Cape treatment works leads with energy-efficiency gains

This recognition affirms the City’s commitment to improving the quality of treated effluent, adopting energy-efficient operations and reducing the impact of climate change by lowering carbon dioxide emissions.

“The City of Cape Town is a beacon for all municipalities to drive quality and to certify their delivery of services against South African and international standards,” says Jodi Scholtz, lead administrator of the SABS.

SANS/ISO 50001 provides a practical way for all organisations to improve energy use through the development and implementation of an energy management system. “Since the plant also has SANS/ISO 9001 certification to validate its quality management, it became easier to facilitate the certification process for their energy management system,” Scholtz explains.

In the past four years, the City has invested more than R179.8 million at the Bellville WWTP, which treats around 44.3 million litres of sewage daily. More recently, two contracts have been approved that will see a further estimated investment of more than R120 million for the last phase of the plant’s diffused aeration upgrade.

So far, the energy-efficiency gains include a more than R1 million annual saving in electricity costs, as well as an approximately 1 000 tonne reduction in carbon dioxide emissions each year. Overall, the energy saved is equivalent to treating 3 000 million litres of wastewater annually.

To obtain SANS/ISO 50001 certification, the Bellville WWTP had to develop an energy baseline, implement performance criteria, procure devices to measure the energy consumption, and then develop an energy policy, as well as an energy management system to ensure efficiency of operations.

Process improvements

Key operational changes to further improve energy-efficiency include:

• Constructing three primary settling tanks to reduce the solids loading and the chemical oxygen demand (COD) of the wastewater before it is treated in the diffused aeration reactors. This will achieve at least a 35% reduction in COD, which means lower airflow is required into the reactors, resulting in reduced energy consumption.

• Replacing ageing blowers with modern, energy-efficient units. A new air distribution system with fine bubble diffusers in the three reactors will be installed with automated dissolved oxygen control. The reactors will be rebuilt to be able to perform full biological nutrient removal, and the new reactor zone configuration – with larger anaerobic and anoxic zones – will be more energy-efficient.

The SABS will conduct surveillance audits at the Belville WWTP over the next two years, as part of the terms and conditions to maintain SABS certification.