Microbial processes in aerobic granules - can we use them to treat wastewater more efficiently?

Aerobic granular sludge-based reactors represent an attractive alternative to conventional activated sludge systems. Compared to activated sludge, the use of aerobic granular sludge reactors is advantageous because (i) considerably less area is required for construction, (ii) less energy is required to operate the system and (iii) growth yield of granular sludge biomass is lower, hence surplus biomass is reduced. One type of aerobic granular sludge reactors is the sequencing batch bubble column reactor. In sequencing batch bubble column reactors the alternation of anaerobic an aerobic periods is (among others) an important parameter for the formation of aerobic granules. The granules developed in such systems can have high biomass concentration, good settling properties, and high organic matter removal efficiencies. Desirable microbial processes that may develop within the granules are those of phosphorus removal and nitrification. In addition, and depending on bulk oxygen concentrations and granule size, denitrification may also occur in the granules core. Hence, sequencing batch reactors operated with granular sludge have the potential to achieve organic matter and nutrient removal in a single compact system. Development of aerobic granular sludge has been mainly studied using acetate as main energy and carbon source and at reactor temperatures of 20°C. However, some industrial streams may have higher temperatures and often contain, besides acetate, other volatile fatty acids as main components (or contaminants). Reports indicate that, in activated sludge systems, the presence of propionate in the wastewater may favor the proliferation of the microorganisms responsible for phosphate removal. The question remains on whether aerobic granular sludge can be developed with other carbon sources as main components (e.g. propionate) or at higher temperatures and if so, what are the physical and metabolic (or microbiological) properties of such sludge. Therefore we explored these issues in the present study. The development of aerobic granular sludge was investigated in sequencing batch bubble column reactors at temperatures of 20 and 30-35°C as well as with different carbon sources in the feed. Preliminary results show that aerobic granular sludge can be formed at higher temperatures but with different predominant microbial populations carrying out different microbial processes. Phosphate removal was only observed at 20°C whereas nitrification was occurring at higher temperatures.

Presented at:
67th Annual Assembly of the Swiss Society of Microbiology (SSM), Interlaken, Switzerland, June 12-13, 2008

 Record created 2011-07-18, last modified 2018-01-28

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