Granular biomass as an alternative of activated sludge for treating urban and industrial wastewaters

Aerobic granular sludge was developed as an alternative technology to conventional activated sludge processes for the treatment of wastewater. The morphological structure of aerobic granular sludge (i.e. high particle diameter and density) provides two main advantages if compared to activated sludge processes: (i) the ability of settling faster, which ease the retention of biomass; and (ii) the existence of substrate profiles across the granule radius, which allows simultaneous aerobic, anoxic and anaerobic processes into the same granule. Both characteristics contribute to reduce the required reactor capacity producing more compact designs, or to treat higher wastewater loading rates, when compared to conventional activated sludge systems. Furthermore, since aerobic granules can be separated from wastewater in the same reactor vessel, external settling units become unnecessary.

We have worked or are currently working with aerobic granular biomass for treating both urban and industrial wastewaters at bench and pilot-scale.

Regarding urban wastewaters, we designed, built and operated during a year a 100 L granular sequencing batch reactor (GSBR) treating a mimicked urban wastewater for simultaneous carbon, nitrogen and phosphorus removal. The COD and N-loading rates applied in the GSBR through the whole operational period were almost twice higher than that applied in conventional municipal WWTPs based on activated sludge. Also in the scope of urban wastewaters, we designed, built and operated during a year a 150 L granular airlift continuous reactor treating a real reject wastewater coming from dewatering sludge system of an urban WWTP. This reactor perfomed stable both full and partial nitritation at high nitrogen removal rates (up to 2 g N/L/d at 30ºC).

Regarding industrial wastewaters, we are working at bench scale with different granular reactors to perfom: (i) aerobic removal of mixtures of phenolic compounds (phenol, cresol, nitrophenol, quinoline), (ii) simultaneous nitritation and aerobic phenols removal, (iii) denitrification via nitrite with phenol as sole organic carbon source in a Upflow Anoxic Sludge Blanket (UASB) reactor.

Finally, as a specific issue we are working with granular Anammox biomass to develop autotrophic nitrogen removal processes for urban and industrial wastewaters using SBR and UASB reactors.

We collaborate in this field with several groups with a strong expertise on granular biomass such as the Environmental Engineering research group of University of Santiago de Compostela (Spain) or the Department of Biotechnology of Delft University of Technology (The Netherlands). 

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