Research finds benefits in operating MBBR with mixed media

A three-year project between Cranfield University's Water Sciences Institute and Warden Biomedia to find more effective wastewater treatment methods has found that mixed media improves the overall performance and increase effluent quality of moving bed biofilm reactors (MBBR) systems.

Dr Joana Dias testing at a wastewater treatment plant

The project investigated the influence of Warden’s biomedia physical properties on moving bed biofilm systems, including mixing, oxygen mass transfer, process start-up and effluent quality during steady state operation.

The aim was to improve efficiency, cost-effectiveness and sustainability of processes such as submerged aerated filters (SAF), MBBR and integrated fixed film activated sludge (IFAS) and trickling filters.

The research was completed by Dr Joana Dias under the supervision of Dr Ana Soares and Professor Tom Stephenson at Cranfield University. 

Dr Soares said: “Moving bed biofilm systems are traditionally designed and operated based on the carrier media surface area or protected surface area. Much attention has been given to maximising the media surface area, neglecting other physical proprieties, such as geometry, size, shape and voidage.

"This has led in the development and use of media with small gaps and narrow spaces for the biofilm to develop, leading to limitations in mass transfer, especially in medium to high carbon loaded wastewater treatment plants.

"The right shape and appropriate gaps and voidage between internal fins of the carrier media can contribute to the improvement of effluent quality, efficiency, cost-effectiveness and overall process sustainability.”

The research concluded that moving bed biofilm systems can be operated with mixed media to generate benefits.

Organic removal can be improved by using spherical media in the first stages of the process (Warden’s Biofil, Bioball and Biomarble media), complemented with a higher protected surface area media to improve nitrification (Warden’s Biopipe and Biotube media).

Strong correlations were achieved between biofilm formation rates, maximum COD utilisation rate and ammonia removal rate and the Warden Biomedia products physical properties. More specifically it was clearly observed that dimensionality (Di) and voidage (Voi) were critical factors, with correlations R2= 0.92-0.95.

Mark Barrett, managing director at Luton-based SME Warden, said: “This unique collaboration has opened up new ways of thinking that will really challenge what the water industry is doing right now. It has given us unprecedented insight which will inform alternative design approaches for the next generation of biofilm processes.

"As with all good research projects, it has pushed the boundaries raising further questions for which we’ll be seeking answers in another phase of research later in the year.”