In many regions dairy farms and milk processing industries, discharge large quantities of their wastes to the surroundings which pose serious environmental risks. With the purpose of treating the combined dairy and domestic wastewater from a small dairy farm in the Negev Desert of Israel, the use of a recent emerging technology of Immersed Membrane BioReactor (IMBR) was evaluated over the course of 500 test hours, under a variety of wastewater feed quality conditions. Field experiments were performed at the Kornmehl farm, an isolated dairy farm located 30 km south of Beer-Sheva, in the Negev Desert of Israel. The operating conditions for this experiment included constant product flow of 7 (L/h)], and the transmembrane pressure was increased smoothly during the experiment from 0.05 to 0.13 bar. Temperatures ranged between 30 degrees C and 37 degrees C, pH ranged between 4 and 9, TSS varied between 353 mg/L to 1000 mg/L and COD changed from 900 mg/L to 12,800 mg/L. The overall performance of a pilot-scale Ultrafiltration (UF) IMBR process for a combined domestic and dairy wastewater was analyzed based on the Facet Analysis (FA) method. Preliminary results of the FA model indicate: (i) the Trans-Membrane Pressure (TMP); the pH and the temperature do not have an effect on the performance of the permeate normalized flux and on the specific normalized flux, and; (ii) the bioreactor is characterized by high concentration of organic matters and it can be estimated that the IMBR normalized flux decline is dependent on other variables (air blower performance, backwash procedure and chemical cleaning). (C) 2009 Elsevier B.V. All rights reserved.