immersed in the reactor to operate it as an anaerobic membrane bioreactor (AnMBR) for low-strength wastewater
treatment. This postulate was tested by comparing the performance with and without a hollow fiber microfiltration
membrane module immersed in UASB reactors operated at two specific organic loading rates (SOLR). Results showed
that membrane filtration enhanced process performance and stability, with over 90% total organic carbon (TOC) removal
consistently achieved. More than 91% of the TOC removal was achieved by suspended biomass, while less than 6% was
removed by membrane filtration and digestion in the membrane attached biofilm during stable AnMBRs operation.
Although the membrane and its biofilm played an important role in initial stage of the high SOLR test, linear increased
TOC removal by bulk sludge mainly accounted for the enhanced process performance, implying that membrane led to
enhanced biological activity of the suspended sludge. The high retention of active fine sludge particles in suspension was
the main reason for this significant improvement of performance and biological activity, which led to decreased SOLR
with time to a theoretical optimal level around 2 g COD/g MLVSS$d and the establishment of a microbial community
dominated by Methanothrix-like microbes. It was concluded that UASB process performance can be enhanced by
transforming such to AnMBR operation when the loading rate is too high for sufficient sludge retention, and/or when
the effluent water quality demands are especially stringent.