Veolia supplies a hybrid sewage treatment plant to Ethiopian Airlines

Veolia Water Technologies South Africa (Veolia) supplied a sewage treatment plant for the Ethiopian Airlines cargo terminal at Addis Ababa International Airport. The solution was supplied as a standard package plant with a hybrid configuration using trickling filter technology, providing the project contractors with a plug-and-play sewage treatment solution for the greenfield terminal construction. 

Veolia’s standard package plants – a range of pre-assembled, adapted Veolia products and technologies – are enabling companies and public authorities to meet a wide variety of municipal and industrial water treatment applications, where short turnaround times are required and lower water volumes treated.  

 “A standard packaged offering with a pre-existing core design means design time and costs are reduced, including fabrication time,” explains Victoria Tutubala, Project Engineer in Engineered Systems Department at Veolia Water Technologies South Africa. These plants are manufactured at Veolia South Africa’s Engineered Systems facility in Sebenza, Johannesburg, and are easily transported to site via road and/or sea freight.

The hybrid configuration standard packaged plant offered, where the anaerobic reactor is a civil structure and the rest of the process equipment containerised, covers a wider range of flow requirements than the fully containerised package, with the former supplying capacities from 25 to 600 m3/day, while the latter supplies a maximum 200 m3/day.

The plant will receive raw sewage and, through a process of screening, primary treatment, trickling filtration, secondary treatment and disinfection, will treat it to RSA General Standards. The treated effluent can then be used for irrigation. The treatment process is as follows:

• Screening: Raw sewage enters the inlet box where objects such as plastic, bottles, towels, etc. are retained by the bar screen, while grey water is allowed to pass through into the anaerobic reactor.
• Primary treatment: Solids and sludge settle in the anaerobic reactor, while biochemical oxygen demand (BOD) is reduced due to the anaerobic conditions which exist in the tank.
• Trickling filtration: The effluent, now semi-treated, is transferred to the trickling filter for further reduction of BOD. Nitrification also takes place in the trickling filter, which promotes the removal of ammonium-nitrogen (NH4-N). Biological film formed on the media removes the two constituents in the sewage water.
• Secondary treatment: Downstream of the trickling filter, effluent is clarified using gravity sedimentation, which separates sludge from the wastewater.
• Disinfection: Finally, the clarified water is disinfected in the chlorine contact tank before it is discharged.

“Trickling filter technology was the best solution for this application for a number of reasons,” Victoria continues. “It is a simple and reliable solution which depends on bacterial growth on the trickling filter media. The plant can accommodate large fluctuations in quality and volume of inflow, including shock loads. The simplicity of the technology also means automation and control requirements can be kept to a minimum; allowing for a reliable and robust solution which requires no skilled operator to operate the plant.”

The system also reduces sludge production, as aerobic sludge produced in the secondary settler is returned to the anaerobic reactor, where it is anaerobically digested to approximately a third of its original volume.