This work investigated the fouling and clogging behavior of the porous polypropylene (PP) membrane during the long-term (1032 h.) biogas recovery operation of the ultrafiltration effluent discharged from an in-house granular anaerobic membrane bioreactor (G-AnMBR) unit. The study implemented different cleaning strategies, evaluated performance loss and recovery due to fouling and cleaning, and characterized the fouling. The normalized CH4 flux dropped by 54 % while the liquid pressure drop increased from 10 to 800 mbar after 312 h. operation. Acid cleaning (AC) with citric acid solution was found to be very effective in removing both reversible and irreversible fouling and restoring the initial membrane performance. Ca2+, and CO32−, were found to be the major inorganic fouling elements. The organic fouling consisted of 79 % aromatic proteins, 17 % fulvic-like substances, and 4 % soluble microbial products. Evidence of biofouling was confirmed by COD and DOC analysis and by detecting nucleic acids in the FTIR analysis.