Attachment, strength and performance of a porous media in an upflow anaerobic filter (UFAF) treating dairy wastewater were investigated. Microscopic examination showed that the number of autofluorescent methanogens varied 15-28% of the number of total bacteria along the UFAF while the number of viable methanogens was 10-70 times less that of autofluorescent methanogens. The most dominant species was found to be Methanococcus followed by short rods, medium rods, long rods, filaments and Methanosarcina. The quantity of attached biomass was the highest at the bottom, 103 mg VSS/media ring and lowest at the top, 23 mg VSS/media ring and an average of 55 mg VSS/media ring in the mid-height inside the UFAF. An average of 50% reduction in compressive strength of the sintered glass media after 8 months of operation was measured. The UFAF was operated up to an organic loading rate of 21 kg COD/m(3).d with a hydraulic retention time of 0.5 day and an average of 80% COD removal efficiency for most of the operating period was achieved.