This paper evaluates the effect of hydraulic retention time (HRT)1 on anaerobic membrane bioreactor
(AnMBR)2 performance, biopolymeric substances production and fouling; also, struvite precipitation is
analyzed based on solubility product equation. A lab-scale UASB reactor coupled with an ultrafiltration (UF)3
membrane was operated under three different HRTs (4, 8 and 12 h) and fed with synthetic municipal
wastewater in two experimental blocks: in the first one, phosphate was supplemented to the influent and in
the second one, no phosphate was added. Results show that biopolymeric substances concentration in UASB
effluent increased with HRT reduction, probably due to the higher shear forces occurring inside the UASB
reactor at lower HRTs, as well as higher upflow velocities and washout conditions. Consequently, chemical
oxygen demand (COD)4 removal decreased slightly at HRT of 4 h (81% vs. 89%). Increase in specific fouling
cake resistance and decrease in particle size were also a consequence of HRT reduction. These results indicate
that AnMBR (UASB-UF) operation at HRT lower than 4 h has an adverse effect on its performance and fouling.
Though struvite components were found in UASB effluent, precipitation analysis showed that they were
undersaturated, so it is presumed that struvite precipitation did not occur.
© 2011