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Two submerged anaerobic membrane bioreactors (SAMBRs) with essentially 100% cell recycle (150 days retention time, SRT), one with powdered activated carbon addition (PAC 1.7 g L −1 ) and one without, were continuously fed a low-strength feed (450 mg COD L −1 ) in order to investigate membrane fouling and to characterize the foulants. The SAMBR which did not receive PAC experienced more fouling, and the molecular weight (MW) distribution showed that there was a greater amount of high-MW compounds in this reactor when compared with the reactor with PAC. Size exclusion chromatography showed that although extracellular polymeric substances (EPS) seemed to contribute to the soluble chemical oxygen demand (COD) inside the reactor, it was mainly rejected by the membrane. High-MW protein and carbohydrate material originating mainly from cell lysis and EPS seemed to be the main organics that contributed to the internal fouling of the membrane.

The effects of biomass acclimatisation and adaptation during the start-up of three 3-litre submerged anaerobic membrane bioreactors (SAMBRs) were studied for the treatment of a sucrose-meat extract based medium strength wastewater (4 gCOD l(-1)). At 30 hours hydraulic retention time, the SAMBRs achieved more than 90% chemical oxygen demand (COD) removal with two different types of initial sludge--one previously adapted in a SAMBR for low strength treatment (SAMBR A), while the other was acclimatised in low shear continuous stirred tank reactors (CSTRs; mixture of biomass from two CSTR reactors fed on sucrose and/or acetate and propionate: SAMBR B--gassed at 5 litres per minute, SAMBR C at 2 litres per minute = 1.2 m3 m(-2) h(-1)). Although acclimatisation (enrichment of sludge adapted in a SAMBR for sewage treatment) took longer (100 days) than adaptation (enrichment and adaptation of sludge to SAMBR conditions) (39 days), the methane potential of the biomass improved substantially from its initial values. For successful start-up of SAMBRs a low initial loading rate, low biogas sparging rate and long acclimatisation and adaptation times were necessary to develop strong bacterial associations for interspecies electron transfer (SAMBRs A and C). The shorter adaptation time in SAMBR B resulted in permanent deterioration of performance, probably because of an insufficient population of methanogens and acetogens, and a reduction in floc size during overloaded conditions. The low value of flux (2 litres per square metre per hour) during high strength treatment was attributed to fine colloids, higher amounts of SMP and a high biomass concentration inside the reactor.

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A knowledge of the formation and rupture mechanisms for agglomerates is essential when seeking to model equipment designed to produce and process such materials. In the work described here, nanoindentation of "two-dimensional" agglomerate films, basically particulate coatings, was carried out to establish a means of identifying the generic breakage mechanisms for agglomerates. Selected applied load and penetration depth data in the range (0.02 mN and 700 nm, respectively) are provided as a function of the loading time during continuous loading for a model system composed rather of monodispersed colloidal silica particles (20-24 nm diameter) bound with a poly(methyl methacrylate) at 5 vol%. It is argued that these data enable the sequence of binder bridge failures to be observed, thus giving an indication of the breakage mechanism of the agglomerate and also the strength of the individual junctions. These data are also incorporated into a mechanical model that describes the rupture and deformation behavior of these planar agglomerate systems.