Dissolved air flotation (DAF) is gaining traction as a post-biological polishing step in municipal wastewater treatment, improving effluent consistency by removing fine solids, algae and nutrient loads that conventional clarification often misses under variable conditions, says water technology company Xylem strategy and marketing manager Chetan Mistry.



In polishing applications, DAF targets the fraction that conventional secondary clarifiers struggle with, helping utilities achieve a more consistent effluent quality.

“When integrated correctly, DAF complements biological treatment by stabilising final effluent rather than replacing biological nutrient removal,” Mistry says.

Compared with conventional clarification, DAF typically delivers more reliable solids separation under variable conditions, and this is especially relevant where algae carry-over or seasonal loading affects discharge compliance.

The flotation is particularly well suited to retrofit and upgrade older, capacity-constrained municipal wastewater treatment plants in South Africa, while its compact footprint makes it suitable for deployment as a permanent installation or as a temporary rental solution during peak flows, maintenance periods or staged upgrades.

Mistry adds that, in South Africa, where many plants are operating beyond their original design envelope, DAF can be integrated with minimal civil works and connected to existing hydraulic and control systems. This enables municipalities to add treatment capacity or improve effluent stability without committing to large-scale infrastructure expansion upfront.

Further, DAF delivers value at multiple points in the wastewater treatment train, depending on the challenge being addressed; during pre-treatment, DAF reduces solids, fats, oils and organic loading to protect downstream biological processes and improve plant resilience.

As post-biological polishing, it enhances the removal of fine solids, algae and particulate nutrients to support tighter discharge limits or reuse objectives.

He adds that municipalities typically decide where to deploy DAF based on influent characteristics, compliance risks, footprint constraints and life-cycle cost considerations: “In practice, many plants use DAF as a flexible tool that can be repositioned or expanded as operational needs evolve”.

Capital Considerations, Optimal Performance

When compared with expanding or refurbishing conventional clarification infrastructure, DAF often presents a lower risk and a more flexible investment path, particularly when considering rental options, Mistry says.

Rental deployments enable municipalities to address immediate capacity or short-term compliance risks without long lead times or heavy upfront capital expenditure and, from an operational perspective, DAF’s compact design and stable performance can reduce downstream stress, helping to control chemical use, sludge handling and unplanned maintenance.

This approach enables utilities to test, optimise and validate treatment improvements before committing to permanent upgrades - an increasingly important consideration in constrained public-sector environments.

He adds that DAF has performed well in markets facing challenges similar to those in South Africa, including ageing infrastructure, variable influent quality, and intermittent and seasonal flows. Its ability to maintain stable separation under fluctuating conditions makes it particularly valuable where hydraulic or load variability undermines conventional settling performance.

Local adaptations typically focus on chemical optimisation, control strategies and operational support to ensure that the system is tuned to site-specific conditions: “This is why DAF is most effective when deployed as part of a consultative, integrated solution, rather than as a standalone piece of equipment,” he concludes.