A major challenge facing the wastewater industry is the production of high quality treated effluents containing reduced concentrations of nutrients. The challenge relates equally to upgrading existing plants as to entirely new construction. The HYBACS process is a new approach to nutrient removal that has been developed from a process originating from South Korea called the RABC process. The process comprises two biological stages followed by clarification (or separation). The first stage comprises SMART units, and the second stage comprises activated sludge tanks. SMART units are a type of rotating biological contactor but the plates, 50 mm thick, are manufactured from mesh with a void of 95%, producing a biological environment containing aerobic, anoxic and anaerobic regions. The following describes the treatment system and the performance results obtained from two pilot demonstration plants installed in the UK and Spain. The plants have demonstrated that they can produce effluents with qualities compliant with the most stringent European nutrient removal standards, albeit supplementary chemical dosing may be needed to obtain compliance with the TP standards. IntroductionThe upgrade of conventional wastewater treatment for nutrient removal is a major challenge for water companies especially when one considers that most upgrade methods require substantial CAPEX for large new treatment tanks, land on which to construct the tanks and substantial OPEX to cover increased energy consumption. Compared with conventional, nutrient removal, activated sludge processes, the HYBACS process has reduced footprint and power consumption and can often be applied to the upgrading of existing activated sludge plants without the need to provide large new reactors.The new HYBACS process is a development of an earlier process, called the RABC process which was originally developed for nutrient removal in South Korea (Kim, 2004) where there are over twenty successful applications treating a range of wastewater types from municipal sewage to abattoir wastewater and landfill leachate. The process comprises two biological stages followed by a separating stage which is normally conventional clarification. The first biological stage comprises RBC-type machines, and the second stage activated sludge (AS) tanks. The process also contains a minimum of two liquor recycle streams, comprising an external recycle from the separation stage to the first biological stage and an internal recycle around the second stage. The second stage may be SBR treatment instead of AS treatment.The RBC-type machines in the first biological stage are very different from conventional RBCs and key to the performance of the overall process. In contrast to the type of plates used in conventional RBCs, plates in HYBACS RBCs are manufactured from a 3D plastic mesh with a void of 95%. The plates are 50 mm thick on a pitch spacing of 95 mm. During operation, the plates quickly fill with biomass comprising aerobic, anoxic and anaerobic regions, giving the plates the capacit...

In this review paper, a physical systems analysis based on thermodynamics has been applied to the observed behaviour of activated sludge as a physical system. The origin of the microecology of activated sludge and its relationship to biofilms and the metabolic consequences of the extracellular polysaccharide (EPS) formation are explained for the first time. Feast‐famine conditions are shown to be the leading candidate for the evolution of the ability of biofilm forming bacteria and activated sludge ‘floc‐formers’ to form EPS. The basis for competition for RBCOD between low F:M filamentous heterotrophic bacteria and ‘floc‐forming’ heterotrophic is presented and its relationship to activated sludge bulking described.

Consolidation is potentially the most cost‐effective of all sludge treatment processes. However, traditional design procedures have been oversimplified such that the process has not generally been fully exploited. The objective of this report is to summarize the Water Research Centre (WRc) procedure for sizing sewage sludge consolidation tanks, and explain the major design aspects which control the effective operation of the plant. The procedure provides a means of sizing tanks to consolidate any particular sewage sludge to any solids concentrations up to the maximum, and is applicable to both the batch and continuous operational modes. To obtain the predicted performance, the essential equipment such as the picket fence and control system, comprising a consolidation plant, must be suitably designed.