FILTRATION & SEPARATION


USING ACADEMIA TO SELECT FILTERS


Mark Barrett, managing director of Warden Biomedia, reviews the latest research findings for filtration in wastewater treatment


P Figure 1 One of our early collaborative research


projects with Cranfield University aimed to shed light on the physical properties of filter media products and their impact on start-up times. The results, published in an academic journal article in 2018, stated that spherical media achieved stable biofilm formation faster than cylindrical media (15-17 days compared to 23-24 days) with more uniform coverage. Uniformity is important to the integrity of the biofilm, and reduces the risk of detachment and biofilm abrasion once the plant is fully operational. Oxygen mass transfer was also higher for spherical media due to their higher voidage. These findings indicated that, for applications like traditional trickling filter beds, the best


rocess engineers are faced with an increasing number of filter media products for wastewater treatment with differing claims of efficiency and performance. In this growing market,


it can be difficult to know which are the best products to choose for fixed film applications such as SAF, MBBR and IFAS.


choice is spherical random filter media such as Figure 2.


This is because they have internal fins and large openings, offering a surface area of between 135m²/m³ and 220m²/m³ with high voidage (between 92% and 95%). The spherical designs enable the biomedia to form more rapidly and to retain their integrity. The structure and surface textures of the biomedia provide a protected environment to host the beneficial bacteria needed for biological treatment processes. High voidage eliminates the problems relating to clogging and puddling which are typically associated with traditional gravel, slag and clinker filter beds.


Selecting filter media for SAF Submerged aerated filters (SAF) or submerged aerated fixed film reactors combine high biomass concentration of fixed film processes with high oxygen transfer efficiency through forced aeration. With the soaring costs of energy in recent years, the efficiency of oxygen transfer has become a major consideration. The clean water baseline tests carried out by


Warden Biomedia in collaboration with Cranfield University proved that media enhanced the overall oxygen transfer efficiency by 23–45% and hydraulic efficiency by 41-53%. These figures were compared with wastewater tests carried out in operational conditions where biofilms were present. The three best- performing filter media designs of the five tested (which proved to be those with spherical designs) increased the hydraulic efficiency to 89, 93 and 100% respectively.


Figure 2


For SAF applications, a filter media with high surface area gives optimum air to wet surface contact time and helps eliminate odour issues (see Figure 3). High voidage is also important, as it means a low pressure drop on the gas side, minimising fan power helping contribute to environmental and sustainability targets. Moving bed biofilm reactors (MBBRs) and integrated fixed film activated sludge (IFAS) processes make more complex demands on the filter media. Through mathematical models developed with Cranfield University, Warden Biomedia introduced a new parameter -“media dimensionality” - which has a direct positive impact on biological start-up time and the process operation during steady state conditions. This provided scientific validation for existing spherical media products recommended in MBBR applications (see Figure 4). Warden used this research to create a new


Figure 4


filter media product, and supported a 3-year PhD project as a Knowledge Transfer Partnership with Cranfield University to compare the performance of this product against other industry options, (see Figure 5). This spherical media product improves biological commissioning times and process security. Its higher biomass retention also increases wastewater treatment capacity and enables the tank volume to be reduced.


Figure 3


Figure 5


Warden Biomedia www.wardenbiomedia.com


JUNE 2026 | PROCESS & CONTROL ENGINEERING 17


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