A sensor comprising a membrane for detecting failure of a membrane filtration apparatus provided upstream of the sensor, the sensor comprising: a first chamber having an inlet and an outlet ; the inlet configured to be disposed in fluid communication with the upstream membrane filtration apparatus for receiving an effluent therefrom; a second chamber having an outlet ; only one membrane , the membrane being disposed between the first chamber and the second chamber for allowing fluid to permeate the membrane from the first chamber to the second chamber , wherein fluid received on the membrane of the sensor is the effluent of the upstream membrane filtration apparatus; a first pressure transducer configured for obtaining a first pressure upstream of the membrane; a second pressure transducer configured for obtaining a second pressure of permeate downstream of the membrane in the second chamber ; a resistance regulator disposed downstream of the second chamber and configured for adjusting the second pressure; and a control unit configured for receiving the obtained first and second pressures, and determining presence of a foulant in the effluent by determining a ratio between (P 1 - P 2 ) and (P 2 ), P 1 being the first pressure and P 2 being the second pressure, and correlating the ratio with a failure of the upstream membrane filtration apparatus, wherein correlating comprises an increase in the ratio indicating sensing of the presence of a foulant in the effluent when compared to the ratio during normal operation of the upstream membrane filtration apparatus, and wherein sensing of the presence of a foulant in the effluent is indicative of failure of the upstream membrane filtration apparatus. a first chamber having an inlet and an outlet ; the inlet configured to be disposed in fluid communication with the upstream membrane filtration apparatus for receiving an effluent therefrom; a second chamber having an outlet ; only one membrane , the membrane being disposed between the first chamber and the second chamber for allowing fluid to permeate the membrane from the first chamber to the second chamber , wherein fluid received on the membrane of the sensor is the effluent of the upstream membrane filtration apparatus; a first pressure transducer configured for obtaining a first pressure upstream of the membrane; a second pressure transducer configured for obtaining a second pressure of permeate downstream of the membrane in the second chamber ; a resistance regulator disposed downstream of the second chamber and configured for adjusting the second pressure; and a control unit configured for receiving the obtained first and second pressures, and determining presence of a foulant in the effluent by determining a ratio between (P 1 - P 2 ) and (P 2 ), P 1 being the first pressure and P 2 being the second pressure, and correlating the ratio with a failure of the upstream membrane filtration apparatus, wherein correlating comprises an increase in the ratio indicating sensing of the presence of a foulant in the effluent when compared to the ratio during normal operation of the upstream membrane filtration apparatus, and wherein sensing of the presence of a foulant in the effluent is indicative of failure of the upstream membrane filtration apparatus. <EOS>