Biomass Acclimatisation and Adaptation During Start‐up of a Submerged Anaerobic Membrane Bioreactor (Sambr)

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.