Biofiltration as a Compact Technique for Small Waste Water Treatment Plants

Abstract

Biological aerated filters combine bacterial degradation of pollution by fixed biomass with physical filtration in a single reactor. Removal rates become independent of clarification and sludge setueability limits, and concentration of biomass is increased. Nitrifiers attach to the media, allowing nitrogen removal without sludge age constraints. Several fullsize plants with the BIOCARBONE process for industrial and municipal wastewater treatment have established the compacity, ease of operation and high removal rates achievable with this advanced treatment system. A new biofilter design offering simplified operation and increased performance is presented, which allows implementation of biofiltration for small wastewater treatment plants. Design data for carbon and nutrient removal were collected during extensive pilot tests. Hydraulic conditions and pollution loadings were varied in order to optimize the biological and operational parameters of the filter. The combination of an anaerobic and an aerobic zone eliminates the need for primary sedimentation. Pollution removal rates up to 20 kg COD/m3 d could be achieved, and a widely fluctuating load of up to twice that average loading can be treated without major effluent deterioration. If lower carbon loadings are used, nitrification is achieved in the upper aerated zone. By recirculating the effluent into the non-aerated lower zone, carbon and ammonia oxidation as well as denitrification and suspended solids retention could be achieved with an overall hydraulic retention time of four hours in one reactor.