Biogranulation for wastewater treatment are aerobic or anaerobic granulation processes in which microorganisms attach to each other and aggregate. These granulates are strong structures, consisting of millions of organisms per gram of biomass and are therefore particularly suitable for treating high-strength wastewater and shock loadings.
A Sequencing Batch Biofilter Granular Reactor (SBBGR) is a discontinuous batch process based on aerobic granular biomass. In the reactor, the granules are not suspended in the tank but are instead confined in what is called a microbial bed; a limited part of the reactor tank is packed with a filling material, producing pores in which the granules are retained. The granular biomass generation is taking place during the reactor start-up period (which normally takes around 3 months), a process where a gradual shift from biofilm growing on the carrier surface to granular biomass is occurring. Crucial factors for a successful start-up phase and growth of granular biomass are trends of hydrodynamic shear forces, operative conditions and bed material features.
The bio filtrating operation of the reactor is based on treatment cycles, each consisting of three consecutive phases. Fill- and draw modes initiate and finalize each cycle, with a biological oxidation phase in between them. In the filling phase (not aerated) a fixed volume of influent is added to reactor, where some liquid volume is retained from the previous treatment cycle. In the biological oxidation phase, the reactor liquid is continuously aerated and recycled through the biomass supporting material (the aeration remained switched off, however, during the first hour of the phase to permit oxidised nitrogen removal). Finally, the treated effluent is drawn by gravity from the reactor and a new treatment cycle can be started. The different steps of the biological treatment all take place in the same tank. In conventional systems, the waste is moved to a secondary settler which is not necessary in this cleaning process since the biomass is retained in pores. Thus, this technique implies greater biomass retention in the reactor (up to 40 kg/m3). Also, the characteristics of the biomass enable a high sludge age value. These two aspects are in turn giving a consequent reduction in sludge production compared to conventional processes.
The technique has been developed by the Water Research Institute (IRSA) of the Italian National Research Council (CNR), also responsible for further improvement of the method in the INNOWATECH project, where it is combined with ozonation to achieve an increased efficiency of the wastewater treatment process and a sustainable water cycle achievement.
Di Iaconi et al. (2011); Sequencing batch biofilter granular reactor for textile wastewater treatment. Water Research volume 42, Issue 12, June 2010, pages 3635-3644.
Di Iaconi et al. (2009); Granular biomass structure and population dynamics in Sequencing Batch Biofilter Granular Reactor (SBBGR). Water Research volume 44, Issue 6, March 2010, pages 1825-1832.
Di Iaconi (2011); Biological treatment and ozone oxidation: Integration or coupling? Bioresource Technology volume 106, February 2012, pages 63-68.