Small Footprint Wastewater Treatment Plants. The Combination of Moving Bed Biofilm Reactors with Ballasted Floc Solids Separation

Over the last few decades much attention has been given to develop compact wastewater treatment methods that do not compromise the effluent quality or construction and operational costs provided by conventional treatment methods, such as activated sludge and trickling filters. As such, technologies as the Biological Aerated Filter (BAF), Membrane Biological Reactor (MBR) and the Moving Bed Biofilm Reactor (MBBR) have emerged and found their place in the market. Of these processes BAF's and MBR's combine both biological treatment and solids separation with dedicated means of solids removal, respectively filtration with back flushing and filtration through semi-permeable membranes. The MBBR on the other hand is solely a biological treatment system that can be coupled with a range of different solids separation systems such as gravitational settling, dissolved air flotation and others.Parallel to the development of the MBBR process French scientists developed a means of solids separation by use of microsand ballasted flocculation to enhance capacities of gravitational settling in the Actiflo® process. This highly efficient process can receive hydraulic loadings of >100 times that of a conventional gravity clarifier. Worldwide there are now more than 500 full scale references with ballasted flocculation. These references can be found within municipal drinking water and wastewater treatment as well as within industrial process water and wastewater treatment.Due to the climate and regulatory provisions in Norway, most Norwegian wastewater treatment plants are covered and placed inside buildings or underground. The footprint of wastewater treatment plants is hence crucial for the overall cost of the plant. In Norway, the MBBR process has been installed at about 200 different plants to comply with the need for compact installations. In recent years several MBBR installations have also used ballasted floc separation as means of solids removal. This combination has enabled the wastewater treatment plants to shrink the footprint even further.Though both MBBR and microsand ballasted floc separation have been used for wastewater treatment for approximately 20 years, the combination of the two processes is novel. The topic of this paper is to describe the concept of this process configuration and to provide an overview of experiences achieved from the existing installations.In the coming year's upgrade of existing wastewater treatment plants or new plants will be needed in highly populated areas. Here the available space for the wastewater treatment plants will belimited and require highly compact processes. The combination of the MBBR and ballasted flocculation are therefore expected to be interesting also for many countries outside of Norway.