The water can be evaporated at 30ºC-40°C as you suggest, however, the efficiency of doing this must be calculated based on the energy required to bring this vapor to 5 kg/cm2. There will be a certain minimum flow of 10 kg/cm2 steam required to pump the vapor and bring it to the saturation temperature of 5 kg/cm2. This involves the basic thermodynamic calculation for enthalpy change from saturated vapor at 30ºC-40°C to saturated vapor at 5 kg/cm2 and the hydraulic calculation for pumping the recovered vapor from vacuum to 5 kg/cm2. This type of energy recovery can also be done with a standard compressor. The same efficiency calculations must be done in order to fully understand the economics of this type of energy recovery.