 ppm |
| Inlet TKN | 50-70 ppm |
| Inlet Ammonia | 30-40 ppm |
| Outlet COD | <30 ppm |
| Outlet TN | <20 ppm |
| Outlet Ammonia | <5 ppm |
THE BENEFITS
- Minimal changes to existing infrastructure
- Quicker implementation and process start-up after upgradation
- Achieving a consistent level of Nitrification even with less than 6 hours HRT for cold climate
- Quick startup of the process and stabilization
Amit Christian is a MSc graduate in Environment Science from Middlesex University, London, UK. He has been active in the field of water and wastewater treatment since 1998. He specializes in the design, engineering, and management of various biological wastewater treatments such as Activated Sludge Process (ASP), Sequencing Batch Reactor (SBR), Moving Bed Bio Reactor (MBBR), and Integrated Fixed Film Activated Sludge (IFAS). He has helped various Industrial and Municipal clients in troubleshooting, and optimizing their biological wastewater treatment processes to achieve the latest Stringent norms for Ammonia Removal.
