Addis Ababa Water and Sewerage Authority invested 750 million ETB for installing membranernbioreactor units in the city. This new technology is expected to double the wastewater treatmentrncapacity of the city. Evaluating the performance of the units is necessary in estimating thernlikelihood of meeting this expectation and predicting the sustainability of the treatment plants.rnThis research explores performance of the installed plants and suggests optimal operationalrnstrategies to enhance the denitrification capacity of the plant while minimizing energy cost.rnMeasures of performance were effluent quality and membrane filtration processes. In order tornevaluate the effluent quality, samples were collected both in dry and wet seasons. The MBR modulernwas evaluated using recorded data of Transmembrane Pressure (TMP), flux & permeability ofrnfive-month operation. Activated sludge model no1 based simulation was used to determine thernoptimal operation strategy. To ensure energy reduction while improving the treated water quality;rnthe suitability of intermittent aeration was explored using the developed model. The average CODrnremoval efficiency was 97%. The ammonium effluent concentration was always lower than 0.5rnmg/L. However, absence of anoxic tank resulted in poor denitrification with consequently increasernnitrate effluent concentration over 100 mg/l. The treated wastewater was found to be completelyrnclear of fecal coliform; making the treated water suitable for reuse. The MBR filtration showedrnstable but low permeability condition. The average operational TMP was less than 20mbar.rnHowever, flux and permeability plot showed the plant was operating with decreasing trend overrntime and maximum of 80LMH/bar. This suggests the need for frequent cleaning or construction ofrna primary tank. Results from the ASM1 simulation indicated that intermittent aeration withrnaerobic-anoxic cycle of 43/54 min was the optimum duration. The proposed operational strategyrnincreased the total nitrogen removal efficiency from 42% to 71% without affecting COD removal.rnThese results indicate that creating optimal aerobic/anoxic conditions within the existing reactorrnis the most competitive solution to upgrade the MBR treatment plant.