WET News

6 WET NEWS august 2015 F ixed film wastewater treatment bioreactors have never really gone away – biological filters are still used in many small works, and even some larger ones – but suspended growth has been the preferred process in most applications for many years. However, fixed film processes, in the form of moving bed biofilm reactors (MBBR) technology, are making a come-back. this has been due to the development of advanced MBBR media, making the process flexible and versatile, and Veolia's anoxKaldnestM media has been at the forefront of those developments since the 1980s. In MBBR systems, low density plastic biofilm carriers, which have specific protected surface areas around 200-1200m2/m3, are free to move within a fully flooded reactor which is aerated using a normal diffused aeration grid. the resulting continuous media movement gives a self-controlling biofilm thickness, maximising the use of the installed surface area without the need for backwashing or air scouring. unlike activated sludge plant, there is no sludge recycle, so only the generated biomass – of the order of 150 250mg tss/l – has to be removed from the treated effluent. the result is a process that combines the high biomass concentration of fixed films with a footprint lower than that of conventional activated sludge processes. Whilst many MBBR plants are pure biofilm processes, like Veolia's BastM, for carbon removal, nitrification/denitrification and post-denitrification, the technology is increasingly being used in combination with suspended growth biomass in the same reactor tank. In these "hybrid" systems, like HYBastM, nitrification takes place mainly in the fixed biofilm, whereas BOD removal and denitrification predominate in the suspended sludge, making them particularly suited to improving existing nitrification efficiency and freeing up process capacity for nitrogen removal. the latest generation of Veolia's anoxKaldnestM media range is Z-MBBR, the result of two decades of development work. Christian Rosen, one of Veolia's Process specialists explains: "Many biological processes use several different types of bacteria all needing different environments. Our challenge was to produce a biofilm carrier that could provide those different micro-environments so as to encourage the growth of selected bacteria. We can do that by precise control of the biofilm thickness which eliminates variations in performance and removes the limitations associated with clogging of the carriers." the Z-MBBR carrier has a unique three-dimensional contoured structure that allows the creation of a self-controlled, pre-determined biofilm thickness on the carrier. this gives a controlled redox gradient and maximises mass transfer. the carriers are customised to give biofilm thicknesses ranging from 200µm for fully aerobic processes like nitrification to 500µm for applications like Veolia's aNItatM- Mox anammox deammonification technology. Deammonification using the new carrier can remove more than 90% of ammonia and 75-85% of total nitrogen from high ammonia streams like anaerobic digester wastes, industrial wastewaters and landfill leachates, without the addition of an external carbon source and consuming considerably less energy than conventional nitrification-denitrification processes. MBBR has other advantages. a joint research project into MBBR biomass (Ødegaard et al 2010) concluded that the particle size distribution of the biomass varies depending on the surface area loading of the media and the reactor hydraulic residence time the lower the loading rate and higher the hydraulic residence time the larger CONtaCt DEtaILs Visit http://technomaps.veoliawatertechnologies. com/mbbr/en/ for further information on MBBR and other biological processes from Veolia. the new Z-MBBR carrier Film Reviews Mike Froom of Veolia Water technologies looks at the new generation of fixed film biological reactors. References Ødegaard H, Cimbritz M, Christensson M, Poulsen Dahl C, 2010 Separation of biomass from moving bed biofilm reactors (MBBRs), Proc Wat Env Fed 1 (7) 212-233. the particles, so operating MBBRs at low loadings means that residual biomass can be easily removed by microstraining. Pairing MBBRs with microstrainers like Veolia's self-cleaning, low headloss DiscfiltertM, results in a small footprint, low cost plant and, in most applications, there is no need for pumping between the MBBR and the microstrainer. ADVERTiSmENT fEATuRE www.flexseal.co.uk 01226 340 888 | sales@flexseal.co.uk Ashley Siddons, Works Operative - Dispatch Working in Dispatch is fast paced; orders are sent to us as soon as they're placed, which we pick and dispatch the same day. Here at Flexseal, we understand the importance of delivering items quickly, that's why we offer same or next day delivery to all of our customers as well as the option to specify delivery of products direct to site. 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