Highly concentrated wastewater streams need large reaction volumes to guarantee sufficient treatment capacity. In addition, in the case of activated sludge systems, even biomass separation from treated effluents requires large sized settling tanks because of the slow sludge-settling rate. Finally, conventional aerobic biological systems are negatively characterised by high sludge production whose management causes serious environmental and economic problems. To overcome the above drawbacks of conventional aerobic biological systems and to develop compact treatment systems, aerobic granular sludge technology has been proposed and nowadays developed (Heijnen and Van Loosdrecht, 1998; Van Loosdrecht and De Kreuk, 2004). The extraordinary settling characteristics of aerobic granular sludge make external settling tanks, or 3-phase settlers, superfluous. Separation of granules and effluent takes place during a short settling phase in a Sequencing Batch Reactor (SBR). Aerobic granular sludge technology can be of great importance to the industry since it enables treatment at significantly lower costs and less environmental impact. Feasibility studies showed that a treatment plant based on granular sludge requires only 25 % of the area that would be used for a conventional activated sludge system. Furthermore, less sludge handling and better oxygen transfer due to the larger building height can save up to 50 % of the energy costs and it is very easy to cover the reactor against odour and aerosol release (De Kreuk and De Bruin, 2004). Another advantage could be that the stability against toxic peaks is expected to be better, which of course is of prime importance in industrial applications.
Aerobic granular sludge is a young technology, up to now grown in well-controlled laboratory scale reactors (fed with a glucose or acetate and ammonia mixture) and pilot plants (De Bruin et al., 2005). Only a few studies have been published about preliminary research using laboratory scale reactors treating industrial effluent malting (Schwarzenbeck et al., 2004), dairy (Arrojo et al., 2004; Schwarzenbeck et al., 2005) and pharmaceutical effluent (Inizanet al., 2004) as well as domestic sewage (De Kreuk and Van Loosdrecht, in press). However, the specific influences of process parameters important for industrial applications have not been assessed yet. For example, the influence of many of the typical characteristics of industrial effluent (suspended solids, toxic compounds, temperature, pH) on granule formation and reactor performance are unknown. In order to compare the different wastewater treatment innovations of the past decade, more insight is needed in granule formation and composition and laboratory scale experiments should be brought to the practical scale to study the granule technology in practice. Therefore, in this project, specifically in WP1, granule formation will be studied at micro-organism, granule and reactor level. The specific objectives are: -Obtaining insight in the structure of aerobic granules by using FISH techniques on sliced granules; -Investigating the influence of particulate and polymeric COD (such as fats, proteins, starch, suspended solids) on granule morphology and removal pathways of these components; -Optimising the simultaneous COD, N and P removal in highly contaminated wastewater (e.g. slaughterhouse effluent); -Studying the influence of high temperatures (30°C-55°C) on granule formation and conversion processes; -Studying the influence of toxic compounds on granule activity; -Investigating and optimising treatment of landfill leachate with a Sequencing Batch Biofilter Granular Reactor (SBBGR) in combination with ozonation; -Investigating and optimising treatment of different wastewaters (e.g. from slaughterhouse and from food industry) following appropriate technologies (such as the UniFed and the NeredaTM system)The obtained results will be used to suggest the optimal design and conditions for the application of aerobic granular sludge. They will be compared to the other treatment methods investigated in the other work packages, to predict the feasibility of this technology for treating different industrial effluents.
Literature
A list of the literature referenced in this text can be found here
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